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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UNDER THE INFLUENCE OF A STRONG DEEP-LAYER RIDGE TO THE NORTH...THE
DEPRESSION CONTINUES TO MOVE RAPIDLY WESTWARD OR 270/18. THIS
GENERAL MOTION IS LIKELY TO CONTINUE DURING THE NEXT DAY OR TWO.
THEREAFTER...A WEAKNESS IN THE RIDGE OVER THE CENTRAL ATLANTIC
SHOULD CAUSE A GRADUAL TURN TOWARD THE WEST-NORTHWEST WITH A
REDUCTION IN FORWARD SPEED.

This is Dean. Notice that he was supposed to turn WNW after a day or two and he ended up tracking the whole way across the Caribbean to the Yucatan Peninsula. This is from the first advisory.
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Irene seems to be moving slightly South of Due West.....
Member Since: September 2, 2007 Posts: 178 Comments: 20443
Good morning everyone.I hope everyone in the path of irene remains safe and not a lot of damage to happen to them.I wonder if the two highs that are squeezing from the east and west are too strong to let Irene move too much furher North?Just wondering.I dont know a whole lot about this stuff but I couldnt see how it would.
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Quoting WeatherNerdPR:
Getting gusty as this approaches:
Yes getting the first effect too, here in the NW of Puerto Rico..as I begin to put my "tormenteras" to protect my glass windows, ...
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12z plots all over the place, but a few apparently have shifted towards the west. TVCN still over southern Florida, in line with 5a.m official track.

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Storwatcher can you post the link to the SWFWMD model map? Thanks.
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Ok guys. I live in Dominican Republic on the north east coast on a peninsula and was wondering if someone could give me a link for the models and which ones are the most predictable. Need to know if she is going more north or more south, either way it will be a lot of wind and rain. Thanks
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3211. MZT
Quoting barotropic:


The comment MZT makes is absurd as a general rule of thumb...the islands have a tremendous impact on hurricanes. Plenty of history supporting that. Of course their are exceptions such as georges.....

What I'm saying is that I've begun disgrading the assumption that the islands will have a major impact. In the last several years I've seen Dennis, Ike, and Gustav all go through Cuba and remain dangerous.

Large storms lose a CAT or two but stay organized and remain large.
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PR local news are not even talking about Irene as they should. my neighbors had no clue that it's gonna be close to us here in the southwest. now they are scrambling for supplies.
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3209. unf97
This system is beginning to remind me of Hurricane David in 1979, which I remember very well living here in Jax, where he passed about 40 miles just off the coast. David was a huge storm which intensified into a category 5 Hurricane on its approach to the Lesser Antilles. Hoever, it moved south of Puerto Rico and then turned NW directly over Hispaniola as a Cat 5. after that it proceeded to weaken down to tropical storm strength going over Eastern Cuba, but then emerged over the Bahamas to restrengthen back to Cat 2 strength, then turned N-NW to make landfall at West Palm Beach and continued to move north just offshore parallel the FL East Coast.

Now, hopefully God forbid Irene won't become a category 5 hurricane. But, It may take on a path similar to David's back in 1979. David's structure was so impressive in that the land interaction he encountered only marginally weakened him.

So, if Irene can continue to get more impressive with a structure being very well stacked and strengthens into a formidable tropical cyclone, then it is very possible she can recover quite quickly after land interaction, similar to David.
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Member Since: July 12, 2007 Posts: 0 Comments: 6049
Quoting StormJunkie:


It's not that they have a huge problem with land...It's the 4k-7k mountain peaks that are scattered across DR/PR & southern Cuba that are so disruptive to tropical systems. Forward speed through them may help a little, but sticking a 7000 foot wall up in to the airstream of a LOW level system is never beneficial to it.


Hati DM have a couple of 10,000 foot peeks.
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Quoting NavarreMark:
I'm thinking that the blob of chicanery known as Irene is going to go well north of the deforested mountains of Hispaniola.


That would be a worst case scenario for the SE.
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Confidence is growing that Greensboro, NC will see a lot of rain with future hurricane Irene. http://wxweb.meteostar.com/sample/sample.shtml?tex t=KGSO&submit.x=0&submit.y=0
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I just posted this below!!!


