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 weatherman12345:
does irene have an eye? if not, what is this?


Irene has no eye...It's just a dry slot.
Member Since: July 15, 2006 Posts: 17 Comments: 10248
Quoting weatherman12345:
does irene have an eye? if not, what is this? dry air intrusion?


HAARP
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look at this guys even a slight jog north and PR would feel rough conditions
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2017. wxhatt
Quoting hurricane23:
00z GFS ensembles...significant clustering across sfl.



That probably won't happen anymore. This new center shift is much further to the north and east. This will keep it well offshore FL and up the coast into NC.
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Quoting NCHurricane2009:


With those center reformations to the north...she is actually been moving WNW (or perhaps NW I might add)...


Oh yea I understand this because of the Trough coming down across the South East and pulling her Northwest.... But remember when the Trough is gone the High Pressure will build back in and move her back to the west or even wwnw on a slower motion....

Taco :o)
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shes getting ready to explode tonight into the morning an on .. gonna be a very intresting few days coming up...NJ has had way to much rain in the last week or so
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Quoting weatherman12345:
does irene have an eye? if not, what is this?

perhaps the beginnings of one....
Member Since: July 31, 2011 Posts: 5 Comments: 877
Quoting reedzone:


Pattern just wont allow Irene to enter the GOM. I agree with the ensembles, an East Coast runner... We know it's going to hit Florida, but how much land interaction will occur and what will the strength be.. That is what we need to find out.


dude, how can u be certain a storm thats like 3000 miles away from florida will hit it?

...

donate ur brain to the NHC or something (maybe not)
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2012. Gearsts
Whats that dry spot on the center of the convection?
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Quoting WeafhermanNimmy:
Holy Smokes! Over 6 inches of rain can fall with future hurricane Emily in Greensboro, NC. http://wxweb.meteostar.com/sample/sample.shtml?tex t=KGSO&submit.x=0&submit.y=0



hmm....
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Quoting KEEPEROFTHEGATE:
T.C.F.W
09L/TS/I/C0
RI FLAG "ON"
MARK
16.60N/60.10W



i have been right on this a while now

keeper what exactly have you been right on -im not challengen you just not sure what you are saying final outcome will be?
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ALRIGHT IM ENDING THIS ARGUMENT NOW!!!!!

this is a perfect example of what eastern cuba can do to a large powerful hurricane...
Member Since: July 31, 2011 Posts: 5 Comments: 877
Quoting Patrap:



With that kind of turning the center has to be within the convection. Looks to be on the brink of being a Cane.
Member Since: August 19, 2005 Posts: 5 Comments: 5405
2005. scott39
There is only a W movement right now.
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2004. Patrap
Member Since: July 3, 2005 Posts: 424 Comments: 128287
If this is truly the start of an eastward shift in the models, they are reflecting what history is: that the east coast is way overdue.
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Quoting MississippiWx:


Lol...That western shift didn't occur. Looks like an eastern one occurred.


Is if just me...or does that eastern clustering of GFS also hint at east coast (as in my neck of the woods) as well?
Member Since: September 15, 2009 Posts: 476 Comments: 3668
2001. ncstorm
Quoting wxhatt:


I know, people up here in Eastern NC, are not going to like this shift one bit!


if this stays off the coast of florida and ride up the gulf stream..well, it aint looking pretty for points northward
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Quoting tpayne105:


Man we in Texas soo need this rain. I know things always tend to even out but we are desparate...


Yeah, they even out, sorta. I guess we shoulda saved some of that rain from June 2003(?) When we got over 40 inches in one month. This June we didn't get .40 here.
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1999. Gearsts
Can someone tell me whats that dry spot on the center of the convection?
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ALRIGHT IM ENDING THIS ARGUMENT... NOW!!!!!

this is a perfect example of what eastern Cuba can do to a large powerful hurricane...
Member Since: July 31, 2011 Posts: 5 Comments: 877
1997. ncstorm
I can not believe that I am still up blogging..
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Quoting Abacosurf:
Wrong?? Full of piss and vinegar tonight I see....

I explained that it was a different situation in my post!!@!

