Irene roars into life; may become the season's first hurricane

By: Dr. Jeff Masters , 12:03 AM GMT en Agosto 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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(post #804)


Yeah, and don't we know it here, too..... People are about to go nuts in the next 3 days here
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Quoting sullivanweather:
I may be alone in this camp but it appears Irene may attempt to slide by to the north of Hispaniola.

The development of very strong convection with Harvey this morning/afternoon is sharpening the upper trough over the central Caribbean. Given that Irene is quickly becoming a more vertical cyclone it's going to be more influenced by the southwest flow emanating from the upper trough.



Another factor is the rather broad and large circulation of Irene. It's entirely possible for a center jump; in the near future due to the lopsided convection and in the future as it approaches Hispaniola. If it enters the Mona Passage such a jump to the north of south of the island given the how large the storm is is quite possible.
I agree
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this blog is going under a RI lol
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Tape + Windows = Useless

Plywood + Windows = Pretty Good

Hurricane Shutters + Windows = Excellent

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967. GoWVU
Had a nice dinner tonight in West Ashley and then friends came over and we had some cold adult beverages by the pool. One thing I have noticed is the animals are acting funny in the back yard. The tree rats in the back yard burring nuts and for the most part not seeing many... Does that mean anything?
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Quoting ackee:
guys look a NAM run so far seem more west the models seem to be more models seem to be trending west in my view even thow some may say NAM not be trusted but the NAM had the sytem further NORTH on previous run also the NAM has not been perform too bad this seasons


0z NAM has it abruptly moving northward into Hispaniola.
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Quoting hurricane23:


Nope..It was an error by tpc. It actually shifted south a bit over the keys a bit.

Seems most of the models shifted to Western part of Pennisula.
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Quoting GoWVU:
Ok all you Charleston weather peeps, what does it look like for us here in Charleston SC?
I would preview hurricane plans and remain close eye on this storm. Too early to tell, but it a good chance it'll impact SE USA. If it get really strong in 2 or 3 days from now, get ready for the storm.
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Quoting Thrawst:


I believe Charley formed a little further west and south of where Irene currently is... so, 2 degrees may be too small for the chart to have Charley in there.


yea I was thinking that after I posted it
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Here on north coast on Dominica island waiting for Irene. Its been overcast and raining most of the afternoon but the big wall is approaching. At 10.30pm local Eastern Caribbean time the sea and breeze is picking up slowly but the lights of the French islands of Mariegalante and Guadeloupe are still clear on the horizon.

Tropical Storm arnings are being been given on local radio, the LIME (former Cable and Wireless)is alerting Saturday night partygoers and others with cell phone texts. We will see what the earlier hours of the morning will bring. Banana and plantain farmers were lamenting the damage that could be caused to them by even 50 mile an hour winds a while ago when I was taking my drinks in the neighbouring village rum shop. We will see how things develop when the sun rises....or before.
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So what is it looking like for Key West florida?
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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.
Thanks Levi...where you flying to?
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Quoting hurricane23:


Nope..It was an error by tpc. It actually shifted south a bit over the keys a bit.

What does TPC mean? Toilet Paper Corporation?
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Quoting CypressJim08:


Coming to FL to be a little closer to the action by chance?


I wish.
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Quoting GoWVU:
Ok all you Charleston weather peeps, what does it look like for us here in Charleston SC?


I'll let you know when to push the panic button...
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Quoting Hurricanes101:


they forgot Charley I think


I believe Charley formed a little further west and south of where Irene currently is... so, 2 degrees may be too small for the chart to have Charley in there.
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Quoting lucreto:




Upset about COMPLETELY MISSING Emily forecast are you?
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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.

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

My plane boards in 30...I can't stay away lol.


