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Monthly Archives: September 2011

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It’s been a whirlwind 24 to 36 hours for Tropical Storm Nate’s track forecast. It’s gone from likely to hit Mexico … to a sudden shift toward threatening to the U.S. Gulf coast … back to likely, and now very likely, to stay away from the U.S. and hit Mexico (if anywhere). From the 10pm NHC discussion:

THERE HAS BEEN A LARGE MODEL CHANGE FROM SIX HOURS AGO…WITH THE GFS/GFDL/HWRF MODELS NOW HAVING A GENERAL WESTWARD TRACK TOWARD MAINLAND MEXICO DUE TO THE CYCLONE BEING TRAPPED BENEATH A NARROW RIDGE OVER THE NORTHERN GULF OF MEXICO. NATE IS FARTHER SOUTH THAN EXPECTED YESTERDAY…SO THE LIKELIHOOD OF A MORE POLEWARD TRACK AHEAD OF THE NEXT TROUGH OVER THE CENTRAL UNITED STATES HAS DIMINISHED. THUS THE NHC FORECAST IS SHIFTED WELL TO THE LEFT AT THIS TIME…BUT BASICALLY ALL RELIABLE MODELS ARE STILL FARTHER TO THE SOUTH. IF CURRENT TRENDS CONTINUE…THE FORECAST WOULD HAVE TO BE ADJUSTED SOUTHWESTWARD AT A LATER TIME.

So basically, the NHC is forecasting Nate to come nowhere near the U.S., and it’s likely the forecast will shift even further away from the U.S. tomorrow, if current trends hold. And so far, they’re holding: the all-important 00Z GFS run, which came out after the 11pm NHC advisory, shows basically the same thing as the 18Z run, with Nate staying to the south and, actually, pretty much falling apart just as it’s about to come ashore in Mexico. (It’s frankly not clear to me why.)

Since this blog’s charge is to track major tropical-cyclone threats to the U.S. coast, and it no longer appears that any of the active storms — Katia, Maria or Nate — pose such a threat, I’m going to call off my updates for now.

If the situation changes and Nate poses a threat again, I’ll be back. In the mean time, check my Twitter feed for the latest — on hurricanes, and college football, and conference realignment, and politics, and whatever else I feel like tweeting about. :)

Nate update: Models lurch back toward Mexico

September 8th, 2011 - 2:12 pm

[NOTE: For the very latest on Nate, check my Twitter feed.]

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No time for a lengthy post, but very briefly: I wrote this morning that “we may be seeing” a turning point whereby the computer models decisively change course and move Nate north toward the Gulf coast. Well…never mind! Most of the model tracks have now shifted back south again — a healthy reminder that the Hurricane Center’s tendency to wait for confirmation before adopting a new computer-model consensus is well grounded in long experience and common sense. That “ping-pong effect” I mentioned can and does really happen!

From the 5pm EDT advisory:

AFTER 36-48 HOURS…THERE REMAINS A VERY LARGE SPREAD IN THE GUIDANCE…HOWEVER THE MODELS HAVE GENERALLY SHIFTED WESTWARD. THE GFS IS ALONG THE EASTERN EDGE OF THE ENVELOPE AND SHOWS A SLOW NORTHWARD TO NORTH-NORTHWESTWARD MOTION OVER THE CENTRAL GULF OF MEXICO. MOST OF THE REMAINDER OF THE TRACK MODELS MOVE NATE MORE WESTWARD TOWARD MEXICO. THE OFFICIAL FORECAST HAS BEEN SHIFTED TO THE LEFT…BUT NOT NEARLY AS FAR WEST AS THE MULTI-MODEL CONSENSUS…OUT OF RESPECT FOR THE GFS AND THE EARLIER ECMWF ENSEMBLE MEMBERS.

Bottom line, it’s once again more likely that Nate will hit Mexico than the United States. But the U.S. Gulf coast isn’t yet out of the woods. That pesky outlier, the GFS, is one of the most reliable models on earth, and for now, it’s still projecting a more northerly motion, toward Texas/Louisiana. Its 18z run is due out around 6:45 PM Eastern Time, so look for that; you can view it here. And all the 00z model runs will be important, for reasons noted earlier. (Links and schedule here.) Stay tuned, as they say. Hopefully, forecasters will have a better handle on Nate by tomorrow morning.

Oh, and by the way, Nate is strengthening. 70 mph. He’ll be a hurricane soon.

P.S. Dr. Jeff Masters has more.

Nate’s Threat to U.S. Gulf Coast Increases

September 8th, 2011 - 10:29 am

[NOTE: For the very latest on Nate, check my Twitter feed.]

