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 cloudburst2011:




I WILL SAY IT EVEN IF IRENE WERE TO TO STALL FLORIDA IS COMPLETELY OUT THE WOODS...IT WOULD EFFECT THE CAROLINAS IF THAT WAS TO HAPPEN BUT IRENE SHOWS NO SIGNS OF STALLING IN FACE THE STEERING CURRENTS HAVE BECOME MORE STABLE IN THE LAST 12 HOURS...



Not quite true, If Irene stalls, she could miss the trof and get caught under the ridge forcing her to move in a more westerly fashion. But she's not stalled at all. Also a stalling system could mean that it found the corner of the ridge and that it is starting to shift to a more northward trajectory.
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70 mph on open SE side... hmm. Pressure is still dropping.
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I swear the nest person to call IRENE a FISH STORM is going to have a bucket of crow thrown at you by ME! This ISN"T a Fish Storm because she already hit the isalnds in the eastern Caribbean and the Bahamas also are in serious trouble. All this talk of Florida and the Carolinas but no one is talking about Irene's first date partners in the Bahamas.

CAT 3-4 in the Bahamas=Disaster also=NO FISH STORM
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Quoting NICycloneChaser:
Time: 14:38:30Z
Coordinates: 20.5167N 70.9667W
Acft. Static Air Press: 691.6 mb (~ 20.42 inHg)
Acft. Geopotential Hgt: 3,010 meters (~ 9,875 feet)
Extrap. Sfc. Press: 976.4 mb (~ 28.83 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 326° at 4 knots (From the NW/NNW at ~ 4.6 mph)
Air Temp: 14.0°C (~ 57.2°F)
Dew Pt: 10.0°C (~ 50.0°F)
Peak (10s) Flt. Lvl. Wind: 8 knots (~ 9.2 mph)
SFMR Peak (10s) Sfc. Wind: 23 knots* (~ 26.4 mph*)
SFMR Rain Rate: 1 mm/hr* (~ 0.04 in/hr*)
(*) Denotes suspect data

so slight wobble to the west.
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1030. 7544
we got a west jog goin on
is that a eye ?
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Quoting Patrap:
IRENE Floater - RGB Color Infrared Loop

TFP's and ZOOM are active


Looks to be pretty much right on the forecast track...
Member Since: December 18, 2006 Posts: 7 Comments: 2685
1028. Buhdog
I don't understand the confusion. Katrina had an eye the whole time...it was just cloud filled till it was a cat 3. This is very easy to understand.

This won't make sense to many, but i am throwing out a new term "dub-stepping" this will be used when a hurricane wobbles. Anyone who has heard dub-step would get it. Most songs have a robotic sound. wobble wobble...

and with that, I think Irene just dubstepped west. :)
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Well looks like all the models are finally coming in agreement
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Quoting Bluestorm5:
Recon plane toward center from SE to NW. Last time they did that, they found 121 mph flight winds.


Recon turned towards southwest as they came into the centre. Peak flight-level winds of 67 knots in south eastern eyewall.
Member Since: August 10, 2010 Posts: 2 Comments: 1971
1025. Patrap
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Time: 14:38:30Z
Coordinates: 20.5167N 70.9667W
Acft. Static Air Press: 691.6 mb (~ 20.42 inHg)
Acft. Geopotential Hgt: 3,010 meters (~ 9,875 feet)
Extrap. Sfc. Press: 976.4 mb (~ 28.83 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 326° at 4 knots (From the NW/NNW at ~ 4.6 mph)
Air Temp: 14.0°C (~ 57.2°F)
Dew Pt: 10.0°C (~ 50.0°F)
Peak (10s) Flt. Lvl. Wind: 8 knots (~ 9.2 mph)
SFMR Peak (10s) Sfc. Wind: 23 knots* (~ 26.4 mph*)
SFMR Rain Rate: 1 mm/hr* (~ 0.04 in/hr*)
(*) Denotes suspect data
Member Since: August 10, 2010 Posts: 2 Comments: 1971
Recon plane toward center from SE to NW. Last time they did that, they found 121 mph flight winds.
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Quoting Patrap:
Why do you keep posting the same image over and over? Once is enough, unless it changes drastically.
Member Since: May 16, 2010 Posts: 0 Comments: 1455
1020. NJ2S
On a serious note....what can NYC expect from Irene? And what's the time frame? If she moves up coast will she pick up speed...?
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Quoting BahaHurican:
.

