Category 2 Irene Approaches The Bahamas

By: Dr. Jeff Masters , 7:51 AM GMT on August 23, 2011

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As of 2am EDT, Hurricane Irene was located at 20.1N, 69.7W, 135 miles southeast of Grand Turk Island. It was moving west-northwest at 12 mph with maximum sustained winds of 100 mph, making it a Category 2 storm on the Saffir-Simpson scale. Irene has a minimum central pressure of 978 mb. Hurricane warnings have been issued for the northern coast of the Dominican Republic from the Haiti board to Cabo Engano, the southeastern and central Bahamas, and the Turks and Caicos islands. Hurricane watches have been posted for the north coast of Haiti from Le Mole, St. Nicholas to the Dominican border and the northwestern Bahamas. Tropical storm warnings are in effect for all of Haiti and the southern coast of the Dominican Republic from Cabo Engano to Santo Domingo.

5AM Update
As of 5am EDT, Hurricane Irene was located at 20.3N, 70.1W, 105 miles southeast of Grand Turk Island. It was moving west-northwest at 12 mph with maximum sustained winds of 100 mph, keeping it a Category 2 storm on the Saffir-Simpson scale. Irene has a minimum central pressure of 978 mb.

Figure 1 shows that Irene is maturing into a vigorous storm, with apparent waves in the western edge of the cirrus outflow.


Figure 1 IR satellite view of Irene taken at 135AM EDT, August 22, 2011

Track Forecast

Irene is forecast to move to the north-northwest, passing over all of the Bahama islands by Thursday evening, at which points it starts curving to the north. Irene is forecast to make landfall in the US near Wilmington, NC Saturday evening. However, it is important to note that this is not a definitive forecast, the average forecast error for day 5 is 250 miles. The timing of Irene's recurvature depends on how quickly several small troughs of low pressure in the Northeastern US move to the east. After Saturday, Irene may pose a threat to the mid-Atlantic coastline and locations further north, but it is too early to make a skillful forecast for those regions.

NHC is forecasting for Irene to become a major hurricane (winds faster than 110 mph), within 24 hours, then reaching peak intensity at 130 mph (Category 4 storm) by 8pm EDT Thursday evening.

Forecast models and adaptive observations
The different forecast models are in rough agreement until Irene nears the Carolinas. The dynamical hurricane forecasting models, GFDL and HWRF, have Irene making landfall near Charleston, SC. NGFDL (a variant of the GFDL that uses NOGAPS for background conditions) has landfall near Morehead City, NC, and the GFS has Irene crossing the Outer Banks. The UKMET forecast track splits the difference, placing Irene near Myrtle Beach, SC at landfall.

To reduce the model spread, and improve the track forecast error, the NOAA Gulfstream IV and an Air Force WC-130J have been flying dropsonde missions north of Irene. A dropsonde is an meteorological instrument package dropped from a plane that can tell you the vertical profile of temperature, pressure, moisture, and winds. By flying these missions, the dropsondes can improve all of the numerical weather prediction models initial picture of the atmospheres, which improves the forecast. Also, NHC has asked NWS offices in the southeastern US that launch weather balloons to do so every 6 hours instead of the normal 12 hour frequency.


Figure 2 Official track forecast of Irene as of 2am.

5AM update
The 00Z ECMWF forecast is available and Figure 3 shows the maximum wind speed over the next week for the eastern coast of the US. Green indicates tropical storm force winds, while yellow and orange are hurricane-force winds. The important thing is not to fixate on the predicted landfall location, but to see that Irene's winds will affect areas far away from landfall. The GFS, not shown, agrees with ECMWF that Irene will have a large area of tropical-storm force winds associated with it.

Figure 3 Maximum wind-speed in mph from the 00Z August 23 ECMWF forecast for the next week.

Impacts

In the immediate future, Irene is expected to have a significant impact on the Bahamas and surrounding islands. Hurricane force winds are forecast to reach the southeastern Bahamas and the Turks and Caicos sometime this afternoon or evening. These locations can also expect 5-10 inches of rain. Three to six inches of rain are forecast over northern Hispaniola, with isolated areas receiving up to 10 inches. This could lead to flash flooding and mudslides in mountaineous terrain. NHC is predicting a storm surge of 9-13 feet above normal tide level for the southeastern Bahamas and the Turks and Caicos.

