A few minutes after I posted my last update, the recon plane sent a new report indicating flight-level winds of 174 mph. According to the standard 90% formula, that translates to 156 mph winds at the surface — literally the very minimum for Category 5 status. But the NHC has decided to continue classifying Dean as a 150 mph Cat. 4 for now. The discussion explains that they’re having trouble getting all the data from the recon plane, and meanwhile other available data suggests a slightly lower intensity:
COMMUNICATIONS PROBLEMS ARE PREVENTING THE RECEIPT OF MOST DATA FROM THE AIR FORCE RECONNAISSANCE AIRCRAFT THIS AFTERNOON…ALTHOUGH A [3:30 PM EDT] VORTEX FIX WAS RECEIVED. AT THAT TIME THE MINIMUM PRESSURE WAS 918 MB…WITH MAXIMUM FLIGHT-LEVEL WINDS OF 151 KT [174 MPH]. EARLIER IN THE FLIGHT…A PEAK SFMR [SURFACE] WIND OF [141 MPH] WAS OBSERVED. DVORAK CLASSIFICATIONS FROM TAFB AND SAB WERE [146 MPH] KT AT [2:00 PM EDT]. BASED ON THESE DATA…THE INITIAL INTENSITY IS HELD AT [150 MPH].
Okay, back to work! (These 15-minute breaks between seminar lectures are great for hurricane-blogging. :)
The most recent recon plane to investigate Dean found a pressure of 924 mb — down just 2 mb from the wee hours of this morning — and top flight-level winds of 161 mph, down from 167 mph this morning. (Multiply by 0.9 for the approximate top surface winds.) As a result, the NHC kept Dean at 150 mph as of the 2:00 PM advisory. So it appears this storm is in no huge hurry to begin rapidly intensifying, my earlier post notwithstanding.
That said, he’s looking better and better organized on the satellite loop, so I still think it’s only a matter of time before he achieves Cat. 5 status:
The next recon mission is set for 8:00 PM EDT. And my break is almost over. Back to the seminar…
From the NHC’s 11 am discussion,
THE NEXT RECONNAISSANCE FLIGHT WILL BE AT 18Z THIS AFTERNOON. IN THE MEANTIME… RECENT MICROWAVE DATA SHOW A SINGLE EYEWALL THAT HAS BECOME BETTER DEFINED WITH COLDER TOPS IN CONVENTIONAL SATELLITE IMAGERY OVER THE PAST COUPLE OF HOURS. THE ADVISORY INTENSITY WILL BE HELD AT 130 KT…BUT LATEST SATELLITE IMAGES INDICATE THAT DEAN IS APPROACHING CATEGORY FIVE STATUS…AND IT IS EXPECTED REACH THAT THRESHOLD LATER TODAY OVER THE DEEP WARM WATERS OF THE WESTERN CARIBBEAN.
The advisory gives a central pressure of 925 mb, sustained winds at 150 mph. Landfall on the Yucatan is expected very early Tuesday morning, but conditions will be deteriorating today as the storm approaches. Hurricane warnings are in effect in Mexico and Belize from Cancun south to the Belize/Guatamala border, and also on the west coast of the Yucatan from south of Progresso to Ciudad del Carmen.
FYI - I’m heading to Nashville in the morning for a two-day State of Tennessee law-clerk seminar thingy, so blogging will be extremely sporadic tomorrow and Tuesday, I’m afraid. The timing sucks, as tomorrow will probably be one of those exciting days for a weatherblogger, filled with amazing and terrifying images of a rapidly intensifying Category 5 hurricane… but what can ya do? Duty calls. At least I should be able to blog from my hotel room tomorrow night as Dean approaches the Yucatan. And I’ve again asked my hurricane guestbloggers to help fill in when I’m indisposed. (Speaking of which, thanks, Brian, for your help today!)
