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 washingaway:


is that the newest 0000z model,i couldn't make it out
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Quoting Bluestorm5:
WeatherNerdPR is in for a rude awakening...
Member Since: August 1, 2011 Posts: 28 Comments: 8046
Quoting MississippiWx:
Ugh...She's looking meaner than a snake. Watch out PR:



And it sure happened quickly! Hard to believe it was just an invest earlier today (or yesterday).
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2368. Patrap
IR Unenhanced

Member Since: July 3, 2005 Posts: 427 Comments: 129457
Quoting zerveftexas:
Irene: In this fall, I'm going to be taking my talents to South Beach :D


Maybe she'll sputter and fall apart in the end like Lebron did.
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Quoting MississippiWx:
Ugh...She's looking meaner than a snake. Watch out PR:



My thoughts exactly. Looks bad to us.
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WeatherNerdPR is in for rude waking...
Member Since: August 1, 2011 Posts: 28 Comments: 8046
Quoting MississippiWx:
Ugh...She's looking meaner than a snake. Watch out PR:

She's the best looking system I have seen so far this year.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
The forecasted intensity by the model consensus over the next three days has steadily been rising.


EDIT: I think the image is updating...it's currently unavailable.
Member Since: August 24, 2010 Posts: 19 Comments: 4358
Quoting MiamiHurricanes09:
well, Irene does look like a hurricane now... remind me of Igor without a eye.
Member Since: August 1, 2011 Posts: 28 Comments: 8046
Quoting KEEPEROFTHEGATE:
how many runs does the gfdl
have under its belt for irene? hows it been doing?
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Ugh...She's looking meaner than a snake. Watch out PR:

Member Since: July 15, 2006 Posts: 17 Comments: 10284
2358. Patrap
Member Since: July 3, 2005 Posts: 427 Comments: 129457
Quoting Stormchaser2007:
I could see how this can become a hurricane later today.

I'll say it'll be updated to hurricane between 11 am to 5 pm today. Got to sleep... I better not wake up finding out Haiti is getting slaugthered by Category 3 storm.
Member Since: August 1, 2011 Posts: 28 Comments: 8046
Quoting caneswatch:


It's worrying me too. I'm living in South Florida, and if Irene does become a Cat. 4 or 5, I'm heading north.


Wow. Went to bed for 4 hours and just woke. I am in SE Florida, lighthouse Point. Leaving Wens To take my son to FSU in the panhandle to get to his dorm. I dont like what i am seein with the models overall esp the eastern shift of the GFDL and the cmc. The last thing i said before going to bed last night was, lets say if it (LLC) reforms further north closer to the mid lev circ. Florida doesnt need this and the islands, esp Haiti.
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Quoting MississippiWx:
Irene is stronger than 50mph...

agreed.
Member Since: August 24, 2010 Posts: 19 Comments: 4358
New center position (2AM) vs previous position and model consensus runs




Assuming, the forecast track doesn't change much (which it shouldn't, given the fact that the models have been fairly consistent and inline with each other) this further north position would take Irene directly over Hispaniola, but offshore (or just slightly onshore) over Cuba, meaning much less land interaction.
Member Since: August 24, 2010 Posts: 19 Comments: 4358
Quoting Stormchaser2007:
Good lord, do I see 928 mb? Dang....
Member Since: August 1, 2011 Posts: 28 Comments: 8046
2351. Patrap
Member Since: July 3, 2005 Posts: 427 Comments: 129457
What I'm finding intriguing right now is that most of these alternatives that we're playing around with right now have been played out by one or the other of the model runs we've seen since about the 12th. I'd be interested, once this storm is done and gone, to see which model runs came closest to capturing Irene's track and intensity.
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Link
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00z Euro is basically an update of the 12z run. No shift with it. Need the UKMET and GFDL to shift east to rule out any sort of GOM interaction...I would imagine that east shift will occur. This late in the game, once the models start shifting one way, it keeps going/stays put.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
2347. Patrap
Quoting WaterWitch11:
evening pat, shouldn't you be sleeping?


Heya over dere..

Im fine, I slept some in the Mid 90's.

