[UPDATE, 2:00 AM: Now Dean is at 150 mph, with 930 mb of pressure. Will it be a Category 5 by the time I wake up in the morning? I wouldn’t be at all surprised.]

As of 11:00 PM, Hurricane Dean has maximum sustained winds of 145 mph, and a minimum central pressure of 937 mb — and he’s not done strengthening. The headline on the public advisory is “CATEGORY FOUR DEAN INTENSIFYING OVER THE EASTERN CARIBBEAN,” and the discussion predicts that Dean will reach 155 mph (1 mph short of Cat. 5 status) in 24 hours.

Personally, I’d bet even money that Dean will become a Cat. 5 sometime tomorrow. Keep in mind, it has increased from 100 mph to 145 mph today, so jumping another 11 mph tomorrow (or 15, really, since they always round to the nearest multiple of five) isn’t exactly a huge stretch. Nor would it be surprising if the NHC’s current forecast is slightly downplaying the potential for further intensification. Because of the difficulty inherent in forecasting the internal dynamics of intense hurricanes, the NHC tends to be rather conservative in its intensity forecasts at this stage of a storm’s life. So just because the forecast has Dean hitting Jamaica in roughly 42 hours with “only” 155 mph sustained winds, it doesn’t necessarily follow that that’s the most likely scenario. I’d wager on 165 mph, myself, but as always, I’m just a layman and that’s just a guess.

The forecast track has shifted ever-so-slightly to the left, and now calls for the eye to rake the south shore of Jamaica instead of crossing the middle of the island from east tip to west tip. Of course, the whole island is easily within the “cone of uncertainty,” and the possibility of small but crucial last-minute “wobbles” means it will probably be impossible to predict Dean’s precise course vis a vis Jamaica until very close to landfall.

What seems fairly certain is this: Jamaica is going to be hit, and hit hard. A direct hit is distinctly possible — and if it’s a direct hit from a Category Five, that would be a first in the island’s history, according to Wikipedia — but even a “glancing blow” from a Cat. 4-5 hurricane would be quite bad. Much like the monster hurricanes of 2005, Dean is growing geographically larger, its wind field expanding as it intensifies. Still, Jamaica’s best hope at this point is for the storm’s eye to track far enough south of the island (or north, but south seems more likely) that the eyewall, or at least the inner portion of the eyewall, doesn’t come ashore. Otherwise, Drudge is right: it will indeed be a “HISTORIC HELL STORM.”

Dean’s exact intensity between now and landfall in Jamaica will depend mostly on eyewall replacement cycles, the dynamics of which meteorologists really don’t fully understand and can’t reliably predict. So another thing to hope for, if Dean does hit land, is a well-timed cycle right before landfall that brings the eyewall ashore during a weakening phase.

Alas, however, there is reason to fear that Dean might come ashore during a strengthening phase. Take a look at the Tropical Cyclone Heat Potential map of the waters surrounding Jamaica:

That white-hot color on either side of the island represents the most dangerously warm waters in the whole Atlantic basin, and just as the Gulf Stream and the Loop Current tend to supercharge hurricanes that pass over them, I fear Dean could get a final, deadly burst of energy from the patch of pink and white just off the eastern shore. That would be a very bad thing, because major hurricanes are worse when they are strengthening than when they’re stable or weakening; the greater instability of the intensification cycle leads to higher wind gusts and such. In other words, the only thing worse than a Category 5 hurricane making landfall is a strengthening Category 5 hurricane making landfall.

It’s probably too late to get the hell out of Jamaica now; I’m told all outbound flights are booked through Sunday afternoon, at which point the storm will be hitting. But if there’s any way to get out, do it, as Alan Sullivan says:

If you are a tourist on Jamaica, get off the island tomorrow — even if you have to go to Cancun. You’ll have a extra day to get out of there. Seriously, you don’t want to be trapped in a hurricane-ravaged Third World country. There will be no utilities, no untainted water or food, scarcely even a secure place to sleep, in areas exposed to the full force of a category four or five storm. Do whatever you have to do, pay whatever it costs, and get out. Jamaica residents should of course rush all preparations to completion. They live there. One hopes they know what to do for their own security.

