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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Evening everyone! For those that use i just got my site updated with all the Graphics and Models on Irene. I also moved all the Interactive Floaters over to Irene and took all the Floaters off Harvey. I can only put 5 Floaters up without slow some computers down.
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Quoting stormpetrol:
With Florida being nearly 1400 miles away, anything can happen, be prepared as always, but don't panic!

For the TX crowd, Harvey's models just put him N into the Bay of Campeche.
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Quoting KennyNebraska:
He posted 'the chart' again.

It is getting serious now.


No, he posted a chart, not The Chart. ;)
Member Since: August 22, 2008 Posts: 12 Comments: 6010
Quoting MiamiHurricanes09:
Now dats a worst case scenario for ya'!



TVCN gonna shift left
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Here's a wonderful site for all your computer model wonders Link enjoy ;)
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Quoting spathy:
I dont think I have ever seen a set of models this far out take slightly dif tracks and end up in essentially the same place.

Any analog modeling?


Yep. Hurricane Ivan, 2004.

And they were all too far east.
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Quoting DookiePBC:
DOOOOOOOOOOOOOOOM!!!!!!!!!!!!!!



I think given the Doc's post on how many areas could be at risk it is time to say it: "We may all be DOOM"



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63. amd
Quoting HurricaneDevo:
Looking at the latest satellite images, is she, dare I say it, going thru RI???


I don't think so. Even though the convection looks awesome, it is all north and northeast of the center of Irene, which is still just south of 15 north following the NHC's center-line exactly. I don't think the center is forming further north.
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Worried in the French Antilles. Gusts to 100 km/h, 4-8 inches of rain, risk of floods and landslides.

Link
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Quoting KennyNebraska:


Yeah, you know in order for it to happen, Irene will have to experience the Atlantic high all the way through the next four days, with barely any influence from the trough that is supposed to be at full amplitude over the east CONUS some few days from now.

How likely is that?
It happens.
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Area Forecast Discussion
Issued by NWS Miami, FL


Excerpt:

.UPDATE...
JUST-FORMED TROPICAL STORM IRENE APPROACHING THE LESSER ANTILLES
FORECAST BY NHC TO APPROACH THE VICINITY OF CUBA, SOUTHERN BAHAMAS
AND STRAITS OF FLORIDA WEDNESDAY THROUGH THURSDAY. DUE TO ITS
FORECAST PROXIMITY TO SOUTH FLORIDA BY THE END OF THE NHC
FORECAST, WIND SPEED PROBABILITY DATA FROM NHC WILL BE EVALUATED
AND PROCESSED THIS EVENING FOR POSSIBLE INCLUSION OF TROPICAL
CONDITION TERMINOLOGY IN ZONE AND MARINE FORECASTS. /MOLLEDA
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting GTcooliebai:
Check post 40


Ah ha, thanks!
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With Florida being nearly 1400 miles away, anything can happen, be prepared as always, but don't panic!
Member Since: April 29, 2007 Posts: 0 Comments: 7932
Quoting spathy:
I dont think I have ever seen a set of models this far out take slightly dif tracks and end up in essentially the same place.

Any analog modeling?
The area changes but they are all together. Its not the norm for sure.
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Quoting MiamiHurricanes09:
Now dats a worst case scenario for ya'!



Yeah, you know in order for it to happen, Irene will have to experience the Atlantic high all the way through the next four days, with barely any influence from the trough that is supposed to be at full amplitude over the east CONUS some few days from now.

How likely is that?
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DOOOOOOOOOOOOOOOM!!!!!!!!!!!!!!



I think given the Doc's post on how many areas could be at risk it is time to say it: "We may all be DOOM"
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Quoting MiamiHurricanes09:
Now dats a worst case scenario for ya'!


O_O
Member Since: July 7, 2010 Posts: 0 Comments: 5690
Member Since: April 29, 2007 Posts: 0 Comments: 7932
someone want to post a GFDL loop for us? site I use hasn't updated yet and I cant be bothered looking for another to see it ten minutes earlier =P
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Quoting HoustonTxGal:


Where are you getting these?? just wondering.. would like to visit the site.

