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 StormJunkie:


Think the center may just be reforming under the convection...Which would be N/NNW of where it was earlier. Hard to tell at night though with no HH in the storm.
Thanks!
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At the airport - look at me I just can't stay away when there's a storm around lol.

NHC forecast point for 06z has Irene on top of Dominica. Radar out of the Antilles shows the center probably already due east of there, and thus it may slip north of the current forecast track.
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Quoting tropicfreak:


I'll agree with you washingtonian, C
Irene has been pulling some surprising on us now.
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Quoting AegirsGal:
Link Been looking at this, and although not formally trained, it seems to me that TS Irene is moving NNW?


On a sat pic like that...that red blob will take all your attention...so indeed it looks to be moving NNW at the end there with the blob floating like that...but that blob is just the highest cloud tops...

Rather...the center was fixed by hurricane hunters to be SW of that blob this afternoon...with the center moving W. It may have taken a brief NW jog I believe...regenerating to 15.5N latitude along the SW edge and closer to that red blob.
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P'Cola!!! HEY! you stole that from me!!

that's ok, looks good on you. :)
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Quoting fire635:
For the first time in several years... A storm has my attention. I live just north of Tampa on the Florida west coast. With Irene's size and her almost certain track towards the southeast... We are GOING to see effects here. It's just a matter of to what degree. A skirt up.Florida's west coast could potentially devestate us here but even if she slides up the east coast I believe her wind and especially her rain will make things bad across the entire state.... Including Tampa Bay. It's best to start getting prepared. This could very well be the reality check most people have forgotten in Florida.


My dad keeps scoffing saying it won't hit us, they never do.....

I'm keeping quiet and not arguing cuz I think he's gonna eat his words this time.
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FunkTop Image

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Quoting AegirsGal:
Link Been looking at this, and although not formally trained, it seems to me that TS Irene is moving NNW?


Think the center may just be reforming under the convection...Which would be N/NNW of where it was earlier. Hard to tell at night though with no HH in the storm.
Member Since: August 17, 2005 Posts: 26 Comments: 16874



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Quoting MississippiWx:


Seems like you do that a lot, Kman. LOL.


Maybe I am psychic or something. Scary :-)
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Quoting ncstorm:
for the Love of GOD and all that is SANE in this life, PLEASE STOP QUOTING TROLLS!!

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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


A) 50 mph...and I expect a more northward central position around 15.5N latitude.....
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Quoting washingtonian115:
Perhaps 60.So im gonna say c.


I'll agree with you washingtonian, C
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Link Been looking at this, and although not formally trained, it seems to me that TS Irene is moving NNW?
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Quoting washingtonian115:
Florida hasn't had a serious threat since Wilma(and Fay to some degree)

Hope it stays that way for all the people on the east coast
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Quoting MississippiWx:
What is so difficult to understand about not quoting/talking to obvious trolls?
People always need something to complain about.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting kmanislander:


Ouch LOL

Good thinking though. That is clearly on the cards.


Seems like you do that a lot, Kman. LOL.
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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
Perhaps 60.So im gonna say c.
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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


A
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Quoting stormpetrol:
All r getting fooled by the expanding convection giving the appearance of a shift further north, gulf coast gotta watch this one!


check mimic out
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If anyone wants me to add their location to my tide blog entry, leave a comment.
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What is so difficult to understand about not quoting/talking to obvious trolls?
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Quoting serialteg:


lol we just stepped on each other's feet :p


Ouch LOL

Good thinking though. That is clearly on the cards.
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739. ackee
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
A
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Quoting serialteg:


looks like heading west


Isnt that a weakness between the two highs? Sorry for the stupid question im trying to learn here?
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Quoting NCHurricane2009:


EXACTLY...and I think the track for immediate term should be more like going S or over Puerto Rico (which I know you don't want to hear)....afterwards making landfall in E tip of DR or tracking along DR's north coast....anyone else agree?

I'm not saying it's in the middle of that burst, just a little closer than before.
Member Since: July 7, 2010 Posts: 0 Comments: 5725
Quoting NCHurricane2009:


EXACTLY...and I think the track for immediate term should be more like going S or over Puerto Rico (which I know you don't want to hear)....afterwards making landfall in E tip of DR or tracking along DR's north coast....anyone else agree?


lets watch that center fix
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734. DFWjc
Quoting HurricaneSwirl:
Seems like my ignore button isn't working. That kinda sucks at a time like now.


clear out your cache on IE/FF then restart....
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Quoting kmanislander:
For the next 24 to 48 hours it is pretty much a track heading of 280 degrees.

Once that settles down we will have a much better handle on where Irene is going



lol we just stepped on each other's feet :p
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Quoting snow2fire:


How do you report someone?

Is there a way to get message/complaint to Wund?




Click the button on the upper right hand corner of the comment.
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Quoting Bluestorm5:
Great.... I had 100 comments, but creating new blog restarted it to 1. lol...


Welcome back new blogger. ;)
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Quoting WeatherNerdPR:
Starting to organize, seems the center has relocated closer to the convection:


EXACTLY...and I think the track for immediate term should be more like going S or over Puerto Rico (which I know you don't want to hear)....afterwards making landfall in E tip of DR or tracking along DR's north coast....anyone else agree?
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Quoting HurricaneSwirl:


Little red exclamation point in the upper right corner of their post. Enjoy :)


Thanks! I looked everywhere...
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Quoting fire635:
For the first time in several years... A storm has my attention. I live just north of Tampa on the Florida west coast. With Irene's size and her almost certain track towards the southeast... We are GOING to see effects here. It's just a matter of to what degree. A skirt up.Florida's west coast could potentially devestate us here but even if she slides up the east coast I believe her wind and especially her rain will make things bad across the entire state.... Including Tampa Bay. It's best to start getting prepared. This could very well be the reality check most people have forgotten in Florida.


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.
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Quoting shadoclown45:
Is a track similar to earl possible once it gets past Hispaniola and cuba?


looks like heading west

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For the next 24 to 48 hours it is pretty much a track heading of 280 degrees.

Once that settles down we will have a much better handle on where Irene is going

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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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