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Tropics quiet; here’s a daily reading list

August 19th, 2013 - 1:48 pm

We’re in a bit of a “calm before the storm” holding pattern in the Atlantic tropics right now. Forecasters continue to expect a burst of activity fairly soon, yet there is nothing happening at all for the time being. Erin and Invest 92L have both officially died, and the first of the predicted series of African tropical waves, Invest 94L, has also fizzled due to dry air and Saharan dust. As a result, the outlook for the Atlantic basin presently looks like this:

atlantic-nothing

In fact, even the over-land waves on the African continent have dissipated for the moment. Moreover, the computer models have shifted their previously bullish outlook, with no predicted storm formations in the next 7 days.

That’s kind of surprising for mid-to-late August; we’re only three weeks away from the season’s climatological peak! (Then again, as Mark Sudduth points out, the tropics looked similarly quiet on August 19, 2005. We all know what happened 10 days later.)

For now, dry, stable air and wind shear, plus the ongoing dust flow caused by high pressure over Europe, keeps suppressing all the potential tropical troublemakers that try to rear the heads. But forecasters still expect this to change soon. My quote of Ghân-buri-Ghân yesterday — “Wind is changing!” — still applies. The crucial Madden–Julian oscillation is about to shift from an unfavorable pattern for tropical development to a highly favorable one. So the expectation is that, by next week or the week after, we’ll have a lot more to talk about.

In the mean time, I thought I would post a quick reading list, to help Weather Nerd readers stay abreast of tropical developments during this “calm before the storm,” during which I likely won’t be blogging much here, and during which my Twitter feed will probably consistent primarily of tweets about news, politics, college football, and other assorted non-weather-related topics.

Official information:
National Hurricane Center, including specifically the Tropical Weather Outlook

Graphics:
NHC/NOAA satellite imagery
Weather Bell Models: The most beautiful computer model graphics on the Internet (pay site; 7-day free trial)
Tropical Atlantic: Free computer model maps

Blogs:
Dr. Jeff Masters gives a thorough daily overview of what’s happening in the tropics (and other major weather events)
Tropical Tidbits: Levi Cowan’s blog & site, including awesome YouTube updates
Hurricane Analytics: Michael Watkins’s blog & site
Hurricane Analytics Tumblr: Watkins again, with helpful graphics and quick but informative analysis
HurricaneTrack: Mark Sudduth’s blog and site
FLhurricane.com: Good, link-heavy summaries
Capital Weather Gang: The Washington Post‘s excellent weather blog; focuses on Beltway area, but covers tropical weather generally when it threatens the U.S.
Houston Chronicle‘s SciGuy: Eric Berger is a long-time favorite. He posts about a variety of topics, when when there’s a tropical threat, he’s a great resource (especially if Texas could be threatened)

Twitter lists:
@AmySweezey/wx-tweeps: As I often say, this is a great one-stop shop. It includes most of the individual tweeps listed below, and many others. Unlike, say, a Twitter Search for a storm-related term, or clicking on a hashtag like #Erin or #92L, you can pretty much rely on the fact that people on this list are meteorologists or at least have some clue what they’re talking about. However, because Twitter lists don’t show @replies by list members (which sometimes contain valuable info), and because not everyone is on Sweezey’s list, I sometimes like to check certain individuals accounts too…

Twitter accounts:
@hurrtrackerapp: Informative graphics and frequent updates
@RyanMaue: The best computer models graphics on the web (from his pay site WeatherBell). Tweets about Pacific storms too.
@clfenwi: Charles Fenwick and I go way back; he was one of the great weatherbloggers back in the Katrina days and before. He doesn’t tweet on anything like a regular schedule, but when he does, it’s always informative and illuminating.
@bigjoebastardi: Joe Bastardi, a colleague of Maue’s at WeatherBell, is an iconoclast, his tweets sometimes require a bit of decoding, and he isn’t shy about reminding readers when he was right in a particular prediction. :) But his analysis and “ideas” (as he often calls his general trend forecasts) are always worth reading and considering.
@tropicaltidbits: Another informative account.
@watkinstrack: Michael Watkins’s Twitter account.
@hurricanetrack: Mark Sudduth’s Twitter account.
@EdPiotrowski: Not hurricane-specific, but lots of good weather tweets, including tropical weather when it’s worth talking about.
@wxbrad: Similar to Piotrowski: not just hurricanes (Brad Panovich is the chief meteorologist for a TV station in Charlotte, NC), but lots of good weather tweet, including tropical weather when it’s worth talking about.

I don’t check all of these links every day, though I probably should (and now that I’ve listed them in one place, maybe I will!) … but it’s a good list if you want to keep abreast of what’s happening. (I may add a few blogs or tweeps if I realize that I’ve forgotten anyone.)

In a development that won’t surprise readers of this blog, but might shock victims of yesterday’s hypestorm on CNN (about which I’ll say more below), both of our late-week tropical disturbances — T.S. Erin in the eastern Atlantic, and “Invest 92L” in the Gulf of Mexico — fizzled on Saturday. These storms were always marginal threats to the U.S., as I tried to make clear, and now they’re essentially no threat at all.

Erin, the “fish” storm that came off Africa on Tuesday and earned its name Thursday morning, was downgraded Saturday night (for a second time, and likely for good) to a tropical depression. Erin will probably dissipate in the next few days.

rgb0-erin

As for “92L” in the Gulf, it now appears highly unlikely to ever become “Fernand,” or even Tropical Depression 6. On Saturday evening, the National Hurricane Center downgraded 92L’s chances for tropical cyclone development to just 10 percent, down from roughly 50/50 yesterday.

Here are a couple of graphical summaries of what happened to 92L:

Basically, the “God of Dry Air” and the “Dark Lord Shearon” struck again, tearing 92L (and for that matter, Erin) apart. Stick a fork in them; they’re done.

Could either system make a Dorian-like comeback from the dead? I suppose it’s theoretically possible, especially in Erin’s case, as — much like Dorian — the storm’s remnants will now likely be steered more due west, because there’s basically nothing left for the upper-level winds to push north. That said, I wouldn’t plan on any resurrections. I think we’ve heard the last of these systems.

