Irene roars into life; may become the season's first hurricane

By: Dr. Jeff Masters , 12:03 AM GMT on August 21, 2011

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Tropical Storm Irene roared into life this evening, transitioning from a tropical wave to a 50 mph tropical storm in just a few short hours. An Air Force hurricane hunter aircraft in the storm was finishing up its mission when it suddenly came across a region with intense thunderstorms and surface winds of 50 mph. The aircraft found that a center of circulation had barely closed off on the southwest edge of this region, though the plane found almost no winds from the west around the circulation center. The 6:10pm EDT center fix found a central pressure of 1007mb, which is quite high for the observed 50 mph winds. Dry air to the north and west is slowing development, as well as moderate wind shear of 10 - 20 knots, as analyzed by the University of Wisconsin CIMSS group. Infrared satellite loops and radar out of Martinique show the storm is poorly organized, with no evidence of spiral bands. The center of Irene is expected to cross over the Caribbean island of Dominica early Sunday morning, but the heaviest thunderstorms lie to the north of the center, and will affect Guadeloupe, Antigua, and St. Kitts and Nevis.


Figure 1. Evening satellite image of Irene.

The computer models have shifted southwards since yesterday, and now take Irene south of Puerto Rico on Monday, and along the south shore of the Dominican Republic on Tuesday. On Wednesday, Irene should pass near or over southern Haiti, Eastern Cuba, and Jamaica. On Wednesday and Thursday, the models agree that a trough of low pressure will dip down over the Eastern U.S., which is likely to turn Irene to the north. The exact timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when Irene will turn to the north. We can expect that Irene will impact Central Cuba, the Bahamas, and the Florida Keys on Thursday, but it is uncertain whether Irene's turn to the north will take the storm into the Gulf of Mexico or not. Irene most reminds me of Tropical Storm Fay of 2008. Fay formed just off the coast of Puerto Rico, and was never quite able to get organized enough to become a hurricane, due to passage over Hispaniola and Cuba. Fay topped out as a strong tropical storm with 70 mph winds, and did over $500 million in damage in the U.S., mostly due to flooding rains in Florida that accumulated to over 25 inches in a few areas. Fay also dumped heavy rains on Hispaniola, triggering flooding that claimed eight lives.


Figure 2. Track of Tropical Storm Fay of 2008.

Irene will be battling dry air and moderate wind shear of 10 - 20 knots through Sunday, and it will take the storm 1 - 3 days to build up an eyewall and intensify into a hurricane. Irene is more of a threat than Tropical Storm Emily of early August was, since Irene has closed off a center farther east than Emily did and has more time to organize before encountering Hispaniola. I don't think passage over Hispaniola will destroy Irene, since it is a fairly large storm, and is likely to be a hurricane by then. However, if Irene follows the NHC forecast, it will have an extended encounter with Hispaniola and Cuba on Tuesday through Wednesday that will probably weaken the storm below hurricane force. Keep in mind that the average error for an official 5-day forecast from NHC for a developed storm is 200 - 250 miles. Irene could easily miss Florida and move up the East Coast and hit North or South Carolina, or pass through the Florida Keys and into Gulf of Mexico, ending up who knows where. Given the uncertainties, this weekend would be a good time to go over your hurricane preparedness if you live anywhere in the Caribbean, Bahamas, or U.S. coast, since Irene could well be paying you a visit as a tropical storm or hurricane sometime in the next week.

Harvey hits Belize
Tropical Storm Harvey made landfall at 2pm EDT on Saturday near Dangriga Town, Belize, as a tropical storm with 60 mph winds. Harvey continues to dump very heavy rains on northern Guatemala, Belize, and portions of Mexico's Yucatan Peninsula as the storm tracks westwards at 12 mph. Dissipation is expected Sunday as the storm pushes inland. Harvey was a small storm, and the strongest winds were confined to a short stretch of coast near where the center came ashore. Winds at Belize City, Belize on Saturday topped out at 15 mph.


Figure 3. Radar image of Harvey taken at 11:30am EDT on Saturday, August 20, 2011, a few hours before landfall in Belize. A small closed eye is visible just south of the offshore islands of Belize. Image credit: Belize National Meteorological Service.

