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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Quoting Grandpato4:
Governor just said they were not even considering coastal evacuations for any areas outside of Dare and Carrituck counties in NC. This is reassuring.


That's interesting because Ocracoke is already being evacuated and it's in Hyde county.

And it's Currituck, not Carrituck.
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Ever been a Hurricane Eileen? Yes but to the best of my knowledge only in the Pacific Ocean.

Link
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Quoting RitaEvac:


I think you're wrong gramps


of course, you thought Emily was headed west.
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Eyewall replacement cycle ahoy, still wobbling as it moves but right now still looks wnw.
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Quoting HiWay:
This dang storm is gonna get me in trouble. I have done absolutely no work besides checking my email when I sat down in my cube this morning.

Work? Who does that?
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Quoting Stats56:


One reason I don;'t think muxh of you. Too full of yourself., imho





I'm sure he's crushed...:(...<----(sad face!)
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Quoting HCW:
Do I need to issue a wobble watch warning ?



LOL
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Quoting Grandpato4:


I think I am going to stop even listening to the NHC. They have lost all credibility in my mind. I will pay attention maybe three days out from now on but no more following it five days or more out.


They said the whole time to be prepared just in case. Can you imagine the 4 mil + that evacuated from the metro houston area. Yet some of them were sorry when they brushed off the storm that came three years later.
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I used to like Joe B, but he has been pretty outlandish over the last year or two with some of his predictions, and has promoted huge events as a marketing tool. Don't get me wrong, I think he has tons of knowledge but, focuses too much on making money rather than making honest weather predictions.
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Quoting Grandpato4:


This is why I am not going to leave unless something changes. I have a good feeling that Irene will not touch the CONUS.


I think you're wrong gramps
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Quoting cloudburst2011:



well people should be greatful if IRENE misses the outer banks..the NHC has a tough job weather is changing every hour and some things that pop up they cant predict...they just have to deal with them and adjust the track the best way they know how...so to say just because IRENE would miss you and the next time you would not heed to the cone if you are inside it this is complete ignorance on your part..I THINK ITS MORE SOUR GRAPES THAT YOU ARE UPSET IRENE IS NOT HITTING YOU...DONT BLAME IT ON THE NHC THEY HAVE DONE AND OUTSTANDING JOB UNDER DIFFICULT CIRCUMSTANCES...


Or maybe concerned that if they say every storm will hit everyone, NO ONE takes them seriously. This will hurt confidence in the projected paths and I think people will delay preparing and/or evacuating given how drastically wrong their predictions have been.

I mean this is supposed to be the first hurricane to hit in 3 years and they are off by literally thousands of miles?
Member Since: August 4, 2011 Posts: 0 Comments: 631
766. HCW
Do I need to issue a wobble watch warning ?
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764. HiWay
This dang storm is gonna get me in trouble. I have done absolutely no work besides checking my email when I sat down in my cube this morning.
Member Since: August 17, 2007 Posts: 0 Comments: 55
763. MahFL
Another jog to the west :P ........
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Quoting Floodman:


Okay, now you know I love you man, and we're in the same dinghy pulling oars on opposite sides, so a word of gentle reminder: egging her on in your outside voice is considered to be in very poor taste. A nice demur golf clap is about all you can really allow yourself in public


Now, now Flood. I could have posted the entire set of lyrics that I came up with this morning in the shower based upon "Come On Eileen." I am sure they would have ruffled some feathers. LOL.

It is nature, Flood. I can't control it, I am only an observer.....JAFO, to be precise.
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The fervor about track shifts in the models is pretty funny. The NHC cone is 3 days long because that's how far the predictions are solid. The 5 day cone gets really wide because the predictions are poor.

Humans have a hard time dealing with probability, and the cone is notionally wide enough to cover 66% of the actual paths, so you can expect 1/3 to move outside it.

For this storm, maybe it's sometimes been in the 1/3 outside the early path, as the models shift east. But what does it matter if it's solidly wrong 5 days out?