Instead, the next tropical threat lies far to the east, beyond ranges and rivers… er, beyond oceans and deserts, that is… over the continent of Africa, from which a series of vigorous-looking tropical waves is set to emerge:

FirefoxScreenSnapz113

Some of the more reliable computer models are projecting that these waves may eventually develop into a succession of tropical cyclones.

Such forecasts should always be taken with a huge grain of salt when we’re talking about something so hypothetical and so many days in the future. But, in general terms, the prediction does make climatological sense. We’re rapidly approaching the seasonal peak for Atlantic hurricanes, and it’s around this time that “Cape Verde” storms — the ones emerging off Africa — typically start to become an issue.

This season has “gotten ahead of itself,” in a certain sense. We’ve had a trio of “Cape Verde”-type storms — Chantal, Dorian and Erin — that formed unusually early, then ultimately fizzled, in part because the ocean and the atmosphere aren’t quite “seasonally ready” for that sort of development yet. But it now appears the pattern is shifting (“wind is changing!“), as one would expect for this time of year, so it makes sense that we’ll probably start to see these African waves have more success, rather than just forming into weak storms and then fizzling out.

That said, it’s waaaaaaaay too early to say anything meaningful about a (presently purely hypothetical) “proto-Fernand”… or “proto-Gabrielle”… or “proto-Humberto”… that might emerge from the Cape Verde hurricane pipeline. We don’t know what will happen. But it’s reasonable to suspect that things will start getting more sustainably active in the Atlantic tropics, with significant storms instead of repeated fizzles, in the coming weeks.

Before I “close the book” on this blog’s Erin and 92L updates, I wanted to briefly discuss two side-issues. First is the “CNN hypestorm” that I mentioned earlier. There was a bit of absurdity yesterday on America’s Most Trusted Name In News (and its website) about the unnamed non-event in the Gulf:

In fairness to Chad Myers, his on-air statement was heavily caveated (but of course the headline-writers on the CNN website didn’t notice that). Also in fairness to him, by “explode” he undoubtedly meant something like 2007′s Humberto, which strengthened from an unnamed nothingburger to a Category 1 hurricane in 24 hours. That was never likely here — because, ahem, warm ocean temperature is only one ingredient of hurricane formation; it is a necessary but not sufficient condition for “explosive” development — but I guess something sorta like it was at least conceivable.

Unfortunately, when average people hear “storm in Gulf could explode at time,” they think of something like Katrina, Rita or Wilma — not a tropical wave that could, maybe, in theory, “explode” into a minimal hurricane (but almost certainly won’t).

Anyway, needless to say, I had some fun at CNN’s expense:

But this is actually a serious issue:

TV weather folks, you’ve got to avoid crap like this. Save the sensationalism for the storms that actually deserve it. Otherwise, when the Big One is bearing down on somebody, your pleas for people to take the major threats seriously are going to fall on deafer ears than they otherwise might.

The second “side-issue” is an interesting tidbit of information about the National Hurricane Center’s plans that emerged by accident on Friday.

First, a quick bit of background: you’ve seen me call the Gulf disturbance “Invest 92L.” That’s a non-unique identifier that the NHC uses to describe a potential storm that it’s watching for possible development, and tracking with computer models, but that hasn’t yet developed sufficiently to “initiate advisories.” Such systems are discussed in NHC’s “Tropical Weather Outlooks,” but no official forecast or storm-specific advisory is issued unless and until an “invest” becomes a tropical depression or storm.

Anyway, it sounds like the lack of official “invest” forecasts might change in future years:

A preview of coming attractions, perhaps? Revealed by an accidental leak! Ha!

Speaking of “coming attractions”: as I said, this will be my last post on Erin and 92L unless something very unexpected happens…but for the latest on the tropics in general, including those possible waves coming off Africa over the next ~10 days, check back here at Weather Nerd, and also follow me on Twitter, where I will tweet or RT any significant developments.

Erin a weak fish; 92L Texas-bound?

August 16th, 2013 - 10:45 am

When I blogged yesterday about Tropical Storm Erin in the far eastern Atlantic and “Invest 92L” (potential future T.D. Six/T.S. Fernand) in the Caribbean, I wrote that neither storm looked like a particularly serious threat to the United States for the time being. That’s become even more true in the ~22 hours since. Far from strengthening en route to becoming a 60 mph storm, as the NHC forecasted yesterday, Erin has become a “skeletal cloud swirl” and appears increasingly likely to dissipate — becoming yet another sacrifice, like Chantal and Dorian before it, to the “God of Dry Air,” with an assist from that pesky Saharan dust. Dr. Ryan Maue illustrates:

Moreover, Erin now appears highly likely to be a “fish” storm, staying well out to sea. The official forecast track no longer calls for a “left turn” late in the forecast period — just the opposite, actually. And the NHC track is actually “south of model consensus,” meaning most models are taking Erin even further “right” and safely out to sea.

Below is a helpful illustration of this concept, again from Dr. Maue. The thick lines at the bottom (“OFCL” and “OFCI”) are NHC forecast tracks from late yesterday.

Much closer to home, Invest 92L (our so-called “proto-Fernand,” though it may never get there) looks mighty disorganized as it emerges over water in the Gulf of Mexico this morning. The low-level center is completely exposed, and most of the thunderstorm activity remains over land, away from the center. 92L still has a fighting chance, to be sure — NHC gives it 50% odds of becoming a tropical cyclone in the next 48 hours, and 60% in the next five days — but right now, I wouldn’t bet on it. Brian McNoldy elaborates:

[T]he surface circulation is devoid of deep convection, and a strong upper-level low to its north is introducing hostile vertical wind shear. … Since it is now reduced to just a low-level circulation, it should track more toward the west-northwest, rather than turning toward the north. This shifts the longer-range landfall location to Texas or northern Mexico… but, “landfall” makes it sound more significant than it really is. Wherever it goes, its biggest impact will be heavy rain — perhaps not even that!

McNoldy does note that a more westward track could help allow 92L to eventually spin up into something, since it will stay further away from that upper-level low producing the wind shear that’s presently hindering it. But even if so, the “current ‘worst case’ model…still isn’t TOO bad.” That model, the HWRF, shows a Category 1 hurricane approaching Brownsville, Texas on Tuesday. (You can see a map of this scenario in McNoldy’s blog post.) This is “not a likely solution,” McNoldy says, noting that “other models are less bullish.”