An exceptionally active early part of hurricane season
It's been a strangely hyperactive season for weak storms in the Atlantic so far this year. Tropical Storm Irene is the 9th named storm this year, and its formation date of August 20 ties 2011 with 1936 as the 2nd earliest date for formation of the season's 9th storm. Only 2005 had an earlier date. The first eight storms this year have stayed below hurricane strength, making 2011 the first hurricane season since record keeping began in 1851 to have more than six consecutive tropical storms that did not reach hurricane strength. As I discussed in Friday's post, a major reason for this is the lack of vertical instability over the tropical Atlantic so far this year. We've had a large amount of dry, sinking air over the tropical Atlantic, and the usual amount of dry, dusty air from the Sahara, both helping to keep the atmosphere stable and stop this year's storms from intensifying into hurricanes. Hurricane activity typically ramps up big-time by August 20, with more than 80% of all the hurricanes and 65% of all the tropical storms occurring after that date. At our current pace, 2011 will become the second busiest Atlantic hurricane season on record, with 24 - 27 named storms. There are only 21 names in the list of names for a hurricane season, so we may have to break out the Greek alphabet again in late October this year, as occurred in 2005. Ironically, this was the last time the current set of names was used in the Atlantic, so 16 of this year's 21 names are repeats of 2005. I'm not too happy about seeing another hurricane season challenge the Hurricane Season of 2005 in any way, and let's hope we don't retire another five names this year, like occurred in 2005! With vertical instability much lower this year than in 2005, and that year having already seen one storm (Dennis) retired by this point in the season, I doubt that will happen, though.


Figure 2. The annual cycle of average hurricane frequency in the Atlantic. Historically, about 35% of all the tropical storms and 15% of all the hurricanes will have occurred by August 20.

Invest 98L near the Cape Verde Islands
A tropical wave near Cape Verde Islands off the coast of Africa, Invest 98L, is spreading heavy rains and strong gusty winds to those islands today. So far this morning, top sustained winds measured in the Cape Verde Islands were 23 mph at Mindelo. 98L has a long stretch of ocean to cross before it could affect any land areas. Approximately 70 - 80% of all tropical cyclones that pass this close to the Cape Verde Islands end up curving out to sea and not affecting any other land areas, according to Dr. Bob Hart's excellent historical probability of landfall charts. The latest set of long-range model runs go along with this idea, and I'd be surprised if 98L threatens any land areas.

Jeff Masters

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Quoting Mikla:
Latest Intensity:

The LBAR seems optimistic.
Member Since: July 7, 2010 Posts: 0 Comments: 5682
When will we see Hurricane Irene?

a)11:00
b)14:00
c)17:00
d)20:00
e)other?

all times EST
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Quoting MZT:
A fully formed hurricane can even cross cuba twice and just drop a CAT. I used to think the islands had more impact, but now I think they mainly matter for small tropical storms. Hurricanes just plow right on through.


Right....David Cat 5 Killed 2000 ...After Islands..Fla..Weakening cat 2


Cleo 1964 Cat 4 ...killler large hurricane turned right crossed east central cuba...Weakened to cat 1 intensified to respectable cat 2 hit S Florida.

Big strong hurricanes get torn up by the islands very often
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Quoting Mikla:
Latest Intensity:
160 knots? You gotta be kidding me...
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3167. divdog
Quoting Gearsts:
Center moving wnwLink
funny that the entry right after yours says wsw. gonna be interesting in here today.
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Quoting StormJunkie:


No, no, no...It was a joke...There is no such thing as "Ridge pumping"

:)


LIAR.........you got a baby don't ya......ROFLMAO
Member Since: September 2, 2007 Posts: 178 Comments: 20439
3165. aquak9
Quoting Bluestorm5:
Sigh, what's new in the last 6 hours. This is the earliest I've waken without using alarm.

(passes coffee to Blue, sugar only)
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Quoting HurricaneHunterJoe:


cuz u r in Tampa u r worried about the models popping back west?


Im worried about the storm hitting anyone in the U.S.

If I could make a wish I could only hope a tropical storm would land in texas and give those folks the water that they really need.
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Quoting aquak9:

When I click on your name, there's no bio on the r'hand side of the screen. But it's no big deal.


