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 lucreto:


You're a bum


Poof
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The stakes are high for Haiti. Perhaps this photo can provide a little perspective for those of us who will be complaining this week about the hassles of storm prep
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Quoting NCHurricane2009:


I am seeing the center at 15.5N along the SW edge of the convection rather than underneath....if it moved WNW from that latitude...wouldn't it track closer or over Puerto Rico and then along the north coast of the DR?


i know. sucks to be us
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Quoting Levi32:


Oh come on Kman it's not getting sheared. The surface low is just having a hard time getting away from the massive sink of low pressure that has been haunting the area between 8N and 14N for the last two days.


It's always getting sheared or ingesting dry air.
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Quoting gulfbreeze:
You must be kidding!!!
or nuts one of the two
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Quoting shadoclown45:


Thanks for the answer


heres the link for the wave tracking layers, each one applies to the force of the wind on the storm for a moment in particular. u have to watch that in order to know what image applies to the storm at the given moment - i used the first two because the storm is over 1000mb, but has the 990-999mb winds of 45-60kt.
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Ughh...Who brought the NAM out? Put it up til fall please ;)
Member Since: August 17, 2005 Posts: 26 Comments: 16505
Quoting Levi32:


Oh come on Kman it's not getting sheared. The surface low is just having a hard time getting away from the massive sink of low pressure that has been haunting the area between 8N and 14N for the last two days.


I thought you were supposed to be getting on a plane LOL.

Why do you dispute that a displaced high overhead is capable of imparting some amount of shear ?
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Quoting Patrap:
Convection is beginning to develop in two lobes on either side of the the center.
Member Since: December 1, 2006 Posts: 2 Comments: 3619
Quoting WeatherNerdPR:

I'm not saying it's in the middle of that burst, just a little closer than before.


I am seeing the center at 15.5N along the SW edge of the convection rather than underneath....if it moved WNW from that latitude...wouldn't it track closer or over Puerto Rico and then along the north coast of the DR?
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Florida is staring down the barrell of a LOADED GUN!!!
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Quoting WeatherNerdPR:
Irene's pretty big.


She is just a TS and looks large enought to fill the GOM already.
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LOL..but if I hear Grain of salt one more time..
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Quoting Levi32:


Oh come on Kman it's not getting sheared. The surface low is just having a hard time getting away from the massive sink of low pressure that has been haunting the area between 8N and 14N for the last two days.


Agree
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Quoting NavarreMark:


Let us pray together that the blob of chicanery now know as Irene, does not interfere with the race at Bristol.

Can I have an AMEN?
You must be kidding!!!
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Quoting kmanislander:
A little SW shear from the displaced high overhead. The deep convection is to the NE of the surface low pressure.



Oh come on Kman it's not getting sheared. The surface low is just having a hard time getting away from the massive sink of low pressure that has been haunting the area between 8N and 14N for the last two days.
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Irene's pretty big.
Member Since: July 7, 2010 Posts: 0 Comments: 5682
Quoting tropicfreak:


I agree, I want to see my boy Denny Hamlin win!!


good driver
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Quoting Patrap:


interesting blowup for us on the island
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Quoting serialteg:


yeah, but even if u go down to deeper millibars it still pushes W

this is the 90kt-112kt product



although i warn u, these things do make u look bad on occasion. i use 'em with a grain or two of salt


Thanks for the answer
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Quoting BahaHurican:
Well, I'm back from the grocery store... wanted to get milk before it was all gone... lol

Had the blog lost its mind yet??? lol
No not really.The usual trolls coming out to stir the pot.Nothing special.Seen way woarse on this blog.
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T.C.F.W.
09L/TS/I/CX
MARK
16.63N/59.29W
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Quoting BahaHurican:
Well, I'm back from the grocery store... wanted to get milk before it was all gone... lol

Had the blog lost its mind yet??? lol


Ironically I did that as well, and we're both on this tiny island... lol.
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Quoting BahaHurican:
Well, I'm back from the grocery store... wanted to get milk before it was all gone... lol

Had the blog lost its mind yet??? lol


yeah im off to walmart to face the herd
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A little SW shear from the displaced high overhead. The deep convection is to the NE of the surface low pressure.

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Troll central tonight.
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I was on here about 6 hours ago reading thru comments discussing how long it would take before we had a depression, and I log on now to find out we have tropical storm Irene. That was FAST!!!!!!!
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Quoting NCHurricane2009:


On a sat pic like that...that red blob will take all your attention...so indeed it looks to be moving NNW at the end there with the blob floating like that...but that blob is just the highest cloud tops...

Rather...the center was fixed by hurricane hunters to be SW of that blob this afternoon...with the center moving W. It may have taken a brief NW jog I believe...regenerating to 15.5N latitude along the SW edge and closer to that red blob.
I was focusing on where the highest cloud tops were, where the lime green was moving about. Thanks for the explanation!
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Quoting BahaHurican:
Well, I'm back from the grocery store... wanted to get milk before it was all gone... lol

Had the blog lost its mind yet??? lol


DMX is on playback..
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Quoting BahaHurican:
Well, I'm back from the grocery store... wanted to get milk before it was all gone... lol

Had the blog lost its mind yet??? lol


Almost --- interesting storm we have here.
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Quoting StratoCumulus:

Hope it stays that way for all the people on the east coast
We would love for Irene to turn out to sea as a whole.But we've been discussing that the pattern setting up this year just won't allow some things to happen.
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Whoever thinks this will be a similar track to Earl in 2010 is smoking something very strong. Earl missed the east coast of florida by 300 miles or so. This will be a Florida storm, make no bones about it.
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Quoting Patrap:
FunkTop Image



...funky...
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Irene Floater - RGB Color Infrared Loop
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Quoting shadoclown45:

Isnt that a weakness between the two highs? Sorry for the stupid question im trying to learn here?


yeah, but even if u go down to deeper millibars it still pushes W

this is the 90kt-112kt product



although i warn u, these things do make u look bad on occasion. i use 'em with a grain or two of salt
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Quoting aquak9:
P'Cola!!! HEY! you stole that from me!!

that's ok, looks good on you. :)


LOL everything looks good on other people thats why copy and paste has taken away all originality from teh internet
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Well, I'm back from the grocery store... wanted to get milk before it was all gone... lol

Had the blog lost its mind yet??? lol
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Quoting StormJunkie:


Think the center may just be reforming under the convection...Which would be N/NNW of where it was earlier. Hard to tell at night though with no HH in the storm.
Thanks!
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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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