For those who can’t leave, Jamaican residents and tourists alike, now is the time to make prudent preparations (like filling bathtubs with water) and get ready to hunker down for the storm… then ride out the aftermath. And it’s also a good time for the rest of us to keep them in our thoughts, and pray for them if we’re so inclined. It’s going to be a very rough few days in paradise.

After Jamaica? The computer models continue to disagree about where Dean will go, and there will be plenty more time to talk about that over the weekend. For now, the only thing I want to say about the storm’s post-Jamaica future is that Dean’s path over the island could be quite significant to the long-term intensity forecast. The more interaction between the hurricane and the mountains, the more likely it is to weaken. Conversely, the further offshore it stays, the better for Jamaicans but the worse, potentially, for residents of the Yucatan Peninsula, who would then be more likely to bear the full brunt themselves. Ultimately, though, it may not matter, since the waters between Jamaica and the Yucatan are plenty warm, and Dean will have plenty of time to get its act back together even if it does weaken over Jamaica. Two Cat. 5 landfalls are certainly not out of the question. In fact, the NHC, which is holding Dean to a high Cat. 4 in its predicted Jamaica landfall (and not specifically predicting any weakening from land interaction), is forecasting it to reach minimal Cat. 5 status in 72 hours, and make landfall as such near Cozumel late Monday or early Tuesday.

And with that, I’m going to bed. I’ll try my best to keep posting storm updates through the weekend, though I also continue to have a ton of errands and housework I desperately need to get done, and it seems like this hurricane-blogging thing very quickly becomes all-consuming. :) As soon as I’m done with one lengthy post, something else happens and I feel the urge to start a new one! And, as I told Becky earlier, all this extra web traffic is like a drug: it makes me want to blog more and more! After all, if lots of people are visiting my blog, I want to give them good, timely information, and not leave them disappointed with what’s here! So I blog and blog and blog. And blog. … Anyway, I’ll do my best to balance the blogging with my other responsibilities over the next few days, so that I can keep giving y’all updates without totally screwing the pooch on everything else (like cleaning our massively untidy house for our houseguest who is arriving in less than a week… AAAHH!!!).

Anyway, g’nite all. Pray for Jamaica. I leave with you with another scary satellite image, from a few hours ago:

P.S. Interesting aside: a blogger in Jamaica notes that the island nation has an general election scheduled for August 27. All campaigning has stopped as the storm approaches, and it is possible the election may need to be postponed, depending on the extent of the damage.

Ahh…all is right with the world. It’s football time again. High-school football in small-town America on a Friday night.

Tonight was a Jamboree, really an extended scrimmage where 8 teams come to play one quarter of football. All’s right with the home team, the Loudon High School Redskins, who managed the most scoring of any team in play, putting in two touchdowns and two 2-point conversions for a 16-0 win over the Tellico Plains Bears.

I now return you to your regularly scheduled hurricane blogging.

“I’m sorry, are you like a demented chicken?” –Becky, to me

“Did you just say you’re boycotting Count Dooku?” –Becky, to me

[FINAL UPDATE: I’ve just finished a new post with all the latest on Dean. … Thanks for the links, Glenn and Hugh! … P.S. If anyone wants to bookmark, or link to, a stable URL that will always point to my most recent Dean-related posts, you can use my 2007 Hurricane Season category.]

[UPDATE, 10:47 PM: I missed it till just now, but the NHC issued a special 9:30 PM update further bumping Dean’s official top wind speed to 145 mph. I thought it was stronger than 135 mph. … The forecast as of 5:00 PM predicted that it would max out at 150 mph, two days from now. What will the 11:00 PM discussion predict? The NHC is usually pretty conservative when predicting further intensification of major hurricanes, so I sort of doubt they’ll bring it to Cat. 5 status (156+ mph) in the forecast; they might call for it to max out at 155, followed by “fluctuations in intensity.” But that’s just a guess. … Anyway, the full 11pm advisory, with discussion, should be out any minute now. I’ll discuss it in a new post above.]