Outside of the islands immediately impacted by Irene, it is my judgement that everybody living on the eastern coast of the US should monitor Irene and review their hurricane preparations over the next few days.

Dr. Masters will have a new blog entry this morning, and Angela Fritz will be covering the afternoon. I'll be back on third shift tonight.

Thanks for reading,

Dr. Rob Carver

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Quoting Hurricanes12:
Honestly, the true beauty of meteorology is attempting to forecast the near impossible and waiting for it to happen. Basically, everyone will be incorrect sometimes and that's normal. Something you would never understand, howtheweater.

I have been trying to guess these things since the late 90's. MAYBE i got 3 right in all these years.
I leave it up to the NHC. OH good morning to all
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Keeper- I found a lugensquash in the garden last week- it was rotten and full of worms

g'morning all- coops- good to see you, now I am hungry, too

east east east
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woke up late or early this mornig and back up again. not only me lots of other bloggers too. nothing like having a cyclone approaching. ran the ir looks as if she is crawling up the edge of hispanola
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You can see a bit of her CDC.
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Quoting charlottefl:


Nope, still open to the S-SE, probably won't happen till she clears Hispanola, it's disrupting inflow into the system.



Looks like a slight west jog to me anyone else agree???
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Quoting BigToe:
@159. Please quit yelling. There's no need for the all caps, OK? Have a nice day.
Don't feed the trolls...
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My concern with the talk of recurve is this.. The weakness may not be strong enough for a full recurve resulting in the storm resuming a more northwesterly motion once the trough lifts out. The ridge may build westward and steer the storm into the coast of North or South Carolina. I think that is where the NHC is at this point. They are not confident that this storm will recurve and until Irene begins a northeastward motion well away from the coast, I don't believe they will change the cone away from NC/SC. Case in point, Hurricanes Isabel and Hugo.


HURRICANE ISABEL 2003

Isabel was forecast to miss the US Coast and recurve out to sea, but it struck the Outer Banks before moving inland. And we know what that did to the Hampton Roads area. Just ask Mike Seidel.

Hurricane Hugo had a similar motion after beginning to curve northward and then turned back toward the northwest striking Charleston SC.


HURRICANE HUGO 1989
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Quoting JrWeathermanFL:
Did Irene ever complete that eyewall? Sorry, I went to bed. lol


Nope, still open to the S-SE, probably won't happen till she clears Hispanola, it's disrupting inflow into the system.

Member Since: December 18, 2006 Posts: 7 Comments: 2685
@159. Please quit yelling. There's no need for the all caps, OK? Have a nice day.
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Quoting JrWeathermanFL:
Did Irene ever complete that eyewall? Sorry, I went to bed. lol
Still looks partial on microwave. Possibly due to land interaction.
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That's one massive wind field.
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Did Irene ever complete that eyewall? Sorry, I went to bed. lol
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Bad for northern DR it's just sitting off coast expanding and probably dumping lots of rain.

Haiti not getting it as bad fortunately.

Link
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Quoting charlottefl:


8AM Maybe a little before. They're probably running now...


thanks...in that case back to bed for awhile
Member Since: August 14, 2007 Posts: 0 Comments: 535
Honestly, the true beauty of meteorology is attempting to forecast the near impossible and waiting for it to happen. Basically, everyone will be incorrect sometimes and that's normal. Something you would never understand, howtheweater.
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Quoting farupnorth:



Replace my "trough" with "shortwave trough" and I think we see the same pattern, except I think she will be further North and feeling it more.


She is just really creeping along right now. It's why I am currently having a hard time completely throwing out the GFDL/HWRF consensus. We just have to wait and see as always. Hopefully today's 12z runs will come in to better agreement.

I will say that systems traveling in this direction usually end up in NC though.
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Quoting SCwannabe:
when will the next round of model runs be completed?


8AM Maybe a little before. They're probably running now...

