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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2421. RyanFSU
Here's a better picture/mouse-scroll of the ECMWF (no offense to the Raleigh plots): 6-days as a Category 2 hurricane, or so.

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Irene is confusing... need bed and hopefully the center will at least be fixed in the morning, and models can run with the new center... I expect either a cat 2 or (given how this season has been) completely dissipated when I wake up!
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Quoting Patrap:
If I was in South Fla below Tampa..Id be thinking about fuel.other needs.



Own a company, 42 employees and my head is already spinning with crap. I will have them all called tomorrow with plans and to accel work for monday and tues. This is not good for business.
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Quoting Patrap:
If I were in PR,,Id be rigging for Cat 1 plus Conditions

Shes a coming West by wnw looks like .
yeah, I'm boarding up at 500am as soon has the sun come out
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Quoting MississippiWx:
Ugh...She's looking meaner than a snake. Watch out PR:



she sure is, remember her center is in the southern part of all that convection,and east of Antigua? I think
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This storm puts me in an interesting position. I'm moving up to Tallahasse for the school year on Tuesday. I live in S Fla so if in fact it is heading SFla's way my parents have accordion shutters so we can close them up prior to leaving in case it does hit.
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2415. Patrap
Avoid the rush crush,,and if it misses, your one step ahead for the next.
Member Since: July 3, 2005 Posts: 427 Comments: 129439
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Here we go.

Model consensus intensity forecast for the short term has steadily been going up.





Model consensus track forecast for the short term has also been shifting west.



However, these images are slightly outdated. Given the new positioning according to the NHC (which may be a little too far south, according to radar observations by Drak) the earlier consensus runs may be better indicators of what the new model consensus would be, had they been initialized at the new coordinates.

Such a path, as already mentioned, would take it closer to PR, more squarely over Hispaniola, however, it would allow it to stay offshore of Cuba, or at least much less centered over Cuba. The net result would be a little more land interaction in the short term, and a lot less land interaction in the long term than the models have been hinting at.

Of course, this is all assuming the model consensus maintained its current trajectory upon initializing in a further north position.
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2412. brianc
Quoting Patrap:
If I was in South Fla below Tampa..Id be thinking about fuel.other needs.


Wow...I've been lurking on here for years and Paptrap is the last person I would accuse of being a wishcaster or catastrophobe...so I guess we all in Miami/S. FL should take heed...gas/shop tomorrow before the media starts ranting...
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Quoting mojofearless:


Where are you?
we are in Puerto Rico, he's in Carolina and I'm in Caguas
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Quoting ProgressivePulse:




That's KTS unfortunately, right?
Indeed, the HWRF and GFDL messed it up though.

However, as Stormchaser pointed out, most other intensity models don't really intensify it after it interacts with HispaƱola/Cuba.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
This is the worst tracking I have seen yet for Florida....
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Here's a charming little August storm that illustrates a potential track for Irene.



Note that WNW movement takes it straight to Central Florida.

Nothing right now precludes Irene from having a similar track, albeit to the south [left] of this.
Member Since: October 25, 2005 Posts: 19 Comments: 22687
Quoting ProgressivePulse:



The WV loop I am looking at shows turning there, what do you think that would be then?


No idea because I don't see it, but there's nothing there depicted by the GFS 200mb analysis at initialization and nothing shown to develop either.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting Stormchaser2007:


Correct.

Its highly skewed from the GFDL and HWRF though.


May not be too far-fetched with minimal land interruptions.
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Quoting Patrap:
Floater - Rainbow Color Infrared Loop


you can see it starting to spin
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Don't see how Irene can miss PR, it looks more like a direct hit, and maybe buy a hurricane
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Quoting ProgressivePulse:




That's KTS unfortunately, right?


Correct.

Its highly skewed from the GFDL and HWRF though.
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6z

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Quoting MiamiHurricanes09:
Intensity consensus:

AL, 09, 2011082106, 03, IVCN, 0, 0N, 0W, 45, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 12, 0N, 0W, 58, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 24, 0N, 0W, 70, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 36, 0N, 0W, 79, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 48, 0N, 0W, 70, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 60, 0N, 0W, 69, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 72, 0N, 0W, 73, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 84, 0N, 0W, 73, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 96, 0N, 0W, 82, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 108, 0N, 0W, 88, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 120, 0N, 0W, 88, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 132, 0N, 0W, 118, 0, , 0, , 0, 0, 0, 0,




That's KTS unfortunately, right?
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Quoting JLPR2:
Earlier the crickets were pretty quiet, but now I don't hear a single one, nothing, it's dead silent outside. :\
Freaky...


Where are you?
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Quoting Patrap:
If I was in South Fla below Tampa..Id be thinking about fuel.other needs.

and plywoods/hurricane shutters
Member Since: August 1, 2011 Posts: 28 Comments: 8046
Quoting MiamiHurricanes09:


she's def getting her game together!!
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Quoting Patrap:
If I was in South Fla below Tampa..Id be thinking about fuel.other needs.



