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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Good evening fellow Wundergrounders,

All my fellow Puerto Ricans a Hola to all!

Looks like an F5 (browser refresh) event is in order. Everything from the Islands to Florida, especially with the model consensus, is rattled.

Seems like this is the storm Emily missed... and what about that centre fix being a little higher?



I'm with Keeper on this one, we may get a higher centre fix at the 11
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Tropical Cyclone activity to date:(August 21st)
1933: 8 Named Storms
1969: 4 Named Storms
1995: 8 Named Storms
1998: 3 Named Storms
2004: 5 Named Storms
2005: 9 Named Storms
2007: 5 Named Storms
2008: 6 Named Storms
2010: 4 Named Storms
2011: 9 Named Storms

So as of August 21st, we are tied with 2005 For FIRST PLACE with 9 named storms, 1998 is last with 3 Named Storms...

Pretty impressive first half of the season, lets see if we can keep it up in the last half...
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Quoting fire635:
For the first time in several years... A storm has my attention. I live just north of Tampa on the Florida west coast. With Irene's size and her almost certain track towards the southeast... We are GOING to see effects here. It's just a matter of to what degree. A skirt up.Florida's west coast could potentially devestate us here but even if she slides up the east coast I believe her wind and especially her rain will make things bad across the entire state.... Including Tampa Bay. It's best to start getting prepared. This could very well be the reality check most people have forgotten in Florida.
Florida hasn't had a serious threat since Wilma(and Fay to some degree)
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Quoting TropicalAnalystwx13:
I don't like how things are shaping up for Florida and the East Coast (My area included)...



Same here in VA
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Quoting weatherguy03:


I agree. When the GFS and Euro are in pretty good agreement I take notice.


Have to agree there, and this morning they were almost locked together - Right where the NHC track is now coming into s. Fl.

They are the 2 heavy hitters, no doubt. Thanks for your updates, Bob!
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660. Relix
*ahem*

Yeah I meant that Irene's center could be further to the north than expected. :P!
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Quoting Bluestorm5:
Got it working now. Thank guys. Btw, is it limited to 5 members?
Nope.
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I think it's kinda ironic that Harvey exsist the picture and Irene comes in.Lol.
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For the first time in several years... A storm has my attention. I live just north of Tampa on the Florida west coast. With Irene's size and her almost certain track towards the southeast... We are GOING to see effects here. It's just a matter of to what degree. A skirt up.Florida's west coast could potentially devestate us here but even if she slides up the east coast I believe her wind and especially her rain will make things bad across the entire state.... Including Tampa Bay. It's best to start getting prepared. This could very well be the reality check most people have forgotten in Florida.
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Quoting lucreto:
Looks like Miami in the clear now looks like a Gulfport/Biloxi storm.


What makes you think that?
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Quoting Bluestorm5:
Got it working now. Thank guys. Btw, is it limited to 5 members?


No. More boxes will show up.
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651. Skyepony (Mod)
TRMM pass of Harvey near landfall. Click pic for quicktime animation. Catches the core nice at the end.
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Quoting NCHurricane2009:


I also think that Irene's center is further north...its gotta be around 15 N by now....


Sorry...I meant at least 15.5 N by now....
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Quoting stormwatcherCI:
LOL. What did I post ?
LOL!
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I don't like how things are shaping up for Florida and the East Coast (My area included)...

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Quoting Eyewall07:


This blog would be so much better if they would just take out the trash


And if the people who always complain about the trash, just wouldn't.
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It seems like a very tough call to say whether or not Irene will stay south of Cuba or possible graze or portions of Hispaniola and Cuba. There are reliable computer forecast models in both camps. The GFDL, UKMET,and the CMC in the southern camp and the GFS, ECMWF, and HWRF in the northern camp. The former camp certainly allows for more intensification of Irene and greater potential as atmospheric conditions and oceanic conditions are supportive of a Major Hurricane. The latter camp is a lot much more complicated; subtle movements of Irene, how much land it crosses over and for how long, will determine how much strengthening can occur before it impacts Florida. If we assume that Irene avoids land minimal as show on the ECMWF (the model I consider to be the most reliable)then the potential for a significant storm is greater than the GFS and HWRF who are in that same camp. Ultimately, it will really come down to how potent the trough is. The Skill Score of the 500mb heights shows the ECMWF and UKMET leading, adding to the difficulty in the forecast since these models are in opposite camps. All in all, everyone in Florida should be on their guard for this storm as there is a high potential for impact from this storm in one way or another. Taking into account the southern solution models, there should be around a medium potential for Louisiana.
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Hurricane Cleo was similar track in 1964 and formed on August 20 also.
If the tracks hold true we will be dealing with a strong TS to Cat 1-2 hurricane. This may be a big rain maker for SE Florida or whoever in on the "dirty" side NE quadrant of the storm.
http://www.stormpulse.com/hurricane-cleo-1964