OK, where is Irene going to go? The models have shifted East this Morning to the East Coast of Florida with some while some hug the West Coast of Florida. Here is my thoughts to consider. Irene is moving at over 20mph. This is a strong indication of how strong this ridge of high pressure is currently. Irene must slow down to move in a different direction. A player that should be considered is Invest 98L which breaks the ridge down some but, in doing so will pump a ridge to its west very fast with very warm air spinning around. Depending upon the strength of 98L will depend upon how strong the ridge that will control Irene. I currently don't really have much of an idea except that the entire state of Florida and now i would have to put Georgia and South Carolina into the mix as the models have moved to the East overnite. Caution tho, as models shift back and forth this far out vey often.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
3201. scott39
The NHC Cone still has a very wide spread. Dont just focus on the center track and models. Yes, we had a relocation center to the N by 60 miles, but this only effected the updated cone by very little. Unless something big happens in the slowing down of Irene and the timing of the trough, I would not expect BIG swings of outside the cone in either direction for at LEAST 72 hours. I think it would be safe to take the 3 day track of the NHC to the bank. IMHO
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3199. Mikla
Starting to take on the "typical" cyclone look...

animation link
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Quoting bocahurricane:


Nope, hubby is en route to NYC right now. I am in wait and see mode. My in laws live in a community near me and they said during the 2004/2005 hurricane seasons trucks of people looking for work were driving through their neighborhood offering to put up shutters so hopefully if needed I can find some or go to FAU


Let us know if u have a problem......
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Where I do not believe it is going to happen, the visible satellite and steering maps (up to mid levels) hint at the possibility of a southward adjustment.

700-850mb


500-850mb


400-850mb
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3195. aquak9
Wart, you have wu-mail, top of screen, red icon.

When was the last time the entire state of Fla was in a Cone'o'Doom? I know we're not there YET, but geesh. All we can do is sit here.
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Quoting stormwatcherCI:



BAMS and NHC seems to have shifted slightly west(left).

Is it me, or are those models (Except the NHC) initializing a bit to the south of Irene's center?
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Quoting MZT:
A fully formed hurricane can even cross cuba twice and just drop a CAT. I used to think the islands had more impact, but now I think they mainly matter for small tropical storms. Hurricanes just plow right on through.



Not really. There's always some disruption. Gustav was a cat 4 when it crossed the narrow Cuban peninsula. This short crossing was enough to 'topple the chimney' and Gustav never recovered from it. Made landfall in the US as a cat 2. Might have been a catastrophic 4 without that land interaction.


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Moving northward into the northeastern quadrant. Things should get interesting now...

125400 1603N 06105W 8429 01575 //// +180 //// 160026 026 019 000 01
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BAMS and NHC seems to have shifted slightly west(left).
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Quoting StormJunkie:


It's not that they have a huge problem with land...It's the 4k-7k mountain peaks that are scattered across DR/PR & southern Cuba that are so disruptive to tropical systems. Forward speed through them may help a little, but sticking a 7000 foot wall up in to the airstream of a LOW level system is never beneficial to it.


The comment MZT makes is absurd as a general rule of thumb...the islands have a tremendous impact on hurricanes. Plenty of history supporting that. Of course their are exceptions such as georges.....but even he was significantly effected. Of course where a hurricane passes over also is important. Western cuba, no problem. Eastern Cube spells trouble for Hurricanes including most of Haiti and DR.
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Quoting stillwaiting:
,seems to have verified i stated this about 8-9 hrs ago,i still think a minumil hurricane briefly makes landfall in se pr

SW PR, not SE.
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3188. Gearsts
Quoting Bretts9112:

funny cause it took a wobble or a turn wsw right now
ok then...lol
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Quoting barotropic:


Get those shutters figured out bocahurricane?