: )
Member Since: July 3, 2005 Posts: 427 Comments: 129457
Quoting MississippiWx:
So now the GFS/CMC/Euro/HWRF are in a more easterly track. The CMC is really the only one that made any sort of a major shift. The UKMET/GFDL are holding onto their GOM track. The Eastern path gained the CMC to its side for a 4-2 advantage.
The GFS & ECMWF tracks seem more reasonable in terms of track and development, since they don't blow this up into a Category 5 Hurricane, not saying in won't happen, but chances are slim, and the fact that when they do shift it's either the West Coast of FL. or East Coast, as for the others we've seen the CMC try to take it into the Yucatan already, & only when the storm actually develops does the GFDL come on board.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting Stormchaser2007:
144 hours
970mbs





Nothing pretty about that.
Member Since: August 19, 2005 Posts: 5 Comments: 5458
I could see how this can become a hurricane later today.

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2343. scott39
I would hope no one is wishing this to them. I dont know if Im picking up on a lack of experience with a direct hit or nerves?
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2341. Patrap
Member Since: July 3, 2005 Posts: 427 Comments: 129457
evening pat, shouldn't you be sleeping?
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sry guys it would be very hard for this to not hit S.fl
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144 hours
970mbs

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NAO went back negative today. East track Maybe?


-0.23023E+00
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2335. 7544
the models do or dont have the new cords yet ?
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2334. cwf1069
Quoting MiamiHurricanes09:
No idea, lol. The new coordinates would argue for a track further north, possibly having the system only interacting with northeastern Haiti. Beyond that, it's off into the Bahamas region. Can't really get into anything too specific since I haven't seen any models with the center reformation ATM.

With less interaction w/ Hispaniola and Cuba, Irene could be stronger. This mean she could feel the weakness earlier and be pulled a tad to the north?
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2333. JLPR2
Dang! Irene's radar presentation really improved in the last hours.
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting charlottefl:
I'm gonna be a little bolder than I normally am, but I think it needs to be said and I'll leave it at that. Irene's ultimate destination is YTBD, but the thinkin that 60 miles of a reformation to the north=100's of miles to the east track wise is well, skewed. As of right now Irene appears to be moving fairly close to due W, with a small center reformation to the north. Calling for drastic changes in the models does not make any sense to me. Now if some serious deviation to the North occurs after this point, that may be plausible, but I don't see it happening given the synoptic pattern that is in place. You may change the starting point, but unless you alter the pattern, the destination remains (roughly) the same.

another sane person,thank you for your inputs
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So now the GFS/CMC/Euro/HWRF are in a more easterly track. The CMC is really the only one that made any sort of a major shift. The UKMET/GFDL are holding onto their GOM track. The Eastern path gained the CMC to its side for a 4-2 advantage.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
2330. Patrap
Enhanced Infrared Loop (IR) Imagery (4 km Mercator)
Member Since: July 3, 2005 Posts: 427 Comments: 129457
hiya keeper, did you see the 2 earthquakes at vanuatu earlier today?
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HWRF is suggusting MAX Winds of 153 kts? That's 180 MPH Category 5 hurricane... wayyyy stronger than Hazel if it hits SC/NC. Savannah, GA will be destoryed (haven't got direct hit since 2 centuries ago).
Member Since: August 1, 2011 Posts: 28 Comments: 8046
Quoting Hurricanes12:
MH09, where do you think Irene is going?
No idea, lol. The new coordinates would argue for a track further north, possibly having the system only interacting with northeastern Haiti. Beyond that, it's off into the Bahamas region. Can't really get into anything too specific since I haven't seen any models with the center reformation ATM.
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Quoting BahaHurican:
Dunno if anybody else has said it yet, but a track across PR will not cause this storm to miss FL. Instead, it would likely move WNW to NW along the north coast of Hispaniola and through the TCI and Bahamas. Then models split on whether it goes through the Keys or up along the E FL coast and north from there. I haven't seen a single model for about 5 days now that miss FL altogether.


the wishcasters interpret the models differently
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Quoting GTcooliebai:
16N. from 15.3N a .7 degree difference and still moving west at 22mph as of the 2am advisory. And your thinking on the steering is the same as my thinking.


Hah, yeah I posted that before I read the NHC's post about it relocating :P lol

Looking at coordinates, it wasn't a big shift north though, just a very typical jump that is common with tropical cyclones early in development. However yes, it really won't matter because what matters is how the large scale steering current behave 5 days from now.

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Quoting Bluestorm5:
Hurricane Hazel, anyone?



Not saying it will happen, but that what this model is suggusting... wow. How's that for my first hurricane :\
Strong Trough just what Texas needs.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
120

Makes landfall by 144 in GA/FL as a strong hurricane.

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2321. Patrap
2km Storm Relative IR Imagery with BD Enhancement Curve


Member Since: July 3, 2005 Posts: 427 Comments: 129457

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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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