In any case, the New Orleans/central Gulf scenario appears to be pretty much off the table now, with virtually all models showing 92L heading toward either Texas or Mexico. Here’s a map from Hurricane Analytics showing the latest predicted tracks for both 92L and Erin from a bunch of the more reliable computer models:

Bottom line, the trend right now is moving away from a significant U.S. threat from either of these storms. Erin, we can pretty much write off at this point, barring something unforeseen. 92L still bears watching, but there’s certainly no cause for alarm, hype or #PANIC at the moment. Far from it.

Last but not least, there is increasing chatter about that wave over Africa that I mentioned yesterday, the one that might be the real “proto-Fernand” if 92L never gets its act together (or “proto-Gabrielle” if it does). The European model depicts this scenario, nine days from now:

More broadly, Joe Bastardi sees a “classic US threat pattern evolving in coming weeks,” above average even for the impending climatological peak of the season. Bastardi points to the African wave as perhaps the forerunner of this threat pattern:

Again, stay tuned. I’ll update this blog as warranted, and in the mean time, follow me on Twitter for the latest on the tropics… and politics… and college football… and rants against the NSA… etc.

Tropics awaken: Erin forms, Fernand next?

August 15th, 2013 - 12:55 pm

As expected, early August was quiet in the Atlantic basin. After Resurrected Zombiestorm “Dorian the White” finally died for good two weeks ago Saturday, we had more than 11 days without an active tropical cyclone. But now that the Saharan dust has subsided somewhat (although not completely!) over the prime hurricane breeding grounds, things can get active again — and they are doing so.

tropics815

For a while Tuesday and Wednesday, “92L” in the Caribbean and the system off the African coast were in a race to become “Erin.” The African wave won that battle, becoming Tropical Depression 5 last night at 11:00 PM Eastern Time, and getting an upgrade this morning at 8:00 AM to Tropical Storm Erin. As the Washington Post‘s Capital Weather Gang notes, this quick spin-up resulted in “the very rare occurrence of tropical storm warnings being issued for parts of the Cape Verde islands!”

Right now, Erin is a minimal tropical storm, with 40 mph winds. She is expected to slowly strengthen for the next 2 to 3 days as she moves west-northwest; the official forecast has Erin attaining 60 mph winds by Saturday. But then a scenario similar to Chantal and Dorian will likely kick in, as Dr. Jeff Masters explains:

[T]he waters beneath Erin will steadily cool to a marginal 26°C by Friday [here's a map showing that -ed.], and the atmosphere will steadily get drier, as the storm encounters the Saharan Air Layer (SAL), discouraging development. Erin’s west-northwest motion will cut the storm off on Sunday from a moist source of air to its south–the semi-permanent band of tropical thunderstorms called the ITCZ (Inter-Tropical Convergence Zone.) The storm should weaken beginning on Sunday. …

We may see a situation like occurred for Tropical Storm Dorian in late July–intensification to a 60 mph tropical storm, followed by a slow decay and dissipation. The latest run of the GFS model calls for Erin to dissipate well before reaching the Lesser Antilles Islands.

Not all of the computer models agree on that last part, as the National Hurricane Center notes in its 11am EDT discussion: “THE GLOBAL MODELS AND THE HWRF SHOW A WEAK OR DISSIPATING SYSTEM BY DAY 5…HOWEVER THE SHIPS AND LGEM SHOW LITTLE CHANGE IN INTENSITY OR EVEN STRENGTHENING.” The NHC’s official forecast “leans a little toward the weaker solution,” taking Erin back down to 40 mph by Tuesday.

What about Erin’s track? As I mentioned, she will move WNW for the next several days, which would tend to imply she’ll be a “fish” storm, staying safely out to sea (like most storms historically near her location). But, again like Chantal and Dorian, Erin’s expected weakening is expected to result in a more due-west track by late this weekend and early next week. Again quoting Dr. Masters: as Erin starts to “weaken beginning on Sunday, [this] would result in Erin turning more to the west as the east-to-west blowing surface trade winds begin to dominate the steering of the shallower storm.” Hence the expected left turn on the official NHC track. But as with the intensity forecast, and closely related thereto, there is disagreement among the models (and among meteorologists — see what Jim Cantore said, for instance). NHC writes:

THE [COMPUTER MODEL TRACK] GUIDANCE IS IN GOOD AGREEMENT ON [A WEST-NORTHWEST] MOTION CONTINUING FOR THE NEXT COUPLE OF DAYS. BY DAY 3…THE SPREAD IN THE GUIDANCE INCREASES. ON THE RIGHT SIDE OF THE GUIDANCE ENVELOPE THE GFDL…GFDL ENSEMBLE MEAN…ECMWF AND UKMET SHOW A NORTHWESTWARD OR WEST-NORTHWESTWARD MOTION. THE FIM…GFS…GFS ENSEMBLE MEAN AND HWRF ALL SHOW A WESTWARD TRACK…CONSISTENT WITH A SHALLOWER SYSTEM BEING STEERED BY THE LOW-LEVEL FLOW. THE NHC FORECAST AT DAYS 3 THROUGH 5 CONTINUES TO FOLLOW THIS SOUTHERN CAMP OF MODELS.

Here’s a good illustration of the divergence among the models, as to both track and intensity:

To summarize: By early next week, Erin will likely be either a weak (perhaps even dissipating or dissipated) storm moving due west, or else a stronger storm moving more northwesterly, toward a “fish” track out to sea. Either way, it’s nothing to worry too much about at the moment. We’ve got a long time to watch it, which means things can change, but for the moment, it seems fairly unlikely to become a big U.S. threat.

Closer to home, what about the system in the Caribbean, known for the moment as “Invest 92L”? Right now, it’s basically just a cloud bank off Belize (photos here). But what does the future hold? Is 92L likely to become Tropical Depression Six, and eventually Tropical Storm Fernand?

