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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maybe this is better
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2470. RyanFSU
I'm sure it's still there. I am at Naval Research Laboratory in Monterey -- now for over a year. I still update the FSU site since it's non-classified and easier.

Quoting yesterway:


How's the "LOVE" building doing?


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2469. emguy
Nothing has really changed with Irene in the general track philosophy since the relocation (at least as far as the governing weather patterns are concerned). Interesting note about that re-location though, there is a slight auto correct going on in that it is moving due west instead of a more west north westerly direction. In fact, the longer loop of the radar since the relocation would imply maybe just a smidge south of due west movement. so the short turn jump in lattitude may be just that, a short term jump with little change in longer term results. Good news for Puerto Rico is now that Irene has an established circulation, it's unlikely to reform north again. In that scenario, as long as it does not bend west north west soon, the anticipated impacts should not be any worse than already forecasted.
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looks like eyewall trying to for near those double little yellow westside walla
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I usually hold my comments to a minimum however I just thought I'd chime in here. First off RyanFSU I love your site that you have up as it's a big help to those who like all the models detailed on one page.
Looking at the Martinique radar you can see on the last frame a slight movement back to the WSW. Just an observation from me and as usual to the regulars keep up the good work. :P
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Quoting AllStar17:


Any good wind observations from the French Antilles?
Not really. Antigua reporting winds towards the NE at 22mph, which would sorta make sense since I see the circulation WSW of there.

Quoting MississippiWx:


You mean east?
Yessir.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
2465. Titoxd
Quoting RyanFSU:
If I had to make bets, I'd always go with the ECMWF global model over the NCEP GFS. Lately, the Canadian model has been outperforming GFS. It has a similar landfall location as ECMWF in 6-days.



Holy Typhoon Tip, Batman!
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715UTC image still shows that an eye wall is possibly forming:

Member Since: July 15, 2006 Posts: 17 Comments: 10160
Quoting MiamiHurricanes09:
I'd put the circulation near 17˚N right now. Looks to be just south of west from Antigua.


You mean east?
Member Since: July 15, 2006 Posts: 17 Comments: 10160
Dynamic MJO forecasts

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Quoting MiamiHurricanes09:
I'd put the circulation near 17˚N right now. Looks to be just south of west from Antigua.


Any good wind observations from the French Antilles?
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Quoting RyanFSU:
If I had to make bets, I'd always go with the ECMWF global model over the NCEP GFS. Lately, the Canadian model has been outperforming GFS. It has a similar landfall location as ECMWF in 6-days.



How's the "LOVE" building doing?
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Quoting cntrclckwiseSpenn:


A lot of it has to do with the steering of the upper atmosphere. Right now there are no troughs strong enough to recurve it. Simply because the center moved farther to the north does not mean it will not resume a more westardly track.


Didnt say it was going to recurve... just said the placement of the ridging will be SE-NW inline with a bahamas-S Carolina hit.. I could be wrong.. but its current location and development will take it on that path.

Land interaction with Hispaniola and it decoupling will bring it more West if it does..otherwise, its Bahamas-S Carolina event
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Quoting MississippiWx:
One good thing about Irene coming closer to PR is that we will have great radar loops...lol.

lolololol...indeed
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Quoting FLWeatherFreak91:
Why is that?


Because they are the only 2 models showing any sort of solution like that, and that's not even thinking about the large northward redevelopment of the center. We'll see, but those 2 look to have no chance at coming about right now.
Member Since: July 15, 2006 Posts: 17 Comments: 10160
Quoting MississippiWx:
Radar could be giving hints that an eye wall is forming:

I'd put the circulation near 17N right now. Looks to be just south of east from Antigua.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
2455. RyanFSU
If I had to make bets, I'd always go with the ECMWF global model over the NCEP GFS. Lately, the Canadian model has been outperforming GFS. It has a similar landfall location as ECMWF in 6-days.

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Quoting brianc:
Paptrap is the last person I would accuse of being a wishcaster or catastrophobe...so I guess we all in Miami/S. FL should take heed...gas/shop tomorrow before the media starts ranting...


