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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This is definitely a bigger threat than Emily.
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Quoting StormJunkie:
Looks like the center should be almost due E of this buoy.


1009 mb. Should be interesting to see if it gets to 1006... as the forecast disc has central pressure.
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Quoting Gearsts:
I see wnw :/
WNW once she is south of Puerto Rico but just to the west of the islands is WSW.
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2818. WxLogic
Looks like the HH is having issues with the equipment. Have been getting messages but no data. I guess they must be testing/repairing things out on ground.
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Quoting mcluvincane:
She might even go north of of Hispanolia and avoid major land interaction which would be very concerning. Let's hope that does not happen


Sad to say this for the sake of the islands in the path; but very true. If she manages to ride N of DR/PR; it could be very bad news for the Bahamas and/or the east coast. Still a long way to go though and a lot of wait and see.
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Good Morning All. I see Irene is hard at work already.
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Quoting InTheCone:
6z gfs for your viewing pleasure, I guess. Even shows another CV storm at the end of the run, UGH!!

Put your coffee down and hang on to something while you watch, I really hope this doesn't happen.

Link


Amazing... puts a new contestant on the dance floor... a suggesting something quite sporty approaching the islands.

To be continued...
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She might even go north of of Hispanolia and avoid major land interaction which would be very concerning. Let's hope that does not happen
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Looks like the center should be almost due E of this buoy.
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*GULP*
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2809. Gearsts
Quoting stormwatcherCI:
Last night all the models were showing a wsw motion for a short time. BTW, Good morning. Here you can see the steering is wsw as soon as she fully enters the E. Caribbean.


I see wnw :/
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2808. bassis
Quoting WeatherNerdPR:
I doubt this is a 50mph storm.


Looks like they have the center pegged pretty good. Last few frames can really see the axis
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Quoting WxLogic:


It is still fighting some, but not as much... also land interaction would serve the purpose of the dry air at keeping it in check if dry air gets fully removed.




Agreed.

If she crosses Hispaniola over the mountains.. and then has to cross the rough part of Cuba (gets to south and west side of guidance)... she could be limping on the other side.

That was of course the conventional wisdom with the local mets here in S. FL last night.

If a center really gets established... and an eye feature gets a real foothold... it's gonna go a long way to figuring the role land is gonna play.

I think the models come Monday are really gonna tell the tale.
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2806. QMiami
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Located @ Dominica

What was strange ... and I have no scientific way of backing this up ... is that I could hear the winds ... but a general background noise far away. Whilst here was very calm.

I see on that Guadeloupe radar that the storm's southern boundary passed over the Saints ... literally 20 miles from here ... so maybe I was right.

We have no industry and no cities and nobody works on a Saturday night ... we go to the top of the hill on New years Eve and watch Guadeloupe's fireworks to give you an idea of closeness.

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5 am cone worries me. I can go through a storm, but can Haiti survive a Hurricane of this size?
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Sorry Pete if my sense of humor is lacking this morning. No harm intended! Emergency Management people are totally in the here and now, as you very well know, ha!



Irene is a little bit too close for comfort for those of us along Florida's east coast.
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Last night all the models were showing a wsw motion for a short time. BTW, Good morning. Here you can see the steering is wsw as soon as she fully enters the E. Caribbean.


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6z gfs for your viewing pleasure, I guess. Even shows another CV storm at the end of the run, UGH!!

Put your coffee down and hang on to something while you watch, I really hope this doesn't happen.

Link
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Quoting NICycloneChaser:


Wherabouts? If you mean the big clear area on the west, it's a wedge of dry air. It does seem to be trying to form an eyewall near the centre of the convection though.
I'm referring to the area near the centre.
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Quoting USAFwxguy:
Wow convection sure displaced from center this morning (bulk of convection)

Large storms take their time to consolidate.
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2797. QMiami
Quoting NICycloneChaser:


The 06Z GFS does everything but avoid Florida.


was referring to that specific chart from WU. I know the models will go back and forth for a bit. just hoping it doesn't come my way but it looks like some effects might
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Quoting WeatherNerdPR:
I doubt this is a 50mph storm.