[UPDATE, 8:01 PM: Dean has been bumped to a Category 4 hurricane as of the 8pm intermediate advisory, with 135 mph winds. The NHC’s decision is apparently based on preliminary recon data. Looking at the satellite, I wouldn’t be at all surprised if there’s a further “bump” at 11:00 PM, based on additional recon data and additional strengthening over the next three hours — but as always, take my opinions with a grain of salt. Dammit, Jim, I’m a law clerk, not a meteorologist!]

On the satellite loop, Dean really looks like he’s getting his act together. See here, too. The hurricane hunter aircraft isn’t expected to arrive until 8:00 PM, which is when the next intermediate advisory from the NHC is due out, so I assume they won’t have any new recon data in time for the advisory, and thus will probably hold off on any major intensity changes until 11:00 PM. I wouldn’t be at all surprised to see a significant bump in strength then — or even perhaps in an “update” in between 8 and 11, if the data justifies it. Nor would I be surprised to wake up tomorrow and find out that Dean went through a rapid deepening cycle overnight and is officially a monster by morning. Check out the visible shot at sunset:

Amid all the talk about computer models and Dean’s future track, let’s not forget Jamaica. Alan Sullivan sums up the situation vis a vis that tropical isle in the bullseye:

I’m impressed with the progress Dean has made today; it’s starting to justify the hype. But the hurricane has not yet made direct contact with the shear field of the upper low in its path. As the distance closes, that should happen tomorrow, unless the low speeds up, Dean slows down, or both. Once these features match speeds, then there will no longer be much likelihood of shear interfering with the storm. In that case, Jamaica will really take a terrible hit. …

Bottom line here: deadly menace to Jamaica. Locals have one nice day to prepare. On Sunday it will start to get stormy. Sunday night, well, pray Dean’s core slips a bit north or south of the island.

[UPDATE, 9:05 PM: The GFDL has shifted back south again, and now shows a 165 mph landfall between Corpus Christi and Houston, rather than a 155 mph hit on central Louisiana. The GFS has also shifted south, and is now predicting landfall in Belize (not the Yucatan) with no significant re-emergence over water until reaching the Pacific — in other words, no threat to the United States. The NOGAPS and UKMET remain essentially unchanged, both taking the storm into Mexico and keeping it away from the U.S. You can view all of the “big four” models here, and even more model tracks here.]

The debate over Hurricane Dean’s future track is boiling down to a simple question: Does the GFDL computer model know something that all the others don’t? Over the last several model runs, the GFDL has been trending northward, while the other models have been trending southward. Take a look at Weather Underground’s model map as of 2:00 PM… the blue line is the GFDL, while the white, purple and red lines represent the other three of the “big four” dynamical models (UKMET, GFS and NOGAPS):

As you can see, the GFDL is stubbornly taking Dean into Louisiana, while the other models are leaning increasingly toward a Mexico landfall. So, what are we to make of this stark disagreement? Dr. Jeff Masters has an excellent post asking the question, “Which model do you trust?” After posting and analyzing a couple of charts of model accuracy, he concludes that “the official NHC forecast outperforms all the individual models, particularly at long ranges. Looking at the individual model plots can be helpful to determine the uncertainty in the forecast, but it’s tough to beat the NHC. In the case of Dean, where one model is an outlier from the rest, it is usually better to believe the consensus of the other models.”

Usually. But what if the GFDL is seeing something the other models are missing? Recall Alan Sullivan’s post from this morning, in which he wrote, “In the real world, as opposed to the world of computer models, I see something happening” — namely, a “mighty sluggish” upper low off Florida defying forecasts that it will quickly get out of the way — that could nudge Dean’s track to the right. Perhaps the GFDL is seeing the same thing Sullivan saw. (It should be noted here that Sullivan, like me, isn’t a meteorologist; he’s a layperson with an intense interest in, and a good deal of lay knowledge about, hurricanes. He’s also a self-described “contrarian.” None of which necessarily means he’s wrong.)

