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 chsstormgirl:


That's correct, he was declared the official poster last night!!
As a matter of fact, he was appointed the official poster, about this time last night. And it was duly noted as such.
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51 hours out c.o.c remains offshore near haiti/dr border but both get heavy rain
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1468. JRRP
00z GFS show Irene stronger than 18z
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1466. JLPR2
Quoting MiamiHurricanes09:
Am I the only one that sees the circulation under the convection to the WSW of Antigua?



The winds report from 11pm from the islands would support that.
Antigua has NE winds, Dominica and Guadeloupe NNW winds.
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting lucreto:


That was based on a bogus run with erroneous data once that was corrected I was spot on.

Wait, you mean the super ultra secret, superior models you were so adamantly relying on?
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1464. KEEPEROFTHEGATE (Mod)
T.C.F.W.
09L/TS/I/CX
MARK
16.60N/60.09W
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Quoting beell:
Using this first look at the 00Z GFS-With just a bit more organization Irene will favor a higher level of steering and a continuation of the WNW/W track.

Both frames @ 24 hrs.
click to enlarge


500mb



700mb




Okay...if that is the 00Z GFS...that is more like it (at least where the X is in that 700 mb vorticity map....). It wouldn't suprise me either if Irene ended up just a tad further north of that X position onto the south coast of PR...
Member Since: September 15, 2009 Posts: 539 Comments: 3712
Quoting Gorty:


I will look into it deeply tomorrow and blog about it.

Up to you but it looks like a repeat Danielle from last year.

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1459. Grothar
Quoting cat5hurricane:

And why do some people refuse to evacuate when a category 3 is approaching.

People will do what people do. That's life.


Even though I live on and Island on the Intracoastal in Ft. Lauderdale. We only have to evacuate for 4's & 5s' There are maps which will tell you. Then do recommend that we do but not necessary.
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I cannot believe how much the Intensity Forecast MODELS have increased...OM FREAKING GOSH!
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Quoting NCHurricane2009:


http://www.ssd.noaa.gov/goes/flt/t2/flash-ir2.htm l

Black clouds (low-level clouds) on that shortwave IR imagery seem to show a more northward position of the center based on the way they swirl in....

....so in order for it to stay as far south of PR as it shows in the GFS....it would have to go slightly WSW right now....

....it seems its going to go either just S of Puerto Rico...or perhaps even over PR if it does any more northward jogging or reformation in its west track...


PR is up at 19N and the center should be no farther north than 16N. That would be a huge jump north...
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Blog is slowing down a bit.
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Quoting cat5hurricane:

And why do some people refuse to evacuate when a category 3 is approaching.

People will do what people do. That's life.

You really have no idea what I was referring to do you?
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Quoting TropicalWeatherGrl88:


Should be a lot of land interaction on this run. probably going to be very week


Sorry weak* too much reading
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1452. ackee
I THINK IRENE CENTRE is still where NHC has it until recon or NHC say otherwise
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Quoting cat5hurricane:

And why do some people refuse to evacuate when a category 3 is approaching.

People will do what people do. That's life.


yeah, we are talking about how many in south Florida???? Almost 14 million people???
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Quoting washingtonian115:
Poor Florida.Always in the cross hairs of a storm.You can't blame hurricanes for hitting the state either.I mean hurricanes probally love to vacation and see the great sits of Florida just like we do.(Don't shoot me).
Yes you can also go eat here :-P

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Quoting lickitysplit:
Hope she misses Haiti. They dont need it.



your telling me they have like 700,000 still in tent city i think
Member Since: May 21, 2006 Posts: 5091 Comments: 115437
1448. Patrap
Member Since: July 3, 2005 Posts: 427 Comments: 129446
Quoting washingtonian115:
Poor Florida.Always in the cross hairs of a storm.You can't blame hurricanes for hitting the state either.I mean hurricanes probally love to vacation and see the great sits of Florida just like we do.(Don't shoot me).


To be expected when half the state is a dangling participle. ;)
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1446. SXMFL
Quoting BahaHurican:
Probably tomorrow more than tonight, though you will likely have some rain / wind tonight.


Thanks, and to actually think I was planning a beach day tomorrow..... hahaha
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Quoting ProgressivePulse:




This is going to be a hard pill to swallow, no doubt. PR folks need to exercise extra caution, this is no Emily. Even on the track, the storm is N & East Loaded. I do believe Nward tugs will occur overnight.


off to sleep. this one's gonna keep me busy tomorrow
Member Since: August 22, 2006 Posts: 2 Comments: 1988
Quoting iahishome:


hehe, ok good...

