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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Quoting hurricane23:
00z GFS ensembles...



Woah.

Enough said?
Member Since: Posts: Comments:
Quoting NCHurricane2009:


With those center reformations to the north...she is actually been moving WNW (or perhaps NW I might add)...


Good call on the reformation...Looks like it has happened.
Member Since: Julio 15, 2006 Posts: 17 Comments: 10284
Quoting Hurricanes101:


wouldn't you be thirsty for orange juice? lol


fixed...lol
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00z GFS ensembles...significant clustering across sfl.

Member Since: Mayo 14, 2006 Posts: 8 Comments: 13839
1965. j2008
I'm out for the night, I'll be back in the morning. Keep an eye on Irene, dont want her to pull any tricks on us.
Member Since: Diciembre 19, 2008 Posts: 1 Comments: 224
Quoting Abacosurf:
Uh yea...exactly what I said in the post too....


And you are still wrong. The Western end of Cuba is not the same as the Eastern. The Western end is not nearly as rugged as the Eastern. It's a totally different situation.
Member Since: Julio 15, 2006 Posts: 17 Comments: 10284
1963. Gearsts
Quoting wxhatt:
Wow! the convection has wrapped up the center now, and doing a more NW move. may just clip NE PR.



Thats not the center.
Member Since: Agosto 2, 2010 Posts: 0 Comments: 1951
Quoting taco2me61:
If the storm is moving west at 22MPH would you think that the Models would also move west as well????

Taco :o)


With those center reformations to the north...she is actually been moving WNW (or perhaps NW I might add)...
Member Since: Septiembre 15, 2009 Posts: 525 Comments: 3701
Quoting hurricanejunky:
Is it me or is it moving NW? I can't find any COC where the tropical forecast points are on NHC satellite imagery.


It's very difficult to judge movement at night with IR. Try and use IR RGB.
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The more N it goes, the more options it has
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ANOTHER FISH STORM IN THE MAKING FOOLED EVERYONE AGAIN MODELS AGAIN ARE WRONG
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1958. Patrap
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Quoting MrstormX:
All this talk about Florida makes me hungry for orange juice.


wouldn't you be thirsty for orange juice? lol
Member Since: Marzo 10, 2010 Posts: 1 Comments: 7869
1956. KEEPEROFTHEGATE (Mod)
T.C.F.W
09L/TS/I/C0
RI FLAG "ON"
MARK
16.60N/60.10W



i have been right on this a while now
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Quoting taco2me61:
If the storm is moving west at 22MPH would you think that the Models would also move west as well????

Taco :o)


No, because a west-northwest motion should begin soon.
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1954. JRRP
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Quoting Drakoen:


If I lived in PR I would prepare for a minimal hurricane.



good advice
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Quoting MississippiWx:


No, Charley did NOT take the path the GFS is showing. Charley went over the Western end of Cuba at probably the thinnest portion of the island.
Uh yea...exactly what I said in the post too....
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All this talk about Florida makes me thirsty for orange juice.
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Quoting Skyepony:


That's about what I'm seeing. It's continued to pull together toward the north. It's way north of it's next forecast point.


Phew...now I don't feel like I am going out on a limb anymore...it has gone further north...it really has...I can't believe this.....
Member Since: Septiembre 15, 2009 Posts: 525 Comments: 3701
Quoting ProgressivePulse:



Really leaning towards a direct hit on PR and north of the islands this evening.
You r not the only one... I been watching that very slow progress towards the west with, shall we say, INTEREST? :o)
Member Since: Octubre 25, 2005 Posts: 19 Comments: 22563
Quoting scott39:
If Irene stays at a moderate TS trying to organize through the Eastern Caribbean....It is not going further N much until the central Caribbean... if not even later. One thing I have learned about the E Caribbean, is that a TD TS or hurricane just hold there own while going through it. Irene just holding her own half way through the Caribbean, means father W. IMHO


aren't u guys watching her reform more N and move more WNW?

us puerto ricans are watching this - is it subjective?

looks to me like she wants to miss the carib at all
Member Since: Agosto 22, 2006 Posts: 2 Comments: 1988
1947. wxhatt
Wow! the convection has wrapped up the center now, and doing a more NW move. may just clip NE PR.



Member Since: Octubre 5, 2005 Posts: 2 Comments: 927
Irene looks scary..
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1945. Drakoen
Quoting Hurricanes101:


Could this in any way make it possible for the system to curve east of Florida far enough to miss it completely with very little impacts?


Good question. Yes that is possible. I would like to see how the models handle this new position of the low level center.
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Well this doesnt lie
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looks
like a bit of sw sheer going on w
/irene,i expect a track just north of west for the next 6-12 hrs then west or even wsw ,possiby making landfall in se pr breifly tomorrow night or monday morning
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well the hwrf for still hasnt come out but the hwrf for irene still hasnt come out yet but the one for harvey has and this is it out to 84 hours 00z hwrf
Member Since: Julio 31, 2011 Posts: 5 Comments: 891
00z CMC has it moving up the Florida coast and has a major hurricane right on a 'little puppy's' doorstep, lol.

