Hurricane Irene Approaches the Bahamas

By: Dr. Jeff Masters , 7:42 AM GMT on August 24, 2011

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As of 2AM EDT, Hurricane Irene was located at 21.3N, 72.6W, 400 miles southeast of Nassau. It was moving west-northwest at 9 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 966 mb. Hurricane warnings have been issued for all of the Bahamas and the Turks and Caicos Islands. Tropical storm warnings are in effect for Haiti from Le Mole St. Nicholas to the Dominican Republic border.

Satellite Views
Figure 1 shows that Irene has a large eye visible in infrared imagery, (26 miles across accoring to a report from the Hurricane Hunters at 130AM) with well-defined outflow cirrus bands. Tuesday evening, TRMM, NASA's tropical research satellite, flew directly overhead Irene, getting a radar scan of the storm using it's downward pointing radar, shown in Figure 2. It is immediately apparent that Irene has well-developed bands of rain showers, with strong storms present in the eyewall.


Figure 1 IR satellite view of Irene taken at 113AM EDT, August 23, 2011


Figure 2 TRMM radar overpass of Irene at 713PM EDT, August 22, 2011. Image courtesy of the Naval Research Laboratory

Track Forecast

Irene is forecast to move to the northwest, passing over all of the Bahamas by Thursday evening, then curving to the north. Irene then makes landfall in the US near or at the Outer Banks Saturday afternoon, then traveling along the mid-Atlantic coastline of the US. After Saturday, Irene may pose a threat to Long Island and the New England coastline. However, NHC is quick to remind us that the average forecast error for day 4 is 200 miles, so don't stop your hurricane preparations if you aren't in the immediate area of landfall. It is also important to note that the windfield of Irene is expected to be large, affecting areas distant from the immediate track of Irene's center. Tropical storm forces winds are expected to be found out to at least 150 miles away from Irene's center on Friday afternoon.

NHC is forecasting for Irene to become a major hurricane (winds faster than 110 mph), within 24 hours.


Figure 3 Official track forecast of Irene at 2AM EDT.

Forecast models and adaptive observations
The different forecast models are in fairly good agreement about Irene's track through the Bahamas and along the east coast of the US. The GFDL, a dynamical hurricane forecasting model, which had been a western outlier from the other models is now agreeing with them. When a set of weather models using slighly different initial views of the atmosphere and slightly different ways of simulating how the atmosphere works all agree on a forecast, then meteorlogists tend to believe that the forecast is more likely to occur. The 00Z GFS and ECMWF (wind swath shown in Figure 4) forecasts are nearly identical, which furthur boosts forecaster confidence.

In the 11PM forecast discussion, the NHC forecaster praises the NOAA Gulfstream IV (aka Gonzo) for providing infomation about the atmosphere around Irene that will influence it's track. Looking at the plan of the day valid for today, it will be a busy day for airborne reconnaissance. Three flights for the Air Force hurricane hunters, two flights for the Gulfstream IV, and two flights for NOAA 42, a WP-3D (aka Kermit).


Figure 4 Plot of the maximum sustained winds in mph over the next week from the 00Z ECMWF forecast.

Impacts

In the immediate future, Irene will have a significant impact on the Bahamas and surrounding islands. Hurricane force winds are ongoing over the Turks and Caicos islands and southeastern Bahamas. These locations can expect storm surges that are 5-8 feet above tide levels. The northwestern Bahamas can expect hurricane force winds Thursday, and storm surges that are 7-11 feet above tide levels. The Turks and Caicos islands and all of the Bahamas can expect 6-12 inches of rain over the next two days.

I still think people living along the east coast of the US should closely monitor Irene and review their hurricane preparations. Irene will be a large storm, impacting areas far from the storm center track.

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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1278. HCW
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The outer band is starting to sweep over Cuba...wide stretch from the East into Central. Wow!
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Quoting nash28:


You're using the wrong steering layer. You want to use the 300-850mb layer for Irene right now.


Can you please post that steering layer map if possible-thanks. Where do you find the steering layer maps?
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You talk about steering layers. Look at this one, if she were to continue to strengthen it would put her in the 940 mb and below this would be her steering layer.

