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 presslord:


Wow!! I guest authored an entry for Jeff Masters called 100 Days Which Changed So Much detailing our Ike relief efforts....amazing that was 971 days ago...


I went thru Ike in TX , Katrina in MS and others over the years and thank you for ytour efforts to help after the storms :o)
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If Irene's motion is still west, and is suppose to gradually become WNW, it puts PR in imminent danger. If she turns WNW it looks as though she will cross PR and possibly encounter the northern edge of DR. She would have to continue moving west for more than the next 48 hours to even come close to Jamaica(which is what the GFDL is suggesting). I know her convection is displaced to the NE, but the convection is already north of PR. With the center gaining latitude and possibly reforming even further north, I don't see any way of PR avoiding a close call with Irene. Just my opinion...
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Quoting TropicalAnalystwx13:
My projected track and intensity:



Check your mail...
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Quoting WeatherNerdPR:

Noticed that too. Crap.


Which agency made that statement about Puerto Rico....I don't see it in the NHC latest forecast....

...and the radar image IMO shows a storm already further north of the beginning of the NHC 11 PM cone...
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Quoting tropicfreak:


The US alone is long overdue.


Yeah, but Florida's even more overdue...
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Quoting wxhatt:
Quite the storm front headed towards PR. A bit of a rough morning ahead form them...


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Quoting TampaFLUSA:

Your in the Tampa area too?
Yeah
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Lots of uncertainties in the forecast. Here is a nice summary of some of the potential options from Tallahassee NWS in the early PM before a TS was declared:

NATIONAL WEATHER SERVICE TALLAHASSEE FL
316 PM EDT SAT AUG 20 2011

IN GENERAL EXPECT A DECREASE IN AMPLITUDE OF THE PATTERN THROUGH THROUGH MOST OF THE PERIOD...FOLLOWED BY AN INCREASE AGAIN TOWARD
THE WEEKEND...BUT WITH HIGH UNCERTAINTY AS TO THE SOUTHWARD EXTENT OF SIGNIFICANT HEIGHT FALLS. THE TIMING MAGNITUDE OF THESE CHANGES IN AMPLITUDE WILL BECOME CRITICAL BECAUSE THE MODELS CONTINUE TO
FORECAST A TROPICAL CYCLONE TO DEVELOP FROM A TROPICAL DISTURBANCE...CURRENTLY LOCATED EAST OF THE LESSER ANTILLES...AS IT APPROACHES CUBA AND THE BAHAMAS NEXT WEEK. A WEAKER TROUGH COULD ALLOW THE SYSTEM TO PROGRESS FURTHER TO THE WEST WHILE A DEEPER TROUGH COULD DRAW THE SYSTEM NORTHWARD MORE QUICKLY. IN ADDITION...THE SLOWER THE SYSTEM DEVELOPS...THE FURTHER WEST IT IS LIKELY TO TRAVEL BEFORE IT BEGINS TO FEEL THE EFFECTS OF THE TROUGH. SUFFICE TO SAY THAT WHILE THE MODEL CONSENSUS REMAINS QUITE GOOD IN INTENSIFYING THE WAVE AS IT APPROACHES CUBA...UNCERTAINTY REMAINS HIGH AS TO ITS EVENTUAL TRACK.

CAMP/GODSEY/DUVAL

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Quoting HoustonTxGal:
More useless trivia... It has been 1071 days since a hurricane hit the US. THe last one was Ike in 2008


Wow!! I guest authored an entry for Jeff Masters called 100 Days Which Changed So Much detailing our Ike relief efforts....amazing that was 971 days ago...
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Quoting P451:


That radar image shows a storm to me that looks like its heading toward the N Lesser Antilles...WNW over or Just S of Puerto Rico...again I feel that this will track along the N edge of the 11 PM cone in the short term...
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Quoting GTcooliebai:
Yep it has come to the point where Hurricanes seem foreign to us now.

Your in the Tampa area too?
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it should be noted that if she foolows the current forecast track the worst of the weather would be placed os south fl mainly dadecounty becuase it is on the easter side of the storm
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Quoting sunlinepr:


Llego la banda era Lavoe...

The main band now is Gran Combo... Que bueno es vivir asi...

Yeah, I know... It's been a while since I saw Gran Combo live.

It's starting to look like Irene wants to be the new lead singer in the band...
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1155. wxhatt
Quite the storm front headed towards PR. A bit of a rough morning ahead form them...

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Quoting CaribBoy:
A HURRICANE WATCH COULD BE REQUIRED FOR PUERTO RICO TOMORROW IF
THERE IS A SIGNIFICANT NORTHWARD ADJUSTMENT TO THE TRACK FORECAST


Looks like the NHC feels that the center may relocate further north...

Noticed that too. Crap.
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Quoting Tazmanian:
would t it be some in if we go too bed has a 50mph TS and wake up too a 882mb and 190mph winds in the AM



heh heh heh
I would like to see a storm get to 200mph but at the same time i dont, Irene has that supercane name to it.
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Quoting HoustonTxGal:
More useless trivia... It has been 1071 days since a hurricane hit the US. THe last one was Ike in 2008
Yep it has come to the point where Hurricanes seem foreign to us now.
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Quoting kmanislander:
See you all tomorrow. Have to rest up for my golf game
in the morning.
I think I'm going to sleep as well.
.
.
.
Good Night Irene.
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Quoting HoustonTxGal:
More useless trivia... It has been 1071 days since a hurricane hit the US. THe last one was Ike in 2008


The US alone is long overdue.
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Quoting Tazmanian:



i am rallyplaying that they keep moveing the track W they keep moveing it W it will save Haiti from mayjor catastrophic and deaths so more W in the track is good news for Haiti


Yes but looking at the system I cant help but wonder if we are going to see continued small jogs to the north. If the LLC stacks with the very pronounced MLC it will likely nudge another 3/4 degree north.
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Quoting MississippiWx:
The 11pm track would keep it pretty weak, at least for South FL.