Me either. more like a 60mph storm.
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2794. WxLogic
Quoting whepton3:


Sure did beat the dry air entrainment.

Today will be interesting.


It is still fighting some, but not as much... also land interaction would serve the purpose of the dry air at keeping it in check if dry air gets fully removed.

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Quoting MoltenIce:
Is that an eye?


Wherabouts? If you mean the big clear area on the west, it's a wedge of dry air. It does seem to be trying to form an eyewall near the centre of the convection though.
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Quoting MoltenIce:
Is that an eye?

I just woke up, and it's cloudy and cold. Can't tell if it's an eye.
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Quoting WeatherNerdPR:
I doubt this is a 50mph storm.
Is that an eye?
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Quoting MississippiWx:


Did Charley run the length of Eastern Cuba, over the mountains and then make landfall in FL? I don't think so...there's a MUCH different solution when you run over the mountains over Eastern Cuba...

Charley:

Donna of 1960 took a similar route, but was far stronger post-Florida and along the coast. I guess it was moving faster. Charley brought A LOT of rain to my hometown of Seaside Heights, New Jersey (yes home of 'Jersey Shore', everybody asks). It was around the 14th or 15th of August 2004. It POURED for hours!
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Quoting NICycloneChaser:


The 06Z GFS does everything but avoid Florida.



please post
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2787. WxLogic
Quoting QMiami:


did the center relocate or jump north


We'll see soon once we get the HH to arrive to the center. Assuming it doesn't run into any problems.
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I doubt this is a 50mph storm.
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Quoting jeanri2000:
Question if the models are now taking it away from Florida with the exception of the two western outliers why hasn't the cone shifted more to the right?


Models have a pretty wide spread... and lots of possibilities yet to be played out.

Wide variance in track at the 4 and 5 day mark... and this was one of the runs.

They may move it around a bit.. but FL is still at risk.
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2783. WxLogic
Quoting Chicklit:

Hi WXLogic. Looks like Irene has consolidated overnight. LinkShortWaveLoop

Do you think she's too far north to go through the Windward Passage? Or is that just an illusion?


I believe she'll be on track... at least that's what I'm seeing at this time, but I give room to some small fluctuation in location due to the eye wall attempting to get better setup. which is going to be a decent eye wall.
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Quoting QMiami:
Yesterday the models covered florida now they look they are avoiding it lol


The 06Z GFS does everything but avoid Florida.
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2781. QMiami
Quoting WxLogic:
Eye feature trying to develop around 17.9N 61.9W.

Models have trended some to the right due to the strength of Irene being a bit stronger than expected so able to fight of the building Bermuda High from E some but still impacting US.


did the center relocate or jump north
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Viz
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2778. WxLogic
Quoting whepton3:


Morning Logic... just getting on myself... 5A disc... center could be attempting to relocate 50NM north... do you think she now tries to get north of Hispaniola?


I believe it will be on track if not a tad to the N if there's a decent fluctuation in location due to eye formation.
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Quoting WxLogic:
Eye feature trying to develop around 17.9N 61.9W.

Models have trended some to the right due to the strength of Irene being a bit stronger than expected so able to fight of the building Bermuda High from E some but still impacting US.


Sure did beat the dry air entrainment.

Today will be interesting.
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I'm scared.
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Quoting weatherjr:
. CaicosRetiredSailor: According to the Guadalupe radar, you note the center moving due west or it have some component west-NW?
It's too ragged to tell with such a short loop
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2774. QMiami
she is supposed to be at 16.4 wow takes up a lot of real estate

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Morning all; I'm not going to say good just yet...

I was afraid last night that she might be trying to skip North of the islands...Hopefully this won't get too ugly.
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Quoting farhaonhebrew:
no hurricanes since George....1998... 13 years ...
D0n't for get Hortence, Cat 1,85mph sEPT. 10,1996, AND Jeaanne, 2004,70mph storm...
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Quoting WxLogic:
Good Morning...

Hi WXLogic. Looks like Irene has consolidated overnight. LinkShortWaveLoop

Do you think she's too far north to go through the Windward Passage? Or is that just an illusion?
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.