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Sometimes, in the life of a tropical cyclone, there is a distinct turning point in the evolution of the track forecast, where the computer models suddenly shift toward a new and markedly different solution. When this happens, the National Hurricane Center — wanting to avoid a “ping-pong effect” of models shifting back and forth, as can happen during periods of forecast uncertainty — generally waits to see a few more model “runs” confirming the new thinking before it fully adopts the new consensus in its official forecast. This memorably happened in 2005 with Hurricane Katrina, when the models shifted early Friday morning toward a solution targeting the New Orleans area, inspiring my “New Orleans in peril” post at midday Friday (which I would later read aloud in Spike Lee’s movie), published eight hours before the NHC actually adopted the track that the models had begun shifting toward almost 24 hours before. More recently, something similar (albeit less drastic) happened with Hurricane Irene, when the models’ eastward trend suddenly stopped, and the forecast began to settle on a track targeting New Jersey/NYC/Long Island.

We may be seeing a similar turning point with Tropical Storm Nate this morning. Yesterday, this storm looked like it was bound for Mexico. But things have changed overnight. This morning, shortly before the National Hurricane Center’s 11am EDT advisory, Charles Fenwick tweeted: “In the Gulf of Mexico, there was a good consensus on Nate heading to Tampico, Mexico. This morning, though, GFDL & HWRF shifted northeast with solutions south of Louisiana and in the middle of the western Gulf of Mexico respectively.”

 
aal15_2011090806_track_late
 

Dr. Jeff Masters summarizes:

Up until last night’s 8 pm EDT runs of the computer models, the models were in general agreement that Nate would meander in the Bay of Campeche for several days, until a ridge of high pressure built in to the north of the storm, forcing it westwards to a landfall in Mexico. However, the latest 2 am EDT run by the GFS model predicts that Nate may gain enough latitude to escape being forced westwards by the ridge, and instead move northwards to make a landfall along the U.S. Gulf Coast. The GFDL, which uses the GFS for its initial conditions, is also on board with this idea, as is the HWRF model, to a lesser degree. The 2 am EDT run of the NOGAPS model did not go along with this idea, though. We will have to wait until the NOAA jet makes its first mission to sample the steering currents in the Gulf of Mexico to get a better idea on how probable this northern path might be; their first flight will be tonight, and the data will make it into the 8 pm models runs that will be available first thing Friday morning.

The Houston Chronicle‘s Eric Berger, in a post titled “The northern Gulf of Mexico is back in play,” elaborates:

Just as it looked like the overnight models were converging on one solution for the track of Tropical Storm Nate, this morning’s models made an almost wholesale change.

Instead of an eventual westerly motion into Mexico, a number of forecast models have switched back to a more northerly movement by late this weekend, bringing Nate toward the northern Gulf of Mexico coast by late Sunday or Monday.

It will be most interesting to watch the newest global model runs, which should come out between noon and 2 p.m. today. I’ll especially be looking to see if the European model switches back to the more northerly solution. If you’ll recall, until yesterday this had been the Euro model’s preferred track. …

Critically, if Nate does move northward it will cross over very warm Gulf waters, and would have several days to intensify. This raises the possibility of a major hurricane striking the New Orleans region.

It still appears Texas will not be directly affected by strong winds and rain from Nate, but this is indeed proving to be a difficult storm to nail down.

Fenwick added: “NHC will probably wait for 12Z models before making any drastic changes to the forecasts, so 11AM forecast package shouldn’t have big track changes.”

The 11am discussion confirmed all of this:

AFTER 36-48 HOURS…THE MODEL SPREAD BECOMES INCREASINGLY LARGE…AS SUBTLE DIFFERENCES IN THE STRENGTH AND ORIENTATION OF A MID/UPPER-LEVEL LOW AND TROUGH EXTENDING FROM THE OHIO VALLEY SOUTHWESTWARD HAVE SIGNIFICANT IMPLICATIONS ON THE FUTURE TRACK OF THE CYCLONE. THE LATEST GFS AND GFDL MODELS…WHICH SHOW A SLIGHTLY DEEPER TROUGH…MOVE NATE NORTHWARD TOWARD THE NORTHERN GULF COAST. THE ECMWF AND NOGAPS MODELS DEPICT A WEAKER TROUGH THAT DOES NOT CAPTURE NATE AND ALLOWS IT TURN TURN WESTWARD TOWARD MEXICO TO THE SOUTH OF A BUILDING RIDGE…ALTHOUGH IT SHOULD BE NOTED THAT THERE IS CONSIDERABLE SPREAD AMONG THE ECMWF ENSEMBLE MEMBERS. THE OFFICIAL FORECAST HAS BEEN SHIFTED TO THE RIGHT AND LIES BETWEEN THESE TWO VIABLE SCENARIOS BUT HAS NOT BEEN SHIFTED AS FAR AS THE TVCA CONSENSUS. THE NOAA G-IV AIRCRAFT IS SCHEDULED TO PERFORM A SYNOPTIC SURVEILLANCE MISSION LATER TODAY…WHICH WILL HOPEFULLY HELP REDUCE THE SPREAD IN THE TRACK GUIDANCE TONIGHT.

