Hurricane Irene Prepares to Leave the Bahamas and Head for the US

By: Dr. Jeff Masters , 7:51 AM GMT on August 25, 2011

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As of 2AM EDT, Hurricane Irene was located at 24.2N, 76.0W, 105 miles east-southeast of Nassau or 760 miles south of Cape Hatteras. It was moving northwest at 12 mph with maximum sustained winds of 115 mph, making it a Category 3 storm on the Saffir-Simpson scale. Irene has a minimum central pressure of 950 mb. Hurricane force winds can be found up to 70 miles from Irene's center, and tropical storm force winds can be found out to 255 miles from the storm's center.

Hurricane warnings are in effect for all of the Bahamas. Hurricane and tropical storm watches will likely be posted for the Carolina coastlines later this morning. At this time, Dare County Emergency Management has issued a mandatory evacuation order for all visitors in their county. Dare County Schools will also be closed Thursday and Friday.

Satellite Views
Figure 1 is the infrared satellite image of Irene at 135EDT. The convection is a bit unbalanced around the storm center, which is going to cause Irene to wobble like an unbalanced clothes washer (Analogy courtesy of Angela Fritz) over the next few hours. At the time this image was taken, the convection around Irene's center appears to be getting more vigorous, as cold cloudtops are starting to increase around the storm center. This is important to note because microwave satellite imagery from Wednesday evening suggested Irene was starting an eyewall replacement cycle. Figure 2 shows passive microwave imagery from a Air Force DMSP polar-orbiting satellite. The two concentric green/yellow bands in the image suggest that two eyewall features are present in Irene, and Hurricane Hunter observations confirm this. This has important consequences for Irene's intensity, because in an eyewall replacement cycle, as the inner eyewall weakens, the storm's intensity drops. However, once the inner eyewall is gone, and the outer eyewall contracts to replace it, the storm intensity will increase again.


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


Figure 2 DMSP F18 microwave overpass of Irene at 824PM EDT, August 24, 2011. Image courtesy of the Naval Research Laboratory

Track Forecast

Irene is forecast to move to the northwest, passing over the northwest Bahamas by Thursday evening, then curving to the northeast. 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. Sunday, Irene may make secondary landfall anywhere from New Jersey to Long Island and the southern New England coastline. In my opinion, New York City may be significantly impacted by Irene. 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 Category 4 storm (winds faster than 130 mph) by Thursday morning. As Irene moves northward into cooler water, the intensity is expected to drop slowly to a Category 2 storm before making landfall in the Outer Banks.


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

Forecast models and today's planned flights
The different forecast models are still in fairly good agreement about Irene's track through the Bahamas and along the east coast of the US. The 00Z GFS run is in close agreement with the 12Z ECMWF run, but the 00Z ECMWF run (shown in figure 4) is continuing the ECMWF's trend of shifting the track westward with each run. NHC forecasters have been placing emphasis on the ECMWF's forecast track when making their forecasts for IRene, so it is possible that the NHC track will shift westwards at the 5AM update.

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 (Gonzo), and two flights for NOAA 42, a WP-3D (Kermit). They may have to give NOAA a littering permit for all of the dropsondes used to monitor Irene and her environment, but the forecast improvements they generate are worth the effort.


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

Impacts

Hurricane force winds will arrive in the northwestern Bahamas today. Storm surge near the center of Irene will be 7-11 feet above tide level. The Bahamas can expect 6-12 inches of rain over the next day or so, and it looks like the Turks and Caicos islands will receive a total of 6-12 inches from Irene. Large, swells from Irene will start landing on the southeastern US coastline later today. Please don't go in the water, as these swells can cause dangerous rip currents. Dr. Masters has catalogued the worst-case storm surge surge scenarios as a function of storm intensity here.

In my opinion, people living from the Carolinas to Cape Cod should pay close attention to Irene and prepare for a wide range of impacts. I think that there is a 75% chance of Irene's secondary landfall will be somewhere between JFK airport and Cape Cod. That said, Irene's size will cause significant impacts for people living far from it's center.

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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Good morning all!!!

Including Irene!

She just heralded in the day here in Boca with a pretty sporty li'l squall passing through as I type.
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Only 180nm or so further west and yowsa!!!!