Easy there little fella...



You said, "Charlie did it". Charlie did nothing that we are talking about in my argument with Hurricanes101.
Member Since: July 15, 2006 Posts: 17 Comments: 10248
and north at 144 hours
Member Since: September 18, 2010 Posts: 0 Comments: 5222
Quoting Abacosurf:
Wrong?? Full of piss and vinegar tonight I see....

I explained that it was a different situation in my post!!@!

Easy there little fella...



Im glad you said it, I was thinking the exact same thing
Member Since: March 10, 2010 Posts: 1 Comments: 7715
They really need to have hurricane warnings up for P.R.

It's going to come plenty close.
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Going straight into Hispaniola. Strong storms have broken apart over the island, and other storms, depending where they entered the island and their direction, they had escaped fairly intact. This storm looks in danger because the direction it may enter the mountainous island. Still can blow up in the gulf though.

I'm in South Korea and yet I'm still monitoring the tropical atlantic hurricane season :)


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IS there any going on with the formatio in GOM?
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Still heading northwest at 120 hours
Member Since: September 18, 2010 Posts: 0 Comments: 5222
1988. scott39
The very outer front rain bands look to be encountering some wind shear. it looks to be blowing them NE.Can anyone help here???
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Perhaps this should be the steering if in fact the pressures are down to 999mb. and we have wind speeds in the 45 to 60 kts. range at the next advisory or when HH get out there...

Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting charlottefl:


Think it may have begun, need another 6 hrs to confirm that...


It did appear earlier when I was forecasting it that it had begun to assume a more poleward component of motion. But it's very difficult to identify low cloud motions using nighttime imagery.
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Quoting hurricane23:
00z GFS ensembles...



Pattern just wont allow Irene to enter the GOM. I agree with the ensembles, an East Coast runner... We know it's going to hit Florida, but how much land interaction will occur and what will the strength be.. That is what we need to find out.
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Quoting KoritheMan:


No, because a west-northwest motion should begin soon.


I agree but we all know or should I say most of us are seeing the Storm more north than where they are saying it is.... I just donot understand why the "West" Movement....

Taco :o)
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Quoting Bluestorm5:
GFS run ends. Look how much rain SE USA is going to get at the end of Irene.





Man we in Texas soo need this rain. I know things always tend to even out but we are desparate...
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Holy Smokes! Over 6 inches of rain can fall with future hurricane Emily in Greensboro, NC. http://wxweb.meteostar.com/sample/sample.shtml?tex t=KGSO&submit.x=0&submit.y=0
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Quoting MississippiWx:


And you are still wrong. The Western end of Cuba is not the same as the Eastern. The Western end is not nearly as rugged as the Eastern. It's a totally different situation.
Wrong?? Full of piss and vinegar tonight I see....

I explained that it was a different situation in my post!!@!

Easy there little fella...

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1978. wxhatt
Quoting NCHurricane2009:


Phew...now I don't feel like I am going out on a limb anymore...it has gone further north...it really has...I can't believe this.....


I know, people up here in Eastern NC, are not going to like this shift one bit!
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Quoting WPBHurricane05:


Woah.

Enough said?
The icing on the cake, LOL.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
Quoting KoritheMan:


No, because a west-northwest motion should begin soon.


Think it may have begun, need another 6 hrs to confirm that...
Member Since: December 18, 2006 Posts: 7 Comments: 2686
Quoting MississippiWx:


Good call on the reformation...Looks like it has happened.


Thanks...for moments back...I thought I was going tired or insane here saying this was happening....LOL
Member Since: September 15, 2009 Posts: 476 Comments: 3668
Quoting hurricane23:
00z GFS ensembles...significant clustering across sfl.



Lol...That western shift didn't occur. Looks like an eastern one occurred.
Member Since: July 15, 2006 Posts: 17 Comments: 10248
1973. Patrap
Member Since: July 3, 2005 Posts: 424 Comments: 128287
Its going to get north of the islands around PR and if that happens and we experience RI all beats are off for it getting any further west than the east coast of FL. I been thinking for 2 days now this is an east coast rider or an east coast direct strike, watch!
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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.