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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i see the center now and it can really see it move W right now has the nhc has it
Member Since: May 21, 2006 Posts: 5091 Comments: 115244
2220. Drakoen
Quoting TomTaylor:
I'd wait a little before jumping to that conclusion.

The area you are looking at is a little over 90 miles away from the radar tower, meaning the radar beam is around 9-10 kft above the ground by the time it reaches 16.9N 60.1W, meaning it's seeing the 700mb level, not the surface level.


Yes, you would wait. I disagree a little with the NHC's new coordinates, but no one knows exactly where the center is until an aircraft is in there. The surface observations are lacking.
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Quoting DontAnnoyMe:


Any such suggestion at this point is not to be taken seriously.
Yeah, I mean where are people getting that this storm is anything like Fran or Hazel. Irene's current position is well to the south of where Fran was in this same area. Floyd and Fran may have both hit NC but these storms DID not take similar paths to get here. Floyd almost made landfall in FL, and turned northward and eastward. Fran came barreling in from the Ocean and went well inland. Floyd made landfall in NC and then continued up the coast. Two very different setups.
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00z ECMWF has initialized. Already 1˚ too south.

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Quoting MississippiWx:


Oh, God. I thought this argument was over. Well, despite what the models say, the NHC sees that not much strengthening would occur with that kind of track.
There's a lot of uncertainty a week out. Maybe not so much with track at the moment, but certainly with intensity.
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2216. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128685
Quoting MiamiHurricanes09:
So you're thinking that even if it moves north of the Greater Antilles, it'll still affect Florida?

Eso si no es bueno.


It would make sense, it doesn't really change the overall synoptic pattern, just the initialization point...
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Could we see Irene possibly undergo RI in the next 24-48 hours here? The conditions are ripe.
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Quoting wunderkidcayman:
yes has been conformed COC has reformed but still SSW of the deepest convection anyway signing off 16.0N 60.4W


I was saying 16N to be conservative...but then that radar imagery from the N Antilles some were suggesting more like 16.9N...and so then I jumped on the 16.9N opinion too...hmmm....

....is it the NHC is being conservative....or is it that I should have stayed on that first hunch of 16N...LOL...
Member Since: September 15, 2009 Posts: 496 Comments: 3688
OK. Have a great night!
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2211. Patrap

2km Storm Relative IR Imagery with BD Enhancement Curve

Member Since: July 3, 2005 Posts: 426 Comments: 128685
2210. JLPR2
Quoting scott39:
Doesnt ch It looks like it doesnt change thier track any.


Track isn't updated in intermediate advisories, you can see it is forecast to go due west, in fact, a little to the WSW, that's them adjusting the other track to the actual location of the system.


Expect a slight change in the 5am one, but should only be significative for people in the islands.
Member Since: September 4, 2007 Posts: 7 Comments: 8735
Quoting hurricane23:


Oh they will in future updated tracks 5am-11am. Intensity wise may go up for sfl.
So you're thinking that even if it moves north of the Greater Antilles, it'll still affect Florida?

Eso si no es bueno.
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Quoting Stormchaser2007:


Yeah, really interested to see if this can avoid Hispaniola for the most part.

Still thinking it could get a good clip of it.


Cuba is the key now. If it hits Hispaniola but not Cuba, it'd still have ample time to restrengthen before any US landfall.
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Quoting Zeec94:


Actually that's the latest from the NHC. Center has relocated to 16.0N 60.4W

It's near it. Regardless, I didn't say it wasnt the location, I'm just saying that radar is not looking at the surface level.
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2205. gugi182
They should start to put HURRICANE WATCHES for PUERTO RICO
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2204. Zeec94
Quoting TomTaylor:
I'd wait a little before jumping to that conclusion.

The area you are looking at is a little over 90 miles away from the radar tower, meaning the radar beam is around 9-10 kft above the ground by the time it reaches 16.9N 60.1W.


Actually that's the latest from the NHC. Center has relocated to 16.0N 60.4W

http://www.nhc.noaa.gov/text/refresh/MIATCPAT4 shtml/210545.shtml?
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Safe to say this cone is shot:
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yes has been conformed COC has reformed but still SSW of the deepest convection anyway signing off 16.0N 60.4W
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Quoting hurricane23:


May not be a pretty storm if it approaches SFL.


Yeah, really interested to see if this can avoid Hispaniola for the most part.

Still thinking it could get a good clip of it.
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2200. 7544
Quoting AllStar17:
They relocated it to 16.0N 60.4 W


thanks for the info

that makes more sense
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Quoting scott39:
Doesnt ch It looks like it doesnt change thier track any.
Track changes only occur in full advisories (5 and 11, respectively). Will be interesting to see how the 06z plots handle the system with the new coordinates.
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AT 200 AM AST...0600 UTC...REPORTS FROM RADAR...SATELLITE...AND
SURFACE OBSERVATIONS INDICATE THE CENTER OF TROPICAL STORM IRENE
HAS REDEVELOPED FARTHER NORTH NEAR LATITUDE 16.0 NORTH...LONGITUDE
60.4 WEST. IRENE IS MOVING TOWARD THE WEST NEAR 22 MPH...35
KM/H...AND A MOTION TOWARD THE WEST-NORTHWEST AT A SLOWER RATE OF
SPEED IS EXPECTED DURING THE NEXT 48 HOURS. ON THE FORECAST
TRACK...IRENE WILL PASS THROUGH THE LEEWARD ISLANDS THIS
MORNING...AND MOVE INTO THE NORTHEASTERN CARIBBEAN SEA THIS
AFTERNOON. IRENE COULD APPROACH PUERTO RICO AND THE DOMINICAN
REPUBLIC ON MONDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 50 MPH...85 KM/H...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 48 HOURS AND
IRENE COULD BECOME A HURRICANE BY MONDAY.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 130 MILES...215
KM...MAINLY TO THE NORTH AND EAST OF THE CENTER.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB...29.71 INCHES.

