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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111 hours out heading for south Florida while gaining strength
Member Since: July 31, 2011 Posts: 5 Comments: 888
GFS blows up Irene in the Gulf Stream.

Could happen with the right conditions.
Member Since: June 9, 2007 Posts: 4 Comments: 15920
Quoting MississippiWx:
She's going to have to have a large jump north to hit PR directly. That just doesn't seem likely. PR is going to be on the bad side though.



That sat. pic....using that pic...I see Irene may be centered as far north as 16N to 16.5N right now...maybe that is why I feel it could get very close to the south coast of PR...doing something like the NOGAPS shows in short-term....

....out of curiosity...do you see it centered around those latitudes....
Member Since: September 15, 2009 Posts: 492 Comments: 3688
996 mb storm toward Florida at 102 hrs out.
Member Since: August 1, 2011 Posts: 28 Comments: 8027
500mb steering layer at 99 hrs

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Quoting Grothar:


We do not evacuate for 1 thru 3. Just sit and scream until it is over. Mrs. Grothar hates when I do that. I would never stay for a 4 or a 5. That is a dangerous decision to stay. Very few structure remain in those conditions. We may laugh and joke about these, because it is a way of release, but they are not funny.


Ok, I have to ask.. you live in a state with the elevation of a ping pong table... why would you stay in anything above a CAT 1?
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1564. gugi182
Tropical Storm Irene looks like a monster!!!!.

2am Update is very important i will not be surprise to see this go North West than West.
Member Since: August 3, 2011 Posts: 0 Comments: 178
GFS through 96 is about 50 miles farther north than 18z, and also stronger.
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jog to the north...? again?
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1561. scott39
Quoting Patrap:
Been a few years since Ive had the pit in my stomach. Oh well move on and deal with it.
Member Since: June 13, 2009 Posts: 0 Comments: 6858
If a Cat 3 came into just north of Tampa Bay...i can't imagine what the City of Tampa would look like.....i don't think most could imagine how bad it would be.
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Overall, a slight northward shift in the GFS so far.
Member Since: July 15, 2006 Posts: 17 Comments: 10282
939mb hurricane in keys with the forecast trip of Irene??????? I mean WTF? iRENE MUST BE ABLE TO STRENGTHEN OVER LAND.
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emerging from the cuban coast in 99 hrs

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Quoting gugi182:
Is Tropical Storm Irene going more north than expected?


no
Member Since: May 21, 2006 Posts: 5091 Comments: 115234
1555. scCane
So far the track hasn't changed at all compared to the GFS's last run.
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Quoting victoriahurricane:
I'm sure this has already been answered multiple times, but where did Weather456 go? Did he just leave the blog?


Yes - wanted to spend more time with family & kids, etc.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Quoting trHUrrIXC5MMX:
any other scary model???

how in the hell can these models be spewing this crap????????????????
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99 hours out continuing a northwestward trek heading towards florida
Member Since: July 31, 2011 Posts: 5 Comments: 888
Quoting victoriahurricane:
I'm sure this has already been answered multiple times, but where did Weather456 go? Did he just leave the blog?


He's stopped by here every once in a while.
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1550. gugi182
Is Tropical Storm Irene going more north than expected?
Member Since: August 3, 2011 Posts: 0 Comments: 178
1549. JLPR2
Well this is interesting. Every winds report from the islands at 12am in WU is either Calm or variable. XD
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Quoting AllStar17:


Forecasting should not be a competition. If that is your forecast, that's fine. However, if another blogger has a different opinion, that's fine as well. Differing opinions and friendly debates should be found on forums like this.
+1000!!!
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Quoting Grothar:


Sorry, I used the German expression. I did not know that the connotation could be misinterpreted as such. I should have just written hmmmmm! Unless there is another nuance of the language which I may have inadvertently overlooked. Please feel to correct me if the idiomatic expressions are incorrect.


Well, I couldn't share the 1906 hurricane experience with you, so I chose to be obnoxious instead...

Sorry.

The large circulation is probably going to keep it from strengthening too rapidly... I'm no expert, but I hope I'm not wrong on that.
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I'm sure this has already been answered multiple times, but where did Weather456 go? Did he just leave the blog?
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No one knows where she will make landfall! The land interaction with Hispinola and Cuba is the key to the forcast and untill we see it then it is up in the air! Everybody settle down. PR on the other hand ___ Hunker down for a rough time. I want to see the latest data from HH before I even think of how strong the storm is! The forcast since yesterday is all over the place. Invest to a TS! She is strong and big we know that.
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1544. HCW
Quoting Grothar:


We do not evacuate for 1 thru 3. Just sit and scream until it is over. Mrs. Grothar hates when I do that. I would never stay for a 4 or a 5. That is a dangerous decision to stay. Very few structure remain in those conditions. We may laugh and joke about these, because it is a way of release, but they are not funny.