The answer for now is “probably,” though it looks a bit less certain than yesterday, when 92L was given a 70% chance of developing during the next 48 hours, and an 80% chance during the next 5 days. Those numbers are down to 50% and 60%, respectively, in the current NHC outlook. There continues to be disagreement among computer models, and the individual runs of each model, about whether 92L will amount to anything at all. (Compare, for instance, the this map with this map.) Dr. Masters, for his part, remains fairly bullish that 92L will at least become a depression:

The tropical wave in the Western Caribbean near the Yucatan Peninsula (92L) is growing more organized this morning, after an evening when it lost most of its heavy thunderstorm activity. Satellite loops show a modest-sized area of heavy thunderstorms that are increasing in intensity and areal coverage, but there are a no signs of a surface circulation. … Wind shear is a moderate 10 – 20 knots over the the wave, which should allow slow development today until…it [goes] over the Yucatan Peninsula Thursday afternoon. …

92L will trek across the Yucatan Peninsula Thursday evening and arrive in the Southern Gulf of Mexico on Friday, when it will have the opportunity to strengthen. The 06Z Thursday SHIPS model forecast predicts that 92L will remain in an area of low to moderate wind shear through Saturday, and ocean temperatures will be a favorable 29 – 30°C. … Given all these factors, 92L should be able to become at least a tropical depression by Saturday.

The good news is that the realistic worst-case scenario right now doesn’t look very bad. We’re probably looking at either: (1) a weak 92L or TD6 or a minimal TS Fernand tracking west toward Mexico, or (2) a moderate tropical storm getting pulled north toward the central Gulf Coast. Nobody is expecting this thing to blow up into a monstrous Gulf hurricane, so there’s no need to #PANIC when you see that some computer models are targeting vulnerable cities like New Orleans or Mobile:

The National Weather Service’s New Orleans office says 92L (or “proto-Fernand,” if you prefer) could be a fairly heavy rain event for the region. But this isn’t some sort of impending calamity, so let’s not get carried away with hype.

Having said all that, it’s really difficult to predict with any confidence what’s going to happen, as Capital Weather Gang explains:

It’s hard to say what [92L's] future will be once it enters into the Gulf of Mexico, because there might not be much left to look at [after it crosses the Yucatan Peninsula]. If it does manage to re-organize, it will take a while, so shouldn’t become anything more than a tropical storm. Of course, once a storm is in the Gulf, it has to make landfall somewhere, and right now, the model consensus is north toward Louisiana, but if it dissipates, a more westward track into Mexico or Texas is likely.

The timing should be around Saturday evening into Sunday morning, but it will just be an anti-climatic increase in rain and thunderstorms. Over the next five days, areas along and to the right of the path can expect 4”+, with locally higher amounts. Given the huge uncertainty in the track, there is also large uncertainty in the rainfall forecast.

Once this system is back over the water tomorrow, we’ll have a better idea of its future track and intensity… right now, there are too many significant unknowns.

Lastly, there’s the possibility that, if 92L doesn’t ever manage to get its act together, the real “proto-Fernand” could be the healthy-looking wave that’s over Africa right now, which some models predict will develop once it reaches the ocean:

“Fernand,” incidentally, is the one of three “new” names for 2013 on the sextennially rotating name list, along with “Dorian” and “Nestor.” They replace the retired storm names Dean, Felix and Noel.

Anyway… stay tuned, as they say. I’ll update this blog as warranted, and in the mean time, follow me on Twitter for the latest.

12 hours after being resurrected, “Dorian the White” has departed from the Grey Havens, as it were, bound for the Uttermost West East.

That’s right, Dorian has been (as expected) sheared apart — again. Thus, the Storm That Wouldn’t Stay Dead has been downgraded once again to a remnant low:

THE DEPRESSION HAS BEEN DEVOID OF DEEP CONVECTION FOR MOST OF THE
DAY…AND IT IS DIFFICULT TO ASCERTAIN IF A CLOSED CIRCULATION STILL EXISTS. ON THIS BASIS…THE DEPRESSION IS NOW CONSIDERED A REMNANT LOW.

So it’s over. He’s dead. We’re finished with Dorian at last.

Right?

THE LOW COULD STILL DEVELOP INTERMITTENT CONVECTION BEFORE DISSIPATION IN A DAY OR SO.

#DOOOOOOOOM!!!

:)

I kid. Actually, I believe the very last line in the discussion means the National Hurricane Center is announcing that they’re washing their hands of ex-Dorian no matter what.

ADDITIONAL INFORMATION ON THIS SYSTEM CAN BE FOUND IN HIGH SEAS FORECASTS ISSUED BY THE NATIONAL WEATHER SERVICE…UNDER AWIPS HEADER NFDHSFAT1 AND WMO HEADER FZNT01 KWBC.

In other words, “if any more discussion of this stupid cloud-swirl is required, some other sub-agency can handle it. We’re outta here.”

Reaction to Dorian’s latest demise:

He’s baaaaaaaack.

Dorian, the tropical storm I initially pronounced a “survivor,” only to see it struggle, crumble, lay down and die — then threaten repeatedly to return from the dead, earning ex-Dorian the nickname “Zombiewave” as he went through various undead, re-dead and really most sincerely dead phases — has returned.

On Tuesday, having seen the National Hurricane Center declare Dorian’s short-term odds of redevelopment to be 0%, I wrote it off, and stopped checking.

Bad idea. Zombiestorm Dorian does not like it when you ignore him.

Last night, it became apparent that Dorian’s remnants — having traveled a couple thousand miles across the Atlantic since officially dissipating almost a week ago, 500 miles east of the Lesser Antilles — were making one last serious bid for a comeback, off the east coast of Florida.

FirefoxScreenSnapz111

I was totally unaware of the situation until Yossi Kudan tweeted at me late in the afternoon. As I then frantically checked up on the situation, it quickly became apparent that this could be the real deal:

Needless to say, I quickly busted out the Lord of the Rings references:

I even referenced wind shear as the “Dark Lord Shearon,” and was disappointed in myself that I hadn’t thought of that sooner. (This got a pretty funny response from a follower.)

Mostly, though, I stuck with the Dorian-as-Gandalf resurrection meme:

This morning, I awoke to the official news of #Dorian’s re-birth…

…and I was finally able to publish the geek-tweet I’d been waiting to post for almost a week:

Also this:

I’m being silly about this, by the way, because Dorian poses essentially no threat. It’s headed away from the coast and out to sea. The computer models all agree on that.