Not everyone thinks the GFDL is on to something. Earlier this afternoon, Eric Berger wrote that the GFDL “continues to jump all over the map, this time from a Galveston landfall [which it was predicting at 8:00 AM] to central Louisiana. This indicates one of two things: [either] 1) the model has not properly initialized Dean and is rendering its path incorrectly, or 2) the model is detecting a trend in the upper atmosphere the other models have missed. Given its inconsistency I’d lead toward the former answer, but there’s no way to know for sure.”

But one man’s “inconsistency” is another man’s “trend.” For the last 24 hours, the GFDL has been trending more to the right, or north, with each model run. At 8:00 PM yesterday, the GFDL showed Dean’s track pointing toward Corpus Christi; at 2:00 AM this morning, an area just south of Houston/Galveston appeared to be the target; at 8:00 AM, Houston/Galveston was in the bull’s eye; and then at 2:00 PM today, Central Louisiana was favored. If that’s a genuine trend — and with only four data points, I admit it’s a somewhat shaky contention — it would seem consistent with Sullivan’s observation that the upper low off Florida is continually refusing to move as predicted. It will be interesting to see what the model comes up with at 8:00 PM.

Berger, though, is looking at a different “trend” — the trend toward a more southward track in the other model runs:

The hurricane center’s afternoon update appears to have nudged the five-day forecast only very slightly southward. As noted below, the models have made a more significant move south. What is happening here is that the hurricane center doesn’t want to have its forecasts, in the wise words of Jeff Masters, have a “windshield-wiper-like” effect.

Therefore if this evening’s model runs show a similiar southward movement, as this morning’s did, I would expect a southward shift in the 10 p.m. forecast track.

As for the GFDL, he writes, “The key feature here is an upper-level low pressure system…that’s moving to the west ahead of Dean. The GFDL model (the outlier at this point) handles the movement of this system differently than the other forecast models. I’ll have more on this tomorrow morning if the models have not agreed upon how to handle the upper-level low, which could steer Dean into Texas or even Louisiana.”

The bottom line continues to be: Stay tuned. There’s still a lot more ink (er, and pixels) to be spilled on this storm before we figure out precisely where it’s going.

UPDATE: In comments, Sullivan writes:

I see the bifurcation in models as part of the same trend. Dean could also turn left if the upper low refuses to move. In effect the hurricane would be trying to sneak underneath the opposing circulation.

In other words, I think all the models may be seeking ways to resolve a single fact: that the hurricane is overtaking the upper low.

I had a similar thought rolling around in my head, but wasn’t sure quite how to express it, or whether it made sense. But yeah. Thanks, Alan.

UPDATE 2: Now Alan has a new post on his blog fleshing out that same thought. Excerpt:

Some [of the computer models] stay with the Jamaica, Yucatan, upper Mexico run — almost a straight line. Others are shifting left toward Nicaragua or even further south. And some are shifting right, into the Gulf.

I have been thinking about the righthand shift all day. The leftward shift in some models surprised me — but only for a moment. Then I had an insight. What if all these diverging models are responding to the same phenomenon — namely the sluggish movement of the upper low near Florida, which the hurricane is steadily overtaking? For Dean could also avoid the encounter by turning left, in effect bouncing off the periphery of the other system’s circulation.

Two effects, one cause…but which way will Dean turn? Or will it simply blow through the opposing system and stay on the straight course?

P.S. Bryan Woods makes an important point about the intensity forecast for Dean, post-Jamaica: “If, as currently indicated, Dean tracks directly over Jamaica, we will have to reevaluate everything. Jamaica has quite large mountains in the center of the island and Hurricanes do very poorly when passing over high elevations. Jamaica could do quite a number on our storm and knock his strength down significantly with the right conditions. Not only will the elevation condense out a lot of water from Dean’s circulation, unstable flow and wave breaking over mountains can cause a redistribution of potential vorticity, which can create several types of lateral instability in the flow.”

