Extremely dangerous Dean heads for Jamaica

By: Dr. Jeff Masters , 3:37 PM GMT on August 18, 2007

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Hurricane Dean put on an impressive round of rapid intensification last night, deepening 49 millibars in just 24 hours. Dean is now a major Category 4 hurricane with 150 mph winds. Reports from Hurricane Hunter aircraft show that Dean has likely peaked in intensity, and may be undergoing an eyewall replacement cycle. The eye has shrunk from 20 miles in diameter yesterday down to 13 miles in diameter this morning. This inner eyewall will probably shrink even more and collapse sometime in the next day, to be replaced by a new outer eyewall 30-40 miles in diameter. Dean's winds may decrease to the lower end of the Category 4 scale, 135-140 mph, if that occurs. The inner eyewall and the new outer eyewall that is forming can be seen on a microwave satellite image from this morning (Figure 1). The 11:02am EDT eye report from the Hurricane Hunters said that the southern portion of the inner eyewall was missing, so the eyewall is probably collapsing now.


Figure 1. Microwave satellite image of Hurricane Dean at 7:31am EDT Saturday August 18. Two small partial rings of strong echoes, marking the boundaries of concentric inner and outer eyewalls, are visible. Image credit: Navy Research Lab.

Dean pounded Martinique, St. Lucia, and Dominica yesterday, and the storm's death toll now stands at three. A 62-year old man died on St. Lucia while trying to save his cow from raging flood waters, and a rain-triggered landslide killed a mother and child in their home in Dominica. Martinique suffered the worst damage, with 100% of the banana crop destroyed, 70% of the sugar cane crop gone, and considerable damage to buildings on the south end of the island. Lesser damage occurred on Dominica and St.Lucia, and overall, it appears that the Lesser Antilles islands were fortunate to get off so lightly.

Puerto Rico
Dean's eye is visible on long range radar out of Puerto Rico. A major spiral band of rain moved over Puerto Rico at about 11am EDT, and will bring up to four inches of rain to the island today. Radar estimated rainfall from the Puerto Rico radar shows up to two inches had fallen as of 1pm EDT. The wind/pressure plot from Buoy 42059 south of Puerto Rico shows that Dean passed just north of that location this morning, bringing wind gusts to 66 knots.

Dominican Republic
The tourist town of Punta Cana on the east tip of the island reported sustained winds of 34 mph, gusting to 46 mph this morning. The capital city of Santo Domingo can expect sustained winds of 40-45 mph today as Dean makes its closest pass to the south. Heavy rains of 1-3 inches in non-mountainous area will create some minor flooding problems in these areas. Mountainous area along the south coast of the Dominican Republic, particularly in the rugged Barahona Peninsula that juts farthest south into the Caribbean, will receive higher rain amounts and are at great risk of life-threatening flash floods.

Haiti
Dean will make a very close passage to the south of Haiti's mountainous southern Peninsula, and the capital city of Port-au-Prince could experience winds just below hurricane force. A Category 4 or 5 hurricane passing so close to Haiti is a serious threat. Deforestation has denuded the mountainsides of protective tree cover, and flood waters will wash down the mountains into populated areas. The only saving grace in this situation may be the relatively rapid forward speed of Dean, which will reduce the amount of rain that will fall, compared to other hurricanes that have affected Haiti.

Jamaica and the Cayman Islands
Jamaica is my greatest concern. A direct hit by Dean would make it the worst hurricane strike on Jamaica for over a century. Jamaica has not received a direct hit by a Category 4 or 5 hurricane since perhaps 1832. The worst strikes of the 20th century were Category 3 Hurricane Gilbert of 1988 and Category 2 Hurricane Charlie of 1951. The Cayman Islands also have much to fear from Dean. Dean could rival Ivan as the Cayman's worst hurricane strike of the past century.

Cuba
Mountainous regions in Cuba area also at risk of dangerous flash flooding from Dean. However, civil defense is so good in Cuba that I don't expect any loss of life. Portions of south Cuba will experience sustained tropical force winds.

Mexico
The models have come into much better agreement this morning on the longer term forecast, and it looks very bad for Cancun and Cozumel. Dean will give those resort areas a pounding like they received from Hurricane Emily (Category 4) in 2005, and Hurricane Gilbert (Category 5) in 1988. Dean will probably not be as bad as Wilma (Category 4) in 2005, since Wilma stalled out over Cancun for three days as a major hurricane. Dean is moving quickly, and will not linger long over any of the regions it strikes.

