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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3321. sigh
Quoting yonzabam:
Last few frames on this loop show Irene's COC make a sharp dive south.

Link


You can't see the COC. If you're talking about the feature that looks like an eye, that's not an eye, Irene's not even close to having an eye yet, and it's not necessarily near the COC.

What you're seeing is just changes in cloud patterns and shifting convection. It may look like the storm is changing direction, but it's just an optical illusion. The storm MIGHT be changing direction, but if it is, you wouldn't be able to tell from watching that imagery.
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Quoting sporteguy03:


Andrew was also a compact storm, a larger and more developed hurricane can create effects across the entire state. Still too early to tell.
True, True. Do you remember how big Jean was? She was soooo big....waiting...waiting...she took up 10 zip codes! padumdum! Though she relly did. And she was moving sort of East to West
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Quoting FLWeatherFreak91:
I agree that the center is moving wsw.


That's just a pocket of dry air wrapping down the west side of the cyclone. The center is currently coming over St.Kitts and Nevis.
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Quoting clwstmchasr:


That's a 60 jump to the north or a wnw to nw movement.


Yep, and I could be dead wrong...But the imagery seems to suggest it to my novice eyes.
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Morning you monsters who've been up all night watching this (checked out 1 am CDT and look at all the pages you've filled).

Apologies if the all night crew discussed this already but when I refreshed the French Antilles rader this morning the circulation still seems to be around the dry hole (almost said dry eye)in the radar. Is this significant? Does it tell us something? Lurking non-mets would love to know. (I left about the time "its an eye! Is NOT! Is too? started).
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Quoting sporteguy03:

Not sure where you are getting that it is great news if anything it will be closer to you. Models will still waffle for a few more days anyways.


Current models don't look good for Savannah and Charleston, two of my favorite cities.
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Quoting scott39:
The models are on a W trend again. This yo--yo has to stop soon. LOL


That will continue for the long range.......gang we gotta remember the ConUs is still 5 days out.......many things can change and the models will continue to shift back and forth. Until we are 3 days out then a good fix will become more certain.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
3312. klew136
Quoting barotropic:


Yes but that was issued prior to the updated forecast track by the NHC being issued at 5am. that entry locations shifts about 100 plus miles east under the new track


well that makes me feel a little better.
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3311. KEEPEROFTHEGATE (Mod)
T.C.F.W
09L/TS/I/C0
MARK
17.55N/62.15W
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Quoting TampaSpin:


Yes, for sure! The larger mountains will tear the hell out of the low level center.....but, we have seen LLC jump and reform very quickly before and reorganize very quickly in those very warm waters in the Bahamas and Keys.


I just have a feeling that Haiti/DR mountians are going to kill the thing....I feel horrible for them!!
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3309. luigi18
Quoting Tropicaldan:
Good morning all

Just popping out of lurkville to give a local weather update here in saint martin

Rain has been incessant for about three hours but is now torrential. Wind is really picking up with some very strong gusts roaring through, almost certainly ts force.

Dan


take care! we here in Puerto Rico getting prepare keep posting!
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Quoting HurricaneSwirl:


No it's not.
I agree that the center is moving wsw.
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Quoting connie1976:
I have noticed that the models are shifting east...do you think that they will keep shifting east? This is great news for us in south florida!!


Connie the experts on here are saying the tracks are pretty much becoming more in agreement with where they are now but they said the tracks might move back west a tiny bit but pretty much back and forth where they are at for now. So anyone from the panhandle of FL to North Carolina should still be watching closley since you never know.
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Quoting connie1976:
I have noticed that the models are shifting east...do you think that they will keep shifting east? This is great news for us in south florida!!

Not sure where you are getting that it is great news if anything it will be closer to you. Models will still waffle for a few more days anyways.
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Models will shift. Irene is still 5 days from landfall (possible Fl. landfall).
That's why the NHC uses such a wide cone at 5 days out.

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Good morning all

Just popping out of lurkville to give a local weather update here in saint martin

Rain has been incessant for about three hours but is now torrential. Wind is really picking up with some very strong gusts roaring through, almost certainly ts force.

Dan
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Quoting FLWeatherFreak91:
Irene will make landfall in Florida. That ridge is not going to end up any weaker than currently forecast. The models thus far this year have been overdoing trofs and underestimating the strength of the bermuda high; I see no reason to assume they'll behave differently with Irene.


Thank you!
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how close to the conus is the high? where will the weakness be?
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Quoting yonzabam:
Last few frames on this loop show Irene's COC make a sharp dive south.

Link


No it's not.
Member Since: July 7, 2008 Posts: 2 Comments: 3237
Nothing added to recon site since 9:04 EST... and nothing added to Google Earth recon since 9:14 EST. I'm expecting 45-55 knots in NE corner of Irene.
Member Since: August 1, 2011 Posts: 28 Comments: 7913
Quoting connie1976:
Tampa,

I noticed that the models are now taking the storm over a lot of those mountains....shouldn't the storm weaken and die over hispanola? Thanks!