Member Since: Septiembre 2, 2009 Posts: 130 Comments: 21194
Is it me or is it moving NW? I can't find any COC where the tropical forecast points are on NHC satellite imagery.
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1939. Patrap






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Quoting iamtheman99:

well there you have it folks me myself and irene


Wow....I was recalling that quote from the Wilmington, NC NWS just as you posted it...that is why I am getting more antsy about Irene up here...indeed it has pulled off a fast one and showing tendencies to regenerate more to the NE as well....that radar image is just an example of that....
Member Since: Septiembre 15, 2009 Posts: 525 Comments: 3701
Quoting Dem86Mets:
Wow what a change in under 24 hours, I will admit I did not expect it to develop this fast.


my dad (doomcaster extraordinaire) told me this was gonna go rapid intensification and i downplayed it a bit, but i gotta say this time he got it down right... unless the shear i saw in cmiss tendencies shows up in a bit and breaks the party up some
Member Since: Agosto 22, 2006 Posts: 2 Comments: 1988
In IE, Tools/Compatibility View should fix the blog stretch. Enable it and refresh.
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Quoting cjswilmingtoneye:
It's not impossible for a storm to strengthen over land... Remember Fay? 10 mb seems like a lot though.



Usually when a storm os over FLorida , parts are still over water
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1933. Gearsts
From StormW:Current shortwave (IR2) imagery indicates there may have been a center reformation from the initial advisory, to the NW and just east of the convection, as she is now north of the forecast points. Imagery also indicates more of a WNW motion at the moment, which I believe may become more westerly (275-280) briefly, based on current steering flow, and the surrounding flow depicted in satellite loop imagery of the Caribbean and NATL close up views.
Member Since: Agosto 2, 2010 Posts: 0 Comments: 1951
1932. scott39
If Irene stays at a moderate TS trying to organize through the Eastern Caribbean....It is not going further N much until the central Caribbean... if not even later. One thing I have learned about the E Caribbean, is that a TD TS or hurricane just hold there own while going through it. Irene just holding her own half way through the Caribbean, means father W. IMHO
Member Since: Junio 13, 2009 Posts: 0 Comments: 6882
1931. Patrap
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Quoting Bretts9112:

FL isnt going to tear a storm up its flat and many storms have gotten stronger such as fay over FL


Fay didn't continue to "bomb out" over Florida. She strengthened slightly, but not enough to make any difference.
Member Since: Julio 15, 2006 Posts: 17 Comments: 10284
Quoting MississippiWx:
And if I must back up my point even more, the GFS shows basically the same track as the NHC. The NHC has a tropical storm at the doorstep of South Florida because of all the land interaction previously.

If this storm was turning further west across Cuba, I wouldn't have much of a problem with a speedy reintensification. However, Oriente, the eastern part of Cuba, is quite mountainous, and these mountains run all along the coast of the "foot" shape at the eastern end.



Having traversed these, Irene is expected to continue up the length of the island for some time. I would be surpised not to see significant disruption to the system as a result. Whether or not we see significant rapid intensification after that point will depend greatly on whether the MLC survives and can quickly build down to the surface once it reaches the warm waters over the Cay Sal bank and the Gulf Stream eddies there.
Member Since: Octubre 25, 2005 Posts: 19 Comments: 22563
Quoting Gearsts:
Soy the Aguadilla :) pero me tienen asustao con lo del centro y q pa arriba o pa abajo:/


we gotta speak english here as per rules. im in ponce. what looks like is it's forming north of its forecast points as other bloggers are pointing out.
Member Since: Agosto 22, 2006 Posts: 2 Comments: 1988
Wow what a change in under 24 hours, I will admit I did not expect it to develop this fast.
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And I think that last GFS run convinced me to stay up and watch the GFDL, HWRF, and the almighty Euro. Ugh…hahaha.
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1924. Drakoen
Quoting gugi182:
Hi i live in Puerto Rico do you think we might get hit by a minimal hurricane? I'm still waiting for the 2am advisory



If I lived in PR I would prepare for a minimal hurricane.
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Quoting mynameispaul:


You noticed that too. LOL


well considering just about every model takes this to Florida, I would guess in this case no one from Florida could post a model run and have it NOT hit their state lol
Member Since: Marzo 10, 2010 Posts: 1 Comments: 7869
Quoting Abacosurf:
Hmm....Charley did it...

I know it crossed cuba on a more perpendicular angle but it only took 18 hours from the north coast of cuba to landfall on North Captiva.

And it went to 145!!



No, Charley did NOT take the path the GFS is showing. Charley went over the Western end of Cuba at probably the thinnest portion of the island.
Member Since: Julio 15, 2006 Posts: 17 Comments: 10284
1921. ncstorm
Quoting NCHurricane2009:


Man o man...I thought I was going out on a limb when I said she was at 16N (using the same radar image posted)...but I guess you all feel she is centered in that green ring on the radar (16.9N)....maybe I was being too conservative instead of going out on a limb....


You did good anyway!! First one to see the northern jog
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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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