Anyway, Dean has now officially cleared the western tip of Jamaica. It never actually made landfall; according to the 11:00 PM discussion, the closest approach occurred when the center of the eye “came within about [23 miles] of Portland Point of the south-central coast.” Tomorrow, we’ll start to find out what kind of damage Dean did. Hopefully it wasn’t too severe, though I’m sure it wasn’t a cakewalk on the island, especially the south shore.
The downside of Dean’s eye failing to hit land is that it didn’t weaken over said land. So now the conditions are ripe for some potentially historic intensification tomorrow. That Dean will become a Category 5 hurricane tomorrow is, I think, almost a foregone conclusion, given the favorable atmospheric conditions, the lack of land interaction, and the extremely warm water:
The brown line is Dean’s approximate track so far; the black line is the approximate forecast track.
The heat potential isn’t quite as high as it would be if Dean were trekking a bit further north, but even so, it’s plenty warm enough to support rapid intensification; indeed, it’s significantly warmer than the water (between the two small black vertical lines near the lower right-hand corner of the map above) in which Dean exploded from a low-end Cat. 2 into a high-end Cat. 4 on Friday. And because of his failure to make landfall in Jamaica, Dean starts his trek into these bathtub-like Western Caribbean waters with a top wind speed of 145 mph and a minimum pressure of 925 millibars. So the question, I think, is not whether he’ll strengthen into a Cat. 5; the question is, how low can he go? Pressure-wise, that is. Gilbert, following a similar track 19 years ago, held the Atlantic-basin record (888 mb) until Wilma surpassed it in 2005 with a mark of 882 mb. Can Dean rival these numbers? I’m not predicting it, but I certainly don’t think it’s out of the question. He dropped 46 millibars in 24 hours on Friday, where the heat potential was, on paper, not even quite high enough to support rapid deepening. Another 46-millibar drop tomorrow, in these far more conducive waters, would break Wilma’s record by 3. I’m just sayin’.
Can anything hold Dean back? Maybe another eyewall replacement cycle… but you’d think that wouldn’t happen for a while, now that the lengthy cycle which continued throughout Dean’s approach and passage of Jamaica is finally over. We’ll see.
In any event, the good news is that Dean now appears to be headed for an area of the Yucatan Peninsula that’s much more sparsely populated than the Cancun/Cozumel area. Hopefully the people who do live along the targeted coast are taking the proper precautions and getting themselves out of harm’s way, because regardless of whether Dean approaches any meteorological records, the bottom line is that they are going to be hit very hard.
Anyway, here’s what the 11:00 PM discussion has to say about Dean’s track and intensity:
DEAN IS HEADING TOWARD 280 DEGREES [i.e., just north of due west] AT ABOUT [20 MPH] WITH STEERING PROVIDED BY A STRENGTHENING MID-LEVEL RIDGE OVER THE SOUTHEASTERN UNITED STATES. THE MODELS ALL AGREE THAT THE RIDGE WILL GET EVEN STRONGER AND MOVE A LITTLE WESTWARD WITH DEAN…MEANING THAT DEAN WILL PROBABLY MOVE IN A RATHER STRAIGHT LINE UNTIL FINAL LANDFALL IN MEXICO. OVERALL THE MODELS HAVE AGAIN EDGED A LITTLE SOUTHWARD…AND SO HAS THE OFFICIAL FORECAST. …
ALL OF THE OBJECTIVE GUIDANCE CALLS FOR STRENGTHENING IN THE NORTHWESTERN CARIBBEAN WHERE THE SHEAR WILL REMAIN WEAK AND THE OCEAN HEAT CONTENT VERY HIGH. THE OFFICIAL FORECAST FOLLOWS SUIT AND INDICATES THAT DEAN COULD REACH CATEGORY FIVE STATUS DURING THE NEXT DAY OR SO. THE HURRICANE WILL WEAKEN WHILE OVER YUCATAN IN PROPORTION TO JUST HOW LONG IT SPENDS OVER LAND. THE OPPORTUNITY FOR RESTRENGTHENING OVER THE SOUTHWESTERN GULF LIKEWISE DEPENDS ON THE EXACT TRACK…AND THAT WINDOW HAS BEEN SHORTENING WITH THE SOUTHWARD SHIFTS IN TRACK. ALTHOUGH NOT EXPLICITLY INDICATED IN THE NEW OFFICIAL FORECAST…IT IS STILL POSSIBLE THAT DEAN COULD RESTRENGTHEN AND AGAIN REACH MAJOR HURRICANE STATUS PRIOR TO FINAL LANDFALL ALONG THE COAST OF MAINLAND MEXICO.