Today would be a good day to follow my schedule and watch as the new computer models come out. Already, the latest GFS model run has seen the track details shift a bit, though the basic concept — a more northerly track, threatening the Gulf coast — remains. As Fenwick explains: “the 12Z GFS…has split the difference between its last 2 solutions & has Nate hanging out in the northwest Gulf of Mexico through day 7.” Here’s what the 7-day model forecast position looks like, with Nate on the left and Maria on the right:

uv900atl_58

Maria, incidentally, appears likely to recurve harmlessly out to sea, much like Katia (though that could change). It’s Nate we need to be watching.

To be clear, there is no reason to panic about possible threats to specific locales. The forecast can and will change in the coming hours and days. But with the Gulf waters being so warm, and so many vulnerable spots along the coast, this is definitely a situation to watch closely.

wv

In a post that went up a couple hours after mine, Dr. Jeff Masters summarizes the forecast thinking regarding Tropical Storm Nate:

Given the favorable environment, in addition to a very warm pocket of sea surface waters in the central Gulf of Mexico, we expect that Nate will intensify modestly over the next few days. The National Hurricane Center forecasts that Nate will become the third hurricane of the season by Friday. The HWRF and ECMWF agree with this forecast–both of these models bring Nate to a category 2 hurricane by Saturday. The IVCN/ICON consensus models that the Hurricane Center relies on are more conservative, peaking at category 1 intensity. Nate’s maximum potential intensity is heavily dependent on its track, which, according to the weather models, has been up in the air for the past few of days. Until this afternoon’s run, the ECMWF has held true to its forecast that Nate will track north and make landfall anywhere from Louisiana to Florida. This afternoon, it backed off of that solution and is now forecasting a northern Mexico landfall. The GFS has consistently forecasted a track that lingers in the Bay of Campeche for a few days before ultimately making dive to the west into Mexico. Over the past few days the Canadian CMC model has been reluctant to develop Nate at all, but today is forecasting the system to track north into the Southeast U.S. states. Now that there is Hurricane Hunter data to ingest (as well as confirmed 45 mph surface wind speeds), we expect the models will come into better agreement on both track and intensity for Tropical Storm Nate.

The National Hurricane Center’s 11pm EDT discussion emphasizes the gradualness of the intensification:

NATE IS FORECAST TO REMAIN IN AN AREA OF LIGHT VERTICAL WIND SHEAR FOR THE NEXT 36-48 HOURS…AND THE INTENSITY GUIDANCE RESPONDS TO THIS LOW SHEAR AND THE WARM UNDERLYING WATERS BY FORECASTING STRENGTHENING. HOWEVER…THERE IS ABUNDANT DRY AIR TO THE NORTHWEST OF NATE WHICH COULD SLOW THE RATE OF STRENGTHENING IF THE STORM INGESTS IT…AND THE CURRENT STORM STRUCTURE IS NOT FAVORABLE FOR RAPID STRENGTHENING. BASED ON THIS…THE INTENSITY FORECAST SHOWS GRADUAL STRENGTHENING INTO A HURRICANE DURING THAT TIME.

You can see the “abundant dry air” in the water vapor image at the top of this post. It’s the orange part.

After 48 hours, there is “uncertainty” and divergence among the models about how strong Nate will get. One reason the intensity depends in part on the track is that the waters have more tropical cyclone heat potential a bit further north. Also, the longer Nate stays in one place, the more it will weaken the water directly underneath it through “upwelling” — its winds and surf bringing up colder water from just beneath the surface.

Anyway, again, with regard to Nate’s track, the general forecast thinking is a path toward the Mexican coast, but there is considerable uncertainty, and the Canadian model taking Nate toward the U.S. Gulf Coast remains, albeit as an outlier. Here’s a look, courtesy of Ryan Maue’s site, at what two models are forecasting in 4 1/2 days’ time: first the HWRF, then the Canadian model.

nate15l.2011090718_37

cmc850uva_27

That’s Nate at left, Maria at right in the bottom (Canadian) image.

