Dr. Jeff Masters' WunderBlog

Irene slightly weaker, but still very dangerous

Posted by: Dr. Jeff Masters, 20:59 GMT le 25 août 2011

+28

An Air Force Reserve hurricane hunter aircraft investigating Irene has found a slightly weaker storm. As of 4pm EDT, the strongest surface winds seen by the aircraft with their SFMR instrument were 91 mph in the storm's northeast eyewall. Highest winds measured at their flight level of 10,000 feet were 114 mph. Assuming the aircraft missed sampling the strongest winds of the hurricane, it's a good guess that Irene has fallen to Category 2 strength with 100 - 105 mph winds, even though the official advisory is higher. The aircraft noted that the eyewall was missing a large chunk on it southwest side, but the central pressure was about the same as early this morning, 950 mb. Satellite imagery from late this morning and early this afternoon showed a distinctly lopsided appearance to Irene's cloud pattern, with not much heavy thunderstorm activity on the southwest side. This was due to moderate wind shear of 10 - 20 knots due to upper-level winds out of the southwest. This shear was able to disrupt Irene's circulation while it was attempting to complete an eyewall replacement cycle, resulting in dry air getting wrapped into the core, which can be seen as a streak of darker clouds in this morning's MODIS satellite image (Figure 1.) satellite loops show that Irene is beginning to recover from this adversity, with a respectable amount of heavy thunderstorms beginning to wrap around to the southwest side from the north. An upper-level wind analysis from the University of Wisconsin CIMSS site shows that Irene's upper-level outflow is much more restricted than was the case 24 hours ago. An upper-level outflow channel that was open to the south is gone, and has been replaced by shearing winds from the west and southwest that are ripping into the hurricane. I think it is 30% likely that Irene will have trouble recovering from this setback, and will not reach the peak intensity of 120 mph winds it had earlier. However, it is more likely that the hurricane will be able to re-establish its upper-level outflow and overcome the shear, based on the latest satellite loops, plus forecasts from the various hurricane models such as the GFDL, HWRF, and ECMWF, which all show Irene at Category 3 strength as it approaches North Carolina on Saturday afternoon.

Figure 1. MODIS satellite image of Hurricane Irene taken at 11:50 am EDT Thursday August 25, when Irene was a Category 3 hurricane with 115