HI Brian, you're so right about Pat :)
I live in SEFL, bought all supplies today and chatted a bit with people at Costco and Publix. Nobody has any clue of what's going on. Thanks to WU and all your info I'm all set :)
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Quoting scottsvb:
I dont see this coming to florida.... I think its more of a Puerto Rico-Hispaniola and Bahamas and
a threat to the Carolinas in 6 days. My assumptions are usually correct so Its a good bet 60% or
more that this might only bring some squalls at most to the east coast of Florida.

Reasons... Formation of the center is further NE.. Model trend on the ECMWF is more east near Nassau and I think it will end up just east of there heading NNW by Thurs near 25N and 76W and get no closer than 79W making landfall in S Carolina.

I could be wrong... but this was suppose to form around 15N and 63W by Sunday morning.. it's already around 16.2N as of this post and 61W... only chance this has of making Florida is a west turn on Sunday (cause its more WNW right now) and its LLC get pulled W of the midlevel Circulation over Haiti due to landfall around 18N and 70W exiting around Port-A-Prince Haiti and then going inland over SE Cuba keeping this a 50mph Tropical Storm until it comes off around 78W and 23N...but that just probably not going to happen...probably come off near Labadee Haiti moving WNW and moving NW thru middle of the Bahamas.


A lot of it has to do with the steering of the upper atmosphere. Right now there are no troughs strong enough to recurve it. Simply because the center moved farther to the north does not mean it will not resume a more westardly track.
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Quoting MississippiWx:
One good thing about Irene coming closer to PR is that we will have great radar loops...lol.



Only the outer rainbands visible right now. Should provide PR residents a reminder that Irene is getting closer.
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Quoting MississippiWx:
One good thing about Irene coming closer to PR is that we will have great radar loops...lol.

yea no kidding.

I can't stand the French Antilles one
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Quoting MississippiWx:


At this point, it would be hard to believe the GFDL and UKMET tracks hold any weight.
Why is that?
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Quoting BahaHurican:
Think I'm going to head out also... didn't plan to stay up until 3 a.m. ..... just 2 hours before the next discussion! How will I sleep?! LOL

G'nite, ya'll.... will be in and out tomorrow; laundry and other stuff has to get done if it's going to be rainy later this week... lol


g'nite baha
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Quoting ProgressivePulse:
Updated with new location. NHC is west of the consensus now and likely will shift track eastward @ 5am.


At the same site I get different results?????

img src="">
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Quoting FLWeatherFreak91:
Not while ukm and gfdl are still west of the current forecast track.


At this point, it would be hard to believe the GFDL and UKMET tracks hold any weight.
Member Since: July 15, 2006 Posts: 17 Comments: 10160
One good thing about Irene coming closer to PR is that we will have great radar loops...lol.

Member Since: July 15, 2006 Posts: 17 Comments: 10160
Quoting ProgressivePulse:
Updated with new location. NHC is west of the consensus now and likely will shift track eastward @ 5am.

Not while ukm and gfdl are still west of the current forecast track.
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Quoting ProgressivePulse:
Updated with new location. NHC is west of the consensus now and likely will shift track eastward @ 5am.


That is essentially a worst case scenario track for the east coast. Provided she survives hispaniola intact (likely given the large circulation), will affect half the east coast while intensifying over the gulf stream! Irene, stop being so interesting so I can go to bed.
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Radar could be giving hints that an eye wall is forming:

Member Since: July 15, 2006 Posts: 17 Comments: 10160
2432, thanks Patrap.
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Quoting BahaHurican:
Here's a charming little August storm that illustrates a potential track for Irene.



Note that WNW movement takes it straight to Central Florida.

Nothing right now precludes Irene from having a similar track, albeit to the south [left] of this.


def plausible
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I dont see this coming to florida.... I think its more of a Puerto Rico-Hispaniola and Bahamas and
a threat to the Carolinas in 6 days. My assumptions are usually correct so Its a good bet 60% or
more that this might only bring some squalls at most to the east coast of Florida.

Reasons... Formation of the center is further NE.. Model trend on the ECMWF is more east near Nassau and I think it will end up just east of there heading NNW by Thurs near 25N and 76W and get no closer than 79W making landfall in S Carolina.

