Irene continues to weaken

By: Dr. Jeff Masters , 8:46 PM GMT on August 26, 2011

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Satellite data and measurements from the Hurricane Hunters show that Irene continues to weaken. A 1:32 pm EDT center fix by an Air Force Reserve aircraft found that Irene's eyewall is still gone, and the central pressure had risen to 951 mb from a low of 942 mb this morning. The winds measured in Irene near the surface support classifying it as a strong Category 1 hurricane or weak Category 2. Satellite imagery shows a distinctly lopsided appearance to Irene's cloud pattern, with not much heavy thunderstorm activity on the southwest side. This is due to moderate southwesterly wind shear of 10 - 20 knots. This shear is disrupting Irene's circulation and has cut off upper-level outflow along the south side of the hurricane. No eye is visible in satellite loops, but the storm's size is certainly impressive. Long range radar out of Wilmington, North Carolina, shows that the outermost spiral bands from Irene have moved ashore over North Carolina. Winds at buoy 41004 100 miles offshore from Charleston, SC increased to 47 mph, gusting to 60 mph at 3 pm EDT, with significant wave heights of 25 feet.


Figure 1. MODIS satellite image of Hurricane Irene taken at 11:50 am EDT Friday August 26, when Irene was a Category 2 hurricane with 105 mph winds. The eyewall collapsed several hours before this image was taken, and no eye is apparent. Image credit: a href=http://rapidfire.sci.gsfc.nasa.gov/gallery/ NASA.


Figure 2. Distribution of Irene's wind field at 3:30 pm EDT Friday August 26, 2011, as observed by the Hurricane Hunters and buoys. The right front quadrant of the hurricane had about 90% of the storm's hurricane-force winds (yellow and warmer colors, bounded by the heavy black line between the "50" and "60" knot thin black lines.) Tropical storm-force winds (heavy black like bounding the light blue area) extended out 290 miles from the center of Irene. Image credit: NOAA/AOML/HRD.

Forecast for Irene
With its eyewall collapsed and just 18 more hours over water before landfall, Irene does not have time to build a new eyewall and intensify. The storm is too large to weaken quickly, and the best forecast is that Irene will be a strong Category 1 hurricane at landfall in North Carolina on Saturday. Based on the latest wind analysis from NOAA's Hurricane Research Division (Figure 2) and Irene's continued weakening trend, I predict that the 80-mile section of North Carolina coast to the right of where Irene makes landfall will receive sustained hurricane-force winds of 75 - 85 mph on Saturday at landfall; the 80-mile section of coast to the left will receive 55 - 75 mph winds. High wind shear of 30 knots will begin ripping into Irene Sunday morning when it is near Southern New Jersey, and more rapid weakening will occur. By the time Irene arrives on Long Island Sunday afternoon, it will probably have top sustained winds in the 65 - 75 mph range. However, since Irene is such a huge storm--tropical storm force winds extend out up to 290 miles from the center--it has set a massive amount of the ocean's surface in motion, which will cause a much larger storm surge than the winds would suggest. At 3:30 pm EDT this afternoon, a wind analysis from NOAA/HRD (Figure 2) indicated that the potential storm surge damage from Irene still rated a 5.0 on a scale of 0 to 6. This is equivalent to the storm surge a typical Category 4 hurricane would have. While this damage potential should steadily decline as Irene moves northwards and weakens, we can still expect a storm surge one full Saffir-Simpson Category higher than Irene's winds when it impacts the coast. Since tides are at their highest levels of the month this weekend due to the new moon, storm surge flooding will be at a maximum during the high tidal cycles that will occur at 8 pm Saturday night and 8 am Sunday morning. Wherever Irene happens to be at those times, the storm surge damage potential will be maximized. I continue to give a 20% chance that a 3 - 4 foot storm surge high enough to over-top the Manhattan flood walls and swamp the New York City subway system will occur on Sunday. The latest 11 am probabilistic storm surge map from NHC shows a 20 - 30% chance of a storm surge in excess of 3 feet in New York Harbor (Figure 4.) Keep in mind that these maps are calculated for normal tide level, and this weekend's high tides will be nearly 1 foot above normal.

Insurance company AIR-Worldwide is estimating that insured damages from Irene in the U.S. will be $1.5 - $6 billion. They estimate losses in the Caribbean at $0.5 - $1.1 billion from Irene.


Figure 3. Storm surge heights, in feet above normal tide level, which have a 20 percent chance of being exceeded during the next 3 days.  The graphic is based upon an ensemble of Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model runs using the current National Hurricane Center (NHC) official hurricane advisory. The exceedance heights depend on the historical accuracy of NHCs forecasts of hurricane track, and wind speed, and an estimate of storm size. Image credit: NOAA.