More evidence for Becky's crusade against the rising price of milk…

Okay, that’s my last Howard Dean joke (well, in a headline anyway), I promise. Because this is deadly serious stuff: the National Hurricane Center issued a special advisory at 1:45 PM upgrading Hurricane Dean all the way from a 105 mph Category 2 to a 125 mph Category 3. It is now expected to have 150 mph winds when it reaches Jamaica in 48 hours. And check out the satellite image:

Yikes.

UPDATE: Okay, okay, one more Howard Dean joke:

Heh.

[UPDATE: Meteorology Ph.D. student and weather blogger Charles Fenwick believes the Army Corps’ numbers are plausible. He knows a lot more about this stuff than I do, and his analysis makes sense.]

The New York Times has an article today declaring that New Orleans is still vulnerable to severe flooding from a hurricane — hardly a surprise, though the timing of the article is interesting, since that fact could become quite relevant in five or six days’ time if the computer models keep shifting Hurricane Dean’s track to the right.

But anyway, what is surprising, to me at least, is the fact that the Army Corps of Engineers has declared that Hurricane Katrina was “a 1-in-396 [years] storm.” That is to say, according to the Corps, residents of New Orleans can expect to go almost 400 years, on average, between storms as bad as Katrina — and even longer, one presumes, between storms that are worse.

I would really like to see the study on which this conclusion is based, and examine the rationale underpinning it, because on the face of it, this conclusion strikes me as peculiar, even bizarre. As I’ve pointed out numerous times, Hurricane Katrina could have been far worse than it actually was for New Orleans: the center passed 30-40 miles east of the city, sparing New Orleans a direct hit; a last-minute bout of dry-air entrainment severely weakened the portion of the eyewall that passed over the city; and, more broadly, the whole storm weakened just before landfall from a Category 5 to a Category 3 and, by the time it reached New Orleans’s latitude, a Category 2. How is that a 400-year storm? (Read more here, re: the NHC’s official report on Katrina.)

Admittedly, Katrina’s storm surge was historic, far worse than a typical Cat. 2 or 3 (worse even than a “typical” Cat. 5, if there is such a thing), because it had been so powerful the day before and was so geographically huge. But the worst of the surge hit Mississippi, not New Orleans. The dangerous right-front quadrant of the eyewall brought a wall of water 30+ feet high into Waveland and environs, while back over in New Orleans, the weakened left-front quadrant was delivering the city what amounted to a glancing blow. The worst damage to New Orleans, by far, was from seeping water slowly filling up the city after the storm; the storm itself wasn’t that bad, except insofar as it breached the deficient levees. I have always contended that, if the track had been slightly different and that massive surge had made a direct hit on southeastern Louisiana, funneling the wall of water up the rivers and canals toward the Big Easy and breaching the levees more quickly and completely, the death toll could have been in the tens of thousands because many, many people who sought refuge on their roofs (and were eventually rescued by helicopter) would have instead drowned in the much higher water levels during the height of the storm — which, in such a scenario, would have been far more deadly, with higher winds, more debris flying around, more wave action, etc.

In any event, the Army Corps’s conclusion makes no sense to me. If Katrina was a once-in-400-years event, that would seem to imply that hurricanes of Category 2 or greater intensity, which were Category 5 less than 24 hours before and are geographically very large, will only pass within 30-40 miles of New Orleans (on either side) every 400 years on average. That conclusion seems obviously wrong, doesn’t it? They do realize that New Orleans is on the Gulf Coast, right?

As I said, though, I’d really like to see the rationale underlying the Corps’s conclusion, because maybe I’m missing something. Perhaps their conclusion is well-founded, for reasons I’m not grasping. As I try to repeat frequently, I’m not actually an expert on this stuff, so I could be wrong. But if I’m not wrong — if the Corps is engaging in some fuzzy math here, perhaps because it wants to pretend it’s gotten New Orleans better prepared than it really has — then I fear for the complacent attitude this sort of thing may cause. If New Orleans residents believe Katrina is as bad as it’s ever likely to get in their lifetimes, or their children’s or grandchildren’s lifetimes for that matter, the ones who stayed put and survived in 2005 will probably stay put again the next time a storm threatens, not realizing that Katrina was just the tip of the iceberg in terms of what New Orleans could potentially face whenever a major hurricane finally decides to make a direct hit on the city.

