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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2071. Patrap
IR Unenhanced
TS IRENE

Member Since: July 3, 2005 Posts: 423 Comments: 127804
Speaking as someone who lives in eastern NC - Elizabeth City to be exact - I can say we would happily welcome Irene... to an extent. If she stays a TS or borderline Cat 1, we would heartily welcome the rain. If we're looking at Cat 3+, then I hope it stays just far enough offshore to give us the rain. The models are interesting though; this is one to watch.
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Quoting bwat:
Im from eastern nc, but until hh get in there and find a true CoC, Im not gonna worry about it too much just yet. Far to many times I have heard people say how incorrect the NHC was about a storm, and in the short term look of things they appeared to be correct. But if you go back and look at archives of the NHC's track of different storms, then look at their actual paths, they've pretty much been nailing them for the last 5 or so years. Not going into panic mode until I see the NHC cone overtop of me.


Completely agree. Whoever states that the NHC is innacurate better have the evidence to prove it.
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2068. scott39
Quoting Drakoen:
The dry slot is exactly what is it, a dry slot.

Here's that image again:

Is that the center to the SW of that convection?
Member Since: June 13, 2009 Posts: 0 Comments: 6750
i guess the hwrf for irene isnt coming out... sigh
Member Since: July 31, 2011 Posts: 5 Comments: 857
2066. Walshy
Quoting WeafhermanNimmy:


That is interesting because you would expect the coast to get more rain.


Hurricane Ivan dumped over 20inches of rain over western North Carolina after hitting Florida. Luckily, I received only 8 inches.
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Do we have a COC in the last frames"

Member Since: August 2, 2010 Posts: 21 Comments: 9780
2:00 am advisory position will be interesting.
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Quoting WHATGARBAGE:
where is the storm heading to now?


Posts 2001 to 2003 back-to-back may say it all...eventually toward the US east coast (FL and Carolinas) if current trends continue....

...short term looks to be Northern Lesser Antilles....Puerto Rico....Dominican Republic...afterward the Bahamas.....
Member Since: September 15, 2009 Posts: 465 Comments: 3652
Irene has no choice but to hit Florida. Everyone from Miami to Jacksonville should be alert, don't panic but start ur preparations. The ridge in the Atlantic should stop Irene from turning out to sea and the ridge in TX should block Irene from touching the GOM. Florida is the target unfortunately. I have Irene hitting or just sliding south of PR tomorrow, then moving WNW over some terrain of Hispaniola. I have her in the Bahamas by Wednesday (potentially strengthening), then either going up the East Coast of Florida, or making a brief landfall between Miami or Melbourne.
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2060. bwat
Quoting NCHurricane2009:


Is if just me...or does that eastern clustering of GFS also hint at east coast (as in my neck of the woods) as well?
Im from eastern nc, but until hh get in there and find a true CoC, Im not gonna worry about it too much just yet. Far to many times I have heard people say how incorrect the NHC was about a storm, and in the short term look of things they appeared to be correct. But if you go back and look at archives of the NHC's track of different storms, then look at their actual paths, they've pretty much been nailing them for the last 5 or so years. Not going into panic mode until I see the NHC cone overtop of me.
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Quoting Abacosurf:
It's a shame because by then PR will have less than 12 hours lead time. May be 15 if they're lucky.


well its still not a cane... i think lol

anyone got new quickscats or ascats or dvoraks? while i go take a bath this heat makes me icky
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Quoting MississippiWx:


Irene has no eye...It's just a dry slot.


I think a dry slot at the center of circulation of a TS can be considered the beginnings of an eye.
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2056. Drakoen
The dry slot is exactly what is it, a dry slot.

Here's that image again:

Member Since: October 28, 2006 Posts: 57 Comments: 30117
2055. Patrap
Member Since: July 3, 2005 Posts: 423 Comments: 127804
Come on Irene
Come on Irene

Irene Ta La Rue I A
Irene
Irene Ta La Rue I A
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2053. KEEPEROFTHEGATE (Mod)
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2052. wxhatt
Quoting ncstorm:


if this stays off the coast of florida and ride up the gulf stream..well, it aint looking pretty for points northward


Unfortunately, that's what is transpiring!
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For all of those making a big deal out of what the CFC is saying, The GFDL is much more accurate than this other models once the storm has formed. I think that in the next runs the GFDL should start moving to the east as well because the scenario with the trof is setting itself this way. One the GFDL start following suit we can be much more sure about posible impacts to Florida.
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so now its a carolina storm dreamcasters are out in force these daysits moving the west, its moving the east' its a fish storm, it's it's superwoman!!
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Quoting weatherman12345:
does irene have an eye? if not, what is this? dry air intrusion?
I think it's dry air, but it sure could be. I was thinking this earlier, but decided it was my imagination. However, if you look closely, the convection is firing solidly around this donut hole.
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2048. scott39
Quoting KoritheMan:


If you're referencing the shift within the models, it could be because, as has been mentioned by others, she appears to have formed a little farther north than the previous suites indicated.
So were just waiting on the officials at the NHC?
Member Since: June 13, 2009 Posts: 0 Comments: 6750
Quoting BahaHurican:
Hey, Nimmy. One of the things I particularly remember about storms like Camille, Agnes, and more recently Ike is that their high rainfall didn't end at the coast. I think as much as 25% of Camille's death toll was incurred in the Appalachians, and Ike carried water well into the midwest, I think as far as Illinois before being absorbed or downgraded. The bulk of Agnes' damage was flooding rainfall over areas well removed from the coast. So heavy rain in the Piedmont from Irene is not impossible.



