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 aquak9:
(replaces Keeper's cup with decaf, too)

*adds 10 pounds of caffeine to your and keep's cups*
Member Since: November 13, 2009 Posts: 2 Comments: 728
3420. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 171 Comments: 53825
Quoting USAFwxguy:


I had edited to .5s, but yes. Looks like that is about it.
Nice to have you on board.

You have added nicely to the quality posters here!!
Member Since: Posts: Comments:
Quoting Hurricanes12:
MH09, how long have they been in Irene? (The HH's)
They got into the system around 7:30a.m EDT.
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Quoting TampaSpin:



Hey Bro,,,,,,NO i mean 98L ......take a look at it...98L should pump some warm air around and aid in building a stronger ridge....IF MY THINKING IS CORRECT......take a look at the models and watch how the affects of 98L are playing.


What do you think the effects will be of the center being adjusted even further north again. Its currently over St. Kitts near 17.2N .....moving west. Thats a big jump north again.
Member Since: August 22, 2010 Posts: 0 Comments: 652
Quoting SavannahStorm:
TWC upping their very scientific "Threat Level"


um... Irene is over medium threat level. What the heck?
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Quoting Bretts9112:

see post 3130 it jogged south and is about to be right on line with nhc track


the wishcasters are coming out of the woodwork again,carolina,ga,florida,fish track, gulf coast,please give it a rest,but guess thats not gonna happen.
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MH09, how long have they been in Irene? (The HH's)
Member Since: June 21, 2010 Posts: 0 Comments: 528
TWC upping their very scientific "Threat Level"


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3407. aquak9
Quoting DookiePBC:


Knots, MPH, or kPH?? Gotta know when it's safe to wow.

any of the above, plus millibars. Oh ehm gee is allowed if two or more numbers go to three digits. It's complicated here.
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Quoting MiamiHurricanes09:
Looks like Irene is still a 50mph cyclone.

133500 1751N 06150W 8440 01559 //// +136 //// 121036 044 045 018 01
Agree.
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3405. KEEPEROFTHEGATE (Mod)
Quoting aquak9:
(replaces Keeper's cup with decaf, too)
puts hand over cup ahhh thats hot
Member Since: July 15, 2006 Posts: 171 Comments: 53825
3404. 900MB
Quoting OrchidGrower:
Thanks, 900MB; I'm marveling to see Irene moving this northerly as she seems to be despite her fast forward speed. I hope she slows down soon...if not, I'm guessing that puts us on the west coast of Florida, a bit more under the gun again.

Do we have a scenario for what happens if Irene manages to just scrape/skip altogether, the Dom. Rep. by passing north?


Right now the models are split between E Coast of Fla and W coast of Fla. If she keeps recentering North, expect the models to shift East from Miami to Jersey, but it's too early to call. We'll see what happens over the next 24 hours (obviously crucial).
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3402. aquak9
(replaces Keeper's cup with decaf, too)
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Quoting sullivanweather:
Good morning, Tampa!
How things?

Do you mean ex-Harvey? Cause I don't think 98L will have any effect on Irene or vice versa.

As far as ex-Harvey goes, it seems the large convective blow-up yesterday morning/afternoon before it made landfall put out a burst of enhanced outflow which helped to carve out a bit of a deeper trough in the Caribbean than global models expected. This aided in creating a broad southwesterly flow over the eastern Caribbean which, I believe, helped Irene to take a more northerly track than forecast. There was already a deep upper trough extending into the Caribbean from the mid-latitudes which is still somewhat evident on water vapor imagery.

I still think this one goes north of the islands. I was saying it yesterday and thus far today all indications are this will continue on this 285° heading or so. Come right over St.Croix, Puerto Rico from Ponce to Mayaguez, into the Mona passage and ride the north coast of Hispaniola.



Hey Bro,,,,,,NO i mean 98L ......take a look at it...98L should pump some warm air around and aid in building a stronger ridge....IF MY THINKING IS CORRECT......take a look at the models and watch how the affects of 98L are playing.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
over 700,00 Haitians live like this...many will die...
Member Since: August 13, 2007 Posts: 0 Comments: 10490
Quoting Bluestorm5:
yea, sorry about that. Still learning about this tropics tracking...

No problem, just look for the surface winds as that gives you the reading of what you feel if you on the ground. That is why the HH use SMFR.
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Quoting aquak9:

(refills cup with decaf)
haha, thanks. Anyway... still waiting for new datas from the plane.
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Looks like Irene is still a 50mph cyclone.

133500 1751N 06150W 8440 01559 //// +136 //// 121036 044 045 018 01
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Quoting MiamiHurricanes09:
Strongest winds being found right now. 42 knots.

133400 1753N 06147W 8428 01573 //// +150 //// 121049 051 042 011 01


Not surprised center is movin west but is consolidating north. Radar puts it directly over st Kitts. Where you are speaking of is just NE of Center. I believe it is at 17.2N 62.6W COC movin west....so another N adjustment

Link

Center over St. Kitts
Member Since: August 22, 2010 Posts: 0 Comments: 652
Quoting FLdewey:
Haha... wow'n is permitted for 3 digit numbers only.


