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 sunlinepr:


sunline, looks like its gonna be a busy sunday
Member Since: Posts: Comments:
Quoting AllStar17:
They relocated it to 16.0N 60.4 W
whoa! still a little south of where I had it, that must be on the south side of the convection.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
2169. gugi182
Center at 16.0N 60.4W 2AM Advisory winds at 50MPH
Member Since: August 3, 2011 Posts: 0 Comments: 178
Quoting yesterway:


Ok I see your point. Well I sure don't wish this on you friend...
yea... to make it worse, I've never been in a hurricane before even though I tracked it since I was 9 in 2004.
Member Since: August 1, 2011 Posts: 28 Comments: 8009
2167. wxhatt
Quoting Bluestorm5:
Yea, missing Florida... but less land for Irene to run over... plus that Ridge over Atlantic is forcing it toward NC. It's warm enough for strengthing... this mean another Hurricane Fran or maybe as extreme as Hurricane Hazel.


Exactly, It's going north of the Lesser Antilles now, almost due NW. That will have little land interaction. Thereafter, a trough is forcast to come across and pick it up. All the South Florida forcasting is probably out now. This will most likely be a dangerous Gulf Stream Hurricane now.
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2166. 7544
isee the cmc finaly join the club

whos posting the new eruo runs for the night shift
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Quoting NCHurricane2009:
This is the first time in a long time that on this blog...you guys are giving suggestions of Fran-like or Hazel-like...this would be very very bad for me if you guys are right....


Any such suggestion at this point is not to be taken seriously.
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2164. scott39
How often does a TC have a center relocation when its a TS?
Member Since: June 13, 2009 Posts: 0 Comments: 6779
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They relocated it to 16.0N 60.4 W
Member Since: June 29, 2009 Posts: 13 Comments: 5313
...CENTER OF IRENE REDEVELOPS FARTHER NORTH...STORM STILL
EXPECTED TO MOVE TOWARD THE LEEWARD ISLANDS AND PUERTO RICO...


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This is the first time in a long time that on this blog...you guys are giving suggestions of Fran-like or Hazel-like...this would be very very bad for me if you guys are right....
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Quoting MississippiWx:
Ya know, IR would really support the center being at where radar is showing. This image of IR is 45 minutes old. A due west motion looks to be occurring right now on radar.

That's what I'm saying I think that was a temporary jog to the northwest to relocate under the MLC, lets see if the WNW track continues.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting Stormchaser2007:


I certainly know one thing....if the center is relocated, that makes Irene look a heck of a lot more organized.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Member Since: July 15, 2006 Posts: 17 Comments: 10247
2156. bwat
Quoting 7544:
whatching irenes shape what is she up too
OMG! Please don't say your impying the......."A" word already!
Member Since: August 18, 2009 Posts: 0 Comments: 353
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2154. JGreco
Quoting Tazmanian:
you no the IR may be fooling you makeing you think it may be moveing NW in fac too me it looks like it moveing W too WNW


Exactly, look how disorganized this thing is. Even on the visible satellite you can't see where the center is just a bunch of MLC activity. I need to see a definite center fix for a shift in the models. Again, with weaker storms you can't just look at the deepest convection for a center, and the models are still days out to pin point real accuracy. It is a wait and see situation. Geez, the hypecasters and wishcasters are out in full force tonight nearly a week before any impact on the United States. It is still a wait and see game:0
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There isn't much doubt where the circulation is looking at this
Member Since: June 29, 2009 Posts: 13 Comments: 5313
blockquote class='blogquote'>Quoting yesterway:


What's wrong with a track like this?


Hurricane Fran was one of the nastiest hurricanes to hit East Coast. It was Cat. 3 when it hit Wilmington and created massive flooding event. Hurricane Floyd almost went on same path and did same thing to NC.
Member Since: August 1, 2011 Posts: 28 Comments: 8009
Ya know, IR would really support the center being at where radar is showing. This image of IR is 45 minutes old. A due west motion looks to be occurring right now on radar.

Member Since: July 15, 2006 Posts: 17 Comments: 10247
2150. Skyepony (Mod)
Great TRMM pass of Irene earlier this evening. Click pic for the really large quicktime..may have took a minute to load here..

Member Since: August 10, 2005 Posts: 162 Comments: 37831
Quoting yesterway:


What's wrong with a track like this?