Updates tomorrow (Thursday) will likely be limited, but you can get the latest from my Twitter feed, and also track down the relevant data yourself, if you so desire, using the links from my “day in the life” post.

two_atl

The Atlantic tropics have been busy since Irene’s demise 10 days ago, what with Hurricane Katia, Tropical Storm Lee, Tropical Storm Maria, and now, as of a few hours ago, Tropical Storm Nate.

Lee dumped copious rain in the Southeast, and now its remnants are causing further flooding in the already saturated Northeast. Katia, which at one point reached Category 4 intensity, threatened for a while to be Irene redux, but now the computer models are extremely confident it will “recurve” safely off to sea. Maria looks likely to remain weak for a while, but could eventually strengthen and become a threat to the East Coast — but it’s way too early to tell, and any possible impact would occur no earlier than mid to late next week.

Nate, however, could become a big deal, and fast. The Hurricane Center named the storm, presently located in the Bay of Campeche / southern Gulf of Mexico, at 5pm EDT today, estimating its winds “conservatively” at 45 mph — and there are signs its intensity could ramp up quickly. Florida State meteorologist Ryan Maue, whose Twitter feed and website are excellent sources for computer model information, tweeted this afternoon, “With the curved cloud band of Nate–I’d expect explosive intensification. Wouldn’t be surprised to see hurricane in < 24 hours. Major < 72?" The waters of the Gulf of Mexico, of course, are very warm with a lot of cyclone heat potential, and there’s virtually no wind shear nearby to weaken Nate. So — with the caveat that, as Irene reminded us, intensity forecasting is a very inexact science — conditions certainly look ripe for significant and perhaps rapid strengthening.

Nate’s location is the other reason for concern. It could potentially pose a threat to anywhere from the Mexican east coast to Florida. The computer models just aren’t sure yet, and the steering currents are weak. A slow track toward Mexico presently seems the most likely, as the official forecast indicates:

223916W5_NL_sm

In light of the generally sparse population along much of the Mexican coastline, that’s preferable to some previous computer model scenarios like a direct, quick strike on New Orleans, a Florida panhandle landfall, or a Mobile hurricane. But, again, it’s just too soon to tell for sure what will happen. Hopefully the models will get a better handle on Nate within the next 24 hours, now that it’s gone from being a hypothetical storm to an actual existing one.

Another big question is what impact Nate might have on the disastrous Texas wildfires. The recent blazes were actually fanned by the winds of Tropical Storm Lee and the cold front that swept in behind it — a cold front whose southern portion then stalled over the Gulf, developed tropical characteristics, and turned into…Tropical Storm Nate. So could Nate, partially a product of the weather system that helped fuel the fires, now help put them out, by bringing tropical rains to Texas?

Unfortunately, that isn’t likely, says Dr. Jeff Masters: “None of the models is hinting at a track towards Texas, and the intense dome of high pressure associated with their record drought and heat wave will tend to discourage any tropical cyclones from making a Texas landfall over the coming seven days.” The Houston Chronicle‘s “SciGuy,” Eric Berger, agrees: “It does appear likely Texas, due to building high pressure over the state, will not see significant rainfall from Nate, especially areas outside of lower Texas.”

Speaking only for myself here, it seems like what Texas might actually need to “root” for is Nate becoming a fairly powerful hurricane — powerful enough to “make its own atmosphere,” and maybe, just maybe, push back a bit against that intense high-pressure dome. But of course, that’s a catch-22. What Texas needs is a tropical storm with soaking rains, not a disastrous major hurricane.

Wherever Nate goes, its formation is historic, or nearly so. Nate is the second-earliest forming “N” storm ever, trailing only the “N” storm of the record-shattering 2005 season — coincidentally also named “Nate,” thanks to the six-year rotating storm name list — which formed just one day earlier. The 2011 season hasn’t seen nearly as many intense hurricanes as we saw in 2005, nor as many devastating landfalling hurricanes. But in terms of sheer numbers, it’s keeping pace thus far, which is amazing. The 2005 season, you may recall, was the first ever to exhaust all 21 listed names (Q, U, X, Y and Z are skipped) and send us into the Greek alphabet, with the season’s final storm, “Zeta” (the sixth Greek letter, and 27th named storm), memorably forming on my wedding day, December 30, and not dying until January 6 of the following year (during my honeymoon). And it turns out there was actually another storm, making the total 28 — Zeta should have been Eta.

Anyway, the point is, we’re presently on 2005′s pace, or within a day of it, which is incredible; I never thought I’d see another season approaching 2005. Who knows if it will continue — probably not. But 2011 is certainly turning out to me one heck of a year. And “Ophelia” may be coming soon to a hurricane tracking map near you.

