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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132 hours out heading nnw
Member Since: July 31, 2011 Posts: 5 Comments: 891
Is it possible the storm tracks over Hispanola/Cuba, but jogs a little bit more west in the Keys into the Gulf of Mexico with the ridge building back-in? I realize that there aren't any troughs to really recurve this thing right now, and it's trying to find the "weakness".
Member Since: Posts: Comments:
Quoting Drakoen:
GFS 00z is just like the ECMWF 12z.


Would be nice if the 00z ECM would follow.

Then maybe we can be a little bit more confident in this one.
Member Since: June 9, 2007 Posts: 4 Comments: 15947
988 mb storm over Orlando/Daytona Beach area at 126 hrs.
Member Since: August 1, 2011 Posts: 28 Comments: 8046




tightening up the COC under convection now
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Quoting Drakoen:
GFS 00z is just like the ECMWF 12z.


If the other camp comes on board this set of runs i'll believe it
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Quoting dfwstormwatch:

120 hours out passing by southern florida
don't think it is "passing it by" in that shot. more like "doing a number on"
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1613. scott39
Quoting farhaonhebrew:
jog to the north...? again?
Look at the rain bands out in front of Irenes center. They are going W. If there is any N movement, I cant see it.
Member Since: June 13, 2009 Posts: 0 Comments: 6912
Repost from last page.


00z seems to be a little more east than 18z.
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Quoting Bluestorm5:
Landfall in Miami area at 120 hrs. 996 mb storm.


At least 990...

Member Since: June 9, 2007 Posts: 4 Comments: 15947
Quoting SXMFL:



L'onde est classée tempête par le NHC c'est donc IRENE qui traverse l'arc Antillais ce weekend. Saint Barth, Saint Martin, Guadeloupe et Martinique en vigilance météo ORANGE (pluies abondantes et rafales de vent à 100kmh) Prudence dans les zones inondables ainsi qu'aux objets emportés par le vent !!!


Waiting for irene in ST Martin, for those of who who don't speak french, the last sentence warns you "to be careful in areas that flood and objects being carried around by the wind"..... wouldn't want to get hit by a cow!


Zut Alors! Evite la vache! Si non, si possible, achete une grande BBQ.
Member Since: September 4, 2007 Posts: 0 Comments: 491
1609. angiest
Quoting Seastep:


Storms just don't surge here like the gulf. Just the way it is.


Indeed, surge does depend in part of the continental shelf and a variety of other factors.

And a century ago they had it backwards. They thought the western gulf couldn't get high surge for precisely the reasons it can, which is part of why the 1900 storm was so deadly. The experts said "it can't happen here."
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Quoting tropicfreak:


00z looks to be a little more east on this run.

ever so slightly.
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Yes HoustonTxGal. Having a lot of problems refreshing the blog, and with posts not formatting correctly. Plus, I can't seem to "quote" to answer your question directly.
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Quoting SXMFL:



I am sitting on my balcony in SXM, it's midnight and there's a loud annoying bug and absolutly NO wind.

is that loud annoying bug called Irene
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Quoting AussieStorm:
I'm making Pancakes, anyone want some?



mmmmmmmmm
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1604. Drakoen
GFS 00z is just like the ECMWF 12z.
Member Since: October 28, 2006 Posts: 57 Comments: 30687
Quoting hunkerdown:
that will happen with Internet Explorer...download Firefox and your problems will be fixed...plus, it is an overall better and safer product.


Thanks for the info :o)
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Landfall in Miami area at 120 hrs. 996 mb storm.
Member Since: August 1, 2011 Posts: 28 Comments: 8046
Quoting dfwstormwatch:

120 hours out passing by southern florida


00z looks to be a little more east on this run.
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Quoting dfwstormwatch:

111 hours out heading for south Florida while gaining strength
She better hurry , the GAP is closing.
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114 hours has a hurricane near Miami.
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Too close to home...

