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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why do people want Irene to stay over water?? Can only be one reason.They want it to strengthen and destroy peoples lives! Just sick!
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Quoting wxhatt:


Georgia has not seen a direct hurricane hit since David in 1979. Residence along the coast should review their hurricane preparedness plans.









Stocked up on water yesterday- will be taking the storm shutters out of storage and stacking them in the backyard this afternoon.
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Guess it's time to come out from the shadows and start paying attention. Still recovering from a lightning strike and now another reason to do a roof check.
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3468. OGal


Storm W is posting on Facebook. I too do not know of the incident but I apprectiate his knowledge of the weather.
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Quoting stormwatcherCI:
I also agree. Seems evident the center is south of 17N imo.


If you watch the overall trends on the visible loop with lat/long you can see it riding along the 17 or .1 or.2 below.

The high is obviously strong due to the fast forward speed as Kman and others have pointed out.

I do not see this going north of hisp.

Have to follow the trends.
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Seems those large rainbands are trying to wrap around the west side.
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Good outflow on the N, limited on the south due to dry air that got into the circulation earlier this morning, which is why the recon is not finding higher winds. Whenever you see a big blowup of convection directly over the COC today is when you'll know Irene is strengthening.
Member Since: July 8, 2005 Posts: 259 Comments: 24576
Quoting SAINTHURRIFAN:
Anyone remember the pre hysteria of hurricane debby 2000?Remember the end result?

Yep I remember, http://en.wikipedia.org/wiki/Hurricane_Debby_(2000 )
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Please Have a look at this Animated. No question its A COC...but is it midlevel with surface center not visible? If it is Surface center its all the way up to near 17.3 near St Kitts. It also looks as if its goin to hit puerto rico not go under PR. Matter of fact based on this northward progression clearly seen it could end up near N coast of hispan. I THINK ITS MID LEVEL ONLY.

Link

Animate loop....ANY IDEAS????
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Quoting USAFwxguy:


Supports the south of 17 fix we mentioned.


Note the time. It's from 12:08:00Z, or 8:08AM EDT
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3461. 900MB
Quoting zparkie:
Last year there was a gentleman called StormW on here, I would read his blogs and he seemed pretty accurate and knowledgable about weather. This year I dont see him blogging. Any one know if he retired from this or what might have happened? If so let me know, everyone would request info from him, I think he got married and there was even a big rumor that proved to be false that he died. but I wonder where he is now? anyone know?


It's a long story....I'm sure someone here can post a link to his blog...Miss him as well, but, I missed the "incident", so I didn't see the whole thing go down.
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Quoting CypressJim08:


Try searching Google for StormW and you will find his website :) He has been on perma-ban from WU since last year.


Why was he banned? :(
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Quoting clwstmchasr:


That's a 60 jump to the north or a wnw to nw movement.
here we go again
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Complete Update

TS BUSTED FORECAST ALIBI





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17.5n91.5w has been re-evaluated&altered for TD.Harvey_12pmGMT_ATCF
17.5n90.9w, 17.6n91.9w are now the most recent positions
Starting 20August_12pmGMT and ending 21August_12pmGMT

The 4 short line-segments represent TropicalDepressionHarvey's path
and the westernmost line-segment is the straightline projection.

Using straightline projection of the travel-speed&heading derived from the ATCF coordinates spanning the 6hours between 6amGMT then 12pmGMT :
TD.Harvey's travel-speed was 11mph(17.7k/h) on a heading of 276.1degrees(W)
TD.Harvey was headed toward dissipation over southern Mexico

Copy&paste isj, 16.7n87.0w-17.0n88.3w, 17.0n88.3w-17.3n89.6w, 17.3n89.6w-17.5n90.9w, 17.5n90.9w-17.6n91.9w, mdb, 17.5n90.9w-18.145n98.7w, mtt into the GreatCircleMapper for more info

The previous mapping (for 21August_6amGMT)
Member Since: August 21, 2007 Posts: 0 Comments: 4860
Quoting wxhatt:


Georgia has not seen a direct hurricane hit since David in 1979. Residence along the coast should review their hurricane preparedness plans.







Not to mentions that they haven't been directly hit by a major hurricane in 100 years.
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Quoting zparkie:
Last year there was a gentleman called StormW on here, I would read his blogs and he seemed pretty accurate and knowledgable about weather. This year I dont see him blogging. Any one know if he retired from this or what might have happened? If so let me know, everyone would request info from him, I think he got married and there was even a big rumor that proved to be false that he died. but I wonder where he is now? anyone know?


Try searching Google for StormW and you will find his website :) He has been on perma-ban from WU since last year.
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Stormjunkie....we're gonna have a bed made just for you out here....
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3451. aquak9
Quoting Vincent4989:

*adds 10 pounds of caffeine to your and keep's cups*

okay thanks vincent gotta run now gotta mop the floor and do 5 loads of laundry and mow and weedeat and board up the cat and duct tape the palm trees and yall stay safe and be safe and review your hurricane preparedness TIA ok thx bai
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3450. JRRP
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Hello, Breald!

It feels great to be back here again! How have you been?

I'm really glad to see some of the regulars are still here. Lots of newbies, though.
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Winds now subsiding as they inch near the circulation. They peaked at 46 knots.