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Quoting reedzone:
I have friends and family on Long Island who are not taking this storm seriously, brushing it off like it's another Earl. If you live on LI, this is historic, we have never seen a storm like this since Hurricane Gloria in 1991. Please, don't shove this one by and start making ur evacuation plans, Long Island is at sea level and when you have a storm that was a Category 4, the surge can be catastrophic. PLEASE, head my advice and prepare for Irene. This isn't an Earl where it recurves at the last minute, the highs are set in place and the weakness will lead it right up the coastline. A category 2 Hurricane is set for landfall as of the 11 a.m. track.


Wishcaster...
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here is the correct map

EDIT

Map will not post
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Posters are really begging for a U.S. landfall, and those who are, are no better than the vultures at the weather channel begging for something news worthy. After a week of reading posts, the media, and this forum continues to pretend that Irene has already made landfall with posts like "Irene a historic storm to slam into North Carolina", etc, etc. Well guess what folks, you can talk and talk about Irene not taking the turn toward the north and east, just like previous storms, but one way or another, this storm will continue to head out to sea. Get over it and salivate over the next tropical wave.
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this wobble is huge for nassau could mean a difference from clean side hit to a direct hit
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beautiful day here in SF :-)
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Quoting Gorty:


What does that mean for Irene?


I added a line to that comment, basically said it may mean Irene could make it a little further West. I don't think to much enough to make a difference for some of the Bahama islands tho...
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GFS 6hrs:
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This is the layered 300-850mb steering, this is used for TC of 950-969mb and 90-112kt. Heading into that weakness. The steering has not changed a lot in 12 hrs, as the A-B high remains pretty much in place.
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Does anyone else have a slight vibe that the model consensus it a little bit too east? I kind of do, and it seems like everyone on the blog does.
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Quoting VAbeachhurricanes:
12z GFS:


Is the new model run coming
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Quoting Joshfsu123:
AFTER THAT TIME...THERE IS SOME QUESTION AS TO WHETHER OR NOT IRENE CONTINUES ON A NORTH-NORTHEAST HEADING OR TURNS BACK TOWARD THE NORTH AHEAD OF A MID-LATITUDE TROUGH APPROACHING THE GREAT LAKES REGION. THE GFDL AND HWRF MODELS REMAIN ALONG THE WEST SIDE OF THE GUIDANCE ENVELOPE AND SHOW A TRACK OVER OR VERY CLOSE TO THE MID-ATLANTIC COAST. THE UKMET AND NOGAPS ARE ALONG THE EASTERN SIDE AND KEEP THE CORE OF THE HURRICANE WELL OFFSHORE. GIVEN THE TYPICAL MODEL AND OFFICIAL TRACK ERRORS...BOTH SCENARIOS ARE VIABLE OPTIONS AT THIS TIME...AND USERS ARE ONCE AGAIN REMINDED NOT TO FOCUS ON SPECIFIC FORECAST POINTS THREE TO FIVE DAYS DOWNSTREAM.


It all comes down to where the TROF of low pressure sets up... won't know that until Friday.



by friday??? it's wednesday morning. It's almost to 75W. Miami is 80w......r u sure about what your saying?
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1260. Buhdog
Quoting E46Pilot:


I remember the track for Wilma was supposed to track west of Lake Okeechobee, but the eye came right over my house in Boca.


That is hardly a bounce...I don't mean to be argumentative. The path was VERY close to the lake
Link
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1259. nash28
Quoting CaneHunter031472:
Ridge is buliding back to the west. I'm not seeing any changes in the models, but I'm sure they will follow soon. Anyone has any comment about this? I'm not going to make wild guesses at this point.


You're using the wrong steering layer. You want to use the 300-850mb layer for Irene right now.
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HH are out 130miles from the center and still encountering hurricane winds
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Quoting CaneHunter031472:
Ridge is buliding back to the west. I'm not seeing any changes in the models, but I'm sure they will follow soon. Anyone has any comment about this? I'm not going to make wild guesses at this point.