And in fact, it appears that Dorian The White, having sent back by the Valar until his task was done (the “task” having apparently been, um, to make some pretty nighttime lightning off the Florida coast??), will head to the Grey Havens and board a ship to the Evermost West (or East, in this instance) quite soon:

It’s been a fun ride, though. I daresay Dorian has earned the title I prematurely gave him: he really has been quite the “survivor.”

I know I said yesterday’s post would be my last for a while, but a quick follow-up is in order, by way of elaboration on my statement that “for now, hurricane trackers can (probably) take a deep breath for a little while” as we head into an expected quiet period. (It’s the calm before the storms; the season’s peak is on its way.) Why the follow-up? Because the Capital Weather Gang has a pretty awesome post about the reason for the forthcoming calm period: a giant cloud of dust from Africa has emerged over the Atlantic, and will almost certainly choke out any potential for tropical development in the immediate future. Here’s what it looks like from NASA’s Terra satellite:

africa-dust

Cool! Think of it as a haboob of epic, oceanic proportions. :) Or not; I just love saying the word “haboob.” Almost as much as I love referencing Sharknado. (“Haboobnado”?)

Anyway, enough silliness. “Gang” member Jason Samenow explains what’s going on:

Africa sneezed, and the tropical Atlantic is choking.

An intense, sprawling dust storm exited the African west coast earlier this week, effectively squashing any tropical storm formation in adjacent Atlantic waters for days to come. …

Over the Atlantic ocean, the storm has formed a highly concentrated layer of atmospheric dust, known as the SAL (Saharan Air Layer). It is characterized by extremely dry air, which acts to suffocate the development of thunderstorms and the organization of tropical weather systems.

More #science in a moment, but first, how about an awesome GIF?

Here’s a nifty 5-day animation, courtesy of CIMSS:

The yellows, oranges, reds and pinks represent dry air and/or Sarahan dust.

Notice, at the beginning of the GIF, how you can see Tropical Storm Dorian on the center-left side of the image. The first frame is from when Dorian was dying, and then you can watch the storm “exit stage left” as he proceeds through his various undead, re-dead and zombiewave phases. As you watch, notice how, in those early frames, tiny scattered pixels of yellow and orange represent the “dry air” that doomed Dorian.

Then notice how, right around the time when ex-Dorian is disappearing off the map on the left-hand side, a massive clump of red and pink explodes off the African coast in the middle of the GIF. That, of course, is our dust cloud — and it makes the “dry air” that killed off Dorian look positively puny by comparison. No wonder these dust clouds suppress development! Yikes!

This dust cloud is expected to cover all the lands with a second darkness span the entire tropical ocean from the coast of Africa to Puerto Rico by the weekend, and then keep moving west from there:

So… why is dust bad for hurricanes, anyway? Dr. Jeff Masters brings the #science:

Saharan dust can affect hurricane activity in several ways:

1) Dust acts as a shield which keeps sunlight from reaching the surface. Thus, large amounts of dust can keep the sea surface temperatures up to 1°C cooler than average in the hurricane Main Development Region (MDR) from the coast of Africa to the Caribbean, providing hurricanes with less energy to form and grow. Ocean temperatures in the MDR are currently 0.7°F above average, and this anomaly should cool this week as the dust blocks sunlight.

2) The Saharan Air Layer (SAL) is a layer of dry, dusty Saharan air that rides up over the low-level moist air over the tropical Atlantic. At the boundary between the SAL and low-level moist air where the trade winds blow is the trade wind inversion–a region of the atmosphere where the temperature increases with height. Since atmospheric temperature normally decreases with height, this “inversion” acts to but the brakes on any thunderstorms that try to punch through it. … The dust in the SAL absorbs solar radiation, which heats the air in the trade wind inversion. This makes the inversion stronger, which inhibits the thunderstorms that power a hurricane.

Dr. Masters adds a third possible affect as well: when dust particles are the right size to serve as “condensation nuclei” capable of assisting in cloud formation, this can have uncertain impacts — potentially positive or negative, depending on the circumstances — which are still being studied. But the overarching theme certainly is that a massive dust cloud like this hurts hurricane formation.

Masters further explains that these oceanic dust clouds, which we tend to generically call “Saharan” (because #racism?), actually come from two different dust-storm-producing regions in west Africa: the southwestern Sahara Desert and the northwestern Sahel region. Sarahan dust “stays relatively constant from year to year,” but there is significant variability in the amount of Sahel dust. Research suggests that the most critical factor in this annual variability is “the level of drought experienced in the northwestern Sahel during the previous year.” Alas, 2012 was actually much wetter than usual in the northwestern Sahel — so, in the longer term, we should see “less dust than usual over the Atlantic this fall, increasing the odds of a busy 2013 hurricane season.”

In other words, beware the fallacy that Michael Watkins warns of in a trio of tweets:

I find it fascinating that even experienced [meteorologists] look at current dry air in the Atlantic and project it to stay all season. #persistancebias … [Look at the] Saharan Air Layer outbreak image/analysis (pre-Irene) from August 1st, 2005 – these happen every year. … Full analysis of research experiment pre-Irene in 2005 – Atlantic systems develop between SAL’s.

So, even a mega-dusty SAL in early August doesn’t prevent, say, a Katrina in late August. Duly noted.

Still, in the immediate short term, this particular massive dust storm — which Dr. Masters says is pretty typical for the peak dust-storm months of June and July — “will sharply reduce the odds of tropical storm formation during the first week of August.” The dust largely explains why “none of the reliable computer models is predicting Atlantic tropical cyclone formation” in that time frame. (Read the whole thing.)

So, in conclusion, this blog should have nothing to write about for a little while. Also, per Jim Cantore, get ready for some gorgeous sunsets in the Caribbean and Florida.

Anyway, I’m out. Like I said last time, this will be my last Weather Nerd post until something else pops up that warrants attention, from the perspective of a possible U.S. threat. In the mean time, follow me on Twitter!