Crap...someone said it...Fran...Fran is the worst storm to hit my area in modern history!
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night all and thanks



we really need the recon out there right now this will help us out a lot
Member Since: May 21, 2006 Posts: 5091 Comments: 115104
Quoting WeafhermanNimmy:


That is interesting because you would expect the coast to get more rain.
Once the storms came onshore they didn't lose all their tropical characteristics right away. Then orographic lifting etc. would have had a role to play in rainfall totals... Some of these systems carry heavy rains as far north as Canada.
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2146. KEEPEROFTHEGATE (Mod)
T.C.F.W
09L/TS/I/C0
RI FLAG "ON"
MARK
16.60N/60.15W
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2145. 7544
whatching irenes shape what is she up too
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very tight isobars, can't wait to see the oo runs, nasty irene.

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Quoting Bluestorm5:
Yea, missing Florida... but less land for Irene to run over... plus that Ridge over Atlantic is forcing it toward NC. It's warm enough for strengthing... this mean another Hurricane Fran or maybe as extreme as Hurricane Hazel.


Ok I see your point. Well I sure don't wish this on you friend...
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Have a great night, Taz.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Quoting AllStar17:


Would be more helpful right now. LOL.

I'm afraid our streak of weak tropical storms may end with a bang.


Well...I agree with all the talk of northward reformation...but I don't think this is strengthening that fast right now...gradually but not fast....
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Quoting AllStar17:


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.
I have a feeling there is some equipment related issue that caused them not to task a flight tonight. I also wonder how they're going to handle tomorrow's flight[s] if Irene does make a WNW / NW run across the Leewards... St. Croix?
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FLOYD maybe?
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Quoting Stormchaser2007:
New position may allow Irene to skirt WNW of Hispaniola and avoid Cuba altogether.

That's a bad mix.
Indeed. Would be nice to get models locked onto the new coordinates to see how it would affect Florida...if at all...down the road.
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2137. Drakoen
Antigua is reporting winds out of the northeast. If the center was as far south as the NHC has it, it should be reporting winds out of the east (due east).
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A relocation of the center is not at all far-fetched because the surface center seen by recon. earlier seemed to be fairly weak, and a relocation back closer to the MLC seemed likely. I wonder if that is what happened.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Quoting yesterway:


What's wrong with a track like this?
Too far North the High isn't positioned like that.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting Stormchaser2007:
New position may allow Irene to skirt WNW of Hispaniola and avoid Cuba altogether.

That's a bad mix.


Although good for the people of Haiti... They've got enough right now.
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I prayed for Irene not to hit Mississippi and I think the heavens have smiled at me because for what I see, Mississippi so far seems to be in the clear. We just recovered or are still recovering from Katrina. Two new casinos and many malls have just opened and you can see great progress happening. We do not need another Hurricane period. I just pray now that Florida gets spared as well, or that at least it doesnt hit florida too strong. Hopefully the heavens will smile at me again. I hope this is a fish storm although I doubt it Florida is in the bullseye right now so time to prepare folks.
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Quoting wxhatt:


Precisely! This is going more East now with the center reformation, and clearly moving more NW.


Yep. Clear jog to the NW in last few frames. Looks to be going north of PR, now.
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Quoting serialteg:


yeah im pumped to surf this... where u from? i see u surf too?


We have to wait for the Rabiza, offshore.... Then you decide... if you are in Metro area, La8, La Perla if you know any local there, La punta or Pine Grove... For pros Aviones or Tocones... Catapulta...
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Quoting charlottefl:
It is my personal opinion based or IR RGB, pressures out of Dominica and Guadeloupe of about 1009MB, and Dominica radar, that the center is on the SW edge of the convection, you can see it if you look close at the RGB, and it is moving north or West, but I don't think by much.
I'm looking at approx. 16.5 N 60W.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
When are HWRF, ECMWF and GFDL putting out the 00 runs?
the CMC and GFS are already up.
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Quoting gugi182:
You guys think they should start to put HURRICANE WATCHES OR WARNINGS for Puerto Rico?
Should of been done on the 11 P.M. advisory.

I suppose they did not have enough info. It would have been prudent IMO.
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Quoting weatherman12345:
but would such a situation lead to the system missing fla all together or...
Yea, missing Florida... but less land for Irene to run over... plus that Ridge over Atlantic is forcing it toward NC. It's warm enough for strengthing... this mean another Hurricane Fran or maybe as extreme as Hurricane Hazel.
Member Since: August 1, 2011 Posts: 28 Comments: 8009
Quoting Bluestorm5:
Little more to north and it's on Hurricane Fran's track... good lord.


