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 MississippiWx:


983mb is not a major hurricane...

And like I said, if it hits the way the GFS is showing, it's way too much land interaction to expect anything stronger than a minimal hurricane (Cat 1).
983 is not a major hurricane, but these models are getting crazy a 939mb hurricane is a major,and by the forecast track of irene should have no business scoming to that conclusion.
Member Since: September 18, 2010 Posts: 0 Comments: 4570
1670. Asta
Thank you for all the great posts on the models everyone. It looks like Irene is currently projected to pass over florida and curve east.. hopefuly sooner than later.. Thanks again for all your sharing... I am learning from everyone.
G'night ( Irene)
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Quoting Hurricanes101:


you are missing my point, forecast models like the GFS have issues with seeing pressures that low, so when you see a pressure like 983mb on a model like the GFS it is indicating a major hurricane



And you are missing my point. There is no way with that much land interaction that you could possibly have a major hurricane. It comes off of Cuba and the next day hits Florida.
Member Since: July 15, 2006 Posts: 17 Comments: 10156
CMCTS Santo Domingo 23.08.2011 12 GMT 980.4 hPa
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1667. SXMFL
Quoting AussieStorm:

is that loud annoying bug called Irene


I wish, at least if it was it'd be gone by tomorrow, but this stupid this is here EVERY night. Like an alarm, I want to squash it!
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Quoting Hurricanes101:


you are kidding right?

model shows 983mb, which in forecast model terms is basically a major hurricane
On a global model, especially the GFS, that's about right. I'd lower the pressure about 10mb-12mb from what it shows, so using the Dvorak Technique that would be a 100mph - 105mph cyclone (approximately of course).
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The trough never materialized as expected..

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Quoting TampaSpin:
Keep in mind that the Eastern part of Cuba has some very high mountains while the Western part of Cuba is very flat.
isn't just the very eastern tip that is mountainous for the most part, with the majority of the island fairly flat ?
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156 hours Savannah,GA hit
Member Since: July 31, 2011 Posts: 4 Comments: 753
Quoting MississippiWx:


983mb is not a major hurricane...

And like I said, if it hits the way the GFS is showing, it's way too much land interaction to expect anything stronger than a minimal hurricane (Cat 1).


you are missing my point, forecast models like the GFS have issues with seeing pressures that low, so when you see a pressure like 983mb on a model like the GFS it is indicating a major hurricane

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Quoting Stormchaser2007:
Getting slammed by 129...

Anything under a 3 and I'm staying.



Same here. Can you imagine the chaos and disorder on the Interstates?
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A lullaby for y'all to go to sleep by tonight.

I was 2 y/o, and I think Grothar was in college when this was recorded. :)

Link

Dave
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Latest sat. looks like it's going to pass over the NE of PR...

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1)Grand Cayman every 2.21 years affected by Dean in 2007 ,this island remains the Hurricane & Tropical Storm capital of the Atlantic basin, brushed or hit by Hurricanes & Tropical Storms 62 times from the 1871 season until now(WOW)
Member Since: September 18, 2010 Posts: 0 Comments: 4570
Quoting Hurricanes101:


you are kidding right?

model shows 983mb, which in forecast model terms is basically a major hurricane


I guess that would apply with the GFS.

The ECMWF has the resolution to correctly plot a realistic pressure.

The 00z will be important.
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Quoting Hurricanes101:


you are kidding right?

model shows 983mb, which in forecast model terms is basically a major hurricane


983mb is not a major hurricane...

And like I said, if it hits the way the GFS is showing, it's way too much land interaction to expect anything stronger than a minimal hurricane (Cat 1).
Member Since: July 15, 2006 Posts: 17 Comments: 10156
1655. SXMFL
Quoting Progster:


Zut Alors! Evite la vache! Si non, si possible, achete une grande BBQ.



Done and done, the BBQ is ready! haha
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Quoting hunkerdown:
with bacon ???

Maybe
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Quoting weatherman12345:
they both have been quite consistant so far


I am actually shocked right now at how consistant they have been. Especially since now we have a TS and it has jogged slightly to the north they still have almost the exact land fall. These models are incredible(with this system)if this pans out!
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1652. Patrap
Member Since: July 3, 2005 Posts: 414 Comments: 125613
1651. angiest
Quoting MississippiWx:
Probably a minimal hurricane hitting S FL on the 00z run. If it hits FL the way the GFS is showing, it won't be anything too terrible wind-wise. However, there might be a considerable amount of flooding with it riding up the state at a relatively slow pace.


