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 Levi32:
As mentioned, they had to adjust slightly north of Dominica, but the overall track is farther west.



IMO...I'd be leaning toward the northern edge of that cone for the short term track....I am suprised at the westward shift.....
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two of the sharpest bloggers here are in college now...and started blogging years ago in high school...and have taught me a lot...
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westward shift will that is some one good new for land mass but at the same time bad news more time overe water
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Quoting Drakoen:
Think the track shifted because of the GFDL.


It's difficult to ignore the UKMET/GFDL/CMC. The more eastern solution has the GFS/Euro/HWRF. It's going to be interesting to see which solution gets the first "big win" this year.
Member Since: July 15, 2006 Posts: 17 Comments: 10156
1066. angiest
Quoting rushisaband:



thanks for this info. take care. btw rum mmmmmmmm


Rum?
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Quoting luigi18:


así mismo, there is a wonderful breeze tonight very weird do.


Always, before the furry of a storm, there is a pleasant calmness...
Even sunset colors are special due to high altitude clouds..
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1064. angiest
Quoting USAFwxguy:


Link


Pssst. I said model, not forecast. ;)
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1063. Lizpr
Quoting JLPR2:


I'm not surprised, but tomorrow the news should cover it better than today.



Yeah, she is going to watch the news at 11pm. She lives in Caguas and in a non flooding area but still you always want to know what's happening.
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Quoting islandblow:
Here on north coast on Dominica island waiting for Irene. Its been overcast and raining most of the afternoon but the big wall is approaching. At 10.30pm local Eastern Caribbean time the sea and breeze is picking up slowly but the lights of the French islands of Mariegalante and Guadeloupe are still clear on the horizon.

Tropical Storm arnings are being been given on local radio, the LIME (former Cable and Wireless)is alerting Saturday night partygoers and others with cell phone texts. We will see what the earlier hours of the morning will bring. Banana and plantain farmers were lamenting the damage that could be caused to them by even 50 mile an hour winds a while ago when I was taking my drinks in the neighbouring village rum shop. We will see how things develop when the sun rises....or before.



thanks for this info. take care. btw rum mmmmmmmm
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I am still anxiously awaiting word from the DOOM:CON council. How will I know whether or not to be vigilant???
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Quoting gulfbreeze:
We do not tape windows waste of time.

And a B^%$# to get off after the sun bakes it on.
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Quoting AussieStorm:
Afternoon all. can someone explain this to me please. From the above Dr. Masters Blog. 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."

So they found 50mph winds, a barely closed of COC and no winds from the west, yet it was named TS Irene. I just don't get it.


They found a few westerly winds, just enough to be declared a tropical cyclone at the time. Judging by the winds, it had JUST closed off, but now it looks like it is stronger and tightening up as it is located under that deep convection.
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1058. Thrawst
Quoting BahaHurican:
Come on... discussion, discussion!


You've got WU Mail :P
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1057. Drakoen
Think the track shifted because of the GFDL.
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Hoorah! School is almost back in session.

Hope the juvenile posters have had their fun and will continue to mature during their time off the blogs. :)
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00z nam 81 hours out
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1054. angiest
Does anyone know if GE for Android support kmz's, so that I can load the ones from tropicalatlantic.com?
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Quoting Levi32:


You may be able to turn off my technology, but my eyes will always be to the sky.

Lol, it is true I have 8 minutes. I will take my leave. We shall see what happens in the morning. Night all.


Have a safe flight Levi. Irene will be waiting for you tomorrow.
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Quoting presslord:



yes...it means you've had too much beer...
Hmmm... was just about to report increased ant agitation... though that may just be the crumbs from the cookies I just ate...
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Posting sign on blog door...

Do Not Feed The Trolls!
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Quoting KeyWestwx:
your name is offensive. You need to go to another blog somewhere fr far awat=y in cyber space. How about this name fer ya blogger
youtoothless,,trailertrash,withmethmouth,who'sdad isalsohisuncle,,,,,blog that


Hey, don't worry, that's the same troll as before.... He will be Zappppppppppped.... soon....
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Quoting Levi32:
As mentioned, they had to adjust slightly north of Dominica, but the overall track is farther west.



based on this cone, why is the storm projected to be only a tropical storm by the time it reaches key west florida..whats all the panic about. am i missing something?
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I like the new cone,
even a bit more than the first one!
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Afternoon all. can someone explain this to me please. From the above Dr. Masters Blog.