Yes, but if the actual track moves a little more to the west, into the gulf and then skirts up the west coast, Fl could be in big trouble.
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My weather friend made the projected path, and I did intensity.

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More useless trivia... It has been 1071 days since a hurricane hit the US. THe last one was Ike in 2008
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Quoting HoustonTxGal:


My birthdays go in reverse now.. I get younger every year! WOO HOO


I just hit that age too. LOL Going backwards now.
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Quoting BiloxiGirl:
To be honest.... the whole peak of hurricane season just gets on my nerves. Hard to make plans etc. My birthday is in September and I can't tell you how many birthdays have been rescheduled for these jokers. Annoying!


I feel you BiloxiGirl my brithday is August 29th, and my anniversary is Sept 1.
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would t it be some in if we go too bed has a 50mph TS and wake up too a 882mb and 190mph winds in the AM



heh heh heh
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Quoting MississippiWx:


It's difficult to ignore the UKMET/GFDL/CMC. The more eastern solution has the GFS/Euro/HWRF. It's going to be interesting to see which solution gets the first "big win" this year.
Yeah, just think if the GFS track pans out, since it was the first to jump on board with development of 97L, and has been showing a consistent track towards FL. give or take West Coast & East Coast, I might just have to buy it a case of beer for calling it right.
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Quoting DookiePBC:
WPTV just lead off the news with a "Tropical Storm Irene" title screen, complete with ominous music. I am going to run outside screaming for a few minutes. Y'all take care!! Stay vigilant!

If I stay vigilant does that make me a vigilante?
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Quoting MississippiWx:


I think you're far from out of the woods on this one. We'll see how it goes. Good luck in your golf game!


I agree. The woods are always lurking. I see this one between Jamaica and Cuba but lots of time to watch it.
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I like that latest discussion by Blake/Brennan.
It pretty much hit the main points in the forecast possibilities. For the average person who relies on the NHC as the beginning and end of the tropical situation they pretty much summed up what we've been talking about here for the last 8000 posts.
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Quoting Tazmanian:



i am rallyplaying that they keep moveing the track W they keep moveing it W it will save Haiti from mayjor catastrophic and deaths so more W in the track is good news for Haiti
but bad news for Cuba,Jamaica, and the u.s
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Quoting PcolaDan:


Wait! WHAT? You can reschedule birthdays? Well, hotdam, I'm rescheduling my next one for 2016 then. :)
I've been doing that for years!
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Quoting wxhatt:
I think the GFDL has been pounding the Red Bull again...



YOWZA thats what im talkin about!
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Quoting kmanislander:


Cone error ?? LMAO


I think you're far from out of the woods on this one. We'll see how it goes. Good luck in your golf game!
Member Since: July 15, 2006 Posts: 17 Comments: 10284
WPTV just lead off the news with a "Tropical Storm Irene" title screen, complete with ominous music. I am going to run outside screaming for a few minutes. Y'all take care!! Stay vigilant!
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Quoting nrtiwlnvragn:
Interesting to note that Miami and Grand Cayman have the same cumulative probability of TS winds.

MIAMI FL 34 X X( X) X( X) X( X) X( X) 3( 3) 8(11)



GRAND CAYMAN 34 X X( X) X( X) X( X) X( X) 6( 6) 5(11)


Cone error ?? LMAO
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Quoting Thrawst:


Just 10 mph, same category though. Either way, it will be potentially catastrophic for Haiti.



i am rallyplaying that they keep moveing the track W they keep moveing it W it will save Haiti from mayjor catastrophic and deaths so more W in the track is good news for Haiti
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Quoting gugi182:
could be our first hurricane of the season just southwest of the island of Puerto Rico. ....


A hurricane, so close to the south and with the attitude of not believing or experiencing one by many (13 years), could be something serious here...

For those who live In Ponce, la Guancha, will be history...
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The Leewards won't escape TS conditions in my opinion!
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Quoting PcolaDan:


Wait! WHAT? You can reschedule birthdays? Well, hotdam, I'm rescheduling my next one for 2016 then. :)


My birthdays go in reverse now.. I get younger every year! WOO HOO
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Quoting EastTexJake:


Always Vigilant!

Isn't that someone's motto?


Mad-Eye Moody in Harry Potter

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Quoting nrtiwlnvragn:
Interesting to note that Miami and Grand Cayman have the same cumulative probability of TS winds.

MIAMI FL 34 X X( X) X( X) X( X) X( X) 3( 3) 8(11)



GRAND CAYMAN 34 X X( X) X( X) X( X) X( X) 6( 6) 5(11)


Lol...Just a wee bit of uncertainty in the long term, eh?
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1123. wxhatt
I think the GFDL has been pounding the Red Bull again...

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See you all tomorrow. Have to rest up for my golf game
in the morning.
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Remember, this blog is for entertainment only.
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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.