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2197. wxhatt
Quoting NCHurricane2009:


Yep...now the center is NE of Guadeloupe on that radar...very clear indeed...we have had MAJOR center reformation to the north this early morning....


It's obvious that there is going to be a major model shift east now.
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Quoting JLPR2:


Well... Yippee! :\

Wasnt expecting that so soon, seems I'm in for more action than I thought.


:-/ Hopefully it won't go any farther north.

Or if it does, maybe it goes WAY north.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting hurricane23:


May not be a pretty storm if it approaches SFL.


Do you mean disorganized and weak or strong and destructive? What's pretty in this instance? TIA.
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Quoting scott39:
Doesnt chIt looks like it doesnt change thier track any.


Oh they will in future updated tracks 5am-11am. Intensity wise may go up for sfl.
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2193. gugi182
Is IRENE moving WEST or WEST NORTH WEST
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2192. scCane
Quoting Drakoen:
hmmm They put it at 16N. I'll take it. Better than extrapolated coordinates lol.
That's where it looked like it was around on the microwave that you posted.
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2191. Patrap
San Juan Radar
NEXRAD RadarType
Velocity Azimuth Display Wind Profile


Member Since: July 3, 2005 Posts: 426 Comments: 128685
I'm sure everybody saw the 2 a.m. update, with the relocation in the centre? 5 a.m. discussion may be a bit interesting.
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Quoting TomTaylor:
He's saying that whatever minimum central pressure the global models are displaying is actually higher than what the model is indicating due to the relatively low resolution of the model.

The idea of a major hurricane after all that land interaction forecasted by the GFS run may not warrant a major in your opinion, however, the model itself says otherwise.

Also, I wouldn't rule out something stronger than a cat 1...



Oh, God. I thought this argument was over. Well, despite what the models say, the NHC sees that not much strengthening would occur with that kind of track.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Well, I was adding Fran/Hazel like track to list of MANY possibilities. I added these storm because the center moved north.
Member Since: August 1, 2011 Posts: 28 Comments: 8030
Quoting Stormchaser2007:
When's recon?

2am?


8 am I believe.
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2186. JLPR2
Quoting Stormchaser2007:
Hm

..CENTER OF IRENE REDEVELOPS FARTHER NORTH...STORM STILL EXPECTED TO MOVE TOWARD THE LEEWARD ISLANDS AND PUERTO RICO...


Well... Yippee! :\

Wasnt expecting that so soon, seems I'm in for more action than I thought.
Member Since: September 4, 2007 Posts: 7 Comments: 8735
Quoting Stormchaser2007:
Hm

..CENTER OF IRENE REDEVELOPS FARTHER NORTH...STORM STILL EXPECTED TO MOVE TOWARD THE LEEWARD ISLANDS AND PUERTO RICO...


May not be a pretty storm if it approaches SFL.
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2184. scott39
Doesnt ch
Quoting hurricane23:
...CENTER OF IRENE REDEVELOPS FARTHER NORTH...STORM STILL
EXPECTED TO MOVE TOWARD THE LEEWARD ISLANDS AND PUERTO RICO...


It looks like it doesnt change thier track any.
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Quoting Drakoen:
hmmm They put it at 16N. I'll take it. Better than extrapolated coordinates lol.


Did you say 16.9? I'll try and remember that later when recon. goes in.
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When's recon?

2am?
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Quoting Drakoen:
Center around 16.9N 60.1W.

I'd wait a little before jumping to that conclusion.

The area you are looking at is a little over 90 miles away from the radar tower, meaning the radar beam is around 9-10 kft above the ground by the time it reaches 16.9N 60.1W, meaning it's seeing the 700mb level, not the surface level.
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Quoting MississippiWx:


983mb is not a major hurricane...

And like I said, if it hits the way the GFS is showing, it's way too much land interaction to expect anything stronger than a minimal hurricane (Cat 1).
He's saying that whatever minimum central pressure the global models are displaying is actually higher than what the model is indicating due to the relatively low resolution of the model.

The idea of a major hurricane after all that land interaction forecasted by the GFS run may not warrant a major in your opinion, however, the model itself says otherwise.

Also, I wouldn't rule out something stronger than a cat 1...

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2178. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128685
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....


Are you near the coast?
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Just wanted to stick around for the 2:00 am update. Have a great night, everyone.
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2175. JGreco
Quoting DontAnnoyMe:


Any such suggestion at this point is not to be taken seriously.


+1000% It's hypecasting scaring people...:0
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Hm

..CENTER OF IRENE REDEVELOPS FARTHER NORTH...STORM STILL EXPECTED TO MOVE TOWARD THE LEEWARD ISLANDS AND PUERTO RICO...
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Quoting AllStar17:
There isn't much doubt where the circulation is looking at this


Yep...now the center is NE of Guadeloupe on that radar...very clear indeed...we have had MAJOR center reformation to the north this early morning....
Member Since: September 15, 2009 Posts: 496 Comments: 3688
2172. Drakoen
hmmm They put it at 16N. I'll take it. Better than extrapolated coordinates lol.
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Quoting sunlinepr:


sunline, looks like its gonna be a busy sunday
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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.