Knots, MPH, or kPH?? Gotta know when it's safe to wow.
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Quoting Bluestorm5:
oh ok. 51 knots on flight level, 42 knots surface just been posted on recon site.
Correct.
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3392. KEEPEROFTHEGATE (Mod)
089

URNT12 KNHC 211228

VORTEX DATA MESSAGE AL092011

A. 21/12:08:00Z

B. 16 deg 46 min N

062 deg 22 min W

C. 850 mb 1477 m

D. 36 kt

E. 304 deg 33 nm

F. 043 deg 43 kt

G. 307 deg 43 nm

H. 1006 mb

I. 16 C / 1529 m

J. 17 C / 1524 m

K. NA / NA

L. NA

M. NA

N. 1345 / 08

O. 0.02 / 3 nm

P. AF300 0209A IRENE OB 02

MAX FL WIND 43 KT NW QUAD 11:48:00Z

;
Member Since: July 15, 2006 Posts: 171 Comments: 53825
Quoting sporteguy03:
Surface winds around 46 MPH though.
yea, sorry about that. Still learning about this tropics tracking...
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Quoting USAFwxguy:
16.8, 62.8 roughly that vicinity you will find the next vortex msg I feel
Agreed. within .1 lol
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3389. aquak9
Quoting Bluestorm5:
Sorry, it's hard to not be wow'in when it reachs 50 knots... it's been awhile since last year.

(refills cup with decaf)
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indeed ....98L will help pump the ridge -- Boom!

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Thanks, 900MB; I'm marveling to see Irene moving this northerly as she seems to be despite her fast forward speed. I hope she slows down soon...if not, I'm guessing that puts us on the west coast of Florida, a bit more under the gun again.

Do we have a scenario for what happens if Irene manages to just scrape/skip altogether, the Dom. Rep. by passing north?
Member Since: Posts: Comments:
Sorry, it's hard to not be wow'in when it reachs 50 knots... it's been awhile since last year.
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Quoting Bluestorm5:
Oh wow... 51 knots founded.
Surface winds around 46 MPH though.
Member Since: Posts: Comments:
Good morning, Tampa!
How things?

Do you mean ex-Harvey? Cause I don't think 98L will have any effect on Irene or vice versa.

As far as ex-Harvey goes, it seems the large convective blow-up yesterday morning/afternoon before it made landfall put out a burst of enhanced outflow which helped to carve out a bit of a deeper trough in the Caribbean than global models expected. This aided in creating a broad southwesterly flow over the eastern Caribbean which, I believe, helped Irene to take a more northerly track than forecast. There was already a deep upper trough extending into the Caribbean from the mid-latitudes which is still somewhat evident on water vapor imagery.

I still think this one goes north of the islands. I was saying it yesterday and thus far today all indications are this will continue on this 285° heading or so. Come right over St.Croix, Puerto Rico from Ponce to Mayaguez, into the Mona passage and ride the north coast of Hispaniola.
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Quoting stormpetrol:
Irene moving due west now.Center basically at same longitude


Correction (latitude) not longitude
Member Since: April 29, 2007 Posts: 0 Comments: 7862
FYI, COC of Irene is almost visible on Puerto Rico long range radar... later today it should become more visible, which will be useful in tracking the storm for those who like to track every wobble and movement.

Remember, tropical systems wobble - it is the average movement of a long period of time that determines the direction, not a wobble here or there.

Right now Irene is moving West (or maybe WNW) towards Puerto Rico and DR.

Puerto Rico NHC Long Range Radar
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Quoting MiamiHurricanes09:
Strongest winds being found right now. 42 knots.

133400 1753N 06147W 8428 01573 //// +150 //// 121049 051 042 011 01
oh ok. 51 knots on flight level, 42 knots surface just been posted on recon site.
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Quoting StormJunkie:


Radar is actually terrible for tracking the center of weaker and developing systems. Can be very confusing. Especially that very short low quality loop.
I think using every source available is most prudent. Every piece of data is important.
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Quoting Abacosurf:
Link

Looks like that mini vorticy is being absorbed into the broader eye feature present on radar.

Very common to see in developing storms.

The larger eye feature is what we need to watch for direction trends. Not the mini swirls inside of it.

The overall trend is in the 275 degree range now IMO.



Agree. Actually the Dominant center visible on radar is directly over St Kitts. That puts the storm further north, althogh overall motion is west. We mat see an adjustment north on next advisory again.
Member Since: August 22, 2010 Posts: 0 Comments: 652
3375. KEEPEROFTHEGATE (Mod)
Quoting Sfloridacat5:


Such a short loop its really hard to get a true direction.
Based on visible sat. the storm looks to moving wnw or time.


here

T.C.F.W
09L/TS/I/C0
MARK
17.55N/62.15W
Member Since: July 15, 2006 Posts: 171 Comments: 53825
Quoting Waltanater:
c'mon people!!! It's "Irene." Florida is her state! Let's welcome her home with open arms!! It's been a long time Irene.


O forgot about that Irene in October 99 was at work right near downtown Miami, another example of not to focus on points in forecast but on cone, that storm was going to hit the west coast, instead came almost directly over Miami. We had to leave work under 70+ gust trees where down all over my works parking lot!
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Moving @ 280-285. IMO
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3371. scCane
Quoting StormJunkie:


Radar is actually terrible for tracking the center of weaker and developing systems. Can be very confusing. Especially that very short low quality loop.
You are right but so far I've found it much easier for tracking Irene. That dry spot on the visible has been throwing me off for a bit.
Member Since: May 9, 2007 Posts: 0 Comments: 154

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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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