Figure 4. Overall chance that storm surges will be greater than 3 feet above normal tide levels during the next 3 days.  The graphic is based upon an ensemble of Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model runs using the current National Hurricane Center (NHC) official hurricane advisory.  Storm surge probabilities depend on the historical accuracy of NHCs forecasts of hurricane track, and wind speed, and an estimate of storm size. Image credit: NOAA.

Links
For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

The National Hurricane Center's Interactive Storm Surge RIsk Map, which allows one to pick a particular Category hurricane and zoom in, is a good source of storm surge risk information.

Wunderblogger Mike Theiss is in Nassau, documenting the storm's impact on the Bahamas.

Internet radio show on Irene at 4:30pm EDT
Wunderground meteorologists will be discussing Hurricane Irene on a special edition of our Internet radio show, the Daily Downpour, today (Friday) at 4:30pm EDT. Shaun Tanner , Tim Roche, Angela Fritz, and Rob Carver will take your questions. The email address to ask questions is broadcast@wunderground.com.

Jeff Masters

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Quoting Patrap:
Note the Shear Markers on the Northern Semi Circle coming ashore,,expect a SPC Tornado Watch Box to be issued soon.



12z sounding for MHX shows a particularly unstable airmass too. That area in SE and S central NC is ripe for these rainbands to produce embedded rotating storms.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting aislinnpaps:
TWC is talking to Mark Potter from Nag's Head and he is saying about how many are not leaving. I think we may see deaths that weren't necessary before this is all over.


The vast majority of people not leaving Nags Head or the OBX in general are the residents, most of whom have weathered these storms multiple times.

Not to sound harsh, but it's the TOURISTS that evacuations are for. When you've got Joe Shmoe from Colorado who's never been in a hurricane in his life standing on his rental property balcony with a webcam, that's when death and injury occurs. I'd personally trust the judgement of a Nags Head resident of 40 years. Heck, around here we (jokingly) say that if the locals leave, it's time to run for the hills, because it's the end of the world.
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Quoting ncstorm:
Water rushing over dunes on Topsail Islands..


They still have a lot of storm to go.

I do recall seeing the storm surge probabilities earlier had a maxima in the sound there at Wilmington. I suppose that the coastal geography will be trapping the water attempting to flee the hurricane and will enhance storm surge?
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I'm not liking these pictures we're seeing already of the water heights in NC. I agree those hold-outs on Nag's Head might be in for more than they bargained for. They could get overrun by water from both sides. Overall, it's looking like a lot of water for a lot of people.
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Quoting presslord:


Joe Bastardi


On steroids!
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Quoting Chicklit:
Bloated Spider Model.

Looks as if most of the dry air to Irene's east and south is becoming blocked from entering the core.
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Quoting Trouper415:
To everyone in the possible path of Irene, I would stay on alert with this one. She might have figured out a way to block out the dry air, and with her going directly over the gulf stream until land fall...I just don't want to see anyone unprepared. She could intensify for all we know.


IMO, the authorities are doing a good job of being reasonably cautious.
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Quoting ecupirate:


Oh hey doomcaster. You stall calling for a cat3?
Wait. Wasn't NHC calling for a cat 3?
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wow
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Quoting presslord:
Who ya gonna trust?

This:



or

This:




*snort* That's the funniest post ever!
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Quoting BahaHurican:
Re #563

@ daddyjames... Not knowing anything never stopped me from posting much.... lol

But this is a great place to learn if u r willing to put up with the background noise, aka the fun and jokes...

It's really great to be back in the blog. I never knew a hurricane passage could be so boring... no light and no phone and heavy shutters means u really have nothing to do but sleep [can't too hot] eat [can't no power] and talk [ everybody else is sleeping or eating].... lol


LOL - I can relate (to the post hurricane) 6 weeks without power after Wilma. Went south of Miami to escape Katrina (that was brillant!). Hang in there. in some ways, it can be a refreshing change, for a day or 2 . . .
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Quoting twincomanche:
If you are talking about on the map it means fifty knots.


Yes, I was. Thank you.
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Quoting ncstorm:
Water rushing over dunes on Topsail Islands..


Are people staying out on that island or did most evacuate?
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Quoting WeatherNerdPR:
This used to be a Tropical Depression.




TD 10 looks VARY good LOL NOT it look like it poofed out RIP TD 10 i wounder if they will upgrade it at post season
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Cells from extreme north outer band are starting to fire up from Irene...um here in South East PA...

