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Monthly Archives: August 2012

Weather Nerd: The Next Generation

August 27th, 2012 - 10:00 pm

If I can be permitted a brief personal aside… today was a momentous day in the Loy household. Our eldest daughter (of 3), age 4 1/2, started kindergarten. Then, because she’s taken an interest in Isaac — she’s a huge Daddy’s Girl; she pretty much takes an interest in everything I do — I asked if she wanted to make a hurricane tracking chart. She was thrilled with the idea. So, without further ado, I give you the new kindergartner’s first ever tracking chart:

20120827-195422.jpg

I wrote the dots; she drew the lines. You’ll note she decided to spare Haiti a direct hit. I don’t think she realized that the hurricane’s track actually is allowed to go over land. Too bad it doesn’t work that way in real life!

She was also curious about how storm surge works, so I gave her & her little sisters (ages 3 and 1) a demonstration using a hose, their back-yard water table, and some grapes (playing the role of houses on the waterfront):

20120827-195743.jpg

Hopefully the folks in the lowest grape got the Hell out!

As I wrote on Twitter, “Out: SLOSH model. In: LFSSWT (Loy Family Storm Surge Water Table). The latest in grape-based surge modeling technology.”

So, there you go. I don’t mean to make light of Isaac; I just wanted to give y’all a little window into my world. :) Many of my Isaac updates and tweets have been written amid the chaos of the under-5 set. Good times.

I’ll have more on the storm shortly. Reader’s Digest version: it’s still not quite a hurricane; almost, maybe in an hour, but not yet. Those prayers to the Patron Saint of Dry Air are working, NOLA. Keep it up.

Isaac: Uncertainty Still Reigns

August 27th, 2012 - 2:56 pm

[NOTE: check the blog homepage and follow me on Twitter for the very latest.]
* * * * *

Just a quick additional note, as an addendum to my post below. There still remains a remarkable amount of uncertainty regarding the details of Isaac’s track, given that we’re only 24-48 hours from landfall. Check out this “4-panel plot” showing the 48-hour positions of the Euro (top left), GFS (top right), HWRF (bottom left) and GFDL (bottom right) models, courtesy of Dr. Ryan Maue and Weather Bell Models:

A1U1fKjCQAAkD8M

This particular forecast is, as Maue says, a nightmare. There’s just been much more uncertainty than with most hurricanes, and that remains true, even at this late date.

As an aside, it looks like Isaac may be upgraded to a hurricane — or else very, very nearly one — at 5:00 PM Eastern. Stay tuned.

P.S. Dr. Jeff Masters has some excellent analysis on the potential storm surge from Isaac:

Storm surge is the primary damage threat from Isaac. Isaac is a huge storm, with tropical storm-force winds that extend out 205 miles from the center. For comparison, Hurricane Katrina at landfall had tropical storm-force winds that extended out 230 miles from its center. Isaac’s large size will enable it to set a large area of the ocean into motion, which will generate a large storm surge once the storm approaches land on the Gulf Coast. Water levels at Shell Beach, Louisiana, just east of New Orleans, were already elevated by 1′ this morning. Conversely, water levels have fallen by 2′ this morning at St. Petersburg, Florida, where strong offshore winds due to Isaac’s counter-clockwise circulation have carried water away from the coast. The latest 6:30 am EDT Integrated Kinetic Energy analysis from NOAA’s Hurricane Research Division put the destructive potential of Isaac’s winds near 0.6 on a scale of 0 to 6, but the destructive potential of Isaacs’s storm surge was 2.1 on a scale of 0 to 6. I expect this destructive potential will rise above 3 by time Isaac makes landfall, making Isaac’s storm surge similar to that generated by Category 2 Hurricane Gustav of 2008, which followed a path very similar to Isaac’s predicted path. Gustav brought a storm surge characteristic of a Category 1 hurricane to New Orleans: 9.5′ to Lake Borgne on the east side of the city. A higher Category 2-scale surge occurred along the south-central coast of Louisiana, and was 12.5′ high in Black Bay, forty miles southeast of New Orleans. Recent model runs indicate Isaac may slow down to a forward speed under 5 mph on Tuesday evening and Wednesday morning, close to the coast. If Isaac is just offshore at this time, the coasts of Southeast Louisiana, Mississippi, Alabama, and the Florida Panhandle will be exposed to a large storm surge with battering waves for two high tide cycles. This sort of extended pounding will be capable of delivering more damage than the storm surge of Hurricane Gustav of 2008.

I’m a bit wary of this sort of forecast — likely Category 1 hurricane to produce uncommonly devastating surge due to its size! — because similar predictions regarding Irene in 2011 and Ike in 2008 were not fully borne out by the reality of what occurred. However, the analogy to Gustav seems apt in this case. We shall see. Certainly, if you live in a storm surge zone, take no chances. Get the Hell out; go to higher ground.

Dr. Masters also has a good overview of the surge’s likely impact on New Orleans, including a handy map of the newly upgraded levees. Read the whole thing, as they say.

How Isaac’s Next 48 Hours Might Unfold

August 27th, 2012 - 1:08 pm

[NOTE: check the blog homepage and follow me on Twitter for the very latest.]
* * * * *

Isaac remains a 65 mph tropical storm as of 11:00 AM EDT. It continues to try to get better organized, but has yet to form an eye or take a more “classic” appearance on satellite.

issac-floater-vis

If New Orleans and the Gulf Coast survive this storm relatively intact, they ought to designate a Patron Saint of Dry Air, and thank that saint. If it weren’t for that single atmospheric feature — dry air getting sucked into the circulation — this storm could well be a monster right now, bearing down on New Orleans along a worst-case track. (It’d be worse than Katrina, in terms of the track.)