I could be wrong... but this was suppose to form around 15N and 63W by Sunday morning.. it's already around 16.2N as of this post and 61W... only chance this has of making Florida is a west turn on Sunday (cause its more WNW right now) and its LLC get pulled W of the midlevel Circulation over Haiti due to landfall around 18N and 70W exiting around Port-A-Prince Haiti and then going inland over SE Cuba keeping this a 50mph Tropical Storm until it comes off around 78W and 23N...but that just probably not going to happen...probably come off near Labadee Haiti moving WNW and moving NW thru middle of the Bahamas.
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Updated with new location. NHC is west of the consensus now and likely will shift track eastward @ 5am.

Member Since: August 19, 2005 Posts: 5 Comments: 5045
Quoting Patrap:
If I was in South Fla below Tampa..Id be thinking about fuel.other needs.



I would also, I have a buddy who lives in Estero,just south of Ft Myers a bit that he really needed to keep an eye on this one. I gave him my best thoughts on the cone,so to speak,but he keeps saying it will fall apart,or it;s just another teaser. I'll keep on him until he's out of the woods or under the gun,so to speak.
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Quoting yesterway:
Does everyone agree with a cat 2 intensity at this point for Florida?


Sill think thats a tough forecast. But I think its increasingly quite possible. More so than I thought yesterday evening.
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Quoting extreme236:


I think we could see some rapid intensification today.


That'd get Taz pretty fired up!
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Does everyone agree with a cat 2 intensity at this point for Florida?
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Think I'm going to head out also... didn't plan to stay up until 3 a.m. ..... just 2 hours before the next discussion! How will I sleep?! LOL

G'nite, ya'll.... will be in and out tomorrow; laundry and other stuff has to get done if it's going to be rainy later this week... lol
Member Since: October 25, 2005 Posts: 19 Comments: 21643
Quoting WaterWitch11:


you can see it starting to spin


Yep. And looks like a consistent WNW track taking shape
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2432. Patrap
Quoting petewxwatcher:
Why is it when tropical storms and hurricanes form some are small and some are big? Andrew was really small and Irene will be big.

I'm not talking about storms that are big and sloppy after land interaction. I mean storms out forming in the ocean. What determines their size?


Usually it is the Wave Axis Girth as it comes off Africa..like this one did, or they can Grow very rapidly and exploselively n Width and Breath as K and Rita did in 05 with Perfect conditions.

Some stay small and compact like Camille and Dolly.

Lotsa research in that area and lotsa opines as well
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Quoting RyanFSU:
Here's a better picture/mouse-scroll of the ECMWF (no offense to the Raleigh plots): 6-days as a Category 2 hurricane, or so.



Taking the next frame it's a Georgia landfall. Never seen one of those.

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Blog is kinda busy for middle of night.
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Quoting MississippiWx:
I really almost expect recon to find a hurricane later today.


I think we could see some rapid intensification today.
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Why is it when tropical storms and hurricanes form some are small and some are big? Andrew was really small and Irene will be big.

I'm not talking about storms that are big and sloppy after land interaction. I mean storms out forming in the ocean. What determines their size?
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I really almost expect recon to find a hurricane later today.
Member Since: July 15, 2006 Posts: 17 Comments: 10160
Quoting ElConando:
This storm puts me in an interesting position. I'm moving up to Tallahasse for the school year on Tuesday. I live in S Fla so if in fact it is heading SFla's way my parents have accordion shutters so we can close them up prior to leaving in case it does hit.


Just like me. I am taking my son up to FSU also....going wens. This is not good.
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2425. Patrap
Sunday is a good day to get er done away from the Monday notice when folks see the morning and Noon news.

Sun is a slow get the word out day.
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2424. scott39
Pat Im not having any phun- with the maps- at all. The ones you sent me back at the end of July-. I did like them- I tried to E-mail you about it but I never got a response. E-mail must have been down. I wanted to get some more. thanks
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2423. Lizpr
Quoting PRweathercenter:
we are in Puerto Rico, he's in Carolina and I'm in Caguas


What part of Caguas are you from? I'm from Caguas too used to live in Villa Del Rey 5ta all my life until I move to Oregon a year ago.
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Gonna try and get some sleep.

I still think the center may be a little more north of the current position.

Recon will have to confirm.
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2421. RyanFSU
Here's a better picture/mouse-scroll of the ECMWF (no offense to the Raleigh plots): 6-days as a Category 2 hurricane, or so.

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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.