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Hurricane Dean--9th strongest hurricane on record

By: Dr. Jeff Masters , 2:46 PM GMT on August 21, 2007

Hurricane Dean powered ashore in Mexico's Yucatan Peninsula this morning as a Category 5 hurricane with 165 mph winds. The pressure of 906 mb measured by the Hurricane Hunters shortly before landfall at 4:30am EDT makes Dean the ninth strongest hurricane on record in the Atlantic. This is the third lowest pressure at landfall behind the 1935 Labor Day hurricane in the Florida Keys and Hurricane Gilbert of 1988 in Cancun Mexico. Dean is also the first Category 5 hurricane to make landfall in the Atlantic Basin since Andrew of 1992.


Figure 1. Dean at landfall, as seen by the Cancun radar. Image credit: Meteorological Service of Mexico.

Radar images at landfall (Figure 1) show that Dean came ashore just north of Chetumal, Mexico, a city of 130,000 people. Dean's center passed about 15 miles north of the city, and Chetumal missed the strongest Category 5 winds of the storm. The strongest winds from Dean were in the right front quadrant on the northern side, since the forward speed of the storm adds to the rotational speed of the winds there. It appears Chetumal was just at the edge of the southern eyewall, and probably experienced sustained winds of Category 3 strength, 115 mph. We don't know, since the weather station stopped reporting data long before the storm arrived. However, a wind analysis done by NOAA's Hurricane Research Division (Figure 2) supports this estimate. The coastal area north of Chetumal where Dean's greatest fury was unleashed has a cruise ship port and a stretch of beach front development, and this region probably suffered near-total destruction.


Figure 2. Dean's winds one hour before landfall. Winds are in knots, multiply by 1.15 to convert to mph. Locations of Chetumal and the Costa Maya Cruise Ship Port are marked. Winds of Category 1 strength (65 kt) are colored yellow, and winds of minimal Category 3 strength (100 knots) are colored pink. Image credit: NOAA/Hurricane Research Division.

Further north, it appears that Cozumel probably got sustained winds near tropical storm force, 39 mph. The weather station there stopped transmitting data before the storm arrived. Cancun's winds topped out at 29 mph, gusting to 54 mph. To the south, Belize City has had top winds of 23 mph, gusting to 35 mph, so far this morning. On the western side of the Yucatan Peninsula, the winds are starting to rise at Campeche. Dean's center will pass south of Campeche, and bring tropical storm or Category 1 hurricane-force winds to the city.

Dean is powerful enough to survive the crossing of the Yucatan as a hurricane, and I expect it will be a Category 2 hurricane with 100 mph winds when it pops out into the Gulf of Mexico later today. Hurricane Janet of 1955, which hit near Chetumal as a Category 5 storm with 170 mph winds, weakened to a Category 2 storm with 105 mph winds when it popped out into the Gulf of Mexico south of Campeche. Janet was moving at about the same speed Dean is, so I expect Dean will behave similarly. Once out over the warm waters of the Gulf of Mexico, Dean has time to intensify by perhaps 15 mph before it makes a second landfall near Poza Rica. Dean will finally dissipate in the mountains about 100 miles north of Mexico City, and could bring heavy rains to the Mexican capital. No hurricane has ever survived the crossing from the Gulf of Mexico to the Pacific over the wide, mountainous portion of Mexico.

Links to follow today:
Campeche, Mexico observations.
Radar from Cancun, Mexico.
Belize City observations.
Morphed microwave animation.

Disturbance 92L
An area of disturbed weather associated with a tropical wave, 92L, is a few hundred miles north of Puerto Rico. This disturbance is less organized than yesterday, despite some rather favorable upper-level winds. There is some dry air to the north that may be interfering with organization, and there is probably not enough turning motion available from this tropical wave to get 92L spinning. I don't expect significant development today given its current state of disorganization, but 92L deserves close scrutiny over the next few days. None of the reliable computer models develop the system.