Thanks!
Check post 40
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hey dfwstormwatch you still out there i need too se more mode runs you post
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Quoting MiamiHurricanes09:
Now dats a worst case scenario for ya'!



Which model is this, and is that 920 I see in there?
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Looking at the latest satellite images, is she, dare I say it, going thru RI???
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I think Ernesto in 2006 is a good analog storm. Very similar track and even formed right around this date (8/24). Cuba essentially destroyed Ernesto...we barely got anything in SoFla.
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Quoting MiamiHurricanes09:
Now dats a worst case scenario for ya'!



Where are you getting these?? just wondering.. would like to visit the site.

Thanks!
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Quoting stormpetrol:


Are these the new model runs?
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44. SLU
The center of IRENE starting to reform further north near the mid level low and if this does happen, the intensity could fall in line with the GFDL and HWRF models very quickly.
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Quoting weatherman12345:
POLL TIME!!
What will the intensity be for Irene for the 11 PM advisory

A.50 MPH
B.55 MPH
C.60 MPH
D.65 MPH
E.70 MPH


Forgot one.

F. DOOM
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Member Since: April 29, 2007 Posts: 0 Comments: 7932
I gotta run. BBL... when the hype is TRULY hyped.... lol

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Quoting stormhank:
Thanks DR. Masters
Here's the link to the GFDL Link
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Quoting stormpetrol:

2808. stormpetrol 12:08 AM GMT on August 21, 2011 +0
Quoting ManicouRiverResort:
Located @ Dominica

Emily was pretty easy for us ... but this looks worse as in rain. If the winds don't go above 60mph we should be OK ... but we have had a lot of rain lately and the ground here is soaked and water moves fast.

Funny ... no gusts no high winds ... nothing yet. I know it will though and around 2 am will be roof shaking. Breezes from the SE as usual so far.

Hope it does not intensify over the next 12 hours.

Wish us all luck.


Take care, and keep safe , the calm before the storm as they say & so true.
Action: Quote | Modify Comment


Ditto. Stay safe.
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Thanks so much Dr Masters. Wait and see, for the CONUS. Preparations, for the Islands
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Now dats a worst case scenario for ya'!

Member Since: September 2, 2009 Posts: 130 Comments: 21194
"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."

This storm is going to be one of the books.
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Quoting spathy:
I dont think I have ever seen a set of models this far out take slightly dif tracks and end up in essentially the same place.

Any analog modeling?


As Dr. M pointed out above, TS Fay may be an appropriate analog.
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Dr. Masters-

"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."


wow......that's a bold statement. Interesting.
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Quoting DookiePBC:
Even the Doc is getting in the spirit of "The Chart"!

Irene looks to be an interesting one that could hit an awful lot of places. Gonna be an interesting one to forecast for sure.
Hey, the Doc was the original ChartPoster... lol

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2808. stormpetrol 12:08 AM GMT on August 21, 2011 +0
Quoting ManicouRiverResort:
Located @ Dominica

Emily was pretty easy for us ... but this looks worse as in rain. If the winds don't go above 60mph we should be OK ... but we have had a lot of rain lately and the ground here is soaked and water moves fast.

Funny ... no gusts no high winds ... nothing yet. I know it will though and around 2 am will be roof shaking. Breezes from the SE as usual so far.

Hope it does not intensify over the next 12 hours.

Wish us all luck.


Take care, and keep safe , the calm before the storm as they say & so true.
Action: Quote | Modify Comment
Member Since: April 29, 2007 Posts: 0 Comments: 7932
Great update, thanks Doc, let's see how many pages we can fill up with this one! LOL!
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LOL..Dr. Masters just put EVERYONE back in the cone!
Member Since: August 19, 2006 Posts: 13 Comments: 15696
Thanks DR. Masters
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T.C.F.W.
09L/TS/I/CX
MARK CENTRE FIX
16.63N/57.69W
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He posted 'the chart' again.

It is getting serious now.
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Quoting RitaEvac:
JA...MAI...CA!!



D'yer Mak'er
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Thanks Jeff, so far TCI is outside the cone. I have NO desire to see Irene In my dreams!
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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.

Now that is scary.
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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.