Instead, even after last night’s re-centering, Isaac is still struggling to get its act together with respect to its internal core structure, which is the only missing prerequisite to significant intensification right now. The overall wind shear is light, the outflow is good, and the water is warm (probably not deeply warm enough for Cat 4/5, but certainly warm enough for Cat 3). But, as I explained in my post four days ago wondering whether Isaac might never become a hurricane (still technically a live question), a storm can’t intensify significantly without a well-structured inner core, no matter how “perfect” the conditions otherwise are. And it’s dry air that’s consistently prevented Isaac from developing a healthy core.

Unfortunately, the possibility of shedding that dry air at the last minute, and intensifying rapidly just before landfall, remains very much alive. It might not happen, but it might, and that’s the chief remaining cause for concern. (Well — the size of the storm, its somewhat slow speed, and the resulting increased & broad-based storm surge and heavy flooding rains are also big concerns.) As the NHC explained this morning:

UNTIL THE DRY AIR MIXES OUT…EROSION OF THE INNER-CORE CONVECTION WILL LIKELY CONTINUE UNTIL ISAAC APPROACHES THE NORTH-CENTRAL GULF COAST IN ABOUT 24 HOURS. AT THAT TIME…INCREASED FRICTIONAL EFFECTS FROM THE GULF COAST LAND MASS IS EXPECTED TO CONTRIBUTE TO AN INCREASE IN CONVECTION IN THE NORTHEAST QUADRANT…WHICH COULD ENABLE THE STRENGTHENING PROCESS.

To illustrate how this might transpire, it’d helpful to look at the most recent run of the most reliable American computer model, the GFS. The model intensifies Isaac more than the NHC is predicting — the NHC forecast intensity tops off at 90 mph; the GFS gets up to 112 mph 99 mph, as you’ll see below — and the GFS’s landfall point is a bit west of the NHC’s. But the general intensification trend is similar. Because Dr. Ryan Maue’s excellent Weather Bell Models site gives us a printout of the GFS projection for every 3 hours between now and landfall, we can go through, step by step, and get a sense of how the next 36 hours might play out. Please don’t focus on the precise details — this is only a single computer model run, not an official forecast, and it is certainly subject to change. I just want to give everyone a general overview of the sort of storm evolution that might occur, according to this trusted model. Don’t make life-or-death decisions based on this model; that’s what the NHC forecast is for. This is just for illustrative purposes.

[UPDATE: As indicated by the crossed-out "112 mph" above, I made an embarrassing and critical error here. I forgot that the wind totals in these graphics, which I converted from knots to mph, also have to be converted from flight level to surface level, which entails a reduction of 10 to 15%. I know that's true of flight-level winds from recon flights and the like, but I totally forgot about it in this context. That helps explain much of the apparent discrepancy between the NHC and GFS forecasts (though the GFS was still a bit more bullish) and forces me to modify some of the text below. I apologize profusely for the error, which I have corrected by reducing each affected figure by 12%. These corrections are made without strikethroughs, for ease of reading.]

First, here’s how the GFS portrayed Isaac as of its “initial” position, at 8:00 AM Eastern Time, with an estimated 55 mph winds and 991.2 mb pressure.

gfs_mslp_uv900gulf_tropical_1

Now, let’s see how the GFS predicted Isaac would evolve from there. (Link goes to the image.)

Monday, 11:00 AM: 56 mph, 989 mb
Monday, 2:00 PM: 58 mph, 987 mb
Monday, 5:00 PM: 60 mph, 985 mb
Monday, 8:00 PM: 65 mph, 983 mb.

The 8:00 PM snapshot shows the first sizable three-hour jump in wind speed — so don’t be surprised if any changes remain incremental all day today. Here’s what it looks like:

gfs_mslp_uv900gulf_tropical_5

Then, according to the GFS, Isaac largely stands pat for about six hours, before beginning to strengthen more rapidly early Tuesday morning:

Monday, 11:00 PM: 65 mph, 982 mb
Tuesday, 2:00 AM: 68 mph, 980 mb
Tuesday, 5:00 AM: 75 mph, 978 mb

So Isaac finally becomes a hurricane in the wee hours of the morning, per the GFS, looking like this:

gfs_mslp_uv900gulf_tropical_8

Tuesday, 8:00 AM: 77 mph, 977 mb
gfs_mslp_uv900gulf_tropical_9

Tuesday, 11:00 AM: 80 mph, 976 mb
gfs_mslp_uv900gulf_tropical_10

Tuesday, 2:00 PM: 82 mph, 973 mb
gfs_mslp_uv900gulf_tropical_11

At this point, it’s tomorrow afternoon, and Isaac is making landfall in Plaquemines Parish, near the mouth of the Mississippi River. According to the GFS (and the official NHC forecast), it will be intensifying as it does so, which is bad news, as intensifying hurricanes are more dynamic, bring heavier wind gusts and generally better organized than steady-state or decaying hurricanes of the same stated intensity. (On the bright side, late intensification — as opposed to earlier intensification and then steady state for a long time before landfall — means Isaac will have less time to build up a massive storm surge ahead of it, a la Katrina and Ike. Given the storm’s size, that’s a very good thing.)

