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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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.
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Oh wow... 51 knots founded.
Member Since: August 1, 2011 Posts: 28 Comments: 8075
Quoting scCane:
Guys use radar when tracking the center it's much easier.

Link


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

its easy i can even make it scroll

Action:
Quote
| Ignore User


Member Since: July 15, 2006 Posts: 108 Comments: 27212





your scrolling text makes all my show/hide buttons disappear.
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3367. scott39
Quoting TampaSpin:


Right down the heart of Florida...and slightly West if not just off the West Coast......98L will help pump the ridge.
Man, that could be a worse case scenerio. Hush yo mouth! LOL
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Quoting Bluestorm5:
wasn't it 48 knots just 5 minutes ago?
Flight-level.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting sigh:


I didn't color it intentionally. I think there's some kind of new bug in the forum software. I can't figure out how to make it NOT create random background colors, which is really annoying.

well i colored it by copying the highlighting code an pasting it
Member Since: November 13, 2009 Posts: 2 Comments: 728
Quoting WeatherNerdPR:
From stormCARIB:
Puerto Rico Update

Update from Caimito Alto, San Juan, Puerto Rico

Published: Sun, Aug 21 06:58 EDT
By Joan Santos
Good morning all,

We are now under a tropical storm warning and hurricane watch. Let's pray that the latter is just a precaution! Currently, the eye of the storm is about 341 miles away from the San Juan area and is moving toward the west at about 21 MPH. According to the National Huricane Center, the storm will continue to move west or west-northwest and motion is expected to slow. It looks as though it will intensify as it passes Puerto Rico and heads toward Hispanola.

About an hour ago, it was eerily quiet - the calm before the storm. As Irene approaches, it has become windy and very rainy with thunder in the distance. Visibility is way down as well.

The most recent rains have left many of the local roads with huge potholes while some have been partially washed away. We're hoping for the best here. In the meantime, we are prepared. We've moved our plants and patio furniture indoors and have cards and dominoes to entertain us should the cable go out.

Stay safe!

Joan
Reporting from Ocean Park, P,R:.Link
Very windy since last night, mostly cloud, but very hot, the humidity must be over 100%. No body is in the beach, the streets are unusual empty to be Sunday on a touristic zone. I am ready, i took water. My mom in the eastern central of the Island is ready too.
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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.

agreed
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Quoting sigh:
"we need those islands to do their job and protect south florida"



Wish I had time to keep browsing back and see who said that. To whoever originally said that: we need South Florida to do its job and protect culturally valuable places like New Orleans. Oh, wait, you don't like the sound of that? Really?

I hope it was a recent post and I can't find the original because he's be banned because that is so over the line. Wishing further disaster on Haiti is pure Evil (capital intended).

OK, back to my morning relief that chances are this baby ain't headed to the GOM.
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Quoting scCane:
Guys use radar when tracking the center it's much easier.

Link


Radar is actually terrible for tracking the center of weaker and developing systems. Can be very confusing. Especially that very short low quality loop.
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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
wasn't it 48 knots just 5 minutes ago?
Member Since: August 1, 2011 Posts: 28 Comments: 8075
3359. 900MB
Quoting OrchidGrower:
Watching the IR satellite loops and motion of the overall storm, the WNW-NW motion is clear in the last few hours. What are the odds Irene scrapes the north coast of Hispaniola rather than plowing the center -- or the odds she stays in water altogether?


I've been Northcasting this thing for the past 2 days (feel a bit vindicated) I'd say it has a chance.
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Is Irene's COC at 17/63.5?
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3357. KEEPEROFTHEGATE (Mod)

its easy i can even make it scroll
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Strongest winds being found right now. 42 knots.

133400 1753N 06147W 8428 01573 //// +150 //// 121049 051 042 011 01
Member Since: September 2, 2009 Posts: 130 Comments: 21194
3355. JRRP
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Quoting connie1976:


Thank you!
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.
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Quoting TampaSpin:


Right down the heart of Florida...and slightly West if not just off the West Coast......98L will help pump the ridge.


?
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3352. scCane
Guys use radar when tracking the center it's much easier.

