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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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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Quoting Gearsts:
Im from PR and im confused to where the center actually is! Can someone Please tell me where the center is?Some here say 16.9N!


yes, east northeast of Guadaloupe.
Member Since: August 23, 2006 Posts: 0 Comments: 1590
1919. Patrap
TS IRENE

TFP's active

Member Since: July 3, 2005 Posts: 426 Comments: 128668
If the storm is moving west at 22MPH would you think that the Models would also move west as well????

Taco :o)
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Quoting MississippiWx:


The models have also been showing it intensifying by 10mb or more OVER Florida. Explain that one. The models are over-doing the nice upper-level conditions and not taking the land issues into account as much.

FL isnt going to tear a storm up its flat and many storms have gotten stronger such as fay over FL
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1915. Skyepony (Mod)
Quoting Drakoen:
Center around 16.9N 60.1W.



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.
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1914. Gearsts
Quoting gugi182:
Oye de que parte eres de Puerto Rico?

Soy the Aguadilla :) pero me tienen asustao con lo del centro y q pa arriba o pa abajo:/
Member Since: August 2, 2010 Posts: 0 Comments: 1803
Quoting lottotexas:
Many went up 59 and got bogged down in traffic in the small towns in e Texas and were caught there when Rita went through.


No Kidding! It was nuts. I lived in a small town on US190 between 59 and I45. Even the cross highway was bumper to bumper. It took me almost an hour to drive the mile thru town from work to home. I stuck it out in my trailer in Onalaska a few hundred yards from Lake Livingston. But I was in the lee of a hill with the lake downwind. So I didn't get those 105mph gusts they did at the dam area.
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Quoting MississippiWx:


Sorry, after going over mountainous terrain and emerging at 99 hours, then making landfall in South FL at 120, that's not enough time to become a major hurricane. As I said before, the wind isn't going to be the issue with Irene IF it takes that track.
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!!

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is Irene froming a eye ?
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Quoting WeatherfanPR:


I see that too.


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....
Member Since: September 15, 2009 Posts: 496 Comments: 3688
1908. gugi182
Has Irene jogged?
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Quoting Walshy:


See what I mean?
Member Since: November 1, 2003 Posts: 4 Comments: 234
Quoting bwat:
How come when someone has the state they live in as part of their username, they always post a model that shows their state getting a direct impact?


You noticed that too. LOL
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Quoting Drakoen:
Center around 16.9N 60.1W.

Aye, good ob. Noted this a while back too (post 1429).
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1904. gugi182
Oye de que parte eres de Puerto Rico?

Quoting Gearsts:
Im from PR and im confused to where the center actually is! Can someone Please tell me where the center is?Some here say 16.9N!
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Quoting MississippiWx:


The models have also been showing it intensifying by 10mb or more OVER Florida. Explain that one. The models are over-doing the nice upper-level conditions and not taking the land issues into account as much.
It's not impossible for a storm to strengthen over land... Remember Fay? 10 mb seems like a lot though.
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Quoting Drakoen:
Center around 16.9N 60.1W.



VERY BIg jog to the north!!
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can we wait in tell the HH too get in and comfrom this
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Quoting Drakoen:


Yes the radar imagery clearly shows this. Link

If anyone is in Puerto Rico,I would advise them to prepare for a minimal Hurricane.


Well, if that's indeed the center then PR is definitely more at risk.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
1897. Patrap
Enhanced Infrared (IR) Imagery (4 km Mercator)


Member Since: July 3, 2005 Posts: 426 Comments: 128668
Quoting Drakoen:


Yes the radar imagery clearly shows this. Link

If anyone is in Puerto Rico,I would advise them to prepare for a minimal Hurricane.


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?
Member Since: March 10, 2010 Posts: 1 Comments: 7823
Quoting ncstorm:
With the RI flag on, I have to go back to what the NWS in wilmington, nc said earlier..

WORTH NOTING MOST OF THE GUIDANCE CONTINUES TO MOVE AN IMPRESSIVE
TROPICAL SYSTEM THROUGH THE CARIBBEAN SEA AND INTO THE
EASTERN/CENTRAL GULF OF MEXICO LATE IN THE PERIOD. STILL A LOT OF
UNCERTAINTY WITH RESPECT TO THIS FORECAST...BUT GIVEN THE CURRENT
LOCATION OF THE FEATURE AND ITS CONDITION THINK THE OCCASIONAL EAST
COAST SOLUTION SHOW BY SOME OF THE GUIDANCE IS NOT BELIEVABLE. FOR
THIS TO HAPPEN THE STORM WOULD NEED TO RAPIDLY DEVELOP WITHIN THE
NEXT 24 HOURS.
And it looks like it is doing just that.
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1893. Gearsts
Im from PR and im confused to where the center actually is! Can someone Please tell me where the center is?Some here say 16.9N!
Member Since: August 2, 2010 Posts: 0 Comments: 1803
1892. bwat
How come when someone has the state they live in as part of their username, they always post a model that shows their state getting a direct impact?
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1891. 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

Quoting Drakoen:


Yes the radar imagery clearly shows this. Link

If anyone is in Puerto Rico,I would advise them to prepare for a minimal Hurricane.
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Quoting VAbeachhurricanes:
Is there an HH flight at 2am? or gotta wait until morning?


