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 MississippiWx:


It has already been discussed here, even by Levi, that the models are probably underestimating the effects of land.
I guess we'll see, lol. I don't believe land interaction will be that bad. The GFS only has Irene inland over Cuba for a few hours whilst it's over eastern Cuba. The NHC has it inland for longer than that, hence the lesser intensity.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
If in the next 12 hours Irene does not start taking a wnw trajectory, the chances for it to miss hispaniola will be greatly increased and the longer it maintains this W trajectory, the greater the chance for it to just skirt the islands and make it to the GOMEX. It's all about the timing.
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Quoting ProgressivePulse:



80W is nearly on top of me in Jupiter, FL.

GPS 80.5W


I used to love to camp at Jonathan Dickenson State Park and surf at Juno Beach...
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Quoting MississippiWx:


Sounds good. But, if you disagree with me, you're disagreeing with the NHC because they share my opinion. In fact, they only have a TS hitting Florida.


you are aware of what the NHC posted in their discussion in regards to the intensity right?
Member Since: March 10, 2010 Posts: 1 Comments: 7866
Quoting angiest:


That's the second time you've said that. Not sure many noticed it.


What's the significance...is that the Dvorak stuff saying the rapid intensification flag is on right now?
Member Since: September 15, 2009 Posts: 525 Comments: 3701
1814. Patrap
Track is everything now,..

Were witnessing a Big Hurricane in the Genesis stage.

H4-5 temps all along her track and west.

A few degrees bearing tonight-72hr's is gonna mean a lot towards a downstream solution.




Member Since: July 3, 2005 Posts: 426 Comments: 129089
Quoting sarahjola:
the models will continue to change. it is still way too early to put all that weight into these models. i mean come on, some of these models have this storm getting stronger over land! what? the people in florida and the east coast need to calm down and just wait and see. there have been times when a storm is right at our door and all of a sudden turns. the main thing is not to panic, and just wait till it gets a little closer before we freak out. for all we know this thing could die in the morning. i live in s.e. louisiana and i am not going to concern myself too much with the tracks and models until it gets a lot closer. these islands can tear a system up. people seem to be getting angry, and upset over difference in opinions, when none of us can really know what this storm is going to do just yet. if i have learned anything in the few years i have been comming here it is that models change, tracks change, and most of the time things that aren't expected happen. now i am trying to learn and can not get one person to answer what i think should be simple for some on here to answer. if someone could please take a shot at this i would very greatful. gom- 23n 87w. do you see that? look on unenhanced check out the spin going on.
tia!


Agreed. Still too early. I don't put much faith in anything past 3 days out and even that's subject to big changes sometimes.
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I guess this image could freak out the untrained eye.


Member Since: August 19, 2005 Posts: 5 Comments: 5452
1811. scott39
post 1751?
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1810. j2008
Quoting serialteg:


r u also in PR?

No I'm not actually, I'm in Arizona but I sure dont like to see anyone anywhere be put at risk by a TC, stay safe.
Member Since: December 19, 2008 Posts: 1 Comments: 224
1809. Drakoen
There is a bit of a northerly component to Irene's movement. Will be interesting to see how that evolves over the next 24 hours.
Member Since: October 28, 2006 Posts: 57 Comments: 30606
Quoting reedzone:
As for the track, I really agree with the EURO, taking it just off the Floridas East Coast. Though the NHCs track is reasonable.


I think I prefer the Euro track too given that the center maybe further N than expected....I am biased toward the right side of the NHC cone on this one right now....
Member Since: September 15, 2009 Posts: 525 Comments: 3701
Quoting MiamiHurricanes09:
The GFS and ECMWF.