Member Since: June 9, 2007 Posts: 4 Comments: 15947
Quoting MiamiHurricanes09:
5 days out and right above me:




it wants too come overe and have a talk with you lol
Member Since: May 21, 2006 Posts: 5091 Comments: 115435
Quoting HoustonTxGal:
Off topic question..... Has anyone else had problems with posts running off the page and not be able to be seen? I have refreshed several times and it will not correct.


Haven't had that problem yet.
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SE FL landfall at 120 hrs

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1592. SXMFL
Quoting JLPR2:
Well this is interesting. Every winds report from the islands at 12am in WU is either Calm or variable. XD



I am sitting on my balcony in SXM, it's midnight and there's a loud annoying bug and absolutly NO wind.
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Quoting NCHurricane2009:


That sat. pic....using that pic...I see Irene may be centered as far north as 16N to 16.5N right now...maybe that is why I feel it could get very close to the south coast of PR...doing something like the NOGAPS shows in short-term....

....out of curiosity...do you see it centered around those latitudes....


No, 15.6N 60.0W is probably about right...

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gfs shift north and east
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Quoting farhaonhebrew:
jog to the north...? again?


Looks that way, but it's not, just a result of convection increasing on the north side and the COC getting tucked underneath it.
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Quoting HoustonTxGal:


Tis the season to be jorry, fa ra ra ra ra ra ra ra ra :o)


Now...that made me laugh! And thanks for the notes to ignore the trolls. Unfortunately, some people just don't get it.
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120 hours out passing by southern florida
Member Since: July 31, 2011 Posts: 5 Comments: 891
5 days out and right above me:


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Quoting HoustonTxGal:
Off topic question..... Has anyone else had problems with posts running off the page and not be able to be seen? I have refreshed several times and it will not correct.
that will happen with Internet Explorer...download Firefox and your problems will be fixed...plus, it is an overall better and safer product.
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This GFS run is more to the north with a bit less land interaction with cuba. The consistency is very impressive I can tell you that.
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Quoting HoustonTxGal:
Off topic question..... Has anyone else had problems with posts running off the page and not be able to be seen? I have refreshed several times and it will not correct.
It'll do that if you are using Internet Explorer.
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The GFS really explodes Irene by 117-123 hours.

Pretty impressive.
Member Since: June 9, 2007 Posts: 4 Comments: 15947
I could understand a cat 1 cat 2 possibly, if it had slowed ans got into the hot gulf waterm but a 939 prob cat4/5 puhhhhlezeeeeeeeeeeeee
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Looks familiar...and its not Fay.

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Quoting TampaSpin:
If a Cat 3 came into just north of Tampa Bay...i can't imagine what the City of Tampa would look like.....i don't think most could imagine how bad it would be.
Thanks for the video, just goes to show you how fast things can change, and if your told to evacuate to get your butt out of there, that's why the NHC got rid of the line.
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1578. Skyepony (Mod)
Quoting AussieStorm:

windsat is what it is, that's a lot of wasted money.


It's lasted more than 5 years beyond it's life expectancy..If our technology still sucked it would still be pretty awesome.
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Florida Keys hit likely coming on the GFS. It might go into the Gulf if it doesn't ride up FL.
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Visible loops would come in quite handy right about now.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
1575. KEEPEROFTHEGATE (Mod)
T.C.F.
09L/TS/I/C0
RI FLAG "ON"
MARK
16.60N/60.09W
Member Since: July 15, 2006 Posts: 176 Comments: 55517
1574. Seastep
Quoting Orcasystems:


Ok, I have to ask.. you live in a state with the elevation of a ping pong table... why would you stay in anything above a CAT 1?


Storms just don't surge here like the gulf. Just the way it is.
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Off topic question..... Has anyone else had problems with posts running off the page and not be able to be seen? I have refreshed several times and it will not correct.
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Quoting JLPR2:
Well this is interesting. Every winds report from the islands at 12am in WU is either Calm or variable. XD


It's the calm before the storm......
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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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