Anyway, sometimes the atmosphere sets up so that paths are very sensitive to initial conditions, and that's what we've had. Seems like the consensus of models has quieted down lately, and the cone could probably be tightened a bit, but boy people would be surprised if the storm went from being an eastern outlier to a western outlier!

Weather is a chaotic process, and models will only ever get so good...probably could be better than they are, but with looming budget issues I wouldn't be surprised if we'll be stuck with this level of accuracy for a long time.
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Quoting zoomiami:
Baha -- check your WU mail

How are the conditions this morning?
Hey zoo. Things are beautiful here... calm before storm weather... u know what I mean... lol

I'm heading out in a few, but if you want to check progress of things here, I'll be posting updates in my blog all through the storm, even if I can't always get on here.
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Quoting yonzabam:


The Dexy's song title was 'Come on Eileen'.

Has there ever been a hurricane Eileen?
I can't believe no one has said "Irene to the right".
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Quoting poknsnok:
when the cone is on us in Florida we are usually safe



and when is not ?
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Quoting cat5hurricane:

LOTS can change.


I understand the forecast can and will change for the NE states. How much can the forecast really change for us in the SE though, given the nearly perfect agreement by ALL the computer models plus NHC track?
Member Since: August 4, 2011 Posts: 0 Comments: 631
Quoting CarolinaHurricanes87:


Exactly. This huge shift from the central gulf to eastern gulf to south florida to SC to NC to the NE...... is going to make millions of people in these areas more likely to ignore future warnings and delay preparations. I know a forecast is what it is, but when they have been dead wrong every day this week, its like the boy who cried wolf... I fear people will take the threat less seriously when they seem clueless on the forecasting


well said!! FEMA and others agencies have been moving people and equiptments alongside the models from a week ago from MS to the east wasting millions of dollars !!!
Member Since: August 3, 2009 Posts: 0 Comments: 137
Quoting cat5hurricane:

LOTS can change.


exactly
Member Since: August 19, 2006 Posts: 13 Comments: 15643
Quoting Patrap:
All Navy ships in Hampton Roads were ordered to prepare to get under way within 24 hours as a precaution.

"We learned last hurricane season with Hurricane Earl that we must be prepared even sooner to make the decision to sortie," Vice Adm. Daniel Holloway, commander of the U.S. 2nd Fleet, said in a news release.



Yeah I remember when I had to Sortie with my ship when Georges hit Mississippi. Sort of sucks lol. Had to tell my wife and newborn son well good luck to you all. Be safe. I guess it's part of serving anyway.
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Because multiple landfalls appear imminent, a more detailed scale seems appropriate.

21.1n71.9w, 21.3n72.5w has been re-evaluated&altered for H.Irene's_12pmGMT_ATCF
21.0n71.9w, 21.3n72.5w, 21.9n73.3w are now the most recent positions
Starting 23August_12pmGMT and ending 24August_12pmGMT

The 4 eastern 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 6amGMT then 12pmGMT :
H.Irene's travel-speed was 11mph(17.7k/h) on a heading of 308.9degrees(NW)
H.Irene was headed toward passage over DelectableBay(Acklins)Bahamas ~3hours from now

Copy&paste hog, 20.4n70.6w-20.7n71.2w, 20.7n71.2w-21.0n71.9w, 21.0n71.9w-21.3n72.5w, 21.3n72.5w-21.9n73.3w, iga, axp, 21.3n72.5w-22.396n73.97w, cri, pwn, lgi into the GreatCircleMapper for more info

The previous mapping (for 24August_6amGMT)
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9-1-1 storms
But hey, does this remind me of anything?
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749. Gorty
Quoting cat5hurricane:

LOTS can change.