I was just trying to see how to edit my bio. I can't even find it. lol
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Quoting TampaBayWX:


Tampa a quote from crown weather for you bro....... "It should be strongly cautioned that further changes in the track forecast with Irene are likely and that a track into the eastern Gulf of Mexico with a hit on the western side of the Florida Peninsula is still very much possible."


Brother, i fully agree......this is one strong high.........a player that i was just looking at tho.....is Invest 98L........it breaks the Ridge also.....but will pump a ridge to its left.......i don't like that setup.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Quoting TampaSpin:


LMAO........a strong cane would do that....it would not take much to move Irene left or right of Florida.......WoW....take your pick right now. Maybe right down the middle.


No, no, no...It was a joke...There is no such thing as "Ridge pumping"

:)
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3159. aquak9
Quoting donna1960ruled:
The ridge is not all that. Through PR...Northern scrape of Hispanola,,,direct hit FL/GA Cat 4.
Enough with this south south south stuff.

Sigh...but I've always been nice to you...
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3157. HCW
Models aren't handling the positioning and strength of the ridge well so look for a shift back to the west in future runs
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Shear may slow development and enhance western movement especially once Irene starts interacting with land.
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Quoting scott39:
Goodmorning everyone, something to ponder......... Irene reminds me of a much bigger and healthier version of Don and Emily. The track entering the E Caribbean is almost matching up for each storm. The BIGGEST difference is that Irene is already a developed TC, but not the best one at the moment. Here is the MILLION DOLLAR Question for me? Which High pressure steering system.....rate of speed.....and the breaking down of the ridge, does Irene compare the closest to, out of both Don and Emily?
,emily imo
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Sigh, what's new in the last 6 hours. This is the earliest I've waken without using alarm.
Member Since: August 1, 2011 Posts: 28 Comments: 8007

Poleward outflow is well defined. Symmetry is improving as well.
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3152. Mikla
Latest Intensity:
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3151. MZT
Quoting Sfloridacat5:
Irene's forward speed and size will allow her to cross Haiti and Cuba intact. Irene could easily be much stronger than the NHC forecast in the Florida straights.
A fully formed hurricane can even cross cuba twice and just drop a CAT. I used to think the islands had more impact, but now I think they mainly matter for small tropical storms. Hurricanes just plow right on through.
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3150. aquak9
Quoting weatherwart:



I'm in Spring Hill, north of Clearwater/Tampa about an hour. I thought I did list my location, but maybe in the wrong place?

When I click on your name, there's no bio on the r'hand side of the screen. But it's no big deal.
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Recon may (or may not) verify, but satellite loops seem to indicate a slightly-south of due west movement at the moment. Of course, in these formative stages, there will be large-scale wobbles that shouldn't be misinterpreted as track changes. Still, it'll be interesting to see where she is 24 hoprus from now...
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3148. Gearsts
Center moving wnwLink
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Quoting TampaBayWX:


good info bro... thanks!


cuz u r in Tampa u r worried about the models popping back west?
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Quoting Gearsts:

Eyewall??
Member Since: July 7, 2010 Posts: 0 Comments: 5682
Member Since: September 2, 2007 Posts: 178 Comments: 20439
I think another factor with less convection on the west side of the circulation is the RAPID WNW motion.

In the same way it is hard to get westerly winds in this environment, the surface convergence would be weaker on this side. She should only gradually be slowing down over the next 72 hours so she's likely to continue to favor convection on the east/northeast sides.

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Quoting donna1960ruled:
The ridge is not all that. Through PR...Northern scrape of Hispanola,,,direct hit FL/GA Cat 4.
Enough with this south south south stuff.

see post 3130 it jogged south and is about to be right on line with nhc track
Member Since: June 22, 2010 Posts: 0 Comments: 140
Quoting TampaSpin:



Yes i did.........Big Shift EAST.


