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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2271. Patrap


Member Since: July 3, 2005 Posts: 429 Comments: 130486
2270. Ryuujin
Irene is starting to put her druthers on and it's not even DMAX. And I still feel that a W and then WNW movement is going to bode illl for the SE US. Ugh, a lovely and terrible sight to behold
Member Since: Posts: Comments:
Quoting FloridaTigers:
Just out of curiousity, when was the last time Miami was under a Hurricane Warning? Or even Hurricane Watch? Wilma in 05? I don't recall a watch for Ike.


2006 Ernesto SoFlo was under a Hurricane Watch.
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2267. 7544
may see a speacial update soon in regards to pr imo
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Quoting CaneHunter031472:
I prayed for Irene not to hit Mississippi and I think the heavens have smiled at me because for what I see, Mississippi so far seems to be in the clear. We just recovered or are still recovering from Katrina. Two new casinos and many malls have just opened and you can see great progress happening. We do not need another Hurricane period. I just pray now that Florida gets spared as well, or that at least it doesnt hit florida too strong. Hopefully the heavens will smile at me again. I hope this is a fish storm although I doubt it Florida is in the bullseye right now so time to prepare folks.
Kinda late for this to be a fish storm; it's going to hit the Leewards and possibly PR in the next 24 hours. Likely to hit the DR after that, and then either Cuba, the Bahamas, or both by mid week. So even if it doesn't devastate the US East Coast, it will have gotten its licks in....

Quoting Drakoen:
hmmm They put it at 16N. I'll take it. Better than extrapolated coordinates lol.
A bit easier to do because they have the Meteo-France Radars there?

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2265. Drakoen
Dr. Maue, what do you think of the NHC's coordinates compared to the apparent center seen on the radar imagery out of Martinique?
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Also we can't assume relocation to the north is occurring its a tropical storm, they are always often more disorganized as far as where the center is then they often look. Also keep in mind, that if it does relocate further north, that doesn't necessarily impact the long term forecast much. It really all depends on how the 2 highs and the weakness between them interacts 5 days from now, as well the effects of the incoming trough.
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Quoting Kowaliga:
Ok, would you call this "280 traj?"...



Not enough frames to say, but if you do long term averages off sat and radar it's fairly close, may be as much as 285, but I don't think any more.
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Quoting RyanFSU:
GFDL 00Z doomcast:



And Animation of Inner nest: Link


Exactly. Thanks for your website! I use it very often!
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Just out of curiousity, when was the last time Miami was under a Hurricane Warning? Or even Hurricane Watch? Wilma in 05? I don't recall a watch for Ike.
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2260. scott39
Quoting charlottefl:


It's less than 60 miles.
exactly and still headed W at 22mph.
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Well, DAMN!

Member Since: September 2, 2009 Posts: 130 Comments: 21194
2258. Ryuujin
Quoting FloridaTigers:


I think it would require yet another NW jog before resuming WNW for this to happen.
not really. A steady diet of true WNW will have it clip just the rather flat east edge of Hispanola and head her right over S/SE FL towards either recurve up the peninsula or into the GOM
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2257. Patrap
Member Since: July 3, 2005 Posts: 429 Comments: 130486
Quoting RyanFSU:
HWRF doomcasts:





It's not like the GFDL isn't a doomcast. Lol.

Member Since: July 15, 2006 Posts: 17 Comments: 10284
2255. RyanFSU
GFDL 00Z doomcast:



And Animation of Inner nest: Link
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Ok, would you call this "280 traj?"...

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2253. scCane
Euro 48 hours
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Quoting scott39:
Yes it reformed .7 degrees N more. Although it is still heading W at 22mph. So are we starting over at .7 N... of the new 5 day track? I would think that this is not that big of a swing E to put Fl. off the target and put it on NC.