Texas and Louisiana
Things are looking much brighter for Louisiana, as the GFDL model has come in line with all of the other models in predicting a landfall in Southern Texas or Northern Mexico. It now appears likely that Mexico's Yucatan Peninsula will knock Dean down a category or two before it can approach the Texas coast. The upper level low that was forecast by the GFDL to potentially steer Dean northwards appears to be weakening and moving westwards, out of the way of Dean. You can watch this upper level low on water vapor satellite loops. It is the counter-clockwise spinning region that has moved west off the Florida coast into the eastern Gulf of Mexico. If this low continues to weaken and move westwards, it will not be able to swing Dean northwestwards towards northeast Texas and Louisiana. If Dean does manage to catch up to the upper level low, the counter-clockwise circulation around the upper low will bring some south-to-north winds over Dean that would steer it on a more northerly track into the Gulf of Mexico.

The NOAA jet is scheduled to fly tonight and Sunday morning, so we should have some excellent model runs available Sunday morning and afternoon.

I'll have a short update tonight by 9pm, and a full update Sunday morning by noon. Tonight's update will focus on Jamaica, and I'll post the relevant radar and current condition links to follow the storm's path. I'll talk about Typhoon Sepat, as well.

Jeff Masters

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141. Africaskies
4:31 PM GMT on August 18, 2007
May I suggest an alternate reason for the current and a possible future northward turn of Dean. As the outbands expanded faster than forecast over the last 24 hours, contact was made with these and PR (and now DR/Haiti). The internal airfflow patterns of Dean are disrupted by this contact and a ripple effect continues to the core/eyewall. This drag dynamic is perhaps a more plausible reason for this sudden turn WNW. The previous movement West 10+ for every 1 segment North. That has now changed to a rate of 2 West for every 1 North. If this holds and the ULL weakens significantly the track will be north of Jam and South of Cuba, but if if the ULL hardens and slow SW of FL as it is heading currently, the trough combined with the drag on Dean's windflow pattern will turn it more northerly, possibly impacting Western Haiti and then Cuba. The more northerly the track, the greater the drag on the outer bands. These have direct effects on the overall flow patterns and can bring a dangerous wobble to the whole system, trimming it's diameter and turning it all at once. Something to consider.
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140. nola70119
4:28 PM GMT on August 18, 2007
WNW still, with wobbles here and there, but the real test will be how far north of Jamaica it gets tommorow.....I would be nervous if I was an Galveston.
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139. V26R
4:29 PM GMT on August 18, 2007
Jflorida, imagine that you have a top spinning at high speed and moving forward, its vertical component will sway back and forth (The present Eye) while its forward motion is basically stay the same (Storms forward motion)
Okay?
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138. VEROBEACHFL1
4:29 PM GMT on August 18, 2007
ILL still think its possible ---depending how the ULL reacts for a more NNW turn.....still need more hrs....
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137. StormJunkie
4:29 PM GMT on August 18, 2007
I agree though E of LA is highly unlikely!!!
Member Since: August 17, 2005 Posts: 26 Comments: 16872
135. CJ5
11:17 AM CDT on August 18, 2007
Posted By: ewolk08 at 11:17 AM CDT on August 18, 2007.
whats the chances of a more northern turn to majorily shift the track


Slim to slight
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134. Crisis57
4:28 PM GMT on August 18, 2007
Posted By: rwdobson at 4:26 PM GMT on August 18, 2007.

SJ, last I saw the GFDL had this thing hitting lousiana. now it's on the tex/mex border. i'd call that a southward shift.

texas is still very much in play. maybe even lousiana. not anywhere east of that.


but no one is talking about east from that and no one is even actually mentioning where it will hit there just speaking of present track
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133. pensacolastorm
11:27 AM CDT on August 18, 2007
CLP5 better be a glitch
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131. ezziboo
4:27 PM GMT on August 18, 2007
Distantfires, thanks for the info!! My brain has un-exploded.
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130. VEROBEACHFL1
4:28 PM GMT on August 18, 2007
for a bit- hows the ULL doing?
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129. StormJunkie
4:27 PM GMT on August 18, 2007
555 see my 4:15GMT post for model run times...
Member Since: August 17, 2005 Posts: 26 Comments: 16872
127. GetReal
4:26 PM GMT on August 18, 2007
Posted By: Dan187 at 4:26 PM GMT on August 18, 2007.