Yes you are right!
Member Since: November 8, 2008 Posts: 12 Comments: 1058
Is there anything else out there we oughta be lookin' at?
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Has Levi made his video today?
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969mb (28.61 inHg) Sea Level (Surface) Pressure extrapolated between surface and 850 mb level since sonde did not reach surface.
1000mb This level does not exist in this area of the storm above the surface level.
925mb 408m (1,339 ft) 24.0°C (75.2°F) 23.5°C (74.3°F) 145° (from the SE) 114 knots (131 mph)
850mb 1,148m (3,766 ft) 20.8°C (69.4°F) 20.3°C (68.5°F) 170° (from the S) 103 knots (119 mph)

Dropsonde in NE eyewall didn't reach the surface. Must have gotten blown away?
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I want to thank the crews of Gonzo , Kermit, the Air Force Reserve aircraft, other aircraft and ship teams we don't hear of, their ground support teams (and their families). These and other under appreciated government workers who get us this critical data. Bouncing around in choppy weather miles from safe land and the duty hours for days on end can't be fun. THANK YOU ALL !!! You are truly life savers. Well done

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Quoting FLdewey:


Hey - fat rat's backside was my band name in college.

I can see you don't understand what I meant by old school. How did we go from old school to your memory problems? So confused. Whatever - you can take anything any way you want it.

Irene continues to move forward. Write that SSN on your dirty milk jugs too.

Always thought you were an idiot now you prove it, Thanks!!
Member Since: February 27, 2010 Posts: 0 Comments: 1125
Quoting Grandpato4:


I think I am going to stop even listening to the NHC. They have lost all credibility in my mind. I will pay attention maybe three days out from now on but no more following it five days or more out.
3 days out is about as good as it gets
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741. IMA
Pat, thanks for bringin' back the funk! That always captures my attention. I think I watched it for a good 15 minutes last night, felt like I'd dropped acid or somethin'. I haven't been able to get "We want the funk, gotta have that funk" outta ma mind for days.
Link
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Quoting HiWay:


The new GFDL and HWRF models, if accurate, would be absolutely devastating.


This is what I was thinking... Seems like it puts large cities on the wrong side of the hurricane. Even at a lower category, if they are on the wrong side, the surge could be big.

Hope she just curves out to sea and we don't see any issues with Irene! Go away!
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737. Gorty
Quoting ncstorm:
Today is Wednesday..the storm is not expected in NC until Sat..things can change..


Yes, track ad intensity models will change constantly.
Member Since: November 8, 2008 Posts: 12 Comments: 1058
when the cone is on us in Florida we are usually safe
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Today is Wednesday..the storm is not expected in NC until Sat..things can change..
Member Since: August 19, 2006 Posts: 13 Comments: 15643
Eye looking more like an eye now and looking very intense. Beautiful storm I'd say.
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Member Since: November 6, 2010 Posts: 11 Comments: 8130
732. Gorty
Quoting atmoaggie:
If this makes you shout, then you should probably evacuate to Salt Lake City and do so right this very minute. I'm afraid you haven't the right mindset to effectively deal with the situation.


At least i am not one of those people that says lolouttosea.

That is dangerous to say.
Member Since: November 8, 2008 Posts: 12 Comments: 1058

Storm Relative 1km Geostationary Visible Imagery


Member Since: July 3, 2005 Posts: 426 Comments: 128617
Funny, some people say that since the models *at two weeks* showed a risk to a large part of the US (from the Gulf through the Carolinas) they are garbage, but if they start to show out to sea that is what will happen.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting cat5hurricane:

Very interesting observation. From what I can tell you now, I believe a track closer to the coast would ensue if that holds true. I'm gonna spend some more time looking at these and similar maps in the next couple updates of them.

I will say when this thing gets across the 75 degree latitude and has not resumed a true NW (310 degree) motion and/or more poleward, I will really start doubting the NHC current track for Irene.


Looks to me like shes already taking a bend NW. I believe the turn has begun, just may not be a sharp turn because of her strength
Member Since: August 4, 2011 Posts: 0 Comments: 631

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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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