Yes, for sure! The larger mountains will tear the hell out of the low level center.....but, we have seen LLC jump and reform very quickly before and reorganize very quickly in those very warm waters in the Bahamas and Keys.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
3297. Ryuujin
Three factors will influence where Irene goes and we will have to watch all three. One is her strength of a storm. Stronger storms tend to pull northward more rapidly. Second is the strength of the break in the ridge and its location. It will determine how much and where Irene will feel it, and lastly her forward speed. If she keeps going fast then that means more west, if she slows down then that means more north. All three of these dance partners will have an effect on where she will go.
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I'm thinking the center may be closer to the 17.5ish range next time recon gets there.
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3295. scott39
Quoting TampaSpin:



Models are favoring the East Coast of Florida.....and if you live in Georgia and South Carolina.....HEADS UP!
The models are on a W trend again. This yo--yo has to stop soon. LOL
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3294. divdog
Quoting naplesdreamer28:
Am I right in the assumption that Irene is large enough to affect a larger area than just the pinpoint tracks? For example, in Florida, if the tracks shift east and west between the coasts, isn't this storm large enough to cover both sides of the state no matter where it ends??
east side of storm is always the worst
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Quoting TampaSpin:



Models are favoring the East Coast of Florida.....and if you live in Georgia and South Carolina.....HEADS UP!
You can't even see Key West underneath all that tracking mess...hey, do you get down here for the poker run (bike week) in Sept?
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The 144h run of the NAEFS shows the split track solution in the ensembles rather well, with 1 zone of uncertainty in the surface pressure field east of FL and another in the central Gulf of Mexico. Since all the pressure fields (40 ensemble members from CMC and GFS) are averaged, the intensity of Irene gets washed out in this product. Still a tough call to make for the NHC.
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Quoting connie1976:
I have noticed that the models are shifting east...do you think that they will keep shifting east? This is great news for us in south florida!!
Irene will make landfall in Florida. That ridge is not going to end up any weaker than currently forecast. The models thus far this year have been overdoing trofs and underestimating the strength of the bermuda high; I see no reason to assume they'll behave differently with Irene.
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Quoting KeyWestwx:
FYI- When Andrew hit S of Miami the only effects Key West experienced were a few 20 mile an hour gusts and cloudy skies. And, of course, a bunch of folks drunk on margaritas.

So if the storm is far enough to your East, don't count on to much interaction, especially since the East side of a storm tends to create the worst weather


Andrew was also a compact storm, a larger and more developed hurricane can create effects across the entire state. Still too early to tell.
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Tampa,

I noticed that the models are now taking the storm over a lot of those mountains....shouldn't the storm weaken and die over hispanola? Thanks!
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Quoting TampaSpin:



High pressure always builds in behind Low pressure. When its tropical that is warm air that is spinning counter clockwise.
that makes perfect 5th grade science sense!
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3285. scott39
Watch the track and to the outside of the NHC cone folks. You will never go wrong and always be prepared. Dr. Steve Lyons drilled that in my head!!
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Quoting yonzabam:
Last few frames on this loop show Irene's COC make a sharp dive south.

Link


You're following a pocket of dry air. That's not the real center.
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Quoting klew136:


24.5 and 80.5 is Islamorada, fl


Yes but that was issued prior to the updated forecast track by the NHC being issued at 5am. that entry locations shifts about 100 plus miles east under the new track
Member Since: August 22, 2010 Posts: 0 Comments: 652



Models are favoring the East Coast of Florida.....and if you live in Georgia and South Carolina.....HEADS UP!
Member Since: September 2, 2007 Posts: 178 Comments: 20439
3281. sigh
"we need those islands to do their job and protect south florida"

That's not their job. There are PEOPLE living on those islands, and frankly those people have MUCH less ability to cope with the impact of a hurricane than people in Florida.

Let's try to cut down on wishing that a disaster will befall some of the poorest people on earth...

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3280. MZT


any deviation might bring some effects to West Coast of FL.

Totally agree. Remember Ivan? When it was in the Caribbean it was suppose to hit West FL or ride up the spine.

IIRC, Ivan was also expected to travel directly across Jamaica. It wobbled a little to the west right before landfall and skirted the island.

30 miles one way or the other can really change the story in this part of the world.
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Last few frames on this loop show Irene's COC make a sharp dive south.

Link
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Quoting scCane:
The majority of the ensembles remain well east of Florida despite the western shift.


but its south of that track and right or dead on with the NHC track
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42 knots and rising.
Member Since: August 1, 2011 Posts: 28 Comments: 7913
3276. ackee
HAITI seem to attract all types of natural disater dont know would be really good if IRENE spare I think the rest of the carrb CAN HANDLE IRENE BUT PRAY that so how Hati WILL miss this
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went out to buy milk at the local gas station and the clerk had no idea a storm was coming!!!!
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I have noticed that the models are shifting east...do you think that they will keep shifting east? This is great news for us in south florida!!
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Latest Tracks......
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Quoting CybrTeddy:
Good morning, overnight Irene did two things. One was ingest dry air, which is why we're seeing weak convection on the S side.. today Irene will be focusing on reorganizing its core with strengthening beginning later today IMO, and could become a hurricane tomorrow PM or Tuesday AM. Another thing is that Irene relocated its core more north, and the overall outflow has become better organized.



yep, yep, and yep....see you got a good sleep....:)
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Recon haven't updated the site since 9:04 EST... wondering what's going on.
Member Since: August 1, 2011 Posts: 28 Comments: 7913

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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.