Mate! where are you located now?
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Almost time for the 11am advisory.
Member Since: August 18, 2011 Posts: 0 Comments: 994
Time: 14:38:30Z
Coordinates: 20.5167N 70.9667W
Acft. Static Air Press: 691.6 mb (~ 20.42 inHg)
Acft. Geopotential Hgt: 3,010 meters (~ 9,875 feet)
Extrap. Sfc. Press: 976.4 mb (~ 28.83 inHg)
D-value: -





Port of track just a smidge
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1015. dader
Quoting Patrap:
12z Early Cycle NHC model tracks
Irene
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)




Dynamic Models (More sophisticated models)





The 12z models are looking better for the entire East Coast.
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1014. HCW
90L model runs look a little wacky


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Quoting smartinwx:


The XTRP model is consistently pointing to New Orleans, but it's clearly an outlier.

someone taught me years ago (and ignore those who criticize you for mentioning it) that the x-trap is merely the course the storm would follow if there were no features to guide it, ie a trough or ridge.
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Quoting snotly:


STORMTOP OUT! ... I mean cloudburst2011...


Is this the same guy? Certainly sounds like him!
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1009. Patrap
IRENE Floater - RGB Color Infrared Loop

TFP's and ZOOM are active
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Quoting libertygirl:
I live in Key West, Fl and we are watching this carefully. Until we see a direct turn towards the North...it's positioning makes it appear that it could come straight up the "alley" and with that big "blob" hanging up off coast of FL/GA - I am wondering if that thing will push it down and track it into the "alley"? Waiting for Wed. afternoon ... on pins and needles.



Key West has only a 10% chance of getting minimal tropical storm force winds, and less than 1% chance of anything more than that. According to the official NHC forecast.
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Quoting Orcasystems:


You are a damn idiot...
Did you happen to notice its going to run over a fair amount of people long before then..


It isn't that he is an idiot, it is the fact that everyone seems to be missing that Irene is SLOWING DOWN and now is moving only 10 MPH towards the WNW
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Quoting MahFL:
One thing is for sure Irene is not going anywhere in a hurry, geeze !


No kidding!

The non perishables people bought for their preparedness kits will perish before it moves!
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Quoting Patrap:


That file image of Katrina is as it appeareed still East of Fla as a Tropical Storm,,it never created a Eye feature till into the GOM.,,as a Hurricane


Actually, Katrina hit Miami-Dade as a Cat1 hurricane
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Quoting cloudburst2011:




I WILL SAY IT EVEN IF IRENE WERE TO TO STALL FLORIDA IS COMPLETELY OUT THE WOODS...IT WOULD EFFECT THE CAROLINAS IF THAT WAS TO HAPPEN BUT IRENE SHOWS NO SIGNS OF STALLING IN FACE THE STEERING CURRENTS HAVE BECOME MORE STABLE IN THE LAST 12 HOURS...


This time of year, it good for everyone to be prepared and aware of tropical weather. Yes, it's unlikely for Irene to stray from her forecast but it won't hurt anyone to keep watch on her.
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Quoting Waltanater:
We've seen hurricanes do this before in the past...just keep moving on defying all models no matter what! This is my point exactly. Just by listenting to the weather people on TV I am not convinced about their confidence level in the models, even though they keep stating the facts which is the storm is still going wnw and hasn't turned yet...comments like, "we are all waiting now to see what it does" doesn't help the model's credibility.