Anyway, GFS has Isaac reaches the borderline of Category 2 status between 2pm and 5pm tomorrow, as it passes over the marshes of Plaquemines:

Tuesday, 5:00 PM: 94 mph, 969 mb
gfs_mslp_uv900gulf_tropical_12

Note the big jump between those last two frames, from 82 mph to 94 mph in just three hours tomorrow afternoon, during landfall in Plaquemines Parish. Not good. But again, the point isn’t the detail of exactly when or where the GFS thinks this will happen, which is subject to change, and is not reflected by the official forecast at this time. The point, rather, is that this sort of thing can happen, and can happen quite close to land, with little or no warning. That’s why the exact track and timing are so important. A storm that might intensify that quickly is a storm that might turn into a mid-range Category 3 a few hours later, if it had just a little bit more time over water to get there. (Conversely, it’s a storm that might remain a low Category 1 or Tropical Storm if it had just a little bit less time.) It looks like Isaac will probably take too long to start strengthening, and thus run out of water before catastrophic last-minute rapid deepening can happen — indeed, contra the GFS, it might even run out of water before it can strengthen much at all — but these model maps illustrate why the difference between a fearsome monster and “overhyped” “dud” of a storm can be a matter of a few hours and/or a few dozen miles in either direction.

Anyway, the next GFS projection takes Isaac up to solid Category 2 status:

Tuesday, 8:00 PM: 99 mph, 967 mb
gfs_mslp_uv900gulf_tropical_13

After that, in the GFS’s forecast, land interaction begins to weaken the storm.

Tuesday, 11:00 PM: 97 mph, 970 mb
Wednesday, 2:00 AM: 99 mph, 974 mb
Wednesday, 5:00 AM: 90 mph, 977 mb
Wednesday, 8:00 AM: 84 mph, 978 mb

The GFS proceeds to show Issac almost stalling over the bayous, and actually gaining a tiny bit of strength midday Wednesday while sitting over that marshy land mass, which would be bad news in several respects. (Primarily due to flooding rains, but also because of a prolonged wind and surge battering.) In the GFS scenario, Isaac retains hurricane or high-end tropical-storm force winds for more than 24 hours over land. I’m not sure how realistic that scenario is, so I won’t dwell on it right now, but it’s certainly something to watch. [UPDATE: I will say this: intensification during landfall can definitely lend itself to slower-than-usual weakening over land. And so can passage over wet, marshy areas. Louisiana ain't Cuba. I do think the inland wind aspect of this storm is something to watch, along with the huge threat of inland flooding rains, of course.]

By Thursday afternoon, the GFS picture of Isaac looks like this:

gfs_mslp_uv900gulf_tropical_27

This would be a significant wind and rain event for all of Louisiana, if it came to pass. But again, my point here is not to “predict” these details, and please remember that this is just one “run” by one computer model, not the official forecast. My point is to illustrate the general parameters of the storm evolution that might occur, and to point out how small differences can have a huge impact on the outcome.

P.S. New Orleans Mayor Landrieu is sticking with the plan of “sheltering in place.” Disregarding the notion of preparing for a storm one category worse than the forecast, he is telling residents to prepare for a “strong Category 1″ (which is precisely what the forecast says), adding, “The good news is it’s not a Category 3.” He’s probably right, of course — and if so, he’ll be hailed for handling the storm well, and nobody will ever read my post bashing him again. But in the less likely but still plausible (20% chance? 10%? 5%?) event that Isaac strengthens dramatically before landfall and brings truly devastating conditions to New Orleans — rather than just a rough, windy, rainy day or two, with minor-to-moderate flooding — history will judge him harshly.

The fact is, Landrieu chose to prepare for the most likely case, and NOT to prepare for the worst. So, hopefully the worst won’t happen. It probably won’t. It usually doesn’t. I still disagree with his decision, and always will, based on the contemporaneous information available yesterday (not 20/20 hindsight) about what the realistic worst-case scenario was. But I do understand the reluctance to evacuate under those maddeningly uncertain circumstances, and I hope it works out for him (because I hope NOLA doesn’t get crushed by Isaac, obviously).

[NOTE: check the blog homepage and follow me on Twitter for the very latest.]
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Isaac remains a tropical storm this morning, still suffering some of the inner core disorganization that has plagued it for days. And while the odds of a direct hit, or near-direct hit, on the New Orleans area are increasing, the odds of a “worst-case scenario” appear to be decreasing, as both the computer models and the official NHC forecast have downgraded their intensity forecasts a bit. Officially, the NHC is now calling for a Category 1 strike, although Category 2 remains very much in play. Category 3+? Still definitely possible, but probably a bit less likely than yesterday.

It’s still way too early for New Orleanians or others in Isaac’s path to let down their guard, though. Intensity is unpredictable, and at least one of the better models, the HWRF, is still calling for major hurricane at landfall:

uv900_mslp_p_13-isaac

But the most accurate (on average) American model, the GFS — which has been driving the grave concern for New Orleans since Saturday afternoon, when it began predicting a Category 3 or 4 landfall there — is now calling for a somewhat less fearsome-looking Isaac, albeit still a low-end Cat. 3, coming in just west of the Mouth of the Mississippi River:

gfs_mslp_uv900gulf_tropical_15-99kt

That scenario would still drive a ton of water into the New Orleans area, especially with the amount of time Isaac will have over the Gulf to push the Gulf waters toward shore ahead of landfall. Perhaps just as important, the possibility of rapid deepening remains frighteningly present, if Isaac could ever manage to get its inner core issues worked out. If that were to happen, say, 12 or 18 hours before landfall, it’d be really, really bad news. That’s why folks in harm’s way should continue to prepare for the worst.