Tropical Storm Flossie was downgraded to a Tropical Depression last night (at 5pm Hawaii Time, 11pm Eastern), and this morning it was declared a “post-tropical remnant low.” The official track shows that, because of the low-level circulation center’s unexpected “right turn” east of the Big Island yesterday, Flossie never technically made landfall as a tropical storm — so it was not, in the end, the first Hawaiian landfall by an active named tropical cyclone in 21 years (since Iniki in 1992) — though the center did brush Kauai this morning as a dying depression, just before Flossie was officially declared to have dissipated.

flossie-track-landfall

That said, the location of the circulation center is relatively meaningless in this case, because as I mentioned here yesterday evening, Flossie “split in two” as she approached Hawaii, with her low-level center turning right while her mid-and-upper-level energy and convection turned left. Thus, Flossie’s heaviest rain and thunderstorms was primarily confined (with isolated exceptions) to the Big Island, Maui and Molokai, even as the storm’s “center” raced off toward Oahu and beyond.

From news accounts out of Hawaii — and from common sense, given how Flossie evolved — it appears the storm’s impact was modest. That was not actually a surprise; Flossie was always a “fairly minor” threat, expected to have only “mild” wind impacts, as I wrote in my initial update. To the extent the storm nevertheless felt “overhyped,” that’s probably due in large part to its novelty: despite its tropical location, Hawaii is rarely hit directly by tropical cyclones, so in that sense, this was more “newsworthy” than a 60mph-weakening-to-35mph storm hitting Florida, say.

Flossie did fake forecasters out a little bit by maintaining its strength over the weekend, but the long-expected weakening (falling apart, really) did ultimately happen; it just didn’t begin in earnest until overnight Sunday night into Monday morning, when landfall was expected imminently. This simultaneous late weakening and right-hand turn (which was a mild surprise) left some in Hawaii feeling a bit underwhelmed, judging by social media anyway. That sense of unfulfilled hype and underwhelming reality, combined the perceived silliness of Flossie’s name, inspired the creation of a rather funny video, which was making the rounds yesterday, captioned “Tropical Storm Flossie has hit Hawaii. Frightening video footage.” Heh:

(For those wondering, and the many asking on Twitter, “where do they come up with these names?!” … well, an international committee of the World Meteorological Organization is responsible for the rotating lists of storm names in the Atlantic basin and the Eastern Pacific. Here’s a primer. The lists rotate and repeat every six years, with the exception of especially deadly or costly landfalling storms, whose names are retired. There will never be another “Katrina,” for instance. But there will be another “Flossie” — six years hence, in 2019, assuming there are at least six tropical storms in the Eastern Pacific that year, which is generally a safe bet. 2019′s Flossie will be the eighth tropical cyclone named “Flossie.” The first was in the Atlantic in 1978, before the current system of sextennially rotating lists was adopted in 1979. Then, pursuant to those lists, there were Pacific “Flossies” on schedule in 1983, 1989, 1995, 2001, 2007 — another close encounter for Hawaii — and, of course, 2013. No “Flossie” has ever made landfall. But 1956′s Hurricane Flossy did make landfall on the Gulf coast; it caused flooding in New Orleans, and “was the first hurricane to affect oil refining in the Gulf of Mexico,” according to Wikipedia. There was also a tropical cyclone named “Flossy” in 1996 in the Indian Ocean. Flossie, incidentally, was a fairly popular female name in the United States around the turn of the century. So anyway… now you know.)

Wet roads, courtesy of Flossie, contributed to a rash of traffic accidents during rush hour yesterday, but fears of widespread flooding (and mudslides) went mercifully unrealized. That’s because the storm’s heavy rains, which were dumping up to 4 inches per hour at times, moved so quickly that they couldn’t dump too much in any one place. The highest reported totals in the 24-hour period ending at 2am HST this morning were at Kaupo Gap in East Maui (5.3 inches), Puu Kukui in the West Maui Mountains (4.3″), Kilohana in Kauai (3.9″), Puu Alii in northeast Molokai (3.8″), and Ulupalakua on the western slopes of Mount Haleakala in Maui (3.6″). Several locations in the Big Island got between 2 and 3 inches of rain. But thankfully, no one saw totals approaching the “up to 15 inches of rain in isolated windward areas” that forecasters had feared.

Meanwhile, wind and lightning left as many as 10,000 customers without power on Maui at one point, along with around 5,000 on the Big Island. In addition, the whole island of Molokai (population ~7,500) lost power for about 45 minutes Monday evening. (Reminder/PSA: Use flashflights, not candles, during storm-caused power outages! Candles can fall over, or be blown over. Houses have burned down during hurricanes because of people using candles! /end PSA)

On Maui, according to the Star-Advertiser, lightning struck a man in the north shore community of Haiku; he was hospitalized in stable condition. Lightning also damaged a home in Kahului, Maui’s largest city, punching a 10-inch hole in the roof; a resident was home at the time, but was not injured.

The big complex of thunderstorms that developed, and began moving from the Big Island toward Maui, while I was writing yesterday evening’s blog post, appears to have been Flossie’s most dramatic and damaging component, at least in heavily populated areas. Social media was ablaze last night with Maui residents marveling at the thunder and lightning show, as Hawaii News Now’s Storify feed shows. For example:

Flossie’s sustained winds apparently did not reach tropical storm force on land. However, gusty winds, probably from that aforementioned big squall, toppled trees and utility poles in the northeast Maui village of Nahiku, blocking the Hana Highway (which anyone who has vacationed in Maui — I honeymooned there — will be familiar with) in both directions. Sounds like Jim Cantore was right when he tweeted last night that he “would not want to be driving the road to Hana right now” (although I’m pretty sure Cantore, the veteran Weather Channel/NBC storm tracker who was sent to Hilo, only to see Flossie turn right and largely spare Hilo, was actually secretly wishing he was reporting from eastern Maui).

Last but not least, a surfer was hospitalized after a shark attack in Oahu. This does not, however, indicate that Flossie was a Sharknado … OR SO THEY WOULD HAVE US BELIEVE!!! ;)

Anyway, there isn’t much more to say about Flossie. I’ll wrap up with a few pretty pictures that I saw on Twitter yesterday, then move on to a brief (final?!) discussion of Zombiewave Dorian.

So… Dorian. Or Ex-Dorian. Or Zombiewave Dorian. Whatever you want to call it, yesterday the remnants of our “survivor” storm were looking quite good for a while, and the National Hurricane Center pegged its odds of redevelopment within two days as high as 50 percent. Folks in South Florida were watching closely again.