Wrong steering layer. That is for a storm with a pressure above 1000 mbs. You need to select a map based upon the pressure of the system and that can be found on the bottom edge of each map available on the page. See the menu at the top of the page from which the correct map is to be selected.
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as I predicted yesterday the storm hasn't made a hard hook to the right and I dont believe it will. The eyewall is now at 74w/22.4n . The NHS had this plotted at 74/24 with this already making its hard hook. They were wrong....

The weak shortwave trough lost the war against the bermuda high. Get ready florida, thats all I can say.
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Quoting IMA:


Dang it, I couldn't find that or the pic of Press-in-a-Dress! Searching has helped keep me from having as many weather tabs open, though


Right click on the photo to get the URL so you can have it on hand for future use...LOL!
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AFTER THAT TIME...THERE IS SOME QUESTION AS TO WHETHER OR NOT IRENE CONTINUES ON A NORTH-NORTHEAST HEADING OR TURNS BACK TOWARD THE NORTH AHEAD OF A MID-LATITUDE TROUGH APPROACHING THE GREAT LAKES REGION. THE GFDL AND HWRF MODELS REMAIN ALONG THE WEST SIDE OF THE GUIDANCE ENVELOPE AND SHOW A TRACK OVER OR VERY CLOSE TO THE MID-ATLANTIC COAST. THE UKMET AND NOGAPS ARE ALONG THE EASTERN SIDE AND KEEP THE CORE OF THE HURRICANE WELL OFFSHORE. GIVEN THE TYPICAL MODEL AND OFFICIAL TRACK ERRORS...BOTH SCENARIOS ARE VIABLE OPTIONS AT THIS TIME...AND USERS ARE ONCE AGAIN REMINDED NOT TO FOCUS ON SPECIFIC FORECAST POINTS THREE TO FIVE DAYS DOWNSTREAM.


It all comes down to where the TROF of low pressure sets up... won't know that until Friday.
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12z GFS:
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1252. Gorty
Quoting charlottefl:


It really depends. For now it shows the AB high is holding steady with it's position and the trough has flattened out before the approach of the 2nd shortwave..


What does that mean for Irene?
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Quoting 69Viking:


Rita I list the points from each advisory and then look at Irene's movement from 3 advirsories combined and she has continued on a very WNW path. It appears NW but she always moves more West than North over a 3 advisory average. Either way you're right, going to be a very close call, just depends on when and where she makes that turn to the North! This is kind of fun when the storms aren't in the Gulf and bearing down on us!


If she is at 77W, even if she starts going North it's already to late in my book
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1250. BrandiQ
Quoting cat5hurricane:

Thnx for the map. Yep, she's digging all the layers, even the deep ones now. She may get caught up. Not saying she will, but this is appearing a bit more likely.


Im not sure what that means... Getting "caught up"...
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Quoting reedzone:


I think the pattern shows it clearly, Irene may head a bit more west then forecast, maybe a brief landfall in NC then the eastern High should start building more to the east and push Irene potentially NNW into NJ or NYC, or Long Island. The USA is NOT escaping this one. It's a Historical storm. Haven't seen a Hurricane hit Long Island since Bob of 1991



I got a buddy that lives in CT. Soon as I told him about this, he has already made plans to go stay with his parents in Flint Michigan for a week. He left today. I told the some of the worst NE Hurricanes in the past were merely a CAT 1/2's. Their expanded windfields when they get at that latitude always seems to be what surprises people the most, that and the speed at which they accelerate up to there at. Hopefully she will be lop-sided to her eastern quadrents.
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Quoting IMA:
For the vets on the block
MLP is everywhere!
Member Since: August 11, 2010 Posts: 0 Comments: 784
1247. 7544
Quoting Lykkan:
Seems like the wobble to the west continues. Cuban radar showing the eye nicely.


morning everyone looks like irenes moving nw at this hour but could we see more wobbles to the west today watching the high
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Quoting Gorty:
The new steering map means nothing to me lol. What is it saying?