Watching her very closely, a hit on either coast is in our service territory. So it's off to 16 hr days until power is restored... Still waiting to buy those EH rated boots for a few more days tho, pretty expensive if I don't need them..
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No big change in the models.

Intensity went down quite a bit.
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Quoting MississippiWx:


There's no upper low depicted in water vapor...



The WV loop I am looking at shows turning there, what do you think that would be then?
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Quoting TomTaylor:
NHC cone has updated, however, the track forecast has not. Only the current position has. Here are the last two warning cones, side by side



Track forecasts are only updated at 5 and 11.
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Quoting KoritheMan:


Agreed. Dry slot is evident to the west.


You agree that there is an upper low?? I don't see that anywhere...
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Intensity consensus:

AL, 09, 2011082106, 03, IVCN, 0, 0N, 0W, 45, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 12, 0N, 0W, 58, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 24, 0N, 0W, 70, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 36, 0N, 0W, 79, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 48, 0N, 0W, 70, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 60, 0N, 0W, 69, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 72, 0N, 0W, 73, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 84, 0N, 0W, 73, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 96, 0N, 0W, 82, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 108, 0N, 0W, 88, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 120, 0N, 0W, 88, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, IVCN, 132, 0N, 0W, 118, 0, , 0, , 0, 0, 0, 0,
Member Since: September 2, 2009 Posts: 130 Comments: 21194
2391. Patrap
Member Since: July 3, 2005 Posts: 427 Comments: 129439
.
Member Since: March 7, 2007 Posts: 602 Comments: 21231
This is looking like the storm we were hoping not to see.
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Member Since: October 25, 2005 Posts: 19 Comments: 22687
Quoting ProgressivePulse:
ULL developing SSW of Irene 13.1N 62W. Seems to be trying to pump some dry air in.



looks like a pretty moist environment to me, not seeing the ULL either.
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Levi is so going to freakout and asking us questions what the heck happened overnight once he lands.
Member Since: August 1, 2011 Posts: 28 Comments: 8046
2385. Patrap
If I was in South Fla below Tampa..Id be thinking about fuel.other needs.

Member Since: July 3, 2005 Posts: 427 Comments: 129439
NHC cone has updated, however, the track forecast has not. Only the current position has. Here are the last two warning cones, side by side

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Quoting ProgressivePulse:
ULL developing SSW of Irene 13.1N 62W. Seems to be trying to pump some dry air in.





There's no upper low depicted in water vapor...
Member Since: July 15, 2006 Posts: 17 Comments: 10284
2382. Patrap
If I were in PR,,Id be rigging for Cat 1 plus Conditions

Shes a coming West by wnw looks like .
Member Since: July 3, 2005 Posts: 427 Comments: 129439
Shift towards the right. Puts south Florida under the gun in 108 hours.

AL, 09, 2011082106, 03, TVCN, 0, 160N, 604W, 0, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, TVCN, 12, 169N, 637W, 0, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, TVCN, 24, 175N, 666W, 0, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, TVCN, 36, 182N, 691W, 0, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, TVCN, 48, 189N, 716W, 0, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, TVCN, 60, 197N, 737W, 0, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, TVCN, 72, 205N, 753W, 0, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, TVCN, 84, 217N, 769W, 0, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, TVCN, 96, 231N, 785W, 0, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, TVCN, 108, 249N, 799W, 0, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, TVCN, 120, 268N, 811W, 0, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, TVCN, 132, 298N, 810W, 0, 0, , 0, , 0, 0, 0, 0,
AL, 09, 2011082106, 03, TVCN, 144, 329N, 806W, 0, 0, , 0, , 0, 0, 0, 0,
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting Stormchaser2007:


and the hwrf has a cat 5 by cocoa beach?? what is going on here?
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2379. JLPR2
Earlier the crickets were pretty quiet, but now I don't hear a single one, nothing, it's dead silent outside. :\
Freaky...
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Quoting Hurricanes12:


Agreed, unfortunately.
sigh, excuse my grammer... "WeatherNerdPR is in for a rude awakening..." and I think it's a 70 MPH tropical storm now. Tomorrow is going to be INTERESTING.
Member Since: August 1, 2011 Posts: 28 Comments: 8046
2377. Patrap
Floater - Rainbow Color Infrared Loop
Member Since: July 3, 2005 Posts: 427 Comments: 129439
ULL developing SSW of Irene 13.1N 62W. Seems to be trying to pump some dry air in.



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2375. Walshy
Next EURO image?
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2374. 7544
shes getting that look peeps get the coffee brewing
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AL, 09, 2011082106, , BEST, 0, 160N, 604W, 45, 1006, TS
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting Bluestorm5:
WeatherNerdPR is in for rude waking...


Agreed, unfortunately.
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Quoting washingaway:


is that the newest 0000z model,i couldn't make it out
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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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