Coming to FL to be a little closer to the action by chance?
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Quoting hurricane23:


Nope..It was an error by tpc. It actually shifted south a bit over the keys a bit.
Hey there.
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949. ackee
guys look a NAM run so far seem more west the models seem to be more models seem to be trending west in my view even thow some may say NAM not be trusted but the NAM had the sytem further NORTH on previous run also the NAM has not been perform too bad this seasons
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Quoting USAFwxguy:
Looks like no shift will be necessary in the 11p.m advisory.
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Quoting hurricane23:


Nope..It was an error by tpc. It actually shifted south a bit over the keys a bit.


Ok, thanks Adrian. I thought it was odd since really none of the models shifted east or north.
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Quoting FrankZapper:
If I were in The Keys I'd be taping my windows.
Not so fast.Has to see what she does next.Watching a storm form and die out is like watching a baby go from adult hood to old age and pass away.like a life cycle.The phase "they grow up so fast" really goes a long way with tropical cyclones.
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Quoting presslord:


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

Have you flown recently. Most of them are even too old for ME!!!!!!
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Hiya Levi, Kman, Drak... all the usual suspects, I see. :)
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941. GoWVU
Ok all you Charleston weather peeps, what does it look like for us here in Charleston SC?
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ok im back and ready to post some models in a hour or two...
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I may be alone in this camp but it appears Irene may attempt to slide by to the north of Hispaniola.

The development of very strong convection with Harvey this morning/afternoon is sharpening the upper trough over the central Caribbean. Given that Irene is quickly becoming a more vertical cyclone it's going to be more influenced by the southwest flow emanating from the upper trough.



Another factor is the rather broad and large circulation of Irene. It's entirely possible for a center jump; in the near future due to the lopsided convection and in the future as it approaches Hispaniola. If it enters the Mona Passage such a jump to the north of south of the island given the how large the storm is is quite possible.
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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.


Nope..It was an error by tpc. It actually shifted south a bit over the keys a bit.
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Quoting NCHurricane2009:


Is Guadeloupe around 15.5N latitude? I really believe that this thing is on that latitude right now....


Guadeloupe covers about 16-16.4N. The surface center is lagging behind that.
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Does anyone have any ideas on what the major steering influences for Irene will be (millibars). Just curious.
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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?


Amen and I'll go one better with a Hallelujah!
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Quoting Drakoen:


Those vorticity maps are not perfect. They are done using a finite difference scheme. We need to remember that numerical solutions produce more errors than the analytic ones. In addition, part of the analysis involves using data from numerical model where data is sparse. They take output primarily from the NOGAPS and this data may be from model forecasted projections.


I'll add that post that the error is not limited to the vorticity maps but other cimss products as well.


Lol...I got blasted for saying something similar to this at the beginning of the season.
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Quoting gulfbreeze:
Is Harvey trying to get into the BOC?

Looks to me like it's still staying south over land.
Link
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931. JLPR2
Quoting serialteg:


hiya jl,

looks like we have an interesting day or two ahead

what part of pr are you in? im in ponce


You are going to get the worst part of it, I'm in the NE, in Carolina.

And you bet, tomorrow should be very interesting.
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There is huge amounts of moisure ahead of Irene to feed on...uh-oh...no link..
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Quoting Levi32:


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


;-)
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Quoting Levi32:
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.


Is Guadeloupe around 15.5N latitude? I really believe that this thing is on that latitude right now....
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Quoting NCHurricane2009:


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....
Direct strike would be nasty.No one wants a Jeanne part 2.
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Wow. That was fast. A few hours ago we were looking for a closed low and now, TS Irene. Guess I should think about, you know, doing something.
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If I were in The Keys I'd be taping my windows.
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Quoting TropicalAnalystwx13:


I haven't, can you post it?


Those vorticity maps are not perfect. They are done using a finite difference scheme. We need to remember that numerical solutions produce more errors than the analytic ones. In addition, part of the analysis involves using data from numerical model where data is sparse. They take output primarily from the NOGAPS and this data may be from model forecasted projections.


I'll add that post that the error is not limited to the vorticity maps but other cimss products as well.
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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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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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