But then an aircraft reconnaissance “hurricane hunter” airplane found no closed circulation — again — and the NHC declared that the chances of redevelopment were “diminishing.” Beaten by wind shear and sinking air, Dorian went from undead to re-dead, and now — apparently — really most sincerely dead. (Yep.)

That means, of course, that it’s time to bust out the Karl Rove jokes:

The NHC puts Ex-Dorian’s chances of redevelopment in the next two days at just 20 percent:

A TROUGH OF LOW PRESSURE…THE REMNANTS OF DORIAN…IS PRODUCING DISORGANIZED SHOWERS AND THUNDERSTORMS THAT EXTENDS A FEW HUNDRED MILES EAST AND NORTHEAST OF THE TURKS AND CAICOS ISLANDS. UPPER-LEVEL WINDS ARE NOT EXPECTED TO BE CONDUCIVE FOR REGENERATION DURING THE NEXT COUPLE OF DAYS AS THE DISTURBANCE MOVES WESTWARD TO WEST-NORTHWESTWARD AT 10 TO 15 MPH. THIS SYSTEM HAS A LOW CHANCE…20 PERCENT…OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS. SHOWERS AND GUSTY WINDS IN SQUALLS ARE SPREADING ACROSS THE TURKS AND CAICOS ISLANDS AND SHOULD BEGIN TO MOVE WESTWARD ACROSS PORTIONS OF THE BAHAMAS BY THIS AFTERNOON INTO EARLY THURSDAY.

Brian McNoldy, a weatherblogger and University of Miami atmospheric researcher, explains what’s going on:

Dorian’s remnants (an open wave)…[have] entered a high-shear environment due to a strong upper-level trough extending down into Cuba and Hispaniola. In the figure below, the wave [a.k.a. "the mid-level circulation of ex-Dorian"] is located approximately at the red X (look north of the Dominican Republic), while the upper-level trough and associated Low are shown with the green arrow and green L. This feature generates very hostile winds for the development of a tropical cyclone.

dorian-wave

… [The wave has] an exposed low-level center and all of the deep thunderstorms displaced downshear, or to the east in this case. … Given the poor organization and the bearish environmental outlook, most models are having a hard time even tracking this feature for very long. So at least for the next few days, the only noticeable effect this will have is to bring enhanced chances of gusty winds and heavy rain to the Dominican Republic, Haiti, Bahamas, and Cuba… and eventually southern Florida by Wednesday evening into Thursday.

I’ll continue to (loosely) watch it… but this will be last blog update on Zombiewave Dorian unless there’s some good reason to mention it again!

Flossie’s fizzle and Dorian’s demise leaves the tropics eerily quiet:

But don’t expect that to last:

In fact, there’s already a hint — grain of salt alert! — of a possible “proto-Erin” in the Atlantic, a ways down the line:

And the Eastern Pacific could soon see Tropical Storm Gil, which might conceivably follow Flossie to Hawaii eventually. But, like “proto-Erin,” that’s very speculative and uncertain. For now, hurricane trackers can (probably) take a deep breath for a little while — and get ready for what will probably be a busy August and September ahead.

This will be my last Weather Nerd post until something else pops up that warrants attention (from the perspective of a possible U.S. threat). In the mean time, follow me on Twitter!

Let me begin with a caveat and a confession. This post is above my pay grade. I just learned yesterday that such a thing as “split flow effects of the Big Island” exist, and I have only the vaguest idea of what that phrase means. (Something about how the Big Island’s massive mountains disrupt air flows and storm structures in a manner that the Atlantic basin’s biggest mountains, on Hispaniola, can only dream of.) So I’m speculating here, and I could well be wrong. But man, look at this visible satellite loop:

A few things. First, the bright diagonal line that sweeps across the image at the beginning represents the transition from infrared imagery (before sunrise) and visible imagery (after sunrise).

Second, Flossie’s low-level center of circulation — which is what defines the storm’s official “location” — is that spinning swirl of scattered-ish looking clouds (in the visible images), rotating counterclockwise. During the course of the GIF, it moves from NE of the Big Island to NW of Big Island to near Maui.

And third, Flossie’s thunderstorms or “convection” — i.e., where most of the rain is happening; the part of the storm that actually feels like a storm — is the big blob of solid white cloud that seems to be moving straight toward the Big Island, before diving SW.

Now that you’ve oriented yourself, what do you notice? I’ll tell you what I notice: it kinda looks like the Big Island of Hawaii has cut Tropical Storm Flossie in half with a giant pair of atmospheric scissors. The low-level circulation center got separated, or “decoupled,” from the convection overnight, and this morning, the two started moving in drastically different directions, with the center staying well away from the Big Island and heading to Maui (likely with minimal rain), while the big blob of convection wobbled south, almost stalled, and finally slammed into the Big Island.

Technically, this arguably means that Flossie is no longer really a tropical cyclone, although the Central Pacific Hurricane Center (CPHC) is keeping advisories going anyway…like they should have done once Hurricane Sandy technically ceased to be tropical…but I digress. Back to the decoupling and divergence of low-level center and mid/high-level convection. You see this sort of thing all the time when tropical storms are getting torn apart by upper-level wind shear, but it rarely looks quite this dramatic, distinct or sudden. Or maybe it does, and I just don’t typically notice because there isn’t the visual cue of an island in the middle of everything to make it look so interesting. Perhaps the Big Island’s presence there is just a coincidence, and this is all purely the result of regular ol’ wind shear, and the same thing would have happened regardless of Mauna Kea and Mauna Loa. But I wonder.