Would you stay for a Cat 3 that has the storm surge of a Cat 5 like Katrina ?
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87 hours out starts to take the bait and slips northward
Member Since: July 31, 2011 Posts: 5 Comments: 888
Landfall in Southern Cuba at 84 hours out.
Member Since: August 1, 2011 Posts: 28 Comments: 8027
1541. Grothar
Quoting trHUrrIXC5MMX:


How about another one like Ike, it was a cat 2 but very serious


We do not evacuate for 1 thru 3. Just sit and scream until it is over. Mrs. Grothar hates when I do that. I would never stay for a 4 or a 5. That is a dangerous decision to stay. Very few structure remain in those conditions. We may laugh and joke about these, because it is a way of release, but they are not funny.
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Quoting lucreto:
I will once again offer a self-imposed ban deal with whatever poster wishes to take me up on it... If the center of Irene makes landfall anywhere east of say the Miss/Al state line I will self-impose a ban on myself for the remainder of the Atlantic hurricane season. Otherwise whoever accepts my deal must impose a self-ban on themselves.


Forecasting should not be a competition. If that is your forecast, that's fine. However, if another blogger has a different opinion, that's fine as well. Differing opinions and friendly debates should be found on forums like this.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Last few images almost looks like it has formed a new LLC around 16.5N 59W

Link
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1538. Seastep
Quoting trHUrrIXC5MMX:


How about another one like Ike, it was a cat 2 but very serious


Doesn't happen here.
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Quoting Skyepony:
Windsat missed...It's messed up though. Look at it's pass of the Caribbean.. click pic & see the bottom of those two last swaths that end south of South America. Same mess up in those areas too.

windsat is what it is, that's a lot of wasted money.
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500 mb vort ht at 72 hrs. clear break in the ridge.

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For people just visiting the site for the first time, or maybe not familiar with WU Ground, you can access storm info about Irene by clicking on "Severe Weather" tab on top of page and then click on "Tropical and Hurricane."



It's best to do this fairly often as the projected path changes according to models, location of Irene's center, and other data that go into projected path/intensity forecasting.
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Quoting P451:
In case it was missed...

Well, good night.

_________
IMO, She's ready to intensify.

Watch her swallow up her surface circulation and draw it into the convection.



This action could cause a northerly jog as a result.

She already appears to be skipping north of the forecast points.

simple, but great! Thanks!
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1533. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128632
Quoting P451:
In case it was missed...

Well, good night.

_________
IMO, She's ready to intensify.

Watch her swallow up her surface circulation and draw it into the convection.



This action could cause a northerly jog as a result.

She already appears to be skipping north of the forecast points.




that what ive been sayin its on the verge of swallowing its llc and wrapping up nice and tight
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78 hours out c.o.c located between n.e Jamaica and s.e Cuba
Member Since: July 31, 2011 Posts: 5 Comments: 888
Interesting warm spot.....

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1529. GetReal
Quoting dfwstormwatch:

66 hours west jogging westward towards Jamaica



Jumping on the GFDL bandwagon????
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Quoting Grothar:


Sorry, I used the German expression. I did not know that the connotation could be misinterpreted as such. I should have just written hmmmmm! Unless there is another nuance of the language which I may have inadvertently overlooked. Please feel to correct me if the idiomatic expressions are incorrect.
I would not worry about a thing, sir.
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still between Haiti/Cuba at 72 hr out.
Member Since: August 1, 2011 Posts: 28 Comments: 8027
Quoting PcolaDan:


To be expected when half the state is a dangling participle. ;)


Yeah, it's like Florida is a breakwater for the rest of the Gulf of Mexico.
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Quoting Grothar:


Thanks a heap, Orca. You guys should go back to thispst #1358 and enlarge it and see what Orca did with my name. Geez, some buddy you are. :)

Quoting Orcasystems:


hey... I just post them... its the models that run them :)

Thats where you live, its the model that put the Cat 4 in your yard

dats phunny.
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Quoting dfwstormwatch:

60 hours out brief landfall/ land interaction on the western tip of the south thing that sticks out of haiti


penninsula
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in between haiti and eastern cuba at 66 hrs.

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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.