Um Irene covers a massive amount of real-estate!
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Quoting K8eCane:
Hey everybody...Press, Pat, Portlight...There is a special place in Heaven for people like you. Here in Wilmington, there are some power outages. Knock on wood there is still power here. Winds are gusty, no hurricane force, lots of rain. Press hope all is well in Charleston.


we're good...our boys are getting ready to deploy...Thanks for the kindness!!!
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Quoting Gorty:


How about dry air?


Again I don't think a couple dozen miles are going to make much of a difference with how much dry air gets entrained, because her circulation is so large.
Member Since: November 24, 2005 Posts: 635 Comments: 26681
Quoting reedzone:
You don't see this every Hurricane Season.



Oh hey doomcaster. You stall calling for a cat3?
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Quoting zingo:
Thank you! Shows my mother in law's place. Maybe now I can keep up with her! LOL
Zingo! Did u create this storm just to send it to your mother-in-laws house?!
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Wilmington, Animated WunderMap®
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Parts of Carolina Beach is flooded ..the pics are on facebook but I cant save them down..pretty bad there..
Member Since: August 19, 2006 Posts: 13 Comments: 15999
Quoting Cotillion:
Irene's size is quite impressive. It is a fighter and while it is struggling with her own inner dynamics, that surge is going to be problematic. Not only the surge, it's also more of a wider area for rainfall. Igor showed that with Newfoundland last year, even though 'only' being a Category One at landfall.

According to the Montreal Gazette: "Hurricane Irene caused as much as $1.1 billion in insured losses in the Caribbean, catastrophe modeling company AIR Worldwide said on Friday, with more expected to come as the storm heads for the U.S. Northeast."

For the Caribbean, that is high.

Link
A lot of rain damage in PR, a lot of wind damage here - is Irene getting ready to complete the hurricane trifecta with serious surge damage in her third landfall?
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You don't see this every Hurricane Season.

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Quoting Joshfsu123:



I'm not Levi but imo, Category 3 won't happen - if Irene could cycle out more dry air tonight, and I think it will, it could increase 5/10 mph since pressure still remains low... but it only has about 18 hours left before landfall in North Carolina.

But Levi knows more about this than I do.


I have been saying for a while that Irene will intensify just before landfall. The SSTs are too warm and shear is too low to have the storm weaken for long. I hope I turn out to be wrong and it doesn't intensify before landfall but it looks like that is exactly what is happening IMO. She has fought the dry air and ( temporarily ) won.
Member Since: July 30, 2011 Posts: 0 Comments: 388
Quoting Bielle:


What does 5 bars on a wind flag mean? Thanks.


The four long bars and the one short bar on the wind barb indicates 45 kt winds (4 x 10 kts plus 1 x 5 kts).
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting K8eCane:
Hey everybody...Press, Pat, Portlight...There is a special place in Heaven for people like you. Here in Wilmington, there are some power outages. Knock on wood there is still power here. Winds are gusty, no hurricane force, lots of rain. Press hope all is well in Charleston.


8:00 PM 73.4 °F - 71.6 °F 94% 29.50 in 3.0 mi NNE 25.3 mph 38.0 mph 0.05 in Rain Heavy Rain

WILIMINGTON
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Topsail Island
Member Since: August 19, 2006 Posts: 13 Comments: 15999
TWC is talking to Mark Potter from Nag's Head and he is saying about how many are not leaving. I think we may see deaths that weren't necessary before this is all over.
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NEW YORK -CENTRAL PARK WEATHER

SATURDAY NIGHT
TROPICAL STORM CONDITIONS EXPECTED WITH HURRICANE
CONDITIONS POSSIBLE. RAIN. RAIN MAY BE HEAVY AT TIMES. HUMID WITH
LOWS IN THE UPPER 60S. EAST WINDS 30 TO 40 MPH WITH GUSTS UP TO
50 MPH...INCREASING TO 40 TO 50 MPH WITH GUSTS UP TO 65 MPH AFTER
MIDNIGHT. CHANCE OF RAIN NEAR 100 PERCENT.
SUNDAY
HURRICANE CONDITIONS EXPECTED. RAIN. RAIN MAY BE HEAVY
AT TIMES. HIGHS IN THE UPPER 70S. NORTHEAST WINDS 55 TO 75
MPH...BECOMING NORTHWEST 55 TO 65 MPH IN THE AFTERNOON. GUSTS UP
TO 80 MPH. CHANCE OF RAIN NEAR 100 PERCENT.
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672. zingo
Quoting KeyWestwx:
No other radar map compares!!!!
Thank you! Shows my mother in law's place. Maybe now I can keep up with her! LOL
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Hey everybody...Press, Pat, Portlight...There is a special place in Heaven for people like you. Here in Wilmington, there are some power outages. Knock on wood there is still power here. Winds are gusty, no hurricane force, lots of rain. Press hope all is well in Charleston.
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Note the Shear Markers on the Northern Semi Circle coming ashore,,expect a SPC Tornado Watch Box to be issued soon.