Would this be the first run not showing a major hitting the US?
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Quoting MississippiWx:
Probably a minimal hurricane hitting S FL on the 00z run. If it hits FL the way the GFS is showing, it won't be anything too terrible wind-wise. However, there might be a considerable amount of flooding with it riding up the state at a relatively slow pace.


you are kidding right?

model shows 983mb, which in forecast model terms is basically a major hurricane
Member Since: March 10, 2010 Posts: 1 Comments: 7233
Quoting Stormchaser2007:
Getting slammed by 129...

Anything under a 3 and I'm staying.

This would be one of the more difficult cyclones to evacuate from. You'd have to go to Panhandle if you don't want to feel any affects, because moving up the Florida coast would be of no use.
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144 hrs out: Florida/Georgia border.
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Down to 986

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144 hours centered over Jacksonville drifting nnw
Member Since: July 31, 2011 Posts: 4 Comments: 753
Quoting Stormchaser2007:
Getting slammed by 129...

Anything under a 3 and I'm staying.

are you back in the states ?
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Keep in mind that the Eastern part of Cuba has some very high mountains while the Western part of Cuba is very flat.
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1643. scott39
Irene is more than likely not going to ride up the W Coast of Fl. Im at the most hoping not!
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1641. JLPR2
Quoting NCHurricane2009:


Gotcha...

Does anyone by the way have radar out of the northern Lesser Antilles...?

Link
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Quoting hunkerdown:
with bacon ???


You had me some bacon lol.
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Quoting Stormchaser2007:


At least 990...

983mb actually.

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Quoting Bluestorm5:
988 mb storm over Orlando/Daytona Beach area at 126 hrs.


...not necessarily! Don't you think you should qualify statements like that?

anyway, off for more shuteye; just wanted an update.
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1637. JLPR2
I know this is probably the MLC but it sure seems like Irene is just east of Guadeloupe.
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Probably a minimal hurricane hitting S FL on the 00z run. If it hits FL the way the GFS is showing, it won't be anything too terrible wind-wise. However, there might be a considerable amount of flooding with it riding up the state at a relatively slow pace.
Member Since: July 15, 2006 Posts: 17 Comments: 10156
Quoting MississippiWx:


No, 15.6N 60.0W is probably about right...



Gotcha...

Does anyone by the way have radar out of the northern Lesser Antilles...?
Member Since: September 15, 2009 Posts: 391 Comments: 3519
Quoting charlottefl:


Looks that way, but it's not, just a result of convection increasing on the north side and the COC getting tucked underneath it.
mmmmmm...i think is moving almos wnw...
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Quoting hunkerdown:
don't think it is "passing it by" in that shot. more like "doing a number on"
LOL!! laughing at the wording, not the storm.
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1631. j2008
Quoting EastTexJake:
Yes HoustonTxGal. Having a lot of problems refreshing the blog, and with posts not formatting correctly. Plus, I can't seem to "quote" to answer your question directly.

It happens when a YouTube video is posted, try puting the view down to 50 comments, it should work again for you.
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Quoting tropicfreak:



mmmmmmmmm

well it is only
61.0F falling
Updated at 14:10 EST

and it is raining just a bit too.
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Quoting MiamiHurricanes09:
5 days out and right above me:



IF this forecast and track hold true, You take care of yourself young man.
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Getting slammed by 129...

Anything under a 3 and I'm staying.

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Quoting EastTexJake:
Yes HoustonTxGal. Having a lot of problems refreshing the blog, and with posts not formatting correctly. Plus, I can't seem to "quote" to answer your question directly.


Was told to get Firefox. the issue seems to be with IE.
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1626. Thrawst
Quoting MiamiHurricanes09:
5 days out and right above me:




120 miles to the WNW of me :P
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1625. Patrap
Member Since: July 3, 2005 Posts: 414 Comments: 125613
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Quoting tropicfreak:



mmmmmmmmm
with bacon ???
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132 hours out heading nnw
Member Since: July 31, 2011 Posts: 4 Comments: 753

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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.