Hopefully you're safe from this one Houston, though I'm sure you could use the rain... My family's in Beaumont, so they've seen Rita and Humberto. They're hoping for a few more years in the clear.

I wasn't in Beaumont for Rita, but I was there before and after... The difference was staggering... About 50% of the trees were gone! Beautiful shady neighborhood was sun-drenched afterwards.


Yes, we could really use sme rain but not from a CAT 4-5 mind you. I have family on the island in Galveston and also family in Orange so I am familiar with the Beaumont area. I hope your family stays safe and they do not see anoter "big one" for a while.
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Hope she misses Haiti. They dont need it.
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Quoting HimacaneBrees:


They gonna do jus fine this year. Highly upset about the fight situation with LSU right now though. I heard Jordan Jefferson kicked a guy in the head while he was down.

Hell, Mr. Jefferson has been kicked while he was down for 3 years. Prolly couldn't stop himself...
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45 hours out d.r getting pummeled
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1439. Grothar
Quoting Orcasystems:


Ummm I warned you about stepping on those spiders... you ummm might get some rain?



Click to enlarge


Thanks a heap, Orca. You guys should go back to thispst #1358 and enlarge it and see what Orca did with my name. Geez, some buddy you are. :)
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Quoting MississippiWx:


Just because the convection is NE of the center doesn't mean the center is going to hit PR. It's fairly common for tropical systems to be heavily weighted on their NE sides, especially when they are developing.


http://www.ssd.noaa.gov/goes/flt/t2/flash-ir2.htm l

Black clouds (low-level clouds) on that shortwave IR imagery seem to show a more northward position of the center based on the way they swirl in....

....so in order for it to stay as far south of PR as it shows in the GFS....it would have to go slightly WSW right now....

....it seems its going to go either just S of Puerto Rico...or perhaps even over PR if it does any more northward jogging or reformation in its west track...
Member Since: September 15, 2009 Posts: 539 Comments: 3712
Member Since: June 9, 2007 Posts: 4 Comments: 15947
Quoting Grothar:


Kids! hummmmmp


Hmmm, I think I'd write hrummph Grothar... I think that says 'kids, hump!' which I can't condone!
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1434. Gorty
Quoting AussieStorm:

I have been checking it out. Models say fish or Bermuda.


I will look into it deeply tomorrow and blog about it.
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Quoting dfwstormwatch:

33 hours p.r's getting pummeled by heavy rains at the very least...


Should be a lot of land interaction on this run. probably going to be very week
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Quoting aquak9:
Blue, I don't think he was being a jerk, y'know it's all in how you read it. I mean, you're not gonna get banned from the blog or anything for posting your own charts.

Some of the late-nighters on here, have slower computers, and they were all very appreciative of him posting the runs, one chart at a time. So they appointed him, that's all.
sigh, ok...
Member Since: August 1, 2011 Posts: 28 Comments: 8046
1431. JLPR2
Almost an hour old, but still...
Dominica
5 mph from NNW
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting dfwstormwatch:

39 hours out center joggin to the w-wnw



thats a little good news
Member Since: May 21, 2006 Posts: 5091 Comments: 115437
Am I the only one that sees the circulation under the convection to the WSW of Antigua?

Member Since: September 2, 2009 Posts: 130 Comments: 21194
The GFS seems to account for a slight reformation to the NW as Irene consolidates if you look at the initialization, hour 3 and hour 6.
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Quoting dfwstormwatch:

well im the only1 who's supposed to be posting it but other people..


You were declared the official poster last night!!
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1426. beell
Using this first look at the 00Z GFS-With just a bit more organization Irene will favor a higher level of steering and a continuation of the WNW/W track.

Both frames @ 24 hrs.
click to enlarge


500mb



700mb

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1424. aquak9
Blue, I don't think he was being a jerk, y'know it's all in how you read it. I mean, you're not gonna get banned from the blog or anything for posting your own charts.

Some of the late-nighters on here, have slower computers, and they were all very appreciative of him posting the runs, one chart at a time. So they appointed him, that's all.
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1423. gugi182
Large wind field heading closer to Puerto Rico?
Member Since: August 3, 2011 Posts: 0 Comments: 178
Poor Florida.Always in the cross hairs of a storm.You can't blame hurricanes for hitting the state either.I mean hurricanes probally love to vacation and see the great sits of Florida just like we do.(Don't shoot me).
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1421. angiest
Quoting Patrap:
D will be fine. They jus worn out from 2 a days here in 96F Plus.

Ingrahm looked fine,


Sept 8th is in Lambeau at least


And you get to play us *again*!
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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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