Still, there is increasingly reason to hope that Isaac will be something less than worst-case. Indeed, most of the intensity models don’t foresee it getting stronger than Category 1:

aal09_2012082712_intensity_early

If the Cat. 1 scenario verifies, that’d be great news (though the surge would still potentially be a big problem, due to the storm’s size and duration). But it would also bring out the cries of “OVERHYPE!!!1!” in force, from folks contending myopically that the entire threat of something worse than Cat. 1 was dreamed up in the fevered imaginations of TV pundits and weatherbloggers. People who are tempted to make this argument would do well to remember what the computer model forecasts looked like Saturday afternoon, and Saturday night, and much of Sunday. I would suggest that those individuals take their unimpeachable 20-20 hindsight and go place a bet on the winner of last year’s Kentucky Derby. Weather forecasting is a difficult and inherently uncertain endeavor, and just because a scenario doesn’t occur, doesn’t mean it wasn’t a realistic concern at the time. If the phrase “prepare for the worst” means anything at all, it makes no sense whatsoever to argue that every worst-case scenario which doesn’t verify was therefore some sort of fraud. Most worst-case scenarios don’t happen. That’s in their nature. But since we don’t know in advance which ones will happen and which won’t, we still have to prepare for each one, in order to ready for the small percentage of them that do happen.

But I’m getting ahead of myself. Isaac remains a real, live threat to life and property, in the here and now. The odds of a total disaster may have dropped somewhat. But there is still plenty of reason to be concerned, especially about the biggest killer, storm surge — and folks in the storm’s path, particularly in New Orleans, need to continue to take it very, very seriously, and prepare accordingly.

[NOTE: check the blog homepage and follow me on Twitter for the very latest.]
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In an overnight development with major implications for both the track and intensity of Tropical Storm Isaac, the storm’s center of circulation has “relocated” underneath the ball of convection (i.e., thunderstorms) that has been blowing up all evening, previously to the north of the center.

avn0

This happens sometimes, and it means Isaac’s strengthening will likely begin in earnest now. I wouldn’t be surprised if he’s a hurricane by morning.

Meanwhile, by spontaneously “moving” 55 miles or so to the northwest of its previous position, Isaac’s center may now be on a different track trajectory, and/or may react slightly differently to the steering currents that drive the storm’s movement. The most recent set of computer model runs are less useful now, since they were based on an incorrect initial storm position, so we’ll have to see a new set of model runs to begin to understand what impact this relocation of the center will have on the track. It seems plausible that it could result in a more easterly track — perhaps increasing the risk to the Mobile area or the Panhandle, or maybe increasing the risk to New Orleans as opposed to the TX/LA border region — but we’ll need to see some model runs to be sure.

Speaking of model runs, there was also another significant development moments ago: the 00Z European model, i.e. the ECWMF or “Euro,” has shifted its landfall point from the AL/FL border region west to the LA/MS border region. It has also decreased its landfall intensity to Category 1. So this brings the Euro and the GFS more in line with one another, specifically by way of the European model joining the American model further west (U-S-A! U-S-A!). This implies the possibility of a dangerous consensus for New Orleans (ignoring the intensity issues for the moment, since that’s much harder to predict). But course, as I just said, the center relocation could throw off any such consensus, so we’ll just have to wait and see what the various 06Z models (and eventually, the 12Z Euro) show.

I’d love to stay up for the 5:00 AM EDT advisory and discussion from the NHC, but I’ve got to get to bed now — it’s 12:30 AM local (Mountain) time, I’ve gotten limited sleep all weekend due to Isaac-tracking, and I’ve got both work and my 4 1/2 year old daughter’s first day of kindergarten tomorrow. So I need to Occupy My Bed, as it were.

I’ll do my best to keep this blog updated tomorrow, and I’ll also inevitably be tweeting extensively throughout the day about Isaac.

[NOTE: check the blog homepage and follow me on Twitter for the very latest.]

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Via Nate Silver, I found this excellent blog post by Weather Channel hurricane specialist Bryan Norcross. It crystallizes a couple of things I’ve been fretting about, but says them more clearly and with more authority that I could (since Norcross is, y’know, an actual meteorologist and all), so I will now quote it extensively:

What a horrendous confluence of events. Tropical storms never get on people’s radar, and the fact that Isaac passed Key West with less effect than a gusty afternoon thunderstorm made the situation worse. Even with a Cat 1 hurricane, will people take action tomorrow that may save their life Tuesday night?

Isaac’s extremely large circulation is one of the factors that should make it intensify relatively slowly, and a track that misses the high heat-content pools in the Gulf should help in that direction as well. Plus it has less than two days over the water before landfall. But, the water ahead is still plenty warm – over 85 degrees – and the atmospheric pattern looks very favorable for strengthening. Taken together, the NHC’s Cat. 2 forecast looks reasonable, though preparations should be made for a Cat. 3, given the lack of skill inherent in intensity forecasting.