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."

So they found 50mph winds, a barely closed of COC and no winds from the west, yet it was named TS Irene. I just don't get it.
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1045. luigi18
Quoting sunlinepr:
LLego la banda... tocando salsa


Here are the first bands arriving...





así mismo, there is a wonderful breeze tonight very weird do.
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1044. Levi32
Quoting kmanislander:


Please turn off and stow all electronic devices. We will tell you when it is safe to use them. These include laptops, blackberries, strawberries, anything with an off and on switch.


You may be able to turn off my technology, but my eyes will always be to the sky.

Lol, it is true I have 8 minutes. I will take my leave. We shall see what happens in the morning. Night all.
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1042. angiest
Quoting USAFwxguy:


Even tight clusters can shift, however.

Notice many of the ensembles are to the left of NHC.


Yeah, a fair number of ensemble members have always pointed west.

I really, really would love to see a model archive for Ike. I know most of the models have been upgraded since then. Still, I would like to know how they changed during its life, starting as a wave.
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Come on... discussion, discussion!
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1040. Vero1
Quoting gulfbreeze:
We do not tape windows waste of time.
But it does make it easier to pickup the broken glass.
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Quoting TropicalAnalystwx13:
BULLETIN
TROPICAL STORM IRENE ADVISORY NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
1100 PM AST SAT AUG 20 2011

...IRENE APPROACHING THE LEEWARD ISLANDS...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...15.3N 59.9W
ABOUT 95 MI...150 KM E OF DOMINICA
ABOUT 120 MI...195 KM SE OF GUADELOUPE
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 22 MPH...35 KM/H
MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES


My earlier comment, post 757:
(a) 50 mph winds, and I think it will be centered along 15.5N latitude....

Heck yeah! my prediction nearly spot on....LOL
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westward shift...
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Quoting GoWVU:


Squeirrels (spelling)


Oh, duh, guess I should have been able to figure that out!!
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Quoting MississippiWx:
The 11pm track would keep it pretty weak, at least for South FL.
Indeed. A lot of interaction with Cuba.

Eager to see the 0z models however, as those should have Recon's data.
Member Since: September 2, 2009 Posts: 130 Comments: 21032
Quoting GoWVU:
Had a nice dinner tonight in West Ashley and then friends came over and we had some cold adult beverages by the pool. One thing I have noticed is the animals are acting funny in the back yard. The tree rats in the back yard burring nuts and for the most part not seeing many... Does that mean anything?
West Ashley? I remembered that area. I was born in Charleston, SC but I don't live there anymore.
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1033. Levi32
As mentioned, they had to adjust slightly north of Dominica, but the overall track is farther west.

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Quoting PRweathercenter:
i lot of people don't know, i hope they give good media coverage


Now at 11PM local news and the gov. Chan. 6 will give advice and an update...
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The 11pm track would keep it pretty weak, at least for South FL.
Member Since: July 15, 2006 Posts: 17 Comments: 10156
Quoting NavarreMark:


Bless you brother Vet.


Back at ya, our most excellent Friend!

Stay tuned to DOOM:COM, as well as our blog, for further relevant updates.

hehehe
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1027. GoWVU
Quoting presslord:



yes...it means you've had too much beer...


LOL, yes I agree, good dinner and lots of beer!!
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1026. 3211976
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Quoting Thrawst:


My mom is not totally believing the models yet... gotta be consistent at least 2 or 3 more times to get the confidence up.
My mom made me go to the grocery store... lol

Quoting zoomiami:


First comment I've seen about the size of the storm. I agree, and think people should take notice. A storm this size will have lots of impact, with the center just being the most concentrated.
Hey, zoo. We've been noticing that... guess pple are more interested in track right now...

You know.... I think it's sad that the trolls are out there taking up all the good blog handles.... just such a WASTE.... lol


Quoting Thrawst:


Ironically I did that as well, and we're both on this tiny island... lol.
LOL... don't want to get stuck in a long grocery line when I could be blogging Irene... lol
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Quoting hurricane23:


Nope..It was an error by tpc. It actually shifted south a bit over the keys a bit.


23, you still think this will be a Emily scenerio as you stated a couple of days ago?
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1022. JLPR2
When are the HHs supposed to fly into Irene?
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Quoting MiamiHurricanes09:
11p.m track:




did the track move march of any?
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.