Don't think she'll get that far though. Maybe another 70-100nm W at the most.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
Anyone know why Irene is forecast to bend not only N, but slightly east before she reaches the NC coast? From the above steering charts, it looks like the high pressure will guide her NNW right into SE NC... what am I missing?
Member Since: August 4, 2011 Posts: 0 Comments: 631
Quoting islander101010:
except for a few relatively poor island



That's too bad, they got a pounding in the NE eyewall. Looks like it will past just west of Great Abaco next.
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Quoting CarolinaHurricanes87:
No hurricane watch for Wilmington. A little surprised given how close Irene is predicted to be off our coast.... I guess this means the NHC is pretty confident the models wont shift much further (if any) west than they already have...


you got to watch it like a hawk today...
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188. Vero1
Quoting wxobsvps:
Hopefully 77W will be the extent of her longitude gains.
The current NHC track has it going as far west as 77.7w at 28.2n in 19 hrs from now
Member Since: July 21, 2008 Posts: 4 Comments: 2233
not to take interest off irene but does anyone know what the blob is that sits over florida next friday through wednesday on the gfs?

getting our first feeder bands coming through wind picked up and it is raining very hard right now in dania beach florida just south of ft lauderdale!!
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Quoting trHUrrIXC5MMX:

The eye is trying to show up again in water vapor


She just might make a run for Nasseau at 77W, 25.5N
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Pretty strong Bermuda High:



You can see that the weakness sure have displaced W some from a previous E Coast position.
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new eyewall
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Quoting NICycloneChaser:
06Z GFS at 384 hours. Of course, it is a very long way out and doesn't necessarily mean anything, but looks like we may have a 1-2 pattern, first recurves, next heads west.

This is what the GFDL predicted 12 hours ago, now the GFS. That last minute hook to the West in Southern NY could be bad news. I hope the news hypes this up soon. I never like hype but people in Eastern NY/NJ area need to know all the possibilities of the storm and not get caught off guard
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No hurricane watch for Wilmington. A little surprised given how close Irene is predicted to be off our coast.... I guess this means the NHC is pretty confident the models wont shift much further (if any) west than they already have...
Member Since: August 4, 2011 Posts: 0 Comments: 631
Quoting ProgressivePulse:
Indeed just west of central Eluthera, whom is taking a beating it the eastern eyewall right now.

25.1333N 76.3W
except for a few relatively poor island http://en.wikipedia.org/wiki/Eleuthera
Member Since: September 11, 2010 Posts: 1 Comments: 4579
Quoting atmosweather:
At the 11PM advisory Irene was centered at 23.8N 75.4W, and the 6AM center fix came in at 25.1N 76.3W. Therefore she is moving more N than W. And at the 2AM advisory, she was centered at 24.1N 75.9W which yields a 4 hour motion of NNW.


And she can feel free to stop any W component now:-)
If she gets past 78W, things get a little hairy.
Member Since: July 11, 2005 Posts: 190 Comments: 16972

The eye is trying to show up again in water vapor
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Quoting atmosweather:
At the 11PM advisory Irene was centered at 23.8N 75.4W, and the 6AM center fix came in at 25.1N 76.3W. Therefore she is moving more N than W. And at the 2AM advisory, she was centered at 24.1N 75.9W which yields a 4 hour motion of NNW.


at the 5 am advisory she was 24.6 n and 76.2 w
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Quoting NasBahMan:


Eye is currently over Rock Sound Eleuthera.



Just west of Palmetto Point based on the latest recon fix.
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Quoting Stormchaser2007:
Recon states there's a well-defined eye under the CDO/convection.


Well, then she will probably begin strengthening soon.
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Quoting wxobsvps:
This may have been covered already and if so my apologies...

Current steering for Irene:


You can see how Irene is caught up in the flow to the NW, which has actually increased from 3hrs ago, as the Atlantic high has nosed westward toward the US coastline


ULL to Irene's west may be helping to "pull" Irene toward the NW at the 315 heading.


Correct. Unfortunately. it appears the trough is not going to be deep enough to kick her E of the Carolinas.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
Recon states there's a well-defined eye under the CDO/convection.

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Indeed just west of central Eluthera, whom is taking a beating it the eastern eyewall right now.

25.1333N 76.3W
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At the 11PM advisory Irene was centered at 23.8N 75.4W, and the 6AM center fix came in at 25.1N 76.3W. Therefore she is moving more N than W. And at the 2AM advisory, she was centered at 24.1N 75.9W which yields a 4 hour motion of NNW.
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Heyas SJ!!

They may have to give NOAA a littering permit for all of the dropsondes used to monitor Irene and her environment, but the forecast improvements they generate are worth the effort.