EDIT: Ok, maybe not quite just yet.. Should be soon tho..
Member Since: December 18, 2006 Posts: 7 Comments: 2685
You people here have no idea how good it is to have a voice of reason to listen to. I have reminded all my friends to come here for info and not watch the panic-mongerers on the various TV channels.
Keep up the great work.
Back to lurking
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when will the next round of model runs be completed?
Member Since: August 14, 2007 Posts: 0 Comments: 535
SJ - get to class - I'll have the sideboard up and running earlier tomorrow.

Choose your menu now, LOL and I'll see if my pantry will support it. :)
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Quoting Hurricanes12:
Does anyone know what direction she's heading? It looks like she's going a bit northwest at the moment on radar.


@290 slowly
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Quoting howtheweather:
THIS SIRE HAS ALWAYS BEEN A JOKE AND ONCE AGAIN THIS STORM HAS PROVEN THAT ONCE AGAIN WRONG WRONG WRONG SO WHERE IS IT GOING THIS HOURS ANY CLUE LMAO IDIOTS


Moms calling, back to bed.
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Quoting Hurricanes12:
Does anyone know what direction she's heading? It looks like she's going a bit northwest at the moment on radar.


You have to take averages over a 6 hour period to get a true motion, hurricanes don't travel in a straight line. Otherwise you're gonna get a whole bunch of different directions in the short term.
Member Since: December 18, 2006 Posts: 7 Comments: 2685
#143

Cheer up! maybe the next cyclone will pass over you.
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what a lugensquash this am
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Quoting StormJunkie:


The trough is already there. It is a shortwave that is supposed to reinforce the trough in the Thursday time frame that will be the one that pulls her out. According to a local met in our area that posted yesterday. That said, if she travels slower then it will take longer for her to feel the effects of the shortwave. Thus traveling further west before that happens.

Again, this is why the slower HWRF, GFDL, and even Ukmet models are further west than the faster GFS. At least this is my basic understanding of the setup and steering right now.



Replace my "trough" with "shortwave trough" and I think we see the same pattern, except I think she will be further North and feeling it more.
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Sorry Tampa Bay - in the busy season I don't cook to order - except maybe the eggs. The rest you have to grab from the sideboard. :)

Besides, no decent mangos up here to make fresh juice with.

Sure hope that shortwave intensifies. Feels a lot like this time last year - when I spent 3 days hoping Earl would recurve. Except I think Irene may be a lot tougher than Earl.....
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Does anyone know what direction she's heading? It looks like she's going a bit northwest at the moment on radar.
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Quoting StormJunkie:


The trough is already there. It is a shortwave that is supposed to reinforce the trough in the Thursday time frame that will be the one that pulls her out. According to a local met in our area that posted yesterday. That said, if she travels slower then it will take longer for her to feel the effects of the shortwave. Thus traveling further west before that happens.

Again, this is why the slower HWRF, GFDL, and even Ukmet models are further west than the faster GFS. At least this is my basic understanding of the setup and steering right now.

CW - I'm fueling up for Avionics class which I have to be at in about an hour. The rest of the crew will have to hold the fort down until morning.


Yeah, the trough is over the western Atlantic, so the more time she takes to get there the more time it has to lift out and allow the ridge to build in thus narrowing the weakness and flattening out the track to the W.
Member Since: December 18, 2006 Posts: 7 Comments: 2685
Quoting StormJunkie:


The trough is already there. It is a shortwave that is supposed to reinforce the trough in the Thursday time frame that will be the one that pulls her out. According to a local met in our area that posted yesterday. That said, if she travels slower then it will take longer for her to feel the effects of the shortwave. Thus traveling further west before that happens.

Again, this is why the slower HWRF, GFDL, and even Ukmet models are further west than the faster GFS. At least this is my basic understanding of the setup and steering right now.

Looks like it could be a close call here in CHS but most likely will skirt to the east-IMO
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Quoting KEEPEROFTHEGATE:


Interesting...LOL
Member Since: December 18, 2006 Posts: 7 Comments: 2685
Anyone wana grab some cracker barrel?
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WC-130 up in the air.
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Quoting KEEPEROFTHEGATE:
don't worry coopswife just like a bad case of the cramps he will pass and be nothing more than a stain on some toilet paper


LMAO!!
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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.