134600 1725N 06217W 8425 01548 //// 156 //// 146047 048 046 005 01
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Anyone remember the pre hysteria of hurricane debby 2000?Remember the end result?
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KEEPEROFTHEGATE 1:45 PM GMT on August 21, 2011 +0 Hide this comment.
089

URNT12 KNHC 211228

VORTEX DATA MESSAGE AL092011

A. 21/12:08:00Z

B. 16 deg 46 min N

062 deg 22 min W



About 16.5N/62.2W

Correct me if I am wrong please.
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Quoting MrstormX:


Whats going on?


Still the same surface winds, however look at post #3437.

Thanks MH09!
Member Since: June 21, 2010 Posts: 0 Comments: 528
Quoting TampaSpin:


I can't post it but someone already did. Maybe someone else can post it or go to my WU Blog.
i got it thank you
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has levi posted his vid?
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Irene was tropical storm prior to reaching the Lesser Antilles and you STILL see lack of thundershowers south of the center. Irene is far from the SA coast & you still have dry air being sucked up. This is why invests usually don't develop until they are out of the Eastern Carribean.
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Flight level winds are at 60, that supports the intensity to stay at 50 mph atm. I expect strengthening though later tonight.
Member Since: July 8, 2005 Posts: 259 Comments: 24576
3439. Thrawst
Quoting SavannahStorm:
TWC upping their very scientific "Threat Level"




Lol, cutting a fine line half way through the Bahamas... that means 1 foot makes ALL the difference in terms of threat level.
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Quoting SavannahStorm:
TWC upping their very scientific "Threat Level"




It's "exclusive" you can't find it anywhere else!
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Quoting Hurricanes12:


Why do you think they are only finding those types of winds?
It's having a hard time intensifying with the dry air intrusion from last night. Circulation also hasn't tightened up too much since the last recon.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
3436. wxhatt


Georgia has not seen a direct hurricane hit since David in 1979. Residence along the coast should review their hurricane preparedness plans.







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3435. breald
Quoting KEEPEROFTHEGATE:


Keeper if that path were to hold up every state in the Southeast could see an impact from this storm. Especially FL!!
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Gentle reminder that i'm wishcasting it not to hurt anyone. But I know it doesn't do any good. This reminds me how when we get snow it's so beautiful and fun to watch it fall but it's also so dangerous because it makes the roads slick and there're accidents from it. It's easy to pretend the accidents don't exist because you don't usually hear about except in small sections of the newspaper - which skip a lot of things too. Similarly, we don't hear about all of the people that get hurt or die or lose their homes. We know it happens, but we skip over the details. Even now, lots of people dying. Weird world.
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Strongest surface winds iv seen so far, still at 50mph.

Peak (10s) Flt. Lvl. Wind: 44 knots (~ 50.6 mph)
SFMR Peak (10s) Sfc. Wind: 45 knots (~ 51.7 mph)
SFMR Rain Rate: 18 mm/hr (~ 0.71 in/hr)
(*) Denotes suspect data

Strange how the sfc winds are stronger than the flt winds.
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Quoting Abacosurf:
Agreed. within .1 lol
I also agree. Seems evident the center is south of 17N imo.
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If Irene follows the foretasted track, I can't see Irene being able to maintain itself across all of the mountains of Hispaniola and Cuba, and be able to stay together. It will most likely be a rain event for south Florida.
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Quoting Hurricanes12:


Why do you think they are only finding those types of winds?


Whats going on?
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3429. WxLogic
12Z NAM @12HR (Purpose: watch High and TROF placement/progress in CONUS):

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3428. zparkie
Last year there was a gentleman called StormW on here, I would read his blogs and he seemed pretty accurate and knowledgable about weather. This year I dont see him blogging. Any one know if he retired from this or what might have happened? If so let me know, everyone would request info from him, I think he got married and there was even a big rumor that proved to be false that he died. but I wonder where he is now? anyone know?
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Not a good situation Press. Looks like it is going to plow right over, or just a hair S of Haiti. Serious flooding concerns at the very least.
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Quoting SavannahStorm:
TWC upping their very scientific "Threat Level"


oh I see... it's not the location threat, but also intensity threat. Medium threat sounds good right now for lands around Irene.
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Quoting MiamiHurricanes09:
They got into the system around 7:30a.m EDT.


Why do you think they are only finding those types of winds?
Member Since: June 21, 2010 Posts: 0 Comments: 528
Gotta...........run, but one things for certain......IRENE is gonna hurt a lot of people in the Islands and in the ConUS!! Everyone have a good day and i will be back later this afternoon!
Member Since: September 2, 2007 Posts: 179 Comments: 20448
3422. breald
Quoting sullivanweather:
Good morning, Tampa!
How things?

Do you mean ex-Harvey? Cause I don't think 98L will have any effect on Irene or vice versa.

As far as ex-Harvey goes, it seems the large convective blow-up yesterday morning/afternoon before it made landfall put out a burst of enhanced outflow which helped to carve out a bit of a deeper trough in the Caribbean than global models expected. This aided in creating a broad southwesterly flow over the eastern Caribbean which, I believe, helped Irene to take a more northerly track than forecast. There was already a deep upper trough extending into the Caribbean from the mid-latitudes which is still somewhat evident on water vapor imagery.

I still think this one goes north of the islands. I was saying it yesterday and thus far today all indications are this will continue on this 285° heading or so. Come right over St.Croix, Puerto Rico from Ponce to Mayaguez, into the Mona passage and ride the north coast of Hispaniola.


Hey Sully, I am glad to see you back on the blog. : )
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Quoting aquak9:
(replaces Keeper's cup with decaf, too)

*adds 10 pounds of caffeine to your and keep's cups*
Member Since: November 13, 2009 Posts: 2 Comments: 728

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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.

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