What's wrong with a track like this?
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night night i be back when re con gos out in a few hrs or so
Member Since: May 21, 2006 Posts: 5091 Comments: 115104
2124. Patrap
Member Since: July 3, 2005 Posts: 424 Comments: 128284
Quoting gugi182:
the tropical storm streak of this year is over?


Not yet.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
PREV DISCUSSION... /ISSUED 256 PM CDT SAT AUG 20 2011/
VERY HOT AND HUMID CONDITIONS WILL CONTINUE ACROSS NORTH TEXAS
WITH THE WORST HEAT INDICES BEING ACROSS THE EASTERN HALF OF NORTH
TEXAS THROUGH MONDAY. WE HAVE EXTENDED THE EXISTING HEAT ADVISORY
THROUGH MONDAY EVENING. NORTHWEST PARTS OF THE ADVISORY AREA WILL
LIKELY BE SEEING SLIGHTLY LESS HUMIDITY...BUT AMBIENT HIGH
TEMPERATURES AROUND 105 DEGREES WHICH IS STILL VERY OPPRESSIVE AND
DANGEROUS.

AS NOTED IN EARLIER UPDATE TODAY...WE WILL BE MAINTAINING THE
POTENTIAL FOR ISOLATED SHOWERS AND STORMS ACROSS THE EASTERN RED
RIVER VALLEY AND ALONG/EAST OF THE I-45 CORRIDOR. THIS IS WHERE
THE BEST AND DEEPEST MOISTURE CURRENTLY RESIDES AND WHERE A WEAK
SHORTWAVE DISTURBANCE EASING SOUTHEAST ACROSS EASTERN OKLAHOMA
WILL TRACK. WITH THE HEAT AND INVERTED V SOUNDING PROFILES DOWN
LOW...CANNOT RULE OUT SOME GUSTY WINDS WITH ANY COLLAPSING...
STRONGER ACTIVITY THROUGH SUNSET. WE ARE HEDGING OUR BETS AND
LEANING TOWARD THE NAM12...SREF...AND ECMWF SOLUTIONS THAT A WEAK
OUTFLOW BOUNDARY FROM OKLAHOMA CONVECTION OVERNIGHT MAY SET UP
ACROSS NORTHEAST COUNTIES AND PLAY A ROLE FOR WIDELY SCATTERED
SHOWERS AND THUNDERSTORMS SUNDAY AFTERNOON THROUGH MONDAY NIGHT
GENERALLY NORTHEAST OF A BOWIE...D/FW...ATHENS LINE. IT MUST BE
STRESSED THAT ACTIVITY WILL BE RELATIVELY ISOLATED AND SHORT-LIVED
WITH DROUGHT CONCERNS CONTINUING.

ELEVATED FIRE WEATHER CONCERNS WILL CONTINUE AS WELL WITH THE
DROUGHT AND VERY DRY FUELS AROUND THE REGION...BUT THANKFULLY
WINDS SHOULD REMAIN LOW AND KEEP THE THREAT FOR WILDFIRES DOWN.

MEDIUM RANGE MODELS DO CONTINUE TO INDICATE THE MOST INTENSE PART
OF THE UPPER HIGH SHIFTING TO THE WEST AND POSSIBLY ALLOW SOME
WEAK NORTH/NORTHWEST FLOW TO OCCUR ACROSS EAST TEXAS BY THE LATTER
HALF OF THE WEEK. A WEAK FRONT APPEARS TO EASE INTO NORTH TEXAS ON
THURSDAY WITH ANOTHER SLIGHT CHANCE OF SHOWERS AND STORMS ACROSS
MAINLY THE SOUTHEAST HALF OF NORTH TEXAS WHERE RICHER MOISTURE
WILL RESIDE AHEAD OF THE FRONT.

AS FOR THE TROPICS...NOTHING HAS CHANGED WITH REGARDS TO THE
SYSTEM NOW MOVING INTO THE EASTERN CARIBBEAN AND LIKELY TO BE
NAMED IRENE IN THE NEAR FUTURE. BASICALLY...MODELS CONTINUE TO
AGREE ON KEEPING AN UPPER TROUGH OVER THE EASTERN CONUS AND
PULLING THIS SYSTEM UP THROUGH THE FLORIDA PENINSULA. AT LEAST
RELATIVELY SPEAKING...HIGH TEMPERATURES WILL MODERATE A BIT BY
NEXT WEEKEND AND POSSIBLY FALL BELOW 100 DEGREES. TIME WILL TELL.

05


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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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