Apparently, according to Silver, in an earlier iteration of his post, Norcross articulated this as a more general statement: “Always prepare for one category higher than forecast, knowing that intensity-forecasting skill is not high.”

Anyway, Norcross’s point that “tropical storms never get on people’s radar” is precisely why I hope Isaac becomes a hurricane overnight. That’s going to happen eventually anyway, and it would be helpful for preparedness if it goes ahead and happens now. Of course, stubborn locals and hype-trolls will still foolishly say “C’mon! It’s just a Category 1!” — ignoring NHC director Rick Knabb’s admonition, “Don’t make preparations based on current intensity, prepare for the stronger #Isaac we’re forecasting. Evacuate if instructed.” — but at least calling it a hurricane would help a little bit.

Back to Norcorss:

In any case, that same large circulation will move a lot more water toward the coast than an average hurricane. The entire Hurricane Warning area – from Louisiana to the western Panhandle – is extremely vulnerable to storm surge flooding. The NHC is forecasting 6 to 12 feet of water ABOVE THE GROUND in spots along that stretch of coast.

Normally, the exact amount of surge will be dependent on the exact track and where in the tide cycle the storm comes in. In Isaac’s case, however, there will be such a long duration of onshore winds, due to the storm’s size and slow forward speed, the water may stay high for more than one tide cycle.

In fact, that size and slow forward speed will make this a hurricane experience like none in memory, if it comes together as forecast. The weather will deteriorate tomorrow (Monday) in the Florida Panhandle, and tomorrow night across the rest of the northern Gulf coast. Then Tuesday the storm approaches the coast and a whole day later it is just inland on the current timetable. Even Thursday there is still onshore wind over part of the coast.

People will experience strong, howling winds and torrential rain for 24 to 36 hours or more in this scenario. They will be trapped at home, many without power.

And then there’s New Orleans. The storm as currently forecast should NOT exceed the capabilities of the new super-strong levees, but what if the storm comes in stronger? What a decision to have to make! Should they call an evacuation or not? In addition, there are populated areas outside of the levee-protection system.

Tomorrow (Monday) will be a day for big decisions from Louisiana to the Florida Panhandle. With life-threatening storm surge expected well away from the landfall point, widespread evacuation orders are likely.

And then there’s the inland flood threat from the torrential rain.

Unless something unexpected happens, it’s truly a nightmare scenario.

New Orleans Now Officially In Isaac’s Path

August 26th, 2012 - 8:41 pm

[NOTE: check the blog homepage and follow me on Twitter for the very latest.]
* * * * *

The official National Hurricane Center forecast as of 11:00 PM EDT calls for a near-worst-case track for New Orleans: a direct hit from the southeast.

212842W_sm

The predicted intensity, 100 mph (Category 2) at landfall, isn’t “worst-case,” though it’s not a walk in the park, either. But there’s a good deal of “downside risk,” if you will, that the intensity could be substantially more severe — possibly due to late, pre-landfall intensification, which is the worst kind (both for preparedness reasons and because, holding their stated intensity constant, intensifying storms are more dynamic and more damaging).

A Category 2 hurricane following the above track would be bad enough. A Category 3 or greater hurricane following the above track would be an absolute disaster.

That said, this official track isn’t some sort of gospel truth. The computer models remain decidedly split, with some taking the storm well west of New Orleans, and some well east of it:

AL09_current-split

New Orleans is the NHC’s landfall point basically because it’s the midpoint of this uneasy model non-consensus right now. But it’s entirely possible that either the western “camp” or the eastern “camp” will be proven right, largely sparing the Big Easy. (New Orleans would prefer an error to the east vis a vis the NHC track. An error to the west would have to be quite substantial to be helpful, since the right-front quadrant is the most dangerous part of the storm, and would bring a massive surge into the NOLA area even if the storm’s center were a ways off to the west.)

Here’s how the 11pm discussion describes the track thinking:

THE MODELS SHOW ISAAC TURNING TOWARD THE NORTHWEST INTO A BREAK IN THE SUBTROPICAL RIDGE. ALTHOUGH THE MODELS AGREE ON THIS TURN…THERE IS AN UNUSUALLY LARGE SPREAD IN THE TRACK GUIDANCE AFTER 24 HOURS. THE SPREAD OF LANDFALL LOCATIONS ALONG THE NORTHERN GULF COAST RANGES FROM THE TEXAS/LOUISIANA BORDER EASTWARD TO THE ALABAMA/FLORIDA BORDER WITH THE HWRF…GFDL…AND GFS NEAR THE WESTERN EDGE AND THE UKMET AND ECMWF ALONG THE EASTERN EDGE OF THE ENVELOPE. OVERALL…THE CONSENSUS HAS SHIFTED A LITTLE WESTWARD AND THE OFFICIAL FORECAST AS BEEN MOVED IN THAT DIRECTION. THE NHC FORECAST IS BETWEEN THE ECMWF AND GFS ENSEMBLE MEANS AND NEAR THE HFIP MULTI-MODEL CONSENSUS. BECAUSE OF THE VERY LARGE SPREAD IN THE GUIDANCE…THERE CONTINUES TO BE GREATER THAN USUAL TRACK FORECAST UNCERTAINTY.