Link
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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.
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I really wish they would get rid of the points in the forecast and just leave a cone! Everybody focuses on the point while in reality the whole cone has about equal chances, just ask the folks in Port Charlotte with
Hurricane Charley and the point was at Tampa, and that was on a short term forecast, on 5 days error is much bigger.
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Quoting scott39:
Where is your bias(gut) at Tampa with the track in 5 days?


Right down the heart of Florida...and slightly West if not just off the West Coast......98L will help pump the ridge.
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Watching the IR satellite loops and motion of the overall storm, the WNW-NW motion is clear in the last few hours. What are the odds Irene scrapes the north coast of Hispaniola rather than plowing the center -- or the odds she stays in water altogether?
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3346. ackee
where does recon put Irene CENTRE not does look it wobble slight south to me
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Irene seems to be on a solid west heading..any deviation of 1 degree north would put her in the D. Republic..Those steeering currents seem to suggest the storm just south of the coast or hugging it. Just my opinion...
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luigi

unless the dry air interferes with the development you can expect what we are getting..and then some.

stay safe

Dan
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3343. scott39
Quoting TampaSpin:


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.
Where is your bias(gut) at Tampa with the track in 5 days?
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Quoting sullivanweather:


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.


That's 40 miles north of the last center fix and would support what I think I see on radar...EDIT: oops, meant Sat imagery END EDIT...be very careful; always take what I "think" with a grain of salt :~)
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Quoting 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 FLWeatherFreak91:
I agree that the center is moving wsw.


Dont agree....moving west. Due west at a fast clip. Mid level clouds being pulled down give appearance of wsw or sw movement. You have to block those out as you watch the loop.
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ECMWF and GFS models.. are the 2 models to really look at... GFDL is decent out to 3 days once it gets the storm initialized correctly. Rest of the models are not worth looking at..
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Quoting barbamz:

Good morning! webcam st-barths
Wow. thanks for posting that. It's the next best thing to being there
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3337. Tampa77
Looks like we may need to enforce our company's business continuity plan later this week. We do have other locations throughout the US to include Charlotte, NC. From what I have seen this could possibly affect that area too. I wouldn't except Hugo type conditions in the area, but some of the runs are hinting towards tropical force winds. Possible? Looking to see what information I can use to better prepare our location to the north. Unfortunately, this dubious honor falls in my lap. Thanks!
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peaked at 48 knots (55 mph) while pasting strongest part of Irene. Plane is turning toward center, going through strongest part of Irene again.
Member Since: August 1, 2011 Posts: 28 Comments: 8075
3335. A4Guy
Interestingly, there is more spread in the models today than there was yesterday.
If you take away the UKMET, there is still a pretty narrow spread, overall, however. I expect we will see a flip-flop on either side of FL over the next few days...as it all depends on where the weakness really sets up on Weds/Thurs. The Florida peninsula is not very wide. and with a storm approaching at such an oblique angle, a slight shift in track can have big implications on landfall location (think about Charley and how he was riding nearly parallel to the coast).
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Irene has the look of a system ready to ramp up this morning. The once NE most convection is filling in and wrapping to the n-ne. Could be an interesting day for intensity; both in the storm and on the blog...lol
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Quoting stormpetrol:
Irene moving due west now.Center basically at same longitude

I wouldnt say due west yet but yes its on track now
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3331. barbamz

Good morning! webcam st-barths
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3330. 34chip
I live in Key West really not sure what to think what we might or might not get.
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Quoting sullivanweather:


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.


Sulli......do you think 98L will help the Ridge build in on its back side some toward Irene.........i just noted it a bit earlier.
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Quoting sullivanweather:


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.


Yeah, and it looks like it's moving due W or the slightest bit N of due W.
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Quoting TampaSpin:


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.
Yep. We better keep two eyes on this storm, Tampa.
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Guys this is why we don't assume anything this far out, heck for all we know in 2 days the model group will be over Mobile AL, I'm joking, but just pointing out that things can change a lot this far out still.
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Irene moving due west now.Center basically at same longitude
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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
Looked on Google Map. Saint Martin is in northern edge of Irene. I think stronger winds is coming your way. Good luck with Irene and be safe!
Member Since: August 1, 2011 Posts: 28 Comments: 8075
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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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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