P.S. In other tropical news, Brian Neudorff notes a tropical storm over Oklahoma — well, the remnants of Erin, anyway, looking mighty spiral-y! — and a potential proto-Felix.
UPDATE, 2:00 AM: Dean’s pressure went up a millibar, to 926… but its top wind speed is up too, to 150 mph.
UPDATE, 7:13 AM: Another eyewall replacement cycle already?? According to the 5am discussion, “OBSERVATIONS FROM THE LAST AIR FORCE HURRICANE HUNTER MISSION AGAIN INDICATED A CONCENTRIC EYEWALL STRUCTURE.”
Hurricane Dean’s eyewall may have stayed just offshore of the heavily populated areas, but don’t let that fool you: it’s been a very bad day in Jamaica, writes Dr. Jeff Masters:
It could have been much worse, but it is very bad for Jamaica. Hurricane Dean’s northern eyewall is just offshore the southern tip of Jamaica, bringing sustained Category 2 hurricane winds to southern Jamaica. A recent wind analysis prepared by NOAA’s Hurricane Research Division (Figure 1) at 3:30pm EDT today shows winds of Category 1 strength (>65 knots, or 74 mph) already affecting the east end of the island. By extrapolating this wind field over the island to the west-northwest, in anticipation of Dean’s track, it is apparent that perhaps 90% of the island will experience sustained winds of 74 mph or greater. At 4pm EDT, Kingston, on the southern side of the island, recorded sustained winds of 81 mph before the instrument failed. We can expect that the southern 1/3 of the island, including Kingston, will receive sustained winds of Category 2 strength–96 to 114 mph. Category 3 and higher winds will be confined to the southernmost 5% of the island, and it appears that the Category 4 winds will stay offshore. The portion of the island affected by the Category 3 winds is very sparsely populated.
Jamaica will suffer billions in damage from Dean. The high winds and rains of up to 20 inches will no doubt claim lives, although probably not as many as the 45 who died during Hurricane Gilbert of 1988. Gilbert cut straight across Jamaica as a Category 3 hurricane with 125-130 mph winds. Kingston measured sustained winds of 116 mph during Gilbert; I expect the top winds in Dean will be 10 mph slower than that.
…or has Hurricane Dean taken a perceptible wobble toward the northwest (as opposed to west or WNW) — that is to say, a wobble toward Jamaica — in the last two or three satellite frames? I know we’re not supposed to read too much into “wobbles,” but yikes, I do hope it starts wobbling back the other way…
UPDATE: Well, okay, not quite northwest. Somewhere between NW and WNW. It’s not as bad as it looked from eyeballing it. Here’s an illustration the eye’s movement on the last three satellite frames:
More importantly, as you can see, the center of the eye has now passed the longitude of Kingston (population 660,000). Barring a sudden and exceedingly unlikely NNW or due north wobble, the eyewall(s) will not hit Kingston. Phew. And notwithstanding the above graphic, the eye may stay offshore entirely, since it may well “wobble” back west again. The southern tip of the island will certainly get hit by at least the outer eyewall, though.
As of the 5pm advisory, Dean is "scraping" the south coast of Jamaica. The eye is 50 miles south of Kingston, moving west. No change in strength. … We, meanwhile, are at Babies R Us. And Becky is uber cute. :)
At 2pm, NHC says Dean is still at 145 mph; pressure is back up to 930 mb. The eye is 80 mi. southeast of Kingston, Jamaica, moving WNW.