The next big event in the evolution of the track forecast will be the release of the 00z GFS around midnight EDT. Less important but still worth watching: the 00z HWRF and GFDL, around 1:30 and 1:45 AM EDT, respectively. Finally, the big one: the ECWMF (Euro) at around 2:10 AM EDT. (Links will cease being broken when the models go live.) If the twice-daily Euro shifts west toward the other models, the NHC’s hair will be on fire about New Orleans by the 5am advisory. If not, we’re probably looking at 12 more excruciating hours of track uncertainty.

The uncertainty can’t go on much longer, though. The divergent model tracks “split” within the next 24 hours. At some point Monday, Isaac will have to choose which way to go. Still, it would be nice to have a clearer idea by morning, so government officials and residents in New Orleans — and elsewhere — can make well-informed decisions first thing. (It would also be nice if Isaac would go ahead and strengthen to a hurricane. It’s psychologically difficult, I think, for people to take a “Tropical Storm” seriously. Isaac being upgraded is just a matter of time, so I think the sooner the better at this point, for the sake of preparedness.)

On the bright side, Isaac’s slight slowdown today has bought them a little more time. This is now looking more like a Wednesday event, rather than a Tuesday-night event, except maybe in Plaquemines Parish. Of course, conversely, a slowdown also potentially means more time to strengthen over the Gulf.

Speaking of which… what about intensity? On satellite, Isaac looks better organized tonight…

rbtop0

…but the strongest thunderstorms remain displaced from the center due to dry air on the storm’s south side. The pressure actually went up a millibar since the last advisory, though weatherblogger and author Mike Smith is skeptical: “The latest Hurricane Hunter aircraft was not able to get the dropsonde instrument exactly where it needed to be. It showed a slight rise in pressure, but that seems doubtful to me as the ‘central dense overcast’ for Isaac — a necessary component of a hurricane — now seems to be developing.”

On Twitter, Joe Bastardi mused that the center may re-form under the convection — which, it strikes me, would have big implications for the track, too, shifting everything to the right because of the center re-forming to the north. It would basically turn those LA/TX models into NOLA models, and the MS/AL models into Florida panhandle models (roughly speaking). But now I’m speculating. The NHC hasn’t said anything about center re-formation.

There’s also the fact that Isaac is a large system, so it can take a longer time to “wind up,” see pressure drops and eventually wind speed increases. One theory is that this process has begun, but is simply going to take a while because of the size of Isaac’s wind field.

Anyway, back to the dry air from the cut-off low southwest of Isaac. The computer models have been expecting that to abate for a while now, and yet it hasn’t, so who knows? Maybe Isaac will continue to be held back. We can hope. Here’s what the NHC writes about the intensity forecast:

THE LARGE SCALE ENVIRONMENTAL FACTORS…WARM WATERS…AND A CONDUCIVE UPPER-AIR PATTERN FAVOR STRENGTHENING DURING THE NEXT COUPLE OF DAYS. HOWEVER…THE LACK OF AN INNER CORE AND LARGE WIND FIELD COULD CONTINUE TO BE IMPEDING FACTORS FOR SIGNIFICANT STRENGTHENING IN THE SHORT TERM. THE NHC INTENSITY FORECAST SHOWS A GRADUAL INCREASE IN WIND SPEED DURING THE NEXT 12 HOURS OR SO…FOLLOWED BY MORE STEADY STRENGTHENING.

The bottom line is that Isaac may strengthen into a major hurricane, or it may continue to struggle a bit. As with the track, NHC basically splits the difference between these two scenarios. So don’t be fooled by the 100 mph peak forecast — it could get worse than that. (Or it could be a Cat. 1.) We just have to keep watching and waiting. Folks in the storm’s path should assume the worst, which would be a major hurricane.

[NOTE: check the blog homepage and follow me on Twitter for the very latest.]

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In a bizarrely low-key press conference that seemed more focused on calming residents’ “anxiety” and vaguely telling them to “be prepared” (and then making of a series of mundane announcements about municipal matters like trash collection and parking restrictions) than on advising them to take specific, concrete steps commensurate to the risk of a possibly major hurricane potentially making a direct hit on America’s most hurricane-vulnerable city starting in about 48 hours, New Orleans Mayor Mitch Landrieu did his best Ray Nagin impression Sunday, announcing a no-evacuation, “shelter in place” plan that suggests a stunning level of confidence that a worst-case scenario won’t happen, at a time when it remains, meteorologically speaking, very much in play.

The possibility that residents would be “sheltering in place” in a “place” the could, in the worst-case scenario, be swallowed up by the Gulf of Mexico, was not mentioned.

Mayor Landrieu said he did not anticipate announcing any revisions to the plan — such as a decision to order evacuations, a possibility he explicitly downplayed — until around noon tomorrow, by which time the onset of bad weather would be around 24 hours away. Despite reams of pre-Katrina literature indicating that it takes 48 to 72 hours to evacuate New Orleans in the event of a major hurricane threatening a direct hit, and despite the experience of 2005′s rushed and incomplete evacuation so flawed that it left 50,000 people to be rescued from rooftops and such by the Coast Guard, Mayor Landrieu apparently thinks 24 hours is enough time to make an evacuation work, if one is needed.

Okay then.