It really depends. For now it shows the AB high is holding steady with it's position and the trough has flattened out before the approach of the 2nd shortwave..Irene may get a little more west before turning north. I don't think much but enough to make a difference for the bahamas..
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1245. dipchip
What some folks don't grasp is that each 6 hour update the NHC collects ooodles of new data that improves their projections for the next forcast.

The initial TS forcast had very little data collected relative to current data. Therefore initial projections have larger errors.

Also the last 24 hour projection error was in a good position east and north of the 24 hour projection. NHC Conservative projections err in favor of less calamity than projected.
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sorry, this is a dumb question on my part, but how do you read this map?

Take for example the down arrow lines to the left of florida and the kind of looping lines to the SE of SE Florida.

I am trying to learn more as I am not as experienced as most everyone on here, thanks
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Ridge is buliding back to the west. I'm not seeing any changes in the models, but I'm sure they will follow soon. Anyone has any comment about this? I'm not going to make wild guesses at this point.
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Quoting wpb:
anyone have the link for noaa satellite quick scan


Link
Member Since: September 23, 2005 Posts: 14 Comments: 11274
The eye has been nailing the NHC tropical points dead on for the last 12 hours.

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Quoting LargoFl:
I have family and friends in wash d.c who also are not taking this seriously, local weather is telling them it will only be a cat 1 by the time it gets there..geez i hope they are right
Hope the quake there yesterday didn't rattle them too badly. Quakes and storms together...
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Quoting RitaEvac:
If she is going NW by the time she gets to 77W, it's check mate for the CONUS


Rita I list the points from each advisory and then look at Irene's movement from 3 advirsories combined and she has continued on a very WNW path. It appears NW but she always moves more West than North over a 3 advisory average. Either way you're right, going to be a very close call, just depends on when and where she makes that turn to the North! This is kind of fun when the storms aren't in the Gulf and bearing down on us!
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Quoting air360:
Although i totally agree with people who say wobbles are not to be given much credit...but viewing this starting at 1315 to the end of the loop does show over an hour of more W motion....which puts it on track to actually miss the next forecast point to the west. just sayin...

Link



That's a big wobble
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Quoting reedzone:


I think the pattern shows it clearly, Irene may head a bit more west then forecast, maybe a brief landfall in NC then the eastern High should start building more to the east and push Irene potentially NNW into NJ or NYC, or Long Island. The USA is NOT escaping this one. It's a Historical storm. Haven't seen a Hurricane hit Long Island since Bob of 1991


Watch it at 77W, key location
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1235. LargoFl
Quoting reedzone:


CORRECTION: Gloria was in 1985, not 1991.. Getting mixed up with Bob and Gloria. Meant to say Gloria in 1985.
I have family and friends in wash d.c who also are not taking this seriously, local weather is telling them it will only be a cat 1 by the time it gets there..geez i hope they are right
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It better shoot the gap quickly because it's getting tighter


Quoting charlottefl:
NEW STEERING MAP:

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1233. Gorty
The new steering map means nothing to me lol. What is it saying?
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Quoting cat5hurricane:

Furthermore, the eastern fringe of the eyewall appears to be undergoing weakening. Now if this is the start to a slight downward fluxuation in intensity, this may also affect her ability to move more NNW.



Here is the next layer down:

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Quoting 69Viking:
Over the last 3 advisories Irene has moved .8N and 1.5W, where I went to school that tells me Irene's motion has been and still is WNW.


Well I got her going 1.1 North and 1.3 West over the last 8 hours, that was from 2 AM position to 10 AM position. So she has made that NW turn, it's just a question is when she decides to make those "other" turns.
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Quoting ILwthrfan:


Are you right in line with the NHC forcast? Or do you this still possible swaying furthur east or west with time? I have noticed that the trough over the midwest is a bit weaker than forcasted. I don't know what implications if any this would have?


I think the pattern shows it clearly, Irene may head a bit more west then forecast, maybe a brief landfall in NC then the eastern High should start building more to the east and push Irene potentially NNW into NJ or NYC, or Long Island. The USA is NOT escaping this one. It's a Historical storm. Haven't seen a Hurricane hit Long Island since Bob of 1991
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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.