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 NCHurricane2009:


EXACTLY...and I think the track for immediate term should be more like going S or over Puerto Rico (which I know you don't want to hear)....afterwards making landfall in E tip of DR or tracking along DR's north coast....anyone else agree?


Yes, I think it has the potential to get pulled north this way.
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Quoting Levi32:


Because the CIMSS shear analysis does not always get the high position correct (and the streamlines are the shear direction, not the upper winds exclusively). Even if it is displaced by a few miles it's not going to be a significant negative effect. I've seen big hurricanes and typhoons without an anticyclone perfectly centered on the CIMSS analysis, which may or may not be accurate at depicting the position.


Levi, you know I respect your opinion but we will have to agree to disagree on this one.
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So are we looking at a more southern path?
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Quoting ncstorm:
well, this helps..



LOL...My thoughts exactly.
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Quoting TropicalAnalystwx13:


You can't wait for me to leave? lol. I bet it is nice in here late at night when all the trolls are in bed. Too bad I have school now and can't stay up late no more.



you can on the weekend lol
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Caribbean Update Special Buletin August 20th 2011

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Quoting galvestonhurricane:
We better hope this is wrong!!
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Quoting galvestonhurricane:


hmmm, that is interesting. That could change things for somebody...
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As I mentioned before: Accidentally posted my (intermediate) mapping for 9pmGMT_NHC in blog1888page3comment105. The previous mapping there has been corrected back to 20August6pmGMT for the appropriate coordinates and viewable map scale.

TS.Harvey_12amGMT_ATCF : Starting 20August_12amGMT and ending 21August_12amGMT

The 4 shorter line-segments represent TropicalStormHarvey's path,
the longest line-segment is the straightline projection, and the 4 unconnected dots are
the highest points of Yucatan(state), QuintanaRoo, Campeche(state), and Belize.

Using straightline projection of the travel-speed&heading derived from the ATCF coordinates spanning the 6hours between 12pmGMT then 6pmGMT :
TS.Harvey's travel-speed was 14.7mph(23.6k/h) on a heading of 283.7degrees(WNW)
TS.Harvey was headed toward reentering the Gulf of Mexico near ElPailebot,Tabasco(state) ~18hours from now

Copy&paste isj, 19.945n89.393w, 18.099n88.9w, 17.9n89.467w, 16.494n89.046w, mtt, 16.1n84.7w-16.3n85.7w, 16.3n85.7w-16.7n87.0w, 16.7n87.0w-17.0n88.3w, 17.0n88.3w-17.3n89.6w, mdb, 17.0n88.3w-18.25n94.0w into the GreatCircleMapper for more info
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Quoting Stormchaser2007:
Recon should be interesting. Can't wait for the night shift when all the kids and trolls go to sleep.



You can't wait for me to leave? lol. I bet it is nice in here late at night when all the trolls are in bed. Too bad I have school now and can't stay up late no more.
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Quoting ncstorm:
well, this helps..



Oh yes, that is oh so helpful..LOL!!

Pick a line, any line :o)
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I think we will see our first hurricane during the first half of tomorrow.
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Quoting aquak9:
P'Cola!!! HEY! you stole that from me!!

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

Wha????? ;)
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Quoting kmanislander:


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 ?


Because the CIMSS shear analysis does not always get the high position correct (and the streamlines are the shear direction, not the upper winds exclusively). Even if it is displaced by a few miles it's not going to be a significant negative effect. I've seen big hurricanes and typhoons without an anticyclone perfectly centered on the CIMSS analysis, which may or may not be accurate at depicting the position.

More than that, there is another logical explanation, as I mentioned.

My plane boards in 30...I can't stay away lol.
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When is dMAX for Irene?
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Irene IR Unenhanced Image


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well, this helps..

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Quoting TropicalAnalystwx13:
I'm expecting to wake up to 65 mph Tropical Storm Irene tomorrow morning.

Oh yes. Maybe 70mph.
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Quoting KEEPEROFTHEGATE:
its all rocket fuel pat by no matter how we look at it rocket fuel if it goes that way best get outta the way something wicked comes this way


hush.
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Recon should be interesting. Can't wait for the night shift when all the kids and trolls go to sleep.

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Quoting AegirsGal:
first rednecks, and now him? what is your problem?


;)
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Quoting TropicalAnalystwx13:
I'm expecting to wake up to 65 mph tomorrow morning.


I'm going a little more conservative with 60 mph.. but 65-70 not out of the possibility.
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Quoting coffeecrusader:
Florida is staring down the barrell of a LOADED GUN!!!

We shall see. No "jumping the gun"....
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Never mind clicked on the wrong one. That's Harvey sorry guys! LOL.
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Quoting serialteg:


and "not an exact science".

but its fun. im totally hooked on it :D


lol..it has it moments..
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I'm expecting to wake up to 65 mph Tropical Storm Irene tomorrow morning.
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Quoting Patrap:





its all rocket fuel pat by no matter how we look at it rocket fuel if it goes that way best get outta the way something wicked comes this way
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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?
haha, we should be more concerned about track in Homestead.... er... I meant city of Miami. Ok, done with jokes. Irene getting serious.
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Irene looks better. Have to say 60mph for 11:00.
I think hurricane tomorrow.
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I'm starting to think these models are forseeing a WSW movement past the islands or a center reforming down there because alot of models are down there in the next 24 to 36 hours and despite what Levi showed earlier all these models dont just make mistakes that large
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Quoting ncstorm:
LOL..but if I hear Grain of salt one more time..


and "not an exact science".

but its fun. im totally hooked on it :D
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.
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It has Irene weakening on the Real Active tropical cyclones webpage to 40 mph.
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http://www.ssd.noaa.gov/goes/east/tatl/avn-l.jpg

Harvey looks like its becoming garbage in a hurry in this view...Irene taking attention
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So umm throwing high heels at this one isn't gonna rip it up like it did for Em I see so what do I need to do to get the trough strong and face to get a north turn soon?
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Quoting FLWeatherFreak91:
Convection is beginning to develop in two lobes on either side of the the center.


Irene looking to balance the center.

Gonna take a while, but shes's learning the dance pretty fast .
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Quoting Levi32:
At the airport - look at me I just can't stay away when there's a storm around lol.

NHC forecast point for 06z has Irene on top of Dominica. Radar out of the Antilles shows the center probably already due east of there, and thus it may slip north of the current forecast track.
What are your thoughts about the rapid fomation of Irene..We were talking of a slower development until monday or tuesday and that would keep her farther south a bit...
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This season is AMAZING for the lack of hurricane strength systems. Something as yet unidentified, which I will call The X Factor, is suppressing their intensification. If Irene follows this pattern in the start of the meat of the season, it will be truly AMAZING! How's that for a curve ball from Mother Nature Dr Gray?
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Quoting LongIslandXpress38:


Easy there Rick Perry...
first rednecks, and now him? what is your problem?
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Quoting lucreto:


You're a bum


Poof
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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.