My live appearance tonight on Internet Partnership Radio
I'll be the guest tonight on the Internet Partnership Radio (http://www.ipr365.com). Tonight's show is called "Center of Circulation", and consists of global severe, winter, and tropical weather news/topics with up to the minute advisories, watches and warnings, safety & preparedness info, and periodic special guests. The host is Charlie Wilson. I hope you can listen in!

I may do a short update this afternoon, and the next full update will be Wednesday morning around 10am EDT.

Jeff Masters

Dean 2007 (nickmini)
A roof dumped atop another house
Dean 2007

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218. bluehaze27
12:42 PM EST on August 21, 2007
Dean is the third strongest landfalling storm in the atlantic basin history according to MSNBC at 906 mb
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217. extreme236
5:41 PM GMT on August 21, 2007
Posted By: bluehaze27 at 5:41 PM GMT on August 21, 2007.

hosweather, it is NOT way to early to write 92l off. It is cooked. It is done. Stick a fork in it.


92L is done right now, and even if it got in the gulf it wouldnt have much time to organize unless it practically stalled
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215. extreme236
5:39 PM GMT on August 21, 2007
Posted By: coffeecrusader at 5:36 PM GMT on August 21, 2007.

"So much for 92L....it won't be Felix....no models are forming it....appears Dr. Lyons comments last night on TWC were correct about conditons not all that favorable for developement....."

Is Dr. Lyons ever wrong?


yes, Dr. Lyons has been wrong before lol
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214. hosweather
5:25 PM GMT on August 21, 2007
92l does not look to be developing soon. But tropical waves tend to be very persistent. The track this one is taking through the Bahamas and eventually into the Gulf is very favorable for development. It is way too soon to be writing this one off.
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213. bluehaze27
12:39 PM EST on August 21, 2007
it looks like 92l is being shredded by an upper level low over hispanola.
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212. bluehaze27
12:37 PM EST on August 21, 2007
It goes to show you that forecasting tropical systems is a psuedo scientific wild ass guess at best.
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211. Yoderfunk
1:36 PM EDT on August 21, 2007
I noticed myself today 92L is going wnw at 29 mph, its gonna hit the coast of florida before it becomes anything. Well thats what Max Mayfield said on channel 10 :P
209. Barkeep1967
5:35 PM GMT on August 21, 2007
hello all, not much damage at chetumel either.


Thats great news. A big ? as to what went on but still great news.
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208. coffeecrusader
5:14 PM GMT on August 21, 2007
"So much for 92L....it won't be Felix....no models are forming it....appears Dr. Lyons comments last night on TWC were correct about conditons not all that favorable for developement....."

Is Dr. Lyons ever wrong?
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206. guygee
5:33 PM GMT on August 21, 2007
Dean's somewhat exposed eye is coming offshore now.
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205. bluehaze27
12:33 PM EST on August 21, 2007
hello all, not much damage at chetumel either.
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204. mgreen91
12:28 PM CDT on August 21, 2007
Posted By: Tazmanian at 12:05 PM CDT on August 21, 2007.

dos any one see this makeing a little turn to the N?

Link
Taz, is Dean turning North?
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203. extreme236
5:31 PM GMT on August 21, 2007
Posted By: indigenous at 5:30 PM GMT on August 21, 2007.

Jim Cantori is on the beach in Mexico and is having trouble finding widespread damage from Dean. I thought Dean was a Cat.5. at landfall. Were surface winds less?


Cantore was in cozumel/cancun. dean made landfall near chetumel, so dean's hurricane force windfield didnt go out that far
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202. extreme236
5:29 PM GMT on August 21, 2007
Posted By: SCEM at 5:23 PM GMT on August 21, 2007.

Thanks! That helps a lot. SC = Seminole County, Florida. I am from the Seminole County Emergency Management Office. We were trying to identify the letters behind 90-99 of the Invests. I appreciate the assistance!