As I previously explained, Hurricanes follow only one thing and it is the law of Physics. Their mission is to cool down the waters of the atlantic by removing the stored heat energy and move it to higher latitudes therefore they will always tend to move north because of Earth roational dynamics. Ridges stop them from doing this so when you see a hurricane moving west more than likely it is because to their norht there is a strong ridge steering them that way, but as soon as they find a weakness norht they go. This is the case here. The weakness is projected to be east of Florida way east of Florida may i say and that explain the track designated by the NHC. For it to do what you claim the ridge would need ot be west enough inside FL and the weaknes to be in the GOMEX. The trof would have to first be really weak and second pull out really fast for this to be possible. It does not seem to be the case this time, but It happened before.
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Quoting LightningCharmer:


'Don't think there ever will be a day when a blogger does not throw in the XTRP model panic joke.



It wont happen any more than when someone does mention it, someone wont actually call them on it.
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1000. Patrap
12z Early Cycle NHC model tracks
Irene
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)




Dynamic Models (More sophisticated models)



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Quoting cloudburst2011:




I WILL SAY IT EVEN IF IRENE WERE TO TO STALL FLORIDA IS COMPLETELY OUT THE WOODS...IT WOULD EFFECT THE CAROLINAS IF THAT WAS TO HAPPEN BUT IRENE SHOWS NO SIGNS OF STALLING IN FACE THE STEERING CURRENTS HAVE BECOME MORE STABLE IN THE LAST 12 HOURS...


What's with all the CAPS? And why do you believe this? Do you have any maps/charts/data to back up your theory? You know people come on here to be educated about tropical systems, making bold statements without back up isn't helping anyone. Also, btw there are people who live in the Bahamas and who WILL be effected by this storm.
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Quoting Orcasystems:


You are a damn idiot...
Did you happen to notice its going to run over a fair amount of people long before then..


LOL!
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Quoting CaicosRetiredSailor:
Morning,

Still no classic "outer bands" have come through Provo, grey and blustry.
I don't expect to be on here a lot, but will update when I can.


Dare I say we'll be keeping an eye out for those posts? ;-) Good to see you.
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ok so I am a bit skeptical of the latest computer model runs. I don't feel to at ease knowing they have shifted so far east now that you might as well start saying this storm will miss the US completely. I just don't feel comfortable with banking on the sharp turn with the location of current Irene.
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Quoting NICycloneChaser:


We all know. It's a joke.


'Don't think there ever will be a day when a blogger does not throw in the XTRP model panic joke.

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994. MahFL
One thing is for sure Irene is not going anywhere in a hurry, geeze !
Member Since: June 9, 2004 Posts: 0 Comments: 3358
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Quoting Matt74:
No. I was being sarcastic.
ok...lol
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Quoting quakeman55:

Then it will run into the Philippines, then Taiwan, China, pop back off and hit Japan, then move across the north Pacific as an extratropical cyclone and slam into the Pacific Northwest, move across the US and move off the coast of New England, then a ridge of high pressure will push it southward, regains tropical characteristics, then rebuilding ridge pushes it west into the GOM, bombs into a Cat 5 and slams into New Orleans.

How's THAT suit ya? LOL

Finally a forecast I can agree with!
So do you think it's moving West?
Seriously, I agree with the XTRAP model!

Sarcasm above for those that didn't get it.

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988. maeko
Quoting JGreco:


I feel ya. I'm supposed to fly out of Chas on Thursday night for DC, but I'm part of the FEMA damage assessment team for disaster. I have to figure out if I need to prepare to stay for major, prep family/pets for minor and go, or if Irene is gonna chase me up the coast. Driving me bonkers!
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Quoting Ninj4:

Seriously, XTRAP isn't a model. It's the current movement extrapolated.

Durr...we use it as sarcasm...
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Quoting PrivateIdaho:


It needs an I.Q. filter.
I think a civilized courtesy filter....
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Quoting Bluestorm5:
gater23, local radar is not a good proof... this storm got "eye", but it's not visible.

Visible image of Katrina shows it didn't have eye



Katrina did have an eye as it passed right over my house. Experienced that period of calmness and blue skies before the trailing edge of the "eye" came through.
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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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