(This is another double post between my weather blog WX-Man.com and Brendan’s)
Dr. Jeff Masters showed this Microwave satellite image of Hurricane Dean from around 7 AM EDT, or as Dr. Masters described it as “Think of this as a weather radar in space.” Like in the enhanced infrared satellite that has been shown here the red areas indicate the thunderstorm convection in the spiral bands and the eyewall. He then points out the the “incomplete double ring of echoes around the dark blue eye. Dean has two eyewalls, concentric around each other.”
This is very interesting to me and I will be the first to admit when I learn something new. I am a meteorologist, but I will be the first to admit that my weakest area in meteorology is Tropical Weather. He has a great discussion on what this “Double Eye” means for Jamaica and the Cayman Islands:
Jamaica is already receiving high winds and heavy rain from an outer spiral band. How bad will it get? The big question is if the eyewall will move over the island. Unfortunately for Jamaica, Dean has two eyewalls, forming concentric rings (Figure 1). The inner eyewall is 15 miles in diameter, and the outer eyewall is 37 miles in diameter. Winds of Category 3 and 4 strength are blowing in both eyewalls, as seen in the latest data from the SFMR surface winds taken by the Hurricane Hunters. So, Dean’s center has to pass more than 25 miles south of Jamaica for the island to be spared the worst of the hurricane. The nation’s capital, Kingston, lies on the southern portion of the island, and will be the hardest-hit major city. The tourist city of Montego Bay is on the northern part of Jamaica, and will fare much better.
The same story holds true for the Cayman Islands. Grand Cayman, the southernmost of the islands, it at greatest risk. If Dean passes more than 30 miles south of the island, they will miss seeing the outer eyewall of Dean and will fare relatively well. It’s going to be a close call, but it appears that both Jamaica and the Cayman will miss seeing the eyewall of Dean.
At the end of this post he gives his thoughts on Dean’s hits on the Yucatan near Cozumel and then south of the Texas/Mexico boarder and how this could be similar to Hurricane Emily.
Also this morning Eric Berger (SciGuy) isn’t ready to clear Texas from being threatened by Dean, but seems to agree a lot with Dr. Jeff Masters:
I’m also not ready to clear Texas yet as possibly being threatened by Dean, although all of the models, at a minimum, now bring the storm in for a final landfall nearly 200 miles south of the border. The models also are beginning to predict some weakening for this final landfall as Dean spends more time over the Yucatan.
Alan Sullivan thinks Hurricane Dean will deliver only a glancing blow to Jamaica:
IÃ¢â‚¬â„¢ve just been studying the latest looped images of hurricane Dean. The storm continues to wobble in its course, but if one flattens the line, the trend is clear. That slight leftward shift I saw last evening was real. DeanÃ¢â‚¬â„¢s eye will stay south of Jamaica. The northern eyewall will touch the jut of land southwest of Kingston, but it will not pass over the city. Sustained winds will likely not exceed 100mph in heavily populated areas. Dean will cause much damage and some loss of life on Jamaica, but this is a glancing blow, compared to what might have happened. The worst danger will probably be flash flooding as the hurricane pulls away from the island. Extremely intense convection has consistently occurred in the trailing feeder band as Dean crossed the Caribbean. South-facing slopes near Kingston could be especially hard-hit tonight.
I hope he’s right. The NHC forecast track agrees with him.
P.S. A random wobble, or another example of the power of prayer? We report, you decide!
