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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957 mb from RECON...no winds strong enough to support an upgrade to major hurricane status yet, although they have not sampled the NE quadrant yet.
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I hope Long Island doesn't take a direct hit. They aren't prepared for that.
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GFS last four cycles


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Despite no northerly turn, they still expect the outer banks to get hit?
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Irene is moving quite slowly...looks pretty strong...
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Kermit & Gonzo are ontask
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10:43:00Z 22.050N 73.300W 752.0 mb
(~ 22.21 inHg) 2,221 meters
(~ 7,287 feet) 968.9 mb
(~ 28.61 inHg) - From 71° at 94 knots
(From the ENE at ~ 108.1 mph) 16.5°C
(~ 61.7°F) 15.0°C
(~ 59.0°F) 95 knots
(~ 109.2 mph) 76 knots
(~ 87.4 mph)
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Upper end Category 1 surface winds in the outer portion of the NW eyewall.
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Quoting victoriahurricane:


The anticyclone has now aligned with her? Do you have an image to confirm that? Not saying I don't trust you, but I want to see it.


It is not aligned it is still to the SW...but that doesn't make a difference concerning her outflow, only the deep layered shear, there is a great amount of divergence aloft and no matter how close the center of the ULH is she will continue to ventilate and expand.
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Quoting NICycloneChaser:


Hasn't aligned yet, still to the SW.






i think that map is old from last night
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arrogant sob jb saying nhc's track is on top of his cone on now!
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Quoting victoriahurricane:


The anticyclone has now aligned with her? Do you have an image to confirm that? Not saying I don't trust you, but I want to see it.


Hasn't aligned yet, still to the SW.


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Quoting Cotillion:


Well, hope all is good for you and yours. :)

---

SOME FLUCTUATIONS IN STRENGTH COULD OCCUR IN 1 TO 2 DAYS
DUE TO EYEWALL REPLACEMENTS. IN FACT...THE UW-CIMSS OBJECTIVE
TECHNIQUE SHOWS A CONSIDERABLY HIGHER THAN CLIMATOLOGICAL
PROBABILITY OF SECONDARY EYEWALL FORMATION WITHIN 24 TO 48 HOURS.

Be interesting to see if it happens.


I always understood that eyewall replacements could play a difference in tracking..an eye could form farther east or west in those cycles..
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Quoting atmosweather:


Right now they go out 40 miles from the center according to the 5AM advisory. But this will only get larger as her windfield continues to expand with her great outflow and anticyclone overhead.


The anticyclone has now aligned with her? Do you have an image to confirm that? Not saying I don't trust you, but I want to see it.
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Quoting ncstorm:


so the hurricane force winds only go out 50 miles from the center?


Right now they go out 40 miles from the center according to the 5AM advisory. But this will only get larger as her windfield continues to expand with her great outflow and anticyclone overhead.
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Quoting CoopsWife:
Morning Cotillion - yep - been a very busy year for us, no time for Mom to play on the WU.

Been saying lots of prayers for our friends to the SSE.

I wish the track would shift a bit more, but getting out of direct hit is pretty darn nice. :)



Well, hope all is good for you and yours. :)

---

SOME FLUCTUATIONS IN STRENGTH COULD OCCUR IN 1 TO 2 DAYS
DUE TO EYEWALL REPLACEMENTS. IN FACT...THE UW-CIMSS OBJECTIVE
TECHNIQUE SHOWS A CONSIDERABLY HIGHER THAN CLIMATOLOGICAL
PROBABILITY OF SECONDARY EYEWALL FORMATION WITHIN 24 TO 48 HOURS.

Be interesting to see if it happens.
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Quoting atmosweather:
RECON about 50 miles N of the center and finding Cat 1 winds at 750 mb. And the heights are already low. Not looking good.


so the hurricane force winds only go out 50 miles from the center?
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100 mph flight level winds already

10:27:30Z 23.033N 73.183W 752.8 mb
(~ 22.23 inHg) 2,439 meters
(~ 8,002 feet) 996.8 mb
(~ 29.44 inHg) - From 106 at 83 knots
(From the ESE at ~ 95.4 mph) 13.4C*
(~ 56.1F*) -* 87 knots
(~ 100.0 mph)
55 knots
(~ 63.2 mph)
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RECON about 50 miles N of the center and finding Cat 1 winds at 750 mb. And the heights are already low. Not looking good.
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157. Vero1
Quoting ncstorm:
this cone is muchhh bigger..something about to develop off of africa?


TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 AM EDT WED AUG 24 2011


2. SHOWERS AND THUNDERSTORMS HAVE INCREASED AND BECOME A LITTLE BETTER
ORGANIZED IN ASSOCIATION WITH A BROAD LOW PRESSURE AREA LOCATED
ABOUT 125 MILES SOUTH-SOUTHEAST OF THE SOUTHERN CAPE VERDE ISLANDS.
ENVIRONMENTAL CONDITIONS APPEAR GENERALLY FAVORABLE FOR SLOW
DEVELOPMENT OF THIS LOW DURING THE NEXT SEVERAL DAYS. THIS SYSTEM
HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS AS IT MOVES WESTWARD AT 10 TO 15 MPH.

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HPC Sea Level Pressures and Fronts
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Quoting JrWeathermanFL:

Dry air was a problem yesterday I think. Was there a reason behind the 10mph drop?


Irene was moving just to the north of Hispaniola pretty slowly, so inflow on her south side was sloping down the high mountains, so she was bringing in dry, sinking air.
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Quoting Hurricanes12:


Alot of storms this year could become majors. MJO is favoring our basin at the moment and conditions seem favorable for major development of these systems that roll off of Africa. Only thing that would deter development would be upper level conditions and dry air, generally.