The letters behind 90-99 indicate what tropical basin the invest is in. "L" is used for the atlantic, "e" is used for the eastern pacific, "w" is used for the western pacific, "b" is used for the indian ocean, "c" is used for the central pacific
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201. indigenous
5:28 PM GMT on August 21, 2007
Jim Cantori is on the beach in Mexico and is having trouble finding widespread damage from Dean. I thought Dean was a Cat.5. at landfall. Were surface winds less?
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200. SlimPBC
5:20 PM GMT on August 21, 2007
What's the MJO up to right now? Anyone know?
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199. extreme236
5:27 PM GMT on August 21, 2007
the cmc dropped 92L, but it looks like it develops a weak system in the catl
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198. TheCaneWhisperer
5:25 PM GMT on August 21, 2007
12Z CMC drops 92L. That is encouraging news, as if the satellite wasn't enough.
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197. Twinkster
5:25 PM GMT on August 21, 2007
http://www.wunderground.com/modelmaps/maps.asp?model=NAM&domain=US


In the Top right click Friday and look what it has of the east coast of Florida
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196. Littleninjagrl
5:22 PM GMT on August 21, 2007
Drak, JP....what do you think about 92l?
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195. SCEM
5:20 PM GMT on August 21, 2007
Thanks! That helps a lot. SC = Seminole County, Florida. I am from the Seminole County Emergency Management Office. We were trying to identify the letters behind 90-99 of the Invests. I appreciate the assistance!
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194. KShurricane
5:22 PM GMT on August 21, 2007
Cool - so being the 9th lowest pressure hurricane doesn't necessarily = being the 9th strongest (windiest) hurricane?

Official hurricane intensity or strength is measured by minimum central pressure ONLY. Winds have nothing to do with it. The SS scale only uses windspeed because the average person watching hurricane updates on the news can't relate to pressure changes. So, if you have hurricane A with 140 mph winds and 912 mb pressure and hurricane B had 170 mph winds and 927 mb pressure, hurricane A would be officially the more intense storm.
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193. guygee
5:19 PM GMT on August 21, 2007
Thanks for posting the data atmoaggie. That is good news for all points west.
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192. hurricane23
1:19 PM EDT on August 21, 2007
In my opinion theres no doupt mr dean had something to do with 92L not developing....Adrian
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191. Barkeep1967
5:20 PM GMT on August 21, 2007
If 92l todally parishes then our rain chances will remain low or nonexistant. lol


While that might be bad news for some. With the route that the models had it taking. It is very good news for many.
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190. Twinkster
5:20 PM GMT on August 21, 2007
http://www.wunderground.com/modelmaps/maps.asp?model=NAM&domain=US


In the Top right click Friday and look what it has of the east coast of Florida
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189. Drakoen
5:18 PM GMT on August 21, 2007
Posted By: Twinkster at 5:17 PM GMT on August 21, 2007.

do you have the link to the updated one then


No. the graphic change sometimes. Usually i use the NHC SFC charts to determine if there is something like a SFC low, tropical wave...etc.
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188. weatherbro
5:08 PM GMT on August 21, 2007
If 92l todally parishes then our rain chances will remain low or nonexistant. lol
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187. Twinkster
5:16 PM GMT on August 21, 2007
do you have the link to the updated one then
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186. atmoaggie
5:17 PM GMT on August 21, 2007
The rammb/cira/csu folks are still doing T#s and digital dvorak, based solely on 2 different temperature points in the IR imagery. I would suspect that CI will drop soon and the 6 hour average T# is in the cat1 range now. Read about it here:
Link