Hurricane Cleo, 1964
Storm Lifecycle
A tropical wave strengthened into a depression on August 20, and was named Tropical Storm Cleo soon after. Cleo moved quickly to the west and strengthened into a Category 4 storm by the time it churned through the Lesser Antilles. The hurricane remained a Category 4 as it passed into the Caribbean, and moved just to the south of Hispaniola on August 24 - and then veered more to the north which brought a landfall on the tip of Haiti. The storm then turned to the north and weakened to a Cat 1 before it struck Cuba, but remained a hurricane the whole time over land. Cleo then brushed against Miami and the east coast of Florida as it weakened from a Category 2 hurricane to a tropical storm. Cleo killed a total of 217 people and caused serious property damage as it travelled through the Caribbean and into Florida, totaling $198 million (1964 dollars) in damage.
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Quoting Eyewall07:


This blog would be so much better if they would just take out the trash



sure would
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Got it working now. Thank guys. Btw, is it limited to 5 members?
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Quoting PRweathercenter:
do you mean Irene?


I also think that Irene's center is further north...its gotta be around 15 N by now....
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I did not say what event would cause the evacuation, just making an observation.

PS. have a nice season...Go Noles
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A track slightly west of hurricane earl is possibe?
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This worries me.

It's old, but still.
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Yeah, this doesn't help my uneasy feelings I already have here.... I am in Key Largo thanks!

Quoting Thrawst:
Check this out... it shows the eye of Irene passing over Key Largo, Florida at 11pm, August 25th, 2011... and then drastically picks up in winds with a change of direction. Found this really cool.



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Quoting ProgressivePulse:



I appreciate your concern. We'll be fine here, just worried about others that come to mind.
Let's all pray for the bloggers in harms way.....Hey that rhymed.
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Quoting weatherguy03:


UKMET model is right up there with the GFDL model and in the long range was one of our best models last season.


Weatherguy03, could I get the link to that chart, I seen it before in previous years but can't remember where. Thanks.
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Quoting weatherguy03:


UKMET model is right up there with the GFDL model and in the long range was one of our best models last season.

As of right now they are the ones that bring it further west to the Yucatan Channel. GFDL and UKMET.
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They need to finish that last stretch of 4 lanes on the Overseas highway between 1st and 2nd pass zones... still construction barriers, although much cleaner than a month ago

Quoting CaneAddict:


What makes you so sure there will be an evacuation?
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Quoting lucreto:
Looks like Miami in the clear now looks like a Gulfport/Biloxi storm.
Anywhere from Brownsville to Long island needs to watch this! Whatchu talkin bout!!
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Wow...the model agreement is starting to be pretty strong...



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Quoting Michfan:
Only time will tell where this is going. It has a done a great job of mixing out the dry air and moistening its own environment. Its large size helped itself on that front.
I think you're right. Size matters ...
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I remember that forecasters originally thought that 2005 was going to be a near average or slightly above average hurricane season.The same was said for this season.I guess forecasting how a season is gonna be is still pretty low.Even though 2008 was almost spot on.
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Once Irene is south of or over Hispaniola, we should pretty much have the track nailed down. Until then, it's going to be wishy-washy. As of now, Florida/Hispaniola/Cuba are at greatest risk.
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Quoting barotropic:


LOL!!
LMAO
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Quoting Huracaneer:

I stand corrected, still the GFS and ECMWF is where I would put my money (nice chart by the way), but it's way too early to pinpoint the track, although I am starting to get spooked.


I agree. When the GFS and Euro are in pretty good agreement I take notice.
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Quoting DontAnnoyMe:


That's it - you need a blog, but not necessarily an entry in it.

Bingo.
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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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