P.S. Much more about the Corps and its blatant failures from Time magazine. (Hat tip: Patrick Cullen.) The article includes a quote from LSU hurricane researcher Ivor van Heerden, who certainly doesn’t sound as if he believes Katrina was a 1-in-400-years storm: “Katrina wasn’t even close to the Big One,” he says. “We better start getting ready.”

If you live in Texas, it’s far too early to think about evacuating from Hurricane Dean — he’s at least five days away yet, and could potentially go anywhere from Belize to Louisiana, or perhaps even further east. But Eric Berger offers some good advice to Texans, particularly in the Houston-Galveston area: review the relevant disaster plans and maps, and decide if you’ll eventually need to evacuate, if Dean heads your way. That advice works well for the whole Gulf coast, actually. As Scar from The Lion King would say: “Be Prepared!”

…leave!

Glenn Reynolds linked this morning to my post last night advising people in Jamaica and the Yucatan to “get the hell out” if they can. My phraseology was, of course, a throwback to my famous Katrina post in the same vein. And I mean it: in Jamaica especially, there is absolutely no reason to keep waiting for further information before making a decision — and by doing so, you risk delaying too much and becoming unable to leave.

Hurricane Dean will hit Jamaica, or pass very near Jamaica. The “macro” track forecast for the next 48 hours, which is the relevant period of time as far as Jamaica is concerned, appaers to be pretty much set in stone at this point. Only the “micro” track details remain to be determined (e.g., will it wobble a handful of miles to the right, and make a direct hit, or a handful of miles to the left, and deliver only a glancing blow?), and those details won’t be determined until it’s too late to evacuate anyway.

Likewise, on the intensity front, it remains to be seen whether Dean will live up to its potential (which, as I noted yesterday, is to become “Gilbert, the sequel“) or whether its growth will be stunted by dry air or shear, as Alan Sullivan suspects. However, again, that won’t be known for certain until it’s too late to evacuate. If the hurricane puts on a burst of rapid intensification 12 hours before landfall and goes from a Cat. 3 to a Cat. 5 in that time — which is entirely plausible — you won’t be able to get out once you realize for certain how bad it’s going to be.

You can’t wait for absolute certainty. It’s already certain enough. Now is the time for action, not deliberation. If you have no choice but to ride out the storm on the island, fine: figure out what is the safest place for you to be (hint: a well-constructed building, able to withstand very high winds, at a location far enough removed from the coast that it’s not vulnerable to storm surge, but not so high in the mountains that it’s vulnerable to mudslides, and not in an area that’s vulnerable to flash flooding) and make plans to go there. But if you can leave, then leave! This isn’t a difficult decision! There is a very serious possibility — not a certainty, but certainty is too much to ask — of a Category 4 or 5 hurricane hitting Jamaica in two days’ time. Choosing to ride out such a monster anywhere, but especially in a third-world country, is a very bad choice.

When Hurricane Gilbert slammed Jamaica in 1988, it killed 45 people and caused $4 billion of damage. It destroyed houses, roads and small aircraft. It “severely damaged all but two medical facilities and 50% of the water supply.” So even if you survive the hurricane, the aftermath will be ugly, if it hits as badly as it could. Seriously — there’s no reason to risk it. Get the hell out.

(If you’re in the Yucatan, you might have an extra day to mull things over. But otherwise, the rest of the above applies equally to you. And personally, if I were your position, I wouldn’t mull; I’d leave ASAP.)

P.S. A commenter going by “HangGlider” left a comment on the previous thread saying: “My daughter and her husband left for Jamaica last Sunday for their honeymoon and have (foolishly - in their Father’s opinion) decided to stay on the island through the hurricane. I just hope the resort people have enough experience to get their customers to a safe location to ride out the storm.” I responded via e-mail, making a plea for him to try again to convince his daughter to change her mind, and I’ve reprinted that e-mail after the jump for anyone who might be in a similar situation.