It has already been discussed here, even by Levi, that the models are probably underestimating the effects of land.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
1806. wxhatt
Quoting serialteg:


looks like its coming for us


I am seeing that too!
Member Since: October 5, 2005 Posts: 2 Comments: 927
1805. angiest
Quoting KEEPEROFTHEGATE:
T.C.F.W
09L/TS/I/C0
RI FLAG "ON"
MARK
16.60N/60.10W


That's the second time you've said that. Not sure many noticed it.
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I'll be back in a couple of hrs. Take care all. and if your not prepared, I suggest to start in the morning.
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Quoting scott39:
Who else is tired of looking at models jump from side to side of S Fl. faster than a politician up for reelection?


forecast models will always jump, its inevitable

but with this storm the jump has been much less than with most; the tracks have been tightly clustered for several days
Member Since: March 10, 2010 Posts: 1 Comments: 7866
Quoting Hurricanes101:


ok guess you are right and every single model run for the last 4 days is dead wrong by keeping the storm strong



Sounds good. But, if you disagree with me, you're disagreeing with the NHC because they share my opinion. In fact, they only have a TS hitting Florida.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
1801. angiest
Quoting lottotexas:
The problem with that , is if it shifts west it'll get you anyway. Had the same thing with Rita. People evacuated Houston to East Texas and got slammed.

If I'm not mistaken, IH-10 east does not have an evaculane. I suppose that means they don't want people going that way.
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Quoting WeatherfanPR:
Also Irene could affect Puerto Rico as a Hurricane.


doomcaster lol
Member Since: August 22, 2006 Posts: 2 Comments: 1988
1799. scott39
Who else is tired of looking at models jump from side to side of S Fl. faster than a politician up for reelection?
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1798. Gearsts
Quoting WeatherfanPR:
I think the center of Irene is north of the forecast track an moving wnw. The center could move much closer to the south coast of Puerto Rico or could move over Puerto Rico.
I agree, but we'll see tomorrow what happens. Conference at 11am...
Member Since: August 2, 2010 Posts: 0 Comments: 1948
Quoting MississippiWx:


And what makes you think after traversing the mountains of Eastern Cuba that Irene would not have a disrupted core?
The GFS and ECMWF.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting Patrap:
Irene may dance with JF,,er,,what was it?

JF, P?..

...JFC?

Shower Curtain Man

img src="Photobucket">
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1794. Patrap
1783

O yeah,,,
Member Since: July 3, 2005 Posts: 426 Comments: 129089
Quoting j2008:

Yup we will, I just looked again and looks like PR will get run over. Ouch hope she desides something or I might pull my hair out in suspence LOL.


r u also in PR?
Member Since: August 22, 2006 Posts: 2 Comments: 1988
1792. KEEPEROFTHEGATE (Mod)
T.C.F.W
09L/TS/I/C0
RI FLAG "ON"
MARK
16.60N/60.10W
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Quoting NCHurricane2009:


http://www.meteo.fr/temps/domtom/antilles/pack-pu blic/animation/animMOSAIC2.html

I don't know...this radar loop suggests to me that this is centered due E of Guadeloupe right now...

Guadeloupe is just north of 16 N latitude....

Irene continues to be hard in defining the center...but for some reason I keep seeing a more northerly position...I am really trying hard to see a more southerly position but I can't....


oh ok I can see what you are saying now but if you look just south of that that is where I saw it and if you could look closely you can see the spin but as I see now it look to be weaking and the one to the N getting stronger but still movin W
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man... the hwrf is taking a LONGGGGG time to init.
Member Since: July 31, 2011 Posts: 5 Comments: 891
Quoting Bluestorm5:
GFS is showing MASSIVE flooding event for NC and Virginia.


DOOM for me!!!
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Quoting AllBoardedUp:
Yes but Ike also pushed ahead of it a Cat 4 size storm surge.


Lol...uhhh, what does that have to do with this argument?
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Also Irene could affect Puerto Rico as a Hurricane.
Member Since: August 23, 2006 Posts: 0 Comments: 1592
1786. Patrap
MAn dats a lotta atmo turning and winding up.

The Bigger ballerina takes a while longer, but shes twirling & swirling.