digial dvorak
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185. extreme236
5:16 PM GMT on August 21, 2007
that WU pressure map has been acting weird, so i wouldnt trust it lol. its had that low pressure east of the antilles for weeks lol
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184. Drakoen
5:16 PM GMT on August 21, 2007
Twinkster that graph is outdated.
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183. Twinkster
5:16 PM GMT on August 21, 2007
that is the graphic
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182. Tazmanian
5:15 PM GMT on August 21, 2007
WXMongrel ok
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181. Twinkster
5:15 PM GMT on August 21, 2007
Low Pressure
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180. WXMongrel
5:11 PM GMT on August 21, 2007
Tazmanian...I thought upper level winds were showing a northerly steer, especially after exiting the Yucatan Peninsula. However, I'm not sure now. The top of the storm is stretching northward implying it is 'pulling north'. Not very confident tho.
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179. Twinkster
5:12 PM GMT on August 21, 2007
one second I will show you the graphic
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178. misquetofarmer
5:12 PM GMT on August 21, 2007
I have been fascinated by Deans development. I have been watching its progress from its disturbance designation. As a result I have engaged in understanding the Saffir-Simpson Scale. It occurs to me that given the wind speed and the division used to classify all hurricanes that Dean would indeed be approaching if not already considered a Catagory 6 using Dr. Saffir and Dr. Simpsons reasoning and breakdown between catagories.
Your correction or comments are very welcome..I want to understand as I live on the gulf coast.
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177. Drakoen
5:10 PM GMT on August 21, 2007
Posted By: Twinkster at 5:05 PM GMT on August 21, 2007.

the broad areas of showers and Thunderstorms over africa is associated with 1001mb surface low.

This needs to be watched as this system moves through the atlantic over the next couple of days


What 1001mb SFC low? Where are you getting that information.
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176. Barkeep1967
5:07 PM GMT on August 21, 2007
What do you guys think about the CMC developing 92L once it hits the gulf side?? Looks like a TD on the east then it blows up in the gulf...

As I said in the last blog. 92L just needs to die at this point even a tropical Low swinging around that high would be a total disaster for the midwest and Ohio Valley.

Link
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175. TheStormWillSurvive
5:06 PM GMT on August 21, 2007
when is RECON going back in
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174. bswigg
5:04 PM GMT on August 21, 2007
thanks clear...i am over here in Delray Beach have been trying to go to TX, but do not want to leave if right away if something is heading this way and it seems like every week we have a slight chance of something...so have been waiting...did you hear the 2 sonic booms over there on your side? I thought someone crashed outside my house...it rattled the townhouse...then I saw on the news what it was...
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173. Twinkster
5:03 PM GMT on August 21, 2007
the broad areas of showers and Thunderstorms over africa is associated with 1001mb surface low.

This needs to be watched as this system moves through the atlantic over the next couple of days
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172. Tazmanian
4:55 PM GMT on August 21, 2007
dos any one see this makeing a little turn to the N?

Link
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171. nash28
5:00 PM GMT on August 21, 2007
92L was dropped earlier this morning.

It'll be interesting to see what the CMC shows at 12z.
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170. guygee
4:51 PM GMT on August 21, 2007
Posted By: LondonLurker at 4:46 PM GMT on August 21, 2007.
Posted By: guygee at 4:28 PM GMT on August 21, 2007.

The funny thing is that is not the principle at all. The principle is "the stronger the pressure gradient, the stronger the winds".

"Cool - so being the 9th lowest pressure hurricane doesn't necessarily = being the 9th strongest (windiest) hurricane?"

That is true, many of the models initialize with a parameter that is related to the pressure outside of the storm, the "pressure environment", which indicates how low the pressure of the storm is in relationship to the surrounding conditions. So if the pressure environment is relatively low, there is a smaller pressure gradient.

Also depends on the size of the storm and the size of the eye, as well as the magnitude of the forward motion. A small tightening eye likely indicates a higher pressure gradient. I remember as Frances stalled and weakened, the wind were slacking and the eye grew to about 50 miles wide.

The thing I noticed about Dean was it was one of those hurricanes that actually intensified at landfall. I watched the cloud tops on the North side cool dramatically as the eye came onshore. You can go back and still look at this on the loops. We will likely never know exactly how strong it got before it finally fully came onshore and started weakening.
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169. StormJunkie
4:59 PM GMT on August 21, 2007
Welcome SCEM ☺

You in SC?

I think there may be a list on the Navy site, but I can not remember where. Maybe it is on Wiki somewhere....Uh, never mind. Look at the bottom of this blog

Thanks STL!
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168. ClearH2OFla
1:00 PM EDT on August 21, 2007
bswigg i think that is possible. Not probable. I did notice the southeast jog towards tampa after it forms.
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Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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