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 presslord:


put the computer away...and go find a flight attendant to flirt with...


But there's only one....it would be too obvious.
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Quoting presslord:


put the computer away...and go find a flight attendant to flirt with...


LOL!!
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Back to entertain me I see.Your phunny.
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Quoting MississippiWx:
TVCN shifted East at 00z, so I'd expect the new cone to be a tad more to the East. It's just going to depend on how much weight they give to the CMC/UKMET/GFDL solutions.



TVCN shifted East dos that mean more water then land?
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Quoting CaicosRetiredSailor:
Fresh NEW CONE
coming at 11pm


Let me get a scoop of vanilla ice cream with my fresh new cone...to the fridge!
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881. Drakoen 9:28 PM EST on August 20, 2011

My quote function has stopped working. I did not see your post but I do know that the 850 mb vort maps were way off for over 24 hrs with Harvey
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Quoting Stormchaser2007:
Shear via SHIPS

Shear?


SHEAR (KT) 3 2 3 4 1 4 8 9 8 16 13 12 13


Irene: Shear..wha? What's that?
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Is Harvey trying to get into the BOC?
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Shortwave IR appears to put the mid-level center due east of Guadeloupe now. It will be interesting to see if the surface center tries to become stacked with it later tonight or tomorrow morning.
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Quoting earthlydragonfly:
Is the GDFL on crack? Well I hope it is on crack!! High end Cat 4??


920 mb should definitely be concerning to most if not all people...
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Quoting JLPR2:


Approximately in 8hrs.


hiya jl,

looks like we have an interesting day or two ahead

what part of pr are you in? im in ponce
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Quoting Levi32:


It could definitely tug the track a tad farther north than if it had waited until tomorrow to develop. I didn't expect the broad low to form any kind of a vortex so soon, weak as it is. Its broadness should keep intensification slow through at least tonight, with the possibility for more rapid intensification later tomorrow once we have a tighter core going. The NHC forecast for a hurricane before Hispaniola looks good, and we could see a solid Cat 1 by then.

The position of the center found tomorrow morning by recon will be interesting, to see how much farther north it may be from the current forecast. It already looks to be coming into the islands nudged north of the 06z forecast point.


put the computer away...and go find a flight attendant to flirt with...
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TVCN shifted East at 00z, so I'd expect the new cone to be a tad more to the East. It's just going to depend on how much weight they give to the CMC/UKMET/GFDL solutions.
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Quoting Drakoen:


He is right and I have made a post already about the CIMSS products. You have seen that right?


I haven't, can you post it?
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Quoting ncstorm:
well, this helps..


I'll happily take any on the far right that lead to deep sea fishing trip for I. Hate all the doom bringers jumping on the barrels of gun talk so early on panic for panic sake is what hurts people taking things seriously when it is more realistic of a call.
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Quoting washingtonian115:
Let's hope Irene misses Haiti completly.If there's any place at potential danger it's them.


This could be possible if Irene's broad center would regenerate NE into the convection...best case scenario for Haiti I see here is a WNW track along the N coast of DR so they get some of the SW rain bands and not a direct hit...

...it looks like they'll get rain from Irene...but I am hoping for them an indirect path rather than a direct strike....
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Quoting Thrawst:


Interesting that no major hurricane has made landfall in the Florida Peninsula with where Irene currently situates.


they forgot Charley I think
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Quoting kmanislander:


Levi, you know I respect your opinion but we will have to agree to disagree on this one.


That's fine. Unfortunately there is no way of proving it either way lol.
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Quoting CaicosRetiredSailor:
Fresh NEW CONE
coming at 11pm

I say its the same or a TAD very little to the west
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Guess I'll get all my home visits done early this week as gas may be an issue later in the week. Got all my clients emergency plans updated in June but will go over each one again as I make my visits. Fortunately we learned a lot from our mistakes in 04 with Charley Francis and Jeanne and are much better prepared this time.
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Beauty for a TS.
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Shear via SHIPS

Shear?


SHEAR (KT) 3 2 3 4 1 4 8 9 8 16 13 12 13
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889. wpb
hope avila gets the pen over the next week and writes the advisories.stewart is vgood too
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Quoting ncstorm:
well, this helps..



LOL - yep - Irene is going to be tough to forecast. We probably won't know a lot about where it's going until it gets past the islands. Then there won't be a lot of time before landfall if that turns out to be south FL. If it goes east or west of south FL, at least there will be more time...
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Fresh NEW CONE
coming at 11pm
Member Since: July 12, 2007 Posts: 0 Comments: 6069
Quoting kmanislander:


Levi, you know I respect your opinion but we will have to agree to disagree on this one.


I'm not sure if it's getting sheared so bad that it's displacing convection that far NE, but I can agree that the center is still SW of the convection.
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884. JLPR2
Quoting ncstorm:
When is dMAX for Irene?


Approximately in 8hrs.
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15.2 N , 58.0 W

IMHO.

Quoting Patrap:
Irene IR Unenhanced Image


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Quoting kmanislander:


Levi, you know I respect your opinion but we will have to agree to disagree on this one.


He is right and I have made a post already about the CIMSS products. You have seen that right?
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Quoting hydrus:
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...


It could definitely tug the track a tad farther north than if it had waited until tomorrow to develop. I didn't expect the broad low to form any kind of a vortex so soon, weak as it is. Its broadness should keep intensification slow through at least tonight, with the possibility for more rapid intensification later tomorrow once we have a tighter core going. The NHC forecast for a hurricane before Hispaniola looks good, and we could see a solid Cat 1 by then.

The position of the center found tomorrow morning by recon will be interesting, to see how much farther north it may be from the current forecast. It already looks to be coming into the islands nudged north of the 06z forecast point.
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Is the GDFL on crack? Well I hope it is on crack!! High end Cat 4??
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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.


School? Its Saturday....

....glad I finished school this past year...nice to have a job and NO HOMEWORK...but you'll get there someday...
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Quoting presslord:
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
Let's hope Irene misses Haiti completly.If there's any place at potential danger it's them.
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Sorry, I'm newbie (not to weather, though...) and don't have lot of links so when the next recon plane?
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838. YOUPEOPLEAREGAY 2:21 AM GMT on August 21, 2011

troll wipe in progress

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Quoting ncstorm:
well, this helps..



Interesting that no major hurricane has made landfall in the Florida Peninsula with where Irene currently situates.
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I cant see this beauty not becoming a hurricane. She will get there...maybe. Lets just hope Hati doesnt get impacted badly. Florida needs the rain. Any one know if Cuba or PR needs it?
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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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