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 whepton3:



Wonder what's driving the E shift in the HRWF..

More intensification and quicker forward motion to catch the weakness more east?


A significant jump/reform to the N is one of the reasons.

Will be interesting to see what da plane finds.
Member Since: August 17, 2005 Posts: 26 Comments: 16859
Quoting stormwatcherCI:
I had to look it up just now but you are right.



Yup :(
Gilbert came into the Caribbean at about the same spot, did not make the turn and careened west then right across Jamrock...eeks!!!
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Quoting barotropic:
cat 4 hurr showin up in bahamas missing florida. This hwrf combines with GFS and the north and east trends suggests really good news for florida


GFS has a landfall.
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Quoting WxLogic:


It is close to the 00Z ECMWF but a bit E of GFS.

For now the cone and track appears to be in shape with a slight shift to the E (closer to the E FL coast) later in the period if other models follow suite by 12Z.



Wonder what's driving the E shift in the HWRF..

More intensification and quicker forward motion to catch the weakness more east?
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Quoting A4Guy:


The HWRF and the Euro both keep the storm well offshore of Florida (i.e., shifted East). I'm sure we'll see some jumping back and forth through the later periods...we always do.


The HWRF really isn't far from the coast, and shows a strong enough system that it would probably be producing hurricane conditions on the east coast of Florida.
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cat 4 hurr showin up in bahamas missing florida. This hwrf combines with GFS and the north and east trends suggests really good news for florida
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2862. WxLogic
Quoting USAFwxguy:


Link


It is close to the 00Z ECMWF but a bit E of GFS.

For now the cone and track appears to be in shape with a slight shift to the E (closer to the E FL coast) later in the period if other models follow suite by 12Z.
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Quoting negriltracy:
I felt a sense of Deja Vu when I checked the reports this morning and sure enough after looking up the old sat images and tracks Irene is looking alot like Gilbert so it will be interesting to see if she takes the expected turn to the north or continues west and slams into Jamaica?!
We haven't taken a direct hit since Gil in 88 so we are way overdue :(
I had to look it up just now but you are right.
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HWRF....adjusted significantly east well into bahamas. This is very good for florida
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Irene DOOMCON levels?
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2857. A4Guy
Quoting USAFwxguy:
HWRF causing major d in the Bahamas.



The HWRF and the Euro both keep the storm well offshore of Florida (i.e., shifted East). I'm sure we'll see some jumping back and forth through the later periods...we always do.
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2856. GetReal
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2854. WxLogic
Looks like 00Z UKM still with GFDL but a bit further E:

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Quoting USAFwxguy:
HWRF doing its thing



Based on graphic you show...looks like its runnin a slight bit north of 00z position and my bet ends up aest also at end.....can u post your hwrf site as mine is slow.
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Quoting coffeecrusader:
Looks like us folks on the west coast of Florida are in the clear... WHOOOOO! Sorry east coast.
I wouldn't jump the gun and say that...
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2850. QMiami
Quoting WxLogic:


That's correct... thanks for that.


ah that makes sense I thought 17.9 would of been a big jump
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Stretch......Yawn......sniff..sniff..

Aqua,

Whats for breakfast?
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Squall ripped through San Juan Metro:
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Good Morning.



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Chances of me getting out of the Nassau, Bahamas airport Friday??? Too soon to tell, I think.
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Antigua and Barbuda


7 AM (11) Aug 21 77 (25) 73 (23) 29.74 (1007) E 30 light rain
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2843. WxLogic
Instruments fixed from the looks of it... data starting to roll.
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Good morning all! Just enjoying my morning coffee and checking in on Irene. Looks like the models have shifted east a bit due to strength and consolidation, which means I may be in luck here in St. Pete, but others are more at risk.

Of course, until it makes it past Hispanola, all bets are off, I suppose.
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HH plane relaying data now, on their way to make the first fix.
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GFS has something developing in the Western Atlantic and heading towards the Caribbean near the end of it run. Still 12 days away but might as well watch, as GFS predicted Irene almost perfectly so far.
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Looks like us folks on the west coast of Florida are in the clear... WHOOOOO! Sorry east coast.
Member Since: August 21, 2006 Posts: 0 Comments: 254
Quoting Gearsts:
xtrap. Sfc. Press: 1007.2 mb* (~ 29.74 inHg*
All of the reported pressures from HH have been flagged as suspect. Seems they may be have issues with their instruments.
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2835. WxLogic
Quoting barotropic:


16.9 not 17.9


That's correct... thanks for that.
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2833. WxLogic
Quoting USAFwxguy:
HWRF is shifted north thus far


Yeap... after the center fix was imputed yesterday and processes by the 00Z runs, I noticed that since the 00Z the weakness moved E a couple hundreds of miles from being located on the E GOM to be right on top of FL/E FL Coast region which would make a system recurve a bit further to the E depending on the strength of the Bermuda High.
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2832. Gearsts
xtrap. Sfc. Press: 1007.2 mb* (~ 29.74 inHg* LOL
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Quoting atmosweather:


She will pass a little to the N of that buoy but we will get some useful information from it still.
Quoting atmosweather:


She will pass a little to the N of that buoy but we will get some useful information from it still.


Interesting... N winds at the buoy.

If she gets a tick N of the buoy... a wind shift should be in order.

I think that's right... still cloudy and just waking up.

May get at least a nice hint about the center from this.
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Quoting seafarer459:


That sucks. Puts me on the ugly side of the storm


...Just watching for now; but a hair more nervous about this 8!&$@
Member Since: August 17, 2005 Posts: 26 Comments: 16859
I felt a sense of Deja Vu when I checked the reports this morning and sure enough after looking up the old sat images and tracks Irene is looking alot like Gilbert so it will be interesting to see if she takes the expected turn to the north or continues west and slams into Jamaica?!
We haven't taken a direct hit since Gil in 88 so we are way overdue :(
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Quoting ManicouRiverResort:
Located @ Dominica

What was strange ... and I have no scientific way of backing this up ... is that I could hear the winds ... but a general background noise far away. Whilst here was very calm.

I see on that Guadeloupe radar that the storm's southern boundary passed over the Saints ... literally 20 miles from here ... so maybe I was right.

We have no industry and no cities and nobody works on a Saturday night ... we go to the top of the hill on New years Eve and watch Guadeloupe's fireworks to give you an idea of closeness.

I think it's possible. At 6 p.m. on 12/31/99, I heard loud booming noises outside, like the noise of fireworks. I had the t.v. on the background. The noises were identical. I guess prevailing conditions were enough for me to hear the roar of the fireworks in London, 6 p.m is their midnight, on the fringe of the U.S. East Coast in New Jersey. This is an odd, but true story. If I was going to make something up, it would be more dramatic than this!
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Quoting WxLogic:
Eye feature trying to develop around 17.9N 61.9W.

Models have trended some to the right due to the strength of Irene being a bit stronger than expected so able to fight of the building Bermuda High from E some but still impacting US.


16.9 not 17.9
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Quoting whepton3:


1009 mb. Should be interesting to see if it gets to 1006... as the forecast disc has central pressure.


She will pass a little to the N of that buoy but we will get some useful information from it still.
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This is definitely a bigger threat than Emily.
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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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