LOL
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Just booked my flight to go to NE NJ. Gotta get some heavier clothes :p

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Plam Beach Fl. is starting to feel the wind even as far away as she is. 35mph to 40 mph winds on the beach and waves look big. With that said even if it don'thit you, You will see some effects from her. They are calling for 11 to 13 foot waves this afternoon and that is very large waves for us this time of year. I have faith in the forcast but wish it was north of us. OK back to lurking.
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Quoting ProgressivePulse:
Morning all, center appears to be just west of Eleuthera.


Eye is currently over Rock Sound Eleuthera.
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Quoting NICycloneChaser:
06Z GFS at 384 hours. Of course, it is a very long way out and doesn't necessarily mean anything, but looks like we may have a 1-2 pattern, first recurves, next heads west.



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06Z GFS at 384 hours. Of course, it is a very long way out and doesn't necessarily mean anything, but looks like we may have a 1-2 pattern, first recurves, next heads west.

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Quoting JrWeathermanFL:
Everyone does know we have TD10?
hey jr watching the carib.
Member Since: September 11, 2010 Posts: 1 Comments: 4579
news was pumping this storm comparing to the secret 1944 great atlantic hurricane she's a major for sure but not like the great ones
Member Since: September 11, 2010 Posts: 1 Comments: 4579
Quoting nash28:


At this point, her strength won't have much to do with the eventual track. It is all up to the break in the ridge. If it holds....Or if it begins to fill in and nudge her further west.
Thanks, Im trying to figure out steering maps. It looks like to me, if the intensity forecast flops, the ridge looks stronger.
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Morning all, center appears to be just west of Eleuthera. Still wobbling around and seemed to wobble N recently, however there also seems to be an embedded vortex which is making it tough this morning.
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000
URNT12 KNHC 251049
VORTEX DATA MESSAGE AL092011
A. 25/10:24:50Z
B. 25 deg 08 min N
076 deg 18 min W
C. 700 mb 2687 m
D. 55 kt
E. 210 deg 27 nm
F. 290 deg 58 kt
G. 208 deg 25 nm
H. 952 mb
I. 12 C / 3045 m
J. 17 C / 3051 m
K. 11 C / NA
L. OPEN SW
M. C30
N. 12345 / 7
O. 0.02 / 2 nm
P. AF300 1909A IRENE OB 11
MAX OUTBOUND AND MAX FL WIND 112 KT NE QUAD 10:32:00Z
EYE WALL WELL DEFINED 020-090
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Quoting oceanblues32:
not to take interest off irene but does anyone know what the blob is that sits over florida next friday through wednesday on the gfs?
don't even go there yet ;)
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There is a very robust vortex on the west side of Irene, i know it is amost impossible, but could this be a centre relocation?
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Quoting StormJunkie:


Morning Nash, haven't checked the ECMWF; but the GFS has shifted slightly W. Not much, but enough to be pretty confident that the OBX are the furthest point E she will go. I would also still be a little nervous if I were in Wilmington. I doubt she'll end up any further W than that.
Both the GFS and GFDL have shifted West. The path of GFS is the same as GFDL 12 hours ago, The GFS has been more reliable. Unfortunatley this track makes NYC area somewhat of a bulls eye. If its a medium stregnth cat 2 when it hits the city, I think, the coastal flooding in subway systems may be significant. Wind will drop trees and power lines. Maybe a church steeple will tumble, a few broken windows...It's more the flooding of the sewer sytems and subway tunnels with all the rain they have had. Possible serious situation here
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Quoting scott39:
Irene doesnt look as good this morning. What happens( in reference to track) if in the next 12 to 24 hours the pressure stays the same or starts rising instead of dropping?


At this point, her strength won't have much to do with the eventual track. It is all up to the break in the ridge. If it holds....Or if it begins to fill in and nudge her further west.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
Everyone does know we have TD10?
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not to take interest off irene but does anyone know what the blob is that sits over florida next friday through wednesday on the gfs?
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Can I invest in whomever makes these dropsondes?
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I sure hope Emily keeps looking like this from this point on. It will give her a chance to collapse even faster structurally once it starts moving NE.
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Quoting ncstorm:
I also want to remind people that even if you are in the tropical storm scenario, that could mean winds anywhere from 39mph to 73mph..
strong thunderstorm thankfully there is a chance now she'll never reach cat 4
Member Since: September 11, 2010 Posts: 1 Comments: 4579
I also want to remind people that even if you are in the tropical storm scenario, that could mean winds anywhere from 39mph to 73mph..
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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.