I,m sorry Dan but I do not see that more west movement your talking about.
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126. louisianaboy444
4:21 PM GMT on August 18, 2007
these models are retarded lol but no dean is not hitting the northern gulf coast...hes the little storm that couldnt lol....but this is a good thing yall didnt want no hurricane heading to louisiana that would have been really bad
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125. Crisis57
4:27 PM GMT on August 18, 2007
Posted By: VEROBEACHFL1 at 4:25 PM GMT on August 18, 2007.

Afternoon All!! Any New Changes------ just popping in for a second-------


hey Vero Dean is moving WNW now
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124. StormJunkie
4:24 PM GMT on August 18, 2007
Thanks V2...lol

Really y'all, no nose job, j/k see it is still the same :~) a little crooked, but no big deal.

dobson, I am also having a hard time discounting the GFDL as well. Granted the 06z run is south. And as far as the models go, actually most of them shifted N, the GFDL shifted S and they are starting to come together. Still I want the next 12z and 00z runs before I have too much confidence in a track.
Member Since: August 17, 2005 Posts: 26 Comments: 16872
123. rwdobson
4:25 PM GMT on August 18, 2007
SJ, last I saw the GFDL had this thing hitting lousiana. now it's on the tex/mex border. i'd call that a southward shift.

texas is still very much in play. maybe even lousiana. not anywhere east of that.
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122. leelee75k
4:23 PM GMT on August 18, 2007
oops didn't mean to neglect Mexico, Haiti or anywhere else that may be in Dean's path, hopefully people there are out shopping and making preparations for Dean too.
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120. Dan187
4:21 PM GMT on August 18, 2007
Last couple Satellite frames appears that it has turned back to the west or just north of due west, rather than the wnw movement it has been.
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119. boiredfish
4:20 PM GMT on August 18, 2007
Rita's forecast path for landfall in the gulf started way south, moved up the Texas coast from just north of Corpus, to Matagorda, to Houston/Galveston, to the Golden Triangle, then it made landfall just east of the Golden Tringle in extreme SW Louisiana. The "cone of uncertainty" is wide 3-5 days out for a reason. Concerning the US mainland, everyone from South Padre to the central La. coast needs to be watching close and be ready to start preparing.
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118. benirica
4:23 PM GMT on August 18, 2007
just a small speck of a shower passed over me at abut 6.30am and i would dare guess the wind in it was to 40mph. were in for a while of rain now, unfortunately when everyone had their guard down. there is rain all over Puerto Rico and still a bit more to come.
some of these showers have very strong winds in them, definitely more than we expected to get from Dean.
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117. wederwatcher555
4:24 PM GMT on August 18, 2007
are the 12z runs out yet? gfs coming in but other than that?
115. Fl30258713
4:20 PM GMT on August 18, 2007
?

Where is this CLP5 model from?

I know it could be fluke that might correct next run, but interesting none the less.
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114. weatherblog
4:11 PM GMT on August 18, 2007
Posted By: guygee at 4:00 PM GMT on August 18, 2007.

I am posting this crude graphic to express my concerns with Dean's track. I know that all of the Global models show Dean's steering high to keep building and moving westward with Dean, but I have been watching the WV loops all morning and I am perceiving that the trough is creating a weakness in the high W and NW of Dean. Of course all three systems are moving west, but just based on my personal observations I am still worried that there may be an eventual northward adjustment in the track. Label me a "northcaster" attm.



You are not a "northcaster", as you supported your opinion with a fact. ;-)
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113. GetReal
4:20 PM GMT on August 18, 2007
Well everyone here has a choice to make. You can believe your lying eyes, or put all your faith in those computer models, but if Dean continues on this more pronounced WNW compass reading, with the NW wobbles thrown in, SW Haiti is in line for a visit from Dean.
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111. Crisis57
4:22 PM GMT on August 18, 2007
Posted By: JFLORIDA at 4:16 PM GMT on August 18, 2007.

there is a HUGE northerly component now.

Its actually striking.