You think that trend will continue....out into the bahamas in general or do you see them going back west or do you think they are pretty much zeroing in?
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3141. dmh1026
Irene is now trying to look like a hurricane....
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3140. Gearsts
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Irene's forward speed and size will allow her to cross Haiti and Cuba intact. Irene could easily be much stronger than the NHC forecast in the Florida straights.
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3137. aquak9
Scoos- it's real pretty out that way. Real peaceful.
UNF- I need more time than that. Can you please set it back a bit to late Sat, maybe even Sun-Mon? St. V's parking garage floods real easy, being right on the river.
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Quoting TampaSpin:
Sure looks Irene is starting to really wrap now......as the LLC of circulation is really easy to pick out now.


Tampa a quote from crown weather for you bro....... "It should be strongly cautioned that further changes in the track forecast with Irene are likely and that a track into the eastern Gulf of Mexico with a hit on the western side of the Florida Peninsula is still very much possible."
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3135. HCW
Quoting shadoclown45:


What is your sites name. TIA


I think that you can find Tampa Spin's site located here. I hope that helps :)

Link
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Quoting StormJunkie:
Wonder what happens if Irene decides to pump the ridge?

lmao


LMAO........a strong cane would do that....it would not take much to move Irene left or right of Florida.......WoW....take your pick right now. Maybe right down the middle.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Quoting JrWeathermanFL:
Not to change from Irene, but are there any T- waves or anything to watch for development in the next few weeks?


Link
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3132. MZT
Quoting TampaSpin:
Sure looks Irene is starting to really wrap now......as the LLC of circulation is really easy to pick out now.
Yeah this seems to be the day she begins "filling in" - this could be a very large storm when all the dry air is wrung out
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3131. scott39
kman take a look at post 3095?
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looks like it took a dip south ? Link
Member Since: June 22, 2010 Posts: 0 Comments: 140
Quoting aquak9:
Wart, where are you? Folks are supposed to put thier location in when they become members, I think, but many people just leave it blank.



I'm in Spring Hill, north of Clearwater/Tampa about an hour. I thought I did list my location, but maybe in the wrong place?
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Quoting WeatherNerdPR:
41mph at the vortex message. It's no mystery where the strongest winds are, though:


Yeah that curved convective band northeast of the center is quite impressive. Some serious divergence driving this band.
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Sure looks Irene is starting to really wrap now......as the LLC of circulation is really easy to pick out now.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Quoting ProgressivePulse:
Morning All. Didn't like this comment from the NHC.

ONCE OVER THE FLORIDA STRAITS...HOWEVER...
IRENE WILL HAVE AT LEAST 24 HOURS OVER SOME OF THE WARMEST WATER IN
THE ATLANTIC TO TAP INTO. THE OFFICIAL FORECAST REMAINS ON THE
CONSERVATIVE SIDE DUE TO LAND EFFECTS AND IS CLOSE TO A BLEND OF
SHIPS AND LGEM STATISTICAL INTENSITY MODELS.


Still pretty rock solid, especially now with the GFDL swinging around.
UKM still takes Irene to the GOM?
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Quoting MiamiHurricanes09:
Lol, that never crossed my mind. They were moving over western Basse-Terre over a volcanic relief during the momentary climb. Already back down to the regular height:

123400 1551N 06123W 8426 01586 //// +174 //// 184022 022 012 002 01

Wow, I forgot too. LOL
Member Since: July 7, 2010 Posts: 0 Comments: 5682
Quoting WeatherNerdPR:
41mph at the vortex message. It's no mystery where the strongest winds are, though:


In that cluster off to the NE. Probably 60 mph in that.

Anyway, time for golf.

Back this afternoon. Have a great day everyone.
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Quoting StormJunkie:
Wonder what happens if Irene decides to pump the ridge?

lmao
good old boys club
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Quoting shadoclown45:


What is your sites name. TIA


Can't post it as i would get banned......maybe someone else can post it tho......go to my blog tho.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
3121. unf97
Quoting aquak9:
YO UNF!!! :) hi scooster

I am on the back porch, three miles inland from JaxBeach. Absolutely GORGEOUS day here, so still, even the willows are not moving. No Way can the weather deteriorate EVER, it's a perfect dream.


It is a beautiful morning here in the river city. Aquak, we may be dealing with something totally opposite of what we are experiencing currently by late Friday into Saturday though. It's going to be an interesting week to say the least.
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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.