(Editor Note: Since I was still up and Brendan asked for some help posting while he sleeps and shops, I am posting the exact same post that is on my site WX-Man.com)
The newest advisory and most important the forecast discussion from the National Hurricane Center is out at 5am. Virtually no change to what was discussed 3 hours ago, but there was verification that Dean did appeared to have weaken slightly based on the overall look and structure…
SATELLITE IMAGERY SHOWS A LESS DISTINCT EYE WITH SOME WARMING OF THE SURROUNDING CLOUD TOPS…ALTHOUGH THE CLOUD PATTERN REMAINS VERY IMPRESSIVE WITH GOOD SYMMETRY AND STRONG OUTFLOW OVER ALL QUADRANTS. THE INITIAL INTENSITY ESTIMATE IS KEPT AT 125 KT FOR THIS ADVISORY…WHICH MAY BE A LITTLE ON THE HIGH SIDE. IF INDEED DEAN HAS WEAKENED…THIS IS LIKELY THE RESULT OF INNER CORE PROCESSES…AND IS PROBABLY ONLY A SHORT-TERM CHANGE. THE LARGE-SCALE ATMOSPHERIC AND OCEANIC ENVIRONMENT STILL APPEAR TO BE VERY FAVORABLE FOR STRENGTHENING…SO….ASIDE FROM INNER-CORE-RELATED FLUCTUATIONS…DEAN HAS THE POTENTIAL TO ATTAIN CATEGORY FIVE HURRICANE STATUS OVER THE NORTHWESTERN CARIBBEAN SEA. THIS IS SUPPORTED BY THE GFDL…SHIPS…LGEM…AND FSSE GUIDANCE.
I agree Dean is probably going to gain Category 5 strength here in the next 24 hours. As it is said above all the conditions seem to be favorable, plus as the northwest quadrant of Dean leaves the influence of Hispaniola and is tapping into warm water with out friction you can see the convection beginning to return around the eye of Dean. I also think that just because the eye of Dean doesn’t directly “Hit” Jamaica it won’t be just as bad if it goes as forecast to the south. Just think of Mississippi and the brunt of the storm surge it got with Katrina. Let’s just pray that people took warnings serious and made all the precautions necessary for this storm. Mainly those who were visiting and could leave.
I don’t know much about annular hurricanes — I only first heard about them from Charles Fenwick’s post during Katrina — but I know they’re scary because they aren’t subject to eyewall replacement cycles (and can therefore maintain high intensities longer), and I know that, in Fenwick’s words, “the tell-tale sign of an annular hurricane is that the convection is uniform, making a perfect circle, i.e. there are no spiraling bands, just a donut.” … Well, take a look at Hurricane Dean:
Watching the satellite loop, does it look to anyone else like Dean getting more and more symmetrical, to the point of appearing almost annular in the image above? Could it be that, when the current eyewall replacement cycle is finally over, the “new and improved” Dean will be an annular hurricane? Because, uh, that wouldn’t be good.
I’d very much appreciate input from actual weather experts here, though, because this is definitely one of those cases where I’m at a major disadvantage, being merely a knowledgeable layperson. I don’t really have the skills to fully analyze what I’m seeing. I just see it, and think, “Uhh… is that what I think it is? Does it mean what I think it means?” But I’m not actually qualified to answer my own question.
[UPDATE: Brian Neudorff, a real live meteorologist, thinks Dean is weakening, possibly due to interaction with Hispaniola’s mountains. And he’s right, the satellite images have indeed gotten a bit more ragged-looking since the very symmetrical shot that I posted above. But the overall shape Dean seems to be trying to resolve himself into is more circular than before, with less pronounced spiral bands, so I still wonder if we might not have an annular — or quasi-annular? (is there such a thing?) — hurricane on our hands when the replacement cycle ends.]
Anyway, I’m off to bed. I have to wake up bright and early for some more Babies R Us shopping, and then I’m planning to go to the Four Leaf Peat concert in downtown Knoxville from 1-3 PM — by which point Dean will be getting very close to Jamaica, if not making landfall. So, what I’m saying is, my hurricane blogging may be a bit limited in the morning and afternoon, even though there will be lots going on to blog about. I’ll try and get some guestbloggers to help fill in, but if there’s nothing new here, I (again) highly recommend Dr. Jeff Masters, Eric Berger and Alan Sullivan, as well as all the other links in my “Hurricane Dean blogroll” at left. (I moved it to the left-hand column because I realized all my visitors from InstaPundit couldn’t see it, because the right-hand column doesn’t appear on permalink pages.)