I’ll try to post an update on Nate (and the other storms) later tonight and/or tomorrow morning. In the mean time, you can get the latest — mixed in with a lot of nonsense about college football, conference realignment, tonight’s GOP presidential debate, and so forth — from my Twitter feed.

A day in the life of hurricane tracking

September 1st, 2011 - 9:24 am

I’m not back in hurricane-tracking mode here on Weather Nerd — Katia, proto-Lee, and far off hypothetical proto-Maria aren’t really threats just yet — but for those who’d like to do some do-it-yourself storm-watching, I thought I’d make a schedule of a typical day of hurricane forecasting developments, with links to the data sources that update around the listed times.

First, a bit of a glossary, and some background. “NHC” is the National Hurricane Center, and their advisories usually come out a few minutes before the official top-of-the-hour timestamp. (So, for instance, the 5pm advisory comes out around 4:45 or 4:50.) “Full” advisories include the all-important meteorological “discussions” and updated 5-day forecasts. “Intermediate” advisories update the current conditions, but don’t generally add much else, and they’re only issued when watches or warnings are up for some coastline somewhere.

“NAM,” “GFS,” “NOGAPS,” “CMC (Canadian),” “HWRF,” “GFDL” and “ECMWF (European)” are seven of the computer models that NHC looks at, with “runs” either two or four times a day. Loosely speaking, the runs are identified by the time that they start (in “Zulu” or Greenwich Mean Time, e.g., “the 00Z run,” “the 06Z run,” etc.), but they take differing amounts of time to complete. So I’ve listed the approximate times that each model usually spits out new forecast maps for us to look at.

The GFS and ECMWF global models are the most accurate models; NAM, NOGAPS and CMC are the least accurate of these seven. HWRF and GFDL are somewhere in the middle. You can read more here about the various computer models, from Dr. Jeff Masters.

In all cases except HWRF and GFDL, the links below go to the individual, model-specific graphic for the latest “run,” from Ryan Maue’s site. (To check if the model has updated, look at the top middle of the linked image where it says something like “MSLP (hPa) 06Z01SEP2011.” Those first three characters of the timestamp, “06Z” in this example, tell you which model “run” you’re seeing.) For the HWRF and GFDL, whose URLs are storm-specific, my links simply go to Maue’s page; those models at the top of his left-hand column.

Keep in mind that computer models can shift wildly from run to run, and are subject to huge errors, especially in their longer-term forecasts. Do not make any life-or-death decisions based on a computer model forecast! If you’re confused by what the computer models show, you’re probably better off ignoring them, and trusting the NHC. Over an entire season, the official forecast generally outperforms any specific model.

That said, for those of us “weather nerds” who can’t help ourselves, the model maps are like, well, #stormporn. :) So, without further ado, here’s the schedule. All times Eastern Daylight Time. I’ve tried to use font size and weight to give a general idea “how important” each event is.

5:00 AM: Full NHC advisory

5:15 AM: NAM 06z run (simulated radar, satellite)

6:45 AM: GFS 06z run

7:30 AM: HWRF 06z run

7:45 AM: GFDL 06z run

8:00 AM: Intermediate NHC advisory*

11:00 AM: Full NHC advisory

11:15 AM: NAM 12z run (simulated radar, satellite)

12:45 PM: GFS 12z run

1:00 PM: NOGAPS 12z run

1:15 PM: CMC (Canadian) 12z run

1:30 PM: HWRF 12z run

1:45 PM: GFDL 12z run

2:00 PM: Intermediate NHC advisory*

2:45 PM: ECMWF (European) 12z run

5:00 PM: Full NHC advisory

5:15 PM: NAM 18z run (simulated radar, satellite)

6:45 PM: GFS 18z run

7:30 PM: HWRF 18z run

7:45 PM: GFDL 18z run

8:00 PM: Intermediate NHC advisory*

11:00 PM: Full NHC advisory

11:15 PM: NAM 00z run (simulated radar, satellite)

12:45 AM: GFS 00z run

1:00 AM: NOGAPS 00z run

1:15 AM: CMC (Canadian) 00z run

1:30 AM: HWRF 00z run

1:45 AM: GFDL 00z run

2:00 AM: Intermediate NHC advisory*

2:45 AM: ECMWF (European) 00z run

*if watches or warnings are in effect

Of course, reconaissance data is also important, but the recon flights’ schedule varies from day to day, and the data can be a bit difficult to decode. But you’re certainly welcome to try your hand at it here. Unless you’re pretty technically minded, though, it’s probably better to wait for the NHC advisories to explain what the planes found.