Meteorologists are always quick to point out, and rightfully so, that the notion of any land mass reliably “deflecting” tropical cyclones is a dangerous, complacency-inducing urban legend — storms can and do make landfall anywhere in their path. At the same time, though, the Central Pacific Hurricane Center did write this last night:

SLIGHTLY STRONGER NORTHERLY FLOW ALOFT WEST OF THE COL MAY ACCOUNT FOR THE SMALL SOUTHERLY TRACK COMPONENT AND LOSS OF LATITUDE. ANOTHER POSSIBILITY IS THAT FLOSSIE IS BEGINNING TO FEEL THE SPLIT FLOW EFFECTS OF THE BIG ISLAND…AT LEAST ALONG ITS WESTERN PERIPHERY. … TRACK GUIDANCE REMAINS TIGHTLY CLUSTERED IN THE SHORT TERM…SHOWING FLOSSIE NEAR THE BIG ISLAND AND MAUI MONDAY MORNING…THEN PASSING SOUTH OF OAHU MONDAY NIGHT AND SOUTH OF KAUAI THROUGH TUESDAY. … [HOWEVER,] IT IS IMPORTANT TO NOTE THAT FLOSSIE IS VERY LIKELY TO TRACK ACROSS AT LEAST A PORTION OF THE BIG ISLAND OVER THE NEXT 36 HOURS … INTRODUCING THE DIFFICULTY OF ACCOUNTING FOR TERRAIN EFFECTS ON SYSTEM TRACK AND INTENSITY. POST-BIG ISLAND TRACK AND INTENSITY FORECASTS MAY BE QUITE DIFFERENT ONCE THESE TERRAIN EFFECTS ARE KNOWN.

So, I’m not just making this up, I swear!

Anyway, this is all really a meteorological curiosity. In terms of Flossie’s actual impacts… well, they haven’t been too bad just yet, but even as I’ve been composing this post, it looks like things have gotten interesting:

Nothing to #PANIC about, nor a cause for hype. But it’s definitely going to be a dark and stormy afternoon and night in parts of Hawaii. If you’re there, stay safe, don’t take dumb risks, and listen to the advice of local authorities.

That’s all for now. As per usual, follow me on Twitter at @brendanloy for updates and RTs. Also follow Amy Sweezey’s “Wx Tweeps” Twitter list; lots of good weather folks there, updating frequently.

There’s been a significant change overnight to Tropical Storm Flossie’s expected path as it moves into Hawaii today. Last night, the forecast called for a direct hit on the Big Island late this morning or around noon Hawaii Time (6pm Eastern) today. Not anymore:

EP062013W

The Central Pacific Hurricane Center (CPHC) explains:

THE CENTER OF FLOSSIE WAS HIDDEN BY HIGH CLOUDS MOST OF THE NIGHT BEFORE VIRS NIGHTTIME VISUAL SATELLITE IMAGERY REVEALED AN EXPOSED LOW LEVEL CIRCULATION CENTER FARTHER NORTH THAN EXPECTED. WE RE-BESTED THE 0600 UTC POSITION BASED ON THE VISIBLE DATA. … THE TRACK HAS BEEN SHIFTED NORTH TO REFLECT THE RE-LOCATED CENTER. THE TRACK GUIDANCE SHIFTED FOLLOWING THE TRACK CHANGE AND WAS CONSISTENT WITH A NEW TRACK FARTHER TO THE NORTH. THE TRACK NOW SHOWS FLOSSIE PASSING OVER MAUI TODAY…OVER OAHU TONIGHT…THEN PASSING SOUTH OF KAUAI EARLY TUESDAY MORNING.

An aside: “VIRS nighttime visual satellite imagery” is a new one for me. Here’s an explanation. (Hat tip: Ryan Maue.)

Anyway, I guess we’ll never know whether, had it continued on its expected course, Flossie would actually have managed to hit its tiny, mountainous target of the Big Island, or whether it would have instead “bounced” or “wobbled” away, due to the split flow effects of those high mountains. (Or maybe we do know? Did the storm’s western circulation hitting the Big Island help cause the center’s relocation to the north? Honestly, I have no idea. Maybe Flossie “bounced” away in fear of Jim Cantore… heh.)

Regardless, maybe the biggest impact of this change is that it delays Flossie’s initial landfall (now expected in Maui) by several hours, to perhaps somewhere in the range of 2-4pm local time (8-10pm Eastern). That’s significant because the storm appears to be rapidly falling apart:

Again quoting the CPHC:

SATELLITE LOOPS SUGGEST A RAPID WEAKENING TREND WITH THE LOW LEVEL CENTER PULLING AWAY FROM A SMALL AREA OF CONVECTION SOUTHEAST OF THE CENTER. IT IS LIKELY THAT CONTINUED NORTHWEST SHEAR WILL MAINTAIN THIS WEAKENING TREND. WE EXPECT FLOSSIE TO WEAKEN STEADILY AS IT TRACKS WEST NORTHWEST AND DISSPATE WITHIN 96 HOURS.

So much for that next SyFy Original Movie…

Heh. Sorry, I couldn’t resist.

On a more serious note, it’s important to remember that tropical storms are not a “point.” Flossie will still impact the Big Island, even though its center of low-level circulation will “miss.” Information on timing of tropical storm conditions:

The Honolulu office of the National Weather Service has more information, including:

Most likely impacts to the Hawaiian islands include heavy rain, dangerous surf conditions along east facing shores, damaging winds and possible flash flooding. Rock and mudslides caused by heavy rain will be possible, especially in steep terrain. Pounding surf will rise rapidly along the east and southeast coasts of the Big Island and Maui, with surf peaking today, with coastal flooding possible. Surf heights along east facing shores will be between 10 and 20 feet. Isolated tornadoes and waterspouts will be possible with tropical storm Flossie, mainly over Maui county and the Big Island.

More info in the Flash Flood Watch bulletin. Speaking of which, Mike Smith notes a silver lining: “While there will be flooding, much of the State of Hawaii has been in a drought, so the storm may be a net plus.” He added later: “These heavy rains will end a drought.”

Meanwhile, back on the Atlantic side, Zombiewave Dorian continues to flirt with resurrection:

Mark Sudduth isn’t so sure:

The remnants of Dorian, labeled as 91L, are flaring up again today with quite a bit of deep convection noted in satellite imagery. However, surface pressures in the area are very high, near 1015-1016 mb and are not falling apparently. I think what we have is a vigorous tropical wave with perhaps a mid-level circulation. While it’s possible for the system to make enough of a comeback to be designated a tropical storm again, I think the odds are against it. Upper level winds are not going to let up enough and the background pressures are just too high.

With that being said, the wave of low pressure will bring showers and gusty winds to portions of the southern Bahamas, Cuba and south Florida over the next few days.

We’ll see. The computer models aren’t sure what to make of the Zombiewave:

Stay tuned. As per usual: I’m on Twitter at @brendanloy, and even more frequent updates by others on Twitter can be found easily via Amy Sweezey’s “Wx Tweeps” list.