Dry air was a problem yesterday I think. Was there a reason behind the 10mph drop?
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My area is looking at over 9inches of rain from Irene
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Quoting JrWeathermanFL:
With only a handfull of storms that are 110mph, Irene could easily become our first major hurricane. It might alreade BE a MH.


Alot of storms this year could become majors. MJO is favoring our basin at the moment and conditions seem favorable for major development of these systems that roll off of Africa. Only thing that would deter development would be upper level conditions and dry air, generally.
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Quoting FLPandhandleJG:


Yikes!!!


Wow in this image she's almost annular. Definitely a CAT3 on it's way to CAT4.
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With only a handfull of storms that are 110mph, Irene could easily become our first major hurricane. It might alreade BE a MH.
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Quoting NICycloneChaser:
06Z GFS is slower than and slightly west of the 00Z run.


yes..I believe even a little 30-40 mile difference is going to make and break it for a lot of folks
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Decent consensus in the major forecast models with the rest being to the E (further out offshore):

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Quoting ncstorm:
this cone is muchhh bigger..something about to develop off of africa?



The track cone is the area in which the centre of the storm could be located. That cone shows that area which could experience TS conditions, hence it is much larger.
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Morning Cotillion - yep - been a very busy year for us, no time for Mom to play on the WU.

Been saying lots of prayers for our friends to the SSE.

I wish the track would shift a bit more, but getting out of direct hit is pretty darn nice. :)

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Quoting ncstorm:
this cone is muchhh bigger..something about to develop off of africa?



Yes, 90L, which was given a 40% chance of developing within the next 48 hours by the NHC.
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06Z GFS is slower than and slightly west of the 00Z run.
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this cone is muchhh bigger..something about to develop off of africa?

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Quoting nrtiwlnvragn:
06Z GFS 108 hours




Noticed too that 00Z ECMWF was a bit more inline with GFS on grazing the E/NE Coast. Which is definitely a good trend.
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06Z GFS 108 hours


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Quoting CoopsWife:
Hey Trauma - long time no see. Too busy this year with the youngest graduating/ heading off to college to pop in and visit.

Of course, now that Irene is on her way, I have to put out the breakfast to fuel all the brains!! :)


Glad to see you in too....Irene has been I am sure a nightmare for our friends in the islands tonight!! I had Krispy Kreme and French Vanilla Coffee out at midnight but unfortunately you can only eat so many donuts!!
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Quoting CoopsWife:
Oops - morning all.

Coffee, juice on the sideboard.

Today's menu -

Pan seared tenderloin, eggs (scrambled are on the sideboard already), home fried potatoes with a little sauteed vidalia onion, and biscuits with jelly...




Hey CW, haven'T seen you in a while.

Morning all, thinking of the T&Cs and bahamas today.
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Definitely prayed for you guys in the Bahamas/Turks & Caicos Islands night so let's hope Irene takes the Eastern end and leave you on its western periphery.

Currently and assuming current direction persists (without jogs/wobbles to the left) that it could past E of the next Forecast point which would be good place to be since it would put most of the islands on the western periphery.
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Good morning -- here again is the link to the Tumblr site with the southern bahamas live observations... sustained winds are in the 60s at 1 of the sites:


http://wunderine.tumblr.com/


And here is a map of the Bahamas:

MAP

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NOAA plane beginning to fly into Irene from the NW and have already found TS winds at the surface more than 175 miles out. She is a massive storm.
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Hey Trauma - long time no see. Too busy this year with the youngest graduating/ heading off to college to pop in and visit.

Of course, now that Irene is on her way, I have to put out the breakfast to fuel all the brains!! :)
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Off to class for me, will check in later. Y'all hold the fort down and for all in the Bahamas; stay safe!
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Kermit and AF303 are going to team up once again on this one.
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Good Morning...
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Good morning, all. I hope our friends in Caicos, the Turks and the Bahama's are all okay. I see Dr. M has Irene headed for Long Island as a cat 1. It's going to be a long weekend with Irene.
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Mornin, HRD most recently completed HWIND. as of 9:30 PM EDT last night.


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21.1n72.0w has been re-evaluated&altered for H.Irene's_6amGMT_ATCF
21.1n71.9w, 21.3n72.5w are now the most recent positions
Starting 23August_6amGMT and ending 24August_6amGMT

The 4 shorter line-segments represent HurricaneIrene's path
and the westernmost line-segment is the straightline projection.

Using straightline projection of the travel-speed&heading derived from the ATCF coordinates spanning the 6hours between 12amGMT then 6amGMT :
H.Irene's travel-speed was 6.8mph(11k/h) on a heading of 289.7degrees(WNW)
H.Irene was headed toward passage over RacoonCay(RaggedIsland)Bahamas ~1day5hours from now (though I wouldn't count on Irene to continue moving that slowly)
after passing over LittleInagua*Bahamas

Copy&paste 20.1n69.7w-20.4n70.6w, 20.4n70.6w-20.7n71.2w, 20.7n71.2w-21.1n71.9w, 21.1n71.9w-21.3n72.5w, iga, dct, 21.1n71.9w-22.36n75.81w, mrk into the GreatCircleMapper for more info

The previous mapping (for 24August_12amGMT)

* The entire island is a national park and wildlife preserve.
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Quoting CoopsWife:
Oops - morning all.

Coffee, juice on the sideboard.

Today's menu -

Pan seared tenderloin, eggs (scrambled are on the sideboard already), home fried potatoes with a little sauteed vidalia onion, and biscuits with jelly...




I'm having some leftover gumbo, conebread, anna glass uh milk. But yours sounds purty good to.
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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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