About 7 hours from now.
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Quoting Dem86Mets:
We also need to take in account that in all likely hood, the east side of this storm will be the dirtiest. So lets say this scraps the west coast of Florida, affects would be worse for central and eastern Florida. If it hugs the east coast, effects may not be that intense. It all depends really, wait and see but be prepared.



West Palm was on the weak side of both Frances & Jeanne. We're not talking a lob sided tropical storm here, could be though depending on land interaction.
Member Since: August 19, 2005 Posts: 5 Comments: 5450
1888. Ryuujin
Quoting Hurricanes101:
16.9?

that is a full 1.5 degree jump north


I'm not going to lay a center fix on radar/sat observations. Lets wait until we get Recon back in there to find out where the surface center is, and if it's tightened or not.
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Irene looking really solid right now

and yeah looking at some loops, does appear to be 16.9N, center now right under that convection
Member Since: March 10, 2010 Posts: 1 Comments: 7823
1886. gugi182
is the center at 15.3N or much higher than that?
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1885. Patrap
TS IRENE 2km Storm Relative IR Imagery with BD Enhancement Curve





The same infrared imagery shown in the earth relative framework is displayed in a storm relative framework, with a 2km resolution and enhanced with the "BD Curve" which is useful for directly inferring intensity via the Dvorak Enhanced IR (EIR) technique. Scaling is provided by two lightly hatched circles around the center. The two circles have radii of 1 and 2 degrees latitude, respectively.


Member Since: July 3, 2005 Posts: 426 Comments: 128668
Quoting Drakoen:
I think Irene has relocated her center further north based on radar imagery.


I see that too.
Member Since: August 23, 2006 Posts: 0 Comments: 1590
1883. Drakoen
Quoting Hurricanes101:
16.9?

that is a full 1.5 degree jump north


Yes the radar imagery clearly shows this. Link

If anyone is in Puerto Rico,I would advise them to prepare for a minimal Hurricane.
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1882. ncstorm
With the RI flag on, I have to go back to what the NWS in wilmington, nc said earlier..

WORTH NOTING MOST OF THE GUIDANCE CONTINUES TO MOVE AN IMPRESSIVE
TROPICAL SYSTEM THROUGH THE CARIBBEAN SEA AND INTO THE
EASTERN/CENTRAL GULF OF MEXICO LATE IN THE PERIOD. STILL A LOT OF
UNCERTAINTY WITH RESPECT TO THIS FORECAST...BUT GIVEN THE CURRENT
LOCATION OF THE FEATURE AND ITS CONDITION THINK THE OCCASIONAL EAST
COAST SOLUTION SHOW BY SOME OF THE GUIDANCE IS NOT BELIEVABLE. FOR
THIS TO HAPPEN THE STORM WOULD NEED TO RAPIDLY DEVELOP WITHIN THE
NEXT 24 HOURS.
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is Irene starting too from a eye ?
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Quoting Drakoen:
Center around 16.9N 60.1W.



To be honest...I wanted to use that same radar image to say the same thing too (16.9N)...but I went more conservative and said just N of 16N....
Member Since: September 15, 2009 Posts: 496 Comments: 3688
1879. j2008
Quoting Patrap:
Nothing like the first wispf the first feeder swirling in from the Seast..


Salty and cool..then Humid and Hot..

Buckle up..

Itsa gonna get a tad Bumpy..


Is it just me or does that look really scary, and a bit like pre-RI.
Member Since: December 19, 2008 Posts: 1 Comments: 224
In regards to strength and land interaction:

I think the obstacle that will hurt Irene is Hispaniola, but it looks like the models move Irene just south of the area.

You have to forget that Irene is likely to be a larger storm in very favorable conditions: low shear, anticyclone, extremely warm SST.

With that said, land interaction will definitely slow down the strengthening process, but not seriously disrupt the storm.

No reason to argue over it. Weather is full of surprises, and I'm sure Irene is full of them. Wait and see.
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Is there an HH flight at 2am? or gotta wait until morning?
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16.9?

that is a full 1.5 degree jump north
Member Since: March 10, 2010 Posts: 1 Comments: 7823
Quoting Hurricanes101:


The NHC also has stated numerous times that intensity is very hard to predict and the basis for your whole argument is using an intensity forecast that is 5 days away.

The track of the GFS is similar to many other models that have shown this system staying strong despite land interaction. The models have been showing this consistently for days, its not something that just came out of nowhere


The models have also been showing it intensifying by 10mb or more OVER Florida. Explain that one. The models are over-doing the nice upper-level conditions and not taking the land issues into account as much.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
1871. scCane
Canadian Model

Link

New Edit: ugh beaten
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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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