I want to be fair here. I’m neither a meteorologist nor a New Orleans official, planner or expert. Perhaps Landrieu is right, and I’m wrong. Perhaps New Orleans now has plans that will allow it to effectively evacuate in 24 hours’ time. My understanding has been that that’s basically impossible, but again, I’m concededly not an expert. It’s certainly true that, by midday tomorrow, we’ll have more and better information about Isaac’s projected path and intensity at landfall, both of which remain maddeningly difficult to pin down right now. So if it’s reasonably possible to wait until tomorrow morning to make the call, that would certainly be preferable. I’m just not so sure it’s reasonably possible. I thought the decision needed to be made today, despite the admittedly imperfect information and the very significant chance of a false alarm.

Even if an evacuation can reasonably be begun tomorrow if necessary, Mayor Landrieu certainly should have done more to prepare residents now for the possibility. In contrast to Governor Bobby Jindal, who explicitly advised residents of low-lying coastal areas to prepare today for a likely evacuation tomorrow (and even urged them to voluntarily leave tonight), Landrieu was maddeningly vague in telling residents what to “prepare” for. He seemed to be advising them to “prepare” to “shelter in place” — in other words, to stock up on essentials, etc. — than to prepare for possible evacuations. Moreover, the city government’s relatively nonchalant attitude at present guarantees that most private employers will take a similar attitude, meaning lots of residents with jobs won’t feel free to take off work tomorrow to evacuate.

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Time For Action

August 26th, 2012 - 12:00 pm

[NOTE: check the blog homepage and follow me on Twitter for the very latest.]

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Mayor Landrieu and Governor Jindal are set to speak within the next 90 minutes or so. I hope what they have to say involves words like evacuations, buses and contraflow, based on an orderly plan starting immediatelya. It’s still very, frustratingly unclear where Isaac will go and how strong it will get — much more unclear than Katrina was — but New Orleans is very much one of the places in danger, and certainty will now come too late. New Orleans takes time to evacuate. Prudent precaution demands that they act NOW. Better safe than sorry.

Time to Get The Hell Out, folks.

I’ll post more once my girls are in bed for naptime (likely after the governor’s and mayor’s pressers).

[NOTE: check the blog homepage and follow me on Twitter for the latest all weekend.]

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As Tropical Storm Isaac continues to churn–and struggle a bit–in the waters off Cuba, Hurricane Watches are up from southeastern Louisiana to the Big Bend of Florida, and the ├╝ber-vulnerable city of New Orleans has moved inside the NHC’s cone of uncertainty. Three of the best American forecast models — the GFS, HWRF and GFDL — are in almost lockstep agreement this morning that Tropical Storm Isaac will track toward southeastern Louisiana over the next 60 or so hours. Here is what the GFS expects last Tuesday night — an intensifying, borderline Category 3-4 hurricane coming ashore on a near worst-case track for the Big Easy:
 
 
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Despite all this, I get the sense that most people aren’t paying attention. Last night I noted that Drudge and NOLA.com still aren’t focusing on the New Orleans threat; well, they still aren’t. Moreover, Twitter searches for “New Orleans evacuation” and “Landrieu evacuation” (Mitch Landrieu is NOLA’s mayor) turn up almost literally no discussion. Not only have evacuations not been ordered yet, it seems nobody is even talking about the possibility. I keep seeing tweets from people who seem genuinely shocked when they learn New Orleans is under threat, like this is something nobody is discussing. Ugh.

Yet 48 hours from now, conditions could be starting to deteriorate in New Orleans. And pre-Katrina studies indicated it takes 48-72 hours to evacuate the city. WAKE UP, PEOPLE!! WAKE UP, MEDIA!! WAKE UP, GOVERNMENT!! This feels like 2005 all over again, in terms of the apathy and inattention at this stage. Isaac might not hit New Orleans — it might very well go elsewhere, I want to emphasize that — and it might very well not be as strong as feared (more on that below). But you don’t make preparations based on wishes and hopes. You make them based on realistic worst-case scenarios. The realistic worst-case scenario for New Orleans right now is really bad. People need to start paying attention to this!! If I lived in New Orleans, I’d already have packed my bags overnight and I’d be getting the Hell out of town this morning, as a precaution. The worst thing that can happen in an unnecessary evacuation is, you get a mini-vacation that proves to have been needless in retrospect because the storm doesn’t intensify much, or goes elsewhere. That’s a lot better than the worst thing that can happen if you stay (or wait too long to decide to leave), and the storm hits. New Orleans, remember, is largely a below-sea-level bowl. If you thought the levees breaking was bad, wait until you see what happens if a storm comes in on a sufficient worst-case track to overtop the levees. The long-studied worst-case scenarios for New Orleans are horrible.

Before I quote the NHC’s 5:00 AM advisory, I want to say a word about the uncertainty of this forecast, regarding the storm’s intensity in particular. Lest anyone believe I treat these computer model intensity projections as gospel, my personal feeling is that I’ll believe the modeled extreme strengthening when I see it actually begin to happen. Isaac has shown a tendency to underperform its intensity models thus far, and the waters in the Gulf aren’t as conducive to insanely rapid deepening as they were in 2005. I’d be pretty surprised if Isaac ever becomes a Cat. 4 or 5, and while I think Cat. 3 is very possible, I think a Cat. 1-2 type situation is also very possible. But again, planners, and folks in harm’s way, must assume the worst! I’m seeing some comments from folks dismissing the threat of a major hurricane as “nonsense,” or hype, given the storm’s current state. That’s ignorant. Don’t mistake your own suspicions and educated guesses for a scientifically unimpeachable forecast that people can rely upon when making life-or-death decisions. Isaac MAY VERY WELL NOT strengthen as much as forecast by the computer models, but that doesn’t mean we can dismiss and ignore those models. We must take them seriously, because what they’re predicting COULD occur. Rapid intensification can and does happen. Isaac wouldn’t be the first storm to look this disorganized, then be a major hurricane two days later. Will it happen? Again, we don’t know for sure, and I’ll fully believe it when I see it. But it’s not some crazy, hype-driven “nonsense” idea. To claim otherwise is not only ignorant but downright dangerous. That sort of false sense of security can literally kill people.