Member Since: July 3, 2005 Posts: 426 Comments: 129089
Quoting Bluestorm5:
180 hrs out. Getting stronger over NC/VA?



I thought Charleston getting hit with a hurricane was always a possibility...just didn't expect it would be Charleston, WV!?!
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Quoting MississippiWx:


You're going to use Ike as an example? Hmmmm...not so smart. Ike went from a Cat 4 to a Cat 2 after hitting Eastern Cuba and stayed a minimal Cat 1 for a couple of days because the core was disrupted so much.



ok guess you are right and every single model run for the last 4 days is dead wrong by keeping the storm strong

Member Since: March 10, 2010 Posts: 1 Comments: 7866
Quoting Patrap:
Irene may dance with JF,,er,,what was it?

JF, P?..

...JFC?



JFV?
Member Since: August 22, 2006 Posts: 2 Comments: 1988
Quoting sarahjola:
the models will continue to change. it is still way too early to put all that weight into these models. i mean come on, some of these models have this storm getting stronger over land! what? the people in florida and the east coast need to calm down and just wait and see. there have been times when a storm is right at our door and all of a sudden turns. the main thing is not to panic, and just wait till it gets a little closer before we freak out. for all we know this thing could die in the morning. i live in s.e. louisiana and i am not going to concern myself too much with the tracks and models until it gets a lot closer. these islands can tear a system up. people seem to be getting angry, and upset over difference in opinions, when none of us can really know what this storm is going to do just yet. if i have learned anything in the few years i have been comming here it is that models change, tracks change, and most of the time things that aren't expected happen. now i am trying to learn and can not get one person to answer what i think should be simple for some on here to answer. if someone could please take a shot at this i would very greatful. gom- 23n 87w. do you see that? look on unenhanced check out the spin going on.
tia!


Now that the center is better defined the models should get a better grast as to where it will be possible for it to go. Th GFDL shifted a bit to the left already but the consensus so far is for a FL trayectory. The NHC has a great forecast for it hitting the keys as a strong TS.
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Quoting Gearsts:


Eye?
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Quoting MississippiWx:


You're going to use Ike as an example? Hmmmm...not so smart. Ike went from a Cat 4 to a Cat 2 after hitting Eastern Cuba and stayed a minimal Cat 1 for a couple of days because the core was disrupted so much.

Yes but Ike also pushed ahead of it a Cat 4 size storm surge.
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1778. emguy
The center is still elongated based on what I'm seeing. Impressive storm action going on but a stronger style of Emily. I suspect a low pressure trough still exsists and it expands to the ssw.
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Quoting MiamiHurricanes09:
Indeed. As long as the inner core is not destroyed, nor decoupled, the cyclone stands a good chance of intensifying as soon as it hits water, should atmospheric conditions be favorable, which they are forecast to be in the Bahamas region in 4-5 days.

96 hours below. That's about a day away from affecting southern Florida, and the system is already depicted as a borderline category 1.



And what makes you think after traversing the mountains of Eastern Cuba that Irene would not have a disrupted core?
Member Since: July 15, 2006 Posts: 17 Comments: 10284
1776. j2008
Quoting sunlinepr:


Well, we will see in the morning....

Yup we will, I just looked again and looks like PR will get run over. Ouch hope she desides something or I might pull my hair out in suspence LOL.
Member Since: December 19, 2008 Posts: 1 Comments: 224
1775. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 129089
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1773. wxhatt
Quoting scottsvb:
If I'm to guess early.. this ends up being further north as I expected and goes into Hispaniola and off the NW coast of Haiti and moves just north of cuba then swings NNW between Florida-Bahamas only giving the Florida some squalls and gustys winds (possible tornados inland as she moves almost due north along 79-80W on Thurs-Friday.


I believe you are correct.
Member Since: October 5, 2005 Posts: 2 Comments: 927
As for the track, I really agree with the EURO, taking it just off the Floridas East Coast. Though the NHCs track is reasonable.
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GFS is showing MASSIVE flooding event for NC and Virginia.
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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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