It's less than 60 miles.
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2251. Drakoen
The 00z HWRF is pretty much east of Florida and the 00z GFDL is west of Florida. lol
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2250. scott39
Quoting scCane:
Euro 24 hours
Very close to the southern Puerto Rico coastline.....
A weak TS. I dont think its going to feel that N pull for awhile.
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This was the 00z GFS position in 24 hours...It's not terribly far from PR at this point, and that's without the center relocation factored in...We'll see if that makes a difference.

Member Since: July 15, 2006 Posts: 17 Comments: 10284
Ok I'm going freaking crazy now, when I left home to go fishing with my friends earlier, Irene was still 97L and it didn't appear it would probably be named for at leas another day, I come home and we have 50 mph Irene.... Holy crap this is crazy!!!

Sorry guys, just having a weather geek moment :)


Anyways, all I got to say is, if you live in Florida, don't panic, but Irene should get us thinking about preparing a plan for a hurricane impact, not just in case Irene threatens, but for the rest of the season as well.

If Irene say skirts the West Coast of Florida, we are talking about a very large tropical cyclone moving fairly slow, which would lead to massive amounts of rain. Honestly, a strong tropical storm or category 1 hurricane could be more beneficial than harmful for Florida. This rain season has come in solid and has helped to ease the drought in Florida. But prior to the frequent heavy the rains, the drought was so bad that even now, there is still more work to be done. One big soaking system on top of the rains we have had could almost completely erase the drought.

Just a thought.
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2247. RyanFSU
HWRF doomcasts:



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Quoting Ryuujin:


Not true at all, she could take a more WNW path north of Hispanola too.


I think it would require yet another NW jog before resuming WNW for this to happen.
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Eastern Hispaniola is a much more favorable area to cross as apposed to West/Central.

Member Since: June 9, 2007 Posts: 4 Comments: 15950
2244. scCane
Euro 24 hours
Very close to the southern Puerto Rico coastline.....
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2243. Ryuujin
Quoting MississippiWx:


That is a possibility for sure, and that's why I said a lot of questions are still waiting to be answered.


And it's one that I REALLY don't want to see repeated
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Quoting Patrap:

2km Storm Relative IR Imagery with BD Enhancement Curve



lookin classic cane there
Member Since: August 22, 2006 Posts: 2 Comments: 1988
2241. Ryuujin
Quoting FloridaTigers:


I think this is key. There's no way she DOESN'T cross atleast a large portion of Hispanola. She probably would've avoided time over the island before the relocation. This could seriously disrupt her intensifcation.


Not true at all, she could take a more WNW path north of Hispanola too.
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2240. scott39
Quoting MiamiHurricanes09:
Track changes only occur in full advisories (5 and 11, respectively). Will be interesting to see how the 06z plots handle the system with the new coordinates.
Yes it reformed .7 degrees N more. Although it is still heading W at 22mph. So are we starting over at .7 N... of the new 5 day track? I would think that this is not that big of a swing E to put Fl. off the target and put it on NC.
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Quoting Ryuujin:


Unless she heads north of the big islands and skirts over The Bahamas int o S Florida, which is scary because it conjures up thoughts of the storm a few letters down


That is a possibility for sure, and that's why I said a lot of questions are still waiting to be answered.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
2238. Ryuujin
Quoting MississippiWx:
The relocation to the north could also put Irene in a position to where she crosses most of the islands, killing her off. A lot of questions are left to be answered now.


Unless she heads north of the big islands and skirts over The Bahamas int o S Florida, which is scary because it conjures up thoughts of the storm a few letters down
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2237. gugi182
well i will try and sleep a little not liking the position of Irene i hope she doesn't moves northwest a little that would mean a lot closer to Puerto Rico
Member Since: August 3, 2011 Posts: 0 Comments: 178
Quoting MississippiWx:
The relocation to the north could also put Irene in a position to where she crosses most of the islands, killing her off. A lot of questions are left to be answered now.


I think this is key. There's no way she DOESN'T cross atleast a large portion of Hispanola. She probably would've avoided time over the island before the relocation. This could seriously disrupt her intensifcation.
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Irene is probably in a position to strengthen quickly now.

Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting gugi182:
the tropical storm streak of this year is over?


i think so gugi, i think so... soon enough
Member Since: August 22, 2006 Posts: 2 Comments: 1988
2233. JGreco
The factual thing that was told to me from Levi earlier in the day was if it was North of 16 @ 60 W it would be very difficult for this system to enter the Gulf. Great news for those residents (as my self) since the system would have immensely strengthen in the very warm water in the Gulf, bad news for those of you from the East Coast further North up the East Coast. Hopefully if the center truly re-developed that far North, it should track over a larger portion of Hispaniola keeping the storm fairly weak as it impacts the Eastern portions of the Florida Atlantic coast and to the North. But unfortunately those poor people in Haiti are getting another severe rain event from Irene. Geez when is their grief going to end.:0
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2232. 7544
itsw dmax time she likes this time of the night as she did last night stay tuned
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And before I go, those in the path of Irene - stay safe!
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Well gona have some sleep it looks like we in PR are ging to ride a Cat 1 tommorow will be a crazy day here has to finish preparation in the morning. Gnight!
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NHC...Irene reforma su centro mas al Norte...aun se espera se mueva en general hacia las Islas de Sotavento y P R...
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I guess I jumped the gun with Fran/Hazel like track... thought the rotation was further up north.
Member Since: August 1, 2011 Posts: 28 Comments: 8075
Quoting AllStar17:
Safe to say this cone is shot:


IMO...I agree...good night to all...stay safe if Irene will impact you in the next hours....

Member Since: September 15, 2009 Posts: 539 Comments: 3712
The relocation to the north could also put Irene in a position to where she crosses most of the islands, killing her off. A lot of questions are left to be answered now.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting MiamiHurricanes09:
00z ECMWF has initialized. Already 1˚ too south.



Models wont have the right coordinates until 06z
Member Since: June 9, 2007 Posts: 4 Comments: 15950
2223. 7544
Quoting washingaway:
AT 200 AM AST...0600 UTC...REPORTS FROM RADAR...SATELLITE...AND
SURFACE OBSERVATIONS INDICATE THE CENTER OF TROPICAL STORM IRENE
HAS REDEVELOPED FARTHER NORTH NEAR LATITUDE 16.0 NORTH...LONGITUDE
60.4 WEST. IRENE IS MOVING TOWARD THE WEST NEAR 22 MPH...35
KM/H...AND A MOTION TOWARD THE WEST-NORTHWEST AT A SLOWER RATE OF
SPEED IS EXPECTED DURING THE NEXT 48 HOURS. ON THE FORECAST
TRACK...IRENE WILL PASS THROUGH THE LEEWARD ISLANDS THIS
MORNING...AND MOVE INTO THE NORTHEASTERN CARIBBEAN SEA THIS
AFTERNOON. IRENE COULD APPROACH PUERTO RICO AND THE DOMINICAN
REPUBLIC ON MONDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 50 MPH...85 KM/H...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 48 HOURS AND
IRENE COULD BECOME A HURRICANE BY MONDAY.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 130 MILES...215
KM...MAINLY TO THE NORTH AND EAST OF THE CENTER.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB...29.71 INCHES.



des thia mean it may miss the moutains or spend more time in the bath to get stronger as all the models are showing a much stronger system now tia
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Quoting sunlinepr:


We have to wait for the Rabiza, offshore.... Then you decide... if you are in Metro area, La8, La Perla if you know any local there, La punta or Pine Grove... For pros Aviones or Tocones... Catapulta...


ponce man. this thing ... we just have to keep an eye out see what she does. shes gettin close and reforming and making it interesting.
Member Since: August 22, 2006 Posts: 2 Comments: 1988
i see the center now and it can really see it move W right now has the nhc has it
Member Since: May 21, 2006 Posts: 5091 Comments: 115505

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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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