I see that
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110. StormJunkie
4:20 PM GMT on August 18, 2007
dobson, I am not sure that is completely the case, I think the questions now are N Tx to lower in Mex, and as I stated earlier, and i am sure you know, how often have the forecast tracks and the models been on target 5 days out?
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109. pensacolastorm
11:20 AM CDT on August 18, 2007
FEMA trailer = Dorothy and Toto
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108. Broward
4:21 PM GMT on August 18, 2007
well it cant hit my 1019 high pressure at my house so it will be back west soon
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107. V26R
4:20 PM GMT on August 18, 2007
SJ had the feeling something was back there
Hope the Schnoz is feeling better
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106. leelee75k
4:19 PM GMT on August 18, 2007
pretty good size feeder band going over PR in that link JFlorida provided, wonder how heavy the rains and wind are in that band?

also anyone know what the windfield for ts force winds are with Dean? Could Key West potentially feel Dean as it passes by?
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105. centex
4:15 PM GMT on August 18, 2007
I'm wishing I could ignore this storm but due to all the uncettaintly I'm going to need to watch it closely. This storm reminds me of Gilbert but if it crosses Gilberts path to the north I will start getting real nervious.
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104. distantfires
4:20 PM GMT on August 18, 2007
For those of you, who like myself, just discovered the importance of the Upper Level Low (ULL). I refer you to the SciGuy from the Houston Chronicle at http://blogs.chron.com/sciguy/.
It's a succinct description of the dynamics between the
current ULL over south Florida and Dean.
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103. ezziboo
4:20 PM GMT on August 18, 2007
Labayourambler: mais cher (sorry, non-cajuns) we'll be there,...how long will it take to get there from New Iberia, and how many canned "refreshments" can your fridge hold?
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102. PBG00
4:22 PM GMT on August 18, 2007
Good luck Jam..stay safe!
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101. fire831rescue
4:17 PM GMT on August 18, 2007
Posted By: BiloxiGirl at 4:17 PM GMT on August 18, 2007.
It is comforting to know that Barbour is on top of things. Its like getting a call from your Daddy or Grandaddy just to make sure you are ok.


But my daddy and granddaddy aint no computer... LMAO. On a more serious note, I wonder when Barbour will declare a state of emergency as Blancstare did... Could be within the next day or two?
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100. jamnkats
4:15 PM GMT on August 18, 2007
Thanks, Dr. Masters. This update is good enough for me to decide to head south. I really hope Dean doesn't swing towards Belize but we'll keep our internet with us and watch. We can always come north if it is looking bad for Belize. Right now impact looks to be 20.5N 87.7W. We're at 20.5N 87.2W. I wonder what we'll come back to.

Thanks so much to all the great folks here giving us help. We're packing up now and will head out early tomorrow morning.
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99. FEEDERBAND
11:19 AM CDT on August 18, 2007
i know and i thought it was really cool. he was incredible after karina and did a great job for mississippi. shows that he is on his toes.
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98. StormJunkie
4:18 PM GMT on August 18, 2007
Yeah V2, I was vain enough to get a nose :c) job and there is an elephant standing in the corner, but we are ignoring that....Go ahead, look over your shoulder, just don't stare, cause that might mean he is really there.

Sorry for those that did not get all of that, it goes back quite a few hours here...
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97. V26R
4:18 PM GMT on August 18, 2007
rwdobson
Nobody is looking at the whole picture, they're just seeing a small part of it and reading into it what they want to
Thats why we keep getting these shifts in movement every few minutes
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96. pensacolastorm
11:16 AM CDT on August 18, 2007
Anyone checked the CMC? Looks like two more to monitor.
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95. samiam1234
4:17 PM GMT on August 18, 2007
Posted By: leelee75k at 4:16 PM GMT on August 18, 2007.

hopefully people in Texas, Jamaica, and Cayman Islands are out shopping and preparing for Dean and members in Florida are outside enjoying the gorgeous day.


Lelee why no mention of Mexico
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93. CajunSubbie
4:15 PM GMT on August 18, 2007
Posted By: samiam1234 at 4:14 PM GMT on August 18, 2007.

Cajun subbie wrong Rita was targetted right at Houston from the get go as it passed florida..

lol.. watch the 5 day forcast.. it doesn't lie.. slow it down even.. and you see how far this path changed... and the point you make after it passed florida.. this storm isn't even close to the gulf.. and we all know where its going right?

http://www.nhc.noaa.gov/archive/2005/RITA_graphics.shtml
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92. BiloxiGirl
4:16 PM GMT on August 18, 2007
It is comforting to know that Barbour is on top of things. Its like getting a call from your Daddy or Grandaddy just to make sure you are ok.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.