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Quoting presslord:
Who ya gonna trust?

This:



or

This:



hahahahahahahaha. That is classic! I love this blog when the kids go away and the adults come out to play
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Bloated Spider Model.

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Quoting wunderweatherman123:
just notice some deeper convection starting to form around the center.. look like she will maintain cat 2 status until landfall but levi now that there is less than 24 hours before landfall, do you see irene right now at this moment becoming a 3 or that appears unlikely.
Quoting wunderweatherman123:
just notice some deeper convection starting to form around the center.. look like she will maintain cat 2 status until landfall but levi now that there is less than 24 hours before landfall, do you see irene right now at this moment becoming a 3 or that appears unlikely.


I still want to see how the next 6 hours or so go, but 115mph might end up being too much to ask. Pressure is holding steady, but we need to see convection go off in the core during the next 6 hours or we won't get any increase in the winds. Irene is so large that it's her undoing in every way. It's hard to strengthen a circulation like that, or weaken it for that matter. If she looks no different by 06z then there's probably no chance of intensification.
Member Since: November 24, 2005 Posts: 635 Comments: 26681
probably will be able to post some pics of irenes first cloud outflow tomorrow here in ns due to her size
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Quoting atmosweather:


Out of all the remarkable bloggers we have here - and we have A LOT of amazingly knowledgeable people - he's the best in my mind. But please take nothing away from Dr. Masters, Dr. Carver and Dr. Fritz...they are all very experienced meteorologists and their advice will save many lives and educate everyone who reads their posts. They have been in the field this long for a very good reason.


I read them all and respect all of their opinions. I am just amazed at Levi's abilities and skill.
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Water rushing over dunes on Topsail Islands..
Member Since: August 19, 2006 Posts: 13 Comments: 15999
Quoting Bielle:


What does 5 bars on a wind flag mean? Thanks.
If you are talking about on the map it means fifty knots.
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Gorty:

Well, the farther east Irene goes....it would seem the weaker the winds would be in the W. Massachusetts area. I'm certainly rooting for Irene to go east, east, east!
Member Since: June 29, 2009 Posts: 13 Comments: 5315
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Irene's size is quite impressive. It is a fighter and while it is struggling with her own inner dynamics, that surge is going to be problematic. Not only the surge, it's also more of a wider area for rainfall. Igor showed that with Newfoundland last year, even though 'only' being a Category One at landfall.

According to the Montreal Gazette: "Hurricane Irene caused as much as $1.1 billion in insured losses in the Caribbean, catastrophe modeling company AIR Worldwide said on Friday, with more expected to come as the storm heads for the U.S. Northeast."

For the Caribbean, that is high.

Link
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Geeks Rule.
Looks like Irene's plans are to visit the Outer Banks.

LinkIreneSWLoop
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657. Gorty
Quoting Levi32:


It's probably not going to make much of a difference either way whether Irene is 50 miles farther east in the outer banks. The center may get pretty close to or over the Jersey coast, but whether it's offshore or not only makes a difference in the specifics of the storm surge near New York. The water off of Long Island is cold, down to 23C, so having the center over water won't mean much.


How about dry air?
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Quoting NOLALawyer:
If she rebuilds her eye and strengthens I am going to be thrilled that the college kid from Alaska had the better forecast than the extremely experienced and educated PhD holder and former H.H. who runs this blog. It is getting to the point where I find Levi to be the best, and least sensational, voice available on the internet regarding tropical systems.


Levi is good - there's no doubt. But Jeff is doing a great job. His blog, as everyone will witness, can become a very dreary place with wishcasters of all sorts, trolls beyond counting, and "experts" of dubious quality.
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Quoting Patrap:
Wilmington, WunderMap®


What does 5 bars on a wind flag mean? Thanks.
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Quoting presslord:


Joe Bastardi
And let me ask you a real question. What has that got to do with forecasting the weather?
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Quoting wunderweatherman123:
just notice some deeper convection starting to form around the center.. look like she will maintain cat 2 status until landfall but levi now that there is less than 24 hours before landfall, do you see irene right now at this moment becoming a 3 or that appears unlikely.



I'm not Levi but imo, Category 3 won't happen - if Irene could cycle out more dry air tonight, and I think it will, it could increase 5/10 mph since pressure still remains low... but it only has about 18 hours left before landfall in North Carolina.

But Levi knows more about this than I do.
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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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