Nope, hubby is en route to NYC right now. I am in wait and see mode. My in laws live in a community near me and they said during the 2004/2005 hurricane seasons trucks of people looking for work were driving through their neighborhood offering to put up shutters so hopefully if needed I can find some or go to FAU
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3186. divdog
Quoting stormwatcherCI:



You should quote this too and not only the part that concerns Florida and the East Coast. He also says :

I strongly urge all of our Crown Weather friends across the rest of the Caribbean, the eastern Gulf coast, the entire Florida Peninsula and the US Southeast coast north to Cape Hatteras to closely monitor this system and go over your hurricane preparedness kits and think about what you would do in case that Hurricane Watches & Warnings are issued for your area. It should be strongly cautioned that further changes in the track forecast with Irene are likely and that a track into the eastern Gulf of Mexico with a hit on the western side of the Florida Peninsula is still very much possible.
makes a difference when u see it in the proper context. Thanks for posting all of it.
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Quoting stillwaiting:
looks
like a bit of sw sheer going on w
/irene,i expect a track just north of west for the next 6-12 hrs then west or even wsw ,possiby making landfall in se pr breifly tomorrow night or monday morning
,seems to have verified i stated this about 8-9 hrs ago,i still think a minumil hurricane briefly makes landfall in se pr
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Quoting WatcherCI:
Does anyone see a center wrapping more north 17.8 62?


It still isn't a perfectly organized system and while I am not sure it is likely; I've been wondering if another reform/form north may be possible.
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Have a nice day everyone, and those in PR stay safe. Time to hit the beach.
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3182. Relix
Quoting Bretts9112:

funny cause it took a wobble or a turn wsw right now


Its moving 280. The cloud movement around the center gives that impression but the overall system is still moving at that due west heading with a touch north.
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It's been gusting in my area to only 15mph for a while now. She's so close, yet so far...
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Quoting clwstmchasr:
From Crown Weather. He's on-board with the Eastern Shift. First time mentioning the Carolinas

There have been some relatively significant changes in the overall forecast with Irene since last night. The reason for these changes is that the combination of a weak upper level low pressure system located over the central Caribbean and the fact that the center has reformed further north in latitude due to deep convection firing thus causing the center to reform about 60 miles further north than it was last evening. This has caused the entire forecast track to change with Irene with most of the latest model guidance shifting further east and it would not surprise me to see some further shifts to the east away from a Gulf of Mexico track and towards a track that takes it up through the Bahamas and towards northeast Florida, Georgia and the Carolinas.



You should quote this too and not only the part that concerns Florida and the East Coast. He also says :

I strongly urge all of our Crown Weather friends across the rest of the Caribbean, the eastern Gulf coast, the entire Florida Peninsula and the US Southeast coast north to Cape Hatteras to closely monitor this system and go over your hurricane preparedness kits and think about what you would do in case that Hurricane Watches & Warnings are issued for your area. It should be strongly cautioned that further changes in the track forecast with Irene are likely and that a track into the eastern Gulf of Mexico with a hit on the western side of the Florida Peninsula is still very much possible.
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Does anyone see a center wrapping more north 17.8 62?
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Quoting Gearsts:
Well i am using radar and clearly shows a wnw movement.

funny cause it took a wobble or a turn wsw right now
Member Since: June 22, 2010 Posts: 0 Comments: 140
12z BAM models have shifted to the East as well. I would expect the global models to stick to the more eastern track with the 12z runs based on that.
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Quoting aquak9:

(passes coffee to Blue, sugar only)
thanks.
Member Since: August 1, 2011 Posts: 28 Comments: 8028
Quoting KeyWestwx:

That's exactly what happened with Wilma.
After her storm surge flooded 1/3 of the island of Key West, Wilma jaunted over to Miami/Fort Lauderdale, keeping and even gaining strength from the warm Everglades waters. A buddy of mine in Ft L lost electricity for 2 WEEKS after she hit! 1000's of vehicles in key west were destroyed and many homes had 5 feet of water in them


we were out of power for almost 2 weeks. At the time I was living in a condo on the Intracoastal in Boynton Beach. I remember the back side being worse then the first.
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3174. Gearsts
Quoting divdog:
funny that the entry right after yours says wsw. gonna be interesting in here today.
Well i am using radar and clearly shows a wnw movement.
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Quoting MZT:
A fully formed hurricane can even cross cuba twice and just drop a CAT. I used to think the islands had more impact, but now I think they mainly matter for small tropical storms. Hurricanes just plow right on through.


It's not that they have a huge problem with land...It's the 4k-7k mountain peaks that are scattered across DR/PR & southern Cuba that are so disruptive to tropical systems. Forward speed through them may help a little, but sticking a 7000 foot wall up in to the airstream of a LOW level system is never beneficial to it.
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Quoting Mikla:
Latest Intensity:

The LBAR seems optimistic.
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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.