That is interesting because you would expect the coast to get more rain.
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Quoting MississippiWx:


At least, that's what it appears to be...The hole in the convection is right where the radar has a "center."


A 2:00 am recon. fix would have been quite beneficial....especially with the storm posing an immediate threat to Puerto Rico and the Lesser Antilles.
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Quoting dfwstormwatch:
ALRIGHT IM ENDING THIS ARGUMENT NOW!!!!!

this is a perfect example of what western cuba can do to a large powerful hurricane...


Um... Ike struck eastern Cuba first, in case you didn't know.
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Quoting reedzone:


Pattern just wont allow Irene to enter the GOM. I agree with the ensembles, an East Coast runner... We know it's going to hit Florida, but how much land interaction will occur and what will the strength be.. That is what we need to find out.


im with ya reed on this one
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Quoting serialteg:


we probably will at 5am if not at the 2
It's a shame because by then PR will have less than 12 hours lead time. May be 15 if they're lucky.
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Quoting KoritheMan:


There is shear ahead, associated with the TUTT, but it is weakening. Actually, it will benefit the storm by providing outflow.


This TUTT I think has been providing that outflow enhancement judging by the way we had great outflow to the north earlier this afternoon when this was 97L....
Member Since: September 15, 2009 Posts: 465 Comments: 3652
Quoting scott39:
Kori, What would have poleward tug on Irene now?


If you're referencing the shift within the models, it could be because, as has been mentioned by others, she appears to have formed a little farther north than the previous suites indicated.
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Quoting wxhatt:


That probably won't happen anymore. This new center shift is much further to the north and east. This will keep it well offshore FL and up the coast into NC.


She'll still ride to the weakness regardless of the N shift. Deep layer steering here.
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If Irene becomes a full blown hurricane and hits where I live, I might reconsider naming my future kid that name..
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Quoting CapeCoralStorm:



hmm....


Oops I meant Irene! Sorry about that.
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Quoting WeafhermanNimmy:
Baha do you see how much Greensboro, NC can get with rain with remnants of Irene. Of course winds is not concern though like you stated.
Hey, Nimmy. One of the things I particularly remember about storms like Camille, Agnes, and more recently Ike is that their high rainfall didn't end at the coast. I think as much as 25% of Camille's death toll was incurred in the Appalachians, and Ike carried water well into the midwest, I think as far as Illinois before being absorbed or downgraded. The bulk of Agnes' damage was flooding rainfall over areas well removed from the coast. So heavy rain in the Piedmont from Irene is not impossible.

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Quoting MississippiWx:


Irene has no eye...It's just a dry slot.


At least, that's what it appears to be...The hole in the convection is right where the radar has a "center."
Member Since: July 15, 2006 Posts: 17 Comments: 10200
it looks to me like the center is at 15n ( smell rubber burning and see smoke i`m thinking again)-------------> back to the lurking stool
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Quoting WHATGARBAGE:
who said it will now be a fish storm? that cant happen its gonna hit florida everyone ses


no it cant because its already impacting the islands


I think your post is whats garbage; just saying :)
Member Since: March 10, 2010 Posts: 1 Comments: 7480
2031. wxhatt
With center displacement this far north and east not only will is miss the land interactions, but the trough coming down will be closer to pull it up to the north!
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Quoting Abacosurf:
They really need to have hurricane warnings up for P.R.

It's going to come plenty close.


we probably will at 5am if not at the 2
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2029. scott39
Quoting KoritheMan:


There is shear ahead, associated with the TUTT, but it is weakening. Actually, it will benefit the storm by providing outflow.
Kori, What would have poleward tug on Irene now?
Member Since: June 13, 2009 Posts: 0 Comments: 6750
2028. Gearsts
Quoting Drakoen:
Further confirmation:

Cant see it.:(
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Quoting taco2me61:


I agree but we all know or should I say most of us are seeing the Storm more north than where they are saying it is.... I just donot understand why the "West" Movement....

Taco :o)


I think they say west because when they issue the advisories...they are assuming it will move west and not reform further to the north...

If this storm was perfectly balanced right now (symmetric convection)...it would indeed move due west now with the present steering currents. The more WNW motion we have been noting on the blog is due to the combination of the due west steering + some northward reformation....
Member Since: September 15, 2009 Posts: 465 Comments: 3652
Quoting scott39:
The very outer front rain bands look to be encountering some wind shear. it looks to be blowing them NE.Can anyone help here???


There is shear ahead, associated with the TUTT, but it is weakening. Actually, it will benefit the storm by providing outflow.
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2024. Drakoen
Further confirmation:

Member Since: October 28, 2006 Posts: 57 Comments: 30117
Quoting KoritheMan:
If this is truly the start of an eastward shift in the models, they are reflecting what history is: that the east coast is way overdue.


It could...
Member Since: July 15, 2006 Posts: 17 Comments: 10200
A 2:00 am recon. would have been awesome given recent trends. Irene's long term prospects continue to be very uncertain.
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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.