(more…)

Hurricane Dean grazed the southern tip of Martinique overnight. Thankfully, he weakened a bit while passing by, probably lessening the blow suffered by the islands. But now he’s strengthening again: 105 mph and counting, as of 11:00 AM.

Unfortunately, there’s some bad news on the computer-model front. Last night I noted that confidence in the forecast might improve this morning because of newly available data from the NOAA jet. It hasn’t worked out that way. Indeed, the 11:00 AM discussion states, “IT SHOULD BE NOTED THAT GUIDANCE FOR DAY 4 AND 5 IS MORE UNCERTAIN TODAY THAN YESTERDAY.” According to Dr. Jeff Masters, “The NOAA jet mission did not help at all with narrowing down the uncertainty in the computer forecasts for the 4-5 day period, which remain divergent.” See for yourself here.

Why this disagreement? In Dr. Masters’s words, “each model has a different solution for the behavior of an upper-level low pressure system expected to be over the Gulf of Mexico early next week, and there is no is currently no way to guess which model will be right.” It also seems like each weather blogger has a different interpretation of the models. For instance, AccuWeather’s Henry Margusity wrote this morning that “South Texas [is] now becoming the only spot in the U.S. where Dean may hit.” On the other hand, his colleague Jesse Farrell wrote, “This morning’s Model Spread seems to shift the tracks up the coast from southern Texas to evenly cover the entire state.” FLhurricane.com notes the same thing: “the track models have begun to shift a bit north… This means, now more than ever, that the entire Gulf should be watching [Dean].”

Eric Berger, in Houston, looks at the scenarios and their implications for Texas. He sounds worried, and it’s not hard to see why. As Farrell notes, and shows graphically, the GFDL is showing a 916 mb Category 5 monster offshore of Houston on Wednesday. That would be, um, bad. The model image is rather scary:

For his part, however, Alan Sullivan wonders whether we should be trusting the models at all. Looking at “the real world, as opposed to the world of computer models,” he “see[s] something happening that could notch down those intensity forecasts” and alter Dean’s track. Specifically, and I quote his analysis almost in its entirety:

I’m watching the upper low off Florida. It looks mighty sluggish. It’s hesitating in response to a deepening polar trough over eastern Canada. As usual this summer, that polar feature is growing abnormally strong, and digging a bit further south than expected. By holding the cut-off low longer, it changes Dean’s prospects in two ways.

First, intensity: Dean is moving very swiftly. It is overtaking the upper-level cyclonic flow that wraps round the base of the cutoff into the northern Caribbean. Unless the low speeds up, its flow will begin to shear Dean. Already we can see a hint of shear in the storm’s shape. Dean’s envelope of outflow is becoming subtly elongated along a NE-SW axis as the NW flank of its circulation begins to encounter the shear-field. At this point I think Dean will encounter enough adversity in the Caribbean to prevent further intensification until it nears Jamaica. Meanwhile it may even weaken back to category one for a time. OK, this is a wild guess, but I’m a contrarian. (Make sure to include that last sentence if you quote me, Brendan!)

Second, track: Dean will probably continue on an unchanged course as it bucks the shear, but as it gets further west it may begin responding to the pressure by edging right. There is more land to the right. All that much-touted deep warm water means little if the hurricane declines to pass over it. Also, should Dean hit mountainous Jamaica head on, or go even further right and skims near the south coast of Cuba, its intensity will be affected by friction with land. A course close to Cuba would eventually take Dean over the western end of the island and onto the Loop Current in the eastern Gulf. Intensity would probably surge there, and Dean could in time present a serious threat to New Orleans or points east.

Meanwhile, watch that upper low. Run the NW Atlantic vapor loop… That will show you how the Florida low is interacting with the polar flow over the northeastern US. Don’t trust the models. They do not seem to see what is happening.