The latest reconaissance flight into Hurricane Dean found a peak flight-level wind of 150 mph. That’s an increase from the previous flight’s 141 mph reading, but it still translates to “only” 135 mph winds at the surface — not enough to support Dean’s official intensity of 145 mph, if the normal formula is being used. The 11:00 pm discussion acknowledged that the official intensity “could be a bit on the high side,” but said they were waiting for more recon data. Now that data is in, and the intensity still appears to be on the high side — yet they didn’t change it in the 2:00 AM advisory.
Why? I suspect this one of those peculiar situations where the NHC forecasters are slightly overestimating the hurricane’s strength, on purpose, because they believe it will restrengthen soon and they don’t want people to let their guard down. The fear, I think, is that by acknowledging that the storm has temporarily weakened a bit, the NHC will encourage a premature sense of relief, which will quickly be replaced by a sort of whiplash effect when Dean blows up again tomorrow — which it probably will, given the low pressure (921 mb) and the fact that it’s completing an eyewall replacement cycle and approaching extremely warm waters. Is this honest? No, but I’ve seen it before, and I can see the logic behind it.
I could be wrong, of course, but that’s how I interpret these events. I think that, in reality, Dean briefly fell to Category 3 status last night, has regained minimal Cat. 4 status this morning, and is now revving up for a return to upper Cat. 4 and perhaps a foray into Cat. 5 territory later today. Let us all continue to pray that Dean spares Jamaica its worst. (Hey — prayer sometimes works!)
[UPDATE, 3:00 AM: Welcome, InstaPundit readers! My latest posts on Dean are here and here. And again, if you want to view all my latest Dean-related posts in one place, constantly updated, go to my hurricane category. Or my homepage, really — I doubt I’ll be blogging about much else today!]
The computer models — including the formerly recalcitrant GFDL — are now unanimous in predicting that Hurricane Dean will not hit the United States. The latest official NHC forecast track, in response to this strengthening consensus, has shifted to the left, and now predicts a final landfall about 210 miles south of the Texas border. Brownsville and Corpus Christi are still within the “cone of uncertainty,” but it appears increasingly likely that this country will be spared Dean’s fury. The Houston Chronicle’s Eric Berger has an excellent discussion of this. He concludes:
South Texas should remain on alert, but if the consensus among the models holds, it’s likely the United States could escape serious harm from an extremely powerful and damaging hurricane. We’re not there yet, but that’s the trend.
Should that come to pass I would hope Texas and the rest of the country would do what it could to help Jamaica and Mexico, as these two nations appear set to bear the brunt of the most intense hurricane to form since 2005’s Wilma.
Here are the current NHC forecast track map and Weather Underground model map:
In other news, the Space Shuttle will return home a day early because of Dean.
P.S. Meanwhile, Alan Sullivan offers a poetic prayer for Jamaica:
Merciful Lord, spare KingstonÃ¢â‚¬â„¢s ramshackle port,
spare Spanish Town and even Montego Bay.
Hammer the sea, but keep your storm offshore.
Let vessels safely reach their quays, and crewmen
lash them down. Let shantytowns stay roofed,
and coconuts not cannonball through walls.
Almighty, if it pleases you to rip
the tamarinds with sheets of windblown tin
and whip the alleyways with sparking wires,
if afterward a plague of flies and boils
afflicts the islanders, vouchsafe them faith
that they may build anew, yet believe in You.
(Hat tip: InstaPundit, who is also blogging heavily about the threat to the Cayman Islands.)
P.P.S. The Palm Beach Post’s Bob King points out: “Anyone looking for news from Jamaica can turn to the Internet radio stream from Power 106FM in Kingston, which is mixing reggae with frequent updates on Dean and advice on how to stay safe and sane.” I’ve added the link to my blogroll at right. Thanks, Bob!