Anyway, from the NHC’s 5am EDT discussion… first, about intensity:

WHILE THE SATELLITE PRESENTATION OF ISAAC REMAINS SOMEWHAT UNIMPRESSIVE…WITH DEEP CONVECTION LIMITED TO A RATHER SMALL AREA NORTH AND EAST OF THE CENTER…AIRCRAFT DATA SUGGEST THAT THE CYCLONE HAS STRENGTHENED A LITTLE OVERNIGHT. PEAK 850-MB FLIGHT-LEVEL WINDS OF 69 KT IN THE NORTHEAST QUADRANT ADJUST TO AN INTENSITY OF 55 KT…WHICH IS THE VALUE FOR THIS ADVISORY. AIRCRAFT DATA INDICATE THAT THE MINIMUM PRESSURE HAS ALSO DROPPED A LITTLE…TO 995 MB. ISAAC STILL APPEARS TO BE BATTLING THE EFFECTS OF SOME LOW- TO MID-LEVEL DRY AIR IN THE WESTERN SIDE OF THE CIRCULATION…AS SEEN IN UPPER-AIR DATA FROM MIAMI AND KEY WEST. ASIDE FROM THIS…HOWEVER…CONDITIONS APPEAR FAVORABLE FOR STEADY INTENSIFICATION AS THE CYCLONE MOVE ACROSS THE FLORIDA STRAITS AND INTO THE EASTERN GULF OF MEXICO. WATERS ALONG THE FORECAST TRACK ARE VERY WARM…AND UPPER-LEVEL WINDS ARE FORECAST BY THE GLOBAL MODELS TO BECOME CONDUCIVE FOR STRENGTHENING.

NHC shows Isaac getting up to 105 mph — Category 2 — before landfall near Mobile, Alabama. But that track may shift further west at 11:00 AM or, more likely, 5:00 PM, depending in large part on whether the ECWMF (Euro) model, due out around 2:00 PM EDT, agrees with the GFS and other models. About the track:

ISAAC WILL MOVE GENERALLY WEST-NORTHWESTWARD OR NORTHWESTWARD AROUND THE WESTERN PERIPHERY OF THE ATLANTIC SUBTROPICAL RIDGE FOR THE NEXT 48 HOURS. BEYOND THAT TIME…THERE IS CONSIDERABLE SPREAD IN THE MODEL GUIDANCE. MOST OF THE MODELS…WITH THE EXCEPTION OF THE UKMET…NO LONGER SHOW ISAAC RECURVING AHEAD OF A SHORTWAVE TROUGH MOVING EASTWARD ACROSS THE EASTERN UNITED STATES. ONE CAMP OF GUIDANCE…INCLUDING THE GFS…HWRF…AND GFS ENSEMBLE MEAN SHOW A NORTHWESTWARD TRACK TOWARD THE CENTRAL GULF COAST AS THE SHORTWAVE BYPASSES ISAAC COMPLETELY. THE ECMWF AND GFDL SHOW HAVE MORE OF A WEAKNESS IN THE RIDGE AND SHOW ISAAC TURNING NORTHWARD TOWARD THE EASTERN GULF COAST. THE NEW NHC FORECAST IS FASTER THAN THE PREVIOUS ONE THROUGH MUCH OF THE PERIOD…BUT IS ALONG THE PREVIOUS TRACK THROUGH 36 HOURS. AFTER THAT TIME…A SIGNIFICANT WESTWARD ADJUSTMENT WAS MADE…AND THE NEW NHC TRACK IS CLOSE TO THE TVCA MULTI-MODEL CONSENSUS AND THE ECMWF…SHOWING A NORTH-NORTHWESTWARD AND NORTHWARD TURN AT DAYS 3 THROUGH 5. GIVEN THE LARGE SPREAD IN THE GUIDANCE…CONFIDENCE IN THE LONG-RANGE TRACK FORECAST IS QUITE LOW…AND IT IS TOO EARLY TO DETERMINE EXACTLY WHERE AND WHEN ISAAC WILL MAKE LANDFALL ALONG THE GULF COAST. FURTHER ADJUSTMENTS TO THE TRACK MAY BE NECESSARY LATER TODAY.

THROUGHOUT THE PERIOD…IT IS IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK SINCE SIGNIFICANT HAZARDS EXTEND WELL AWAY FROM THE CENTER.

As I mentioned earlier, the GFDL has left the “Euro camp” and joins the “GFS camp.” (Mercifully, the GFDL shows a lot less strengthening the GFS or the HWRF.) If the Euro moves west too this afternoon, we’ll have a consensus forecast, and the confidence should increase in the 5pm discussion. Stay tuned.

For a schedule of forecasting-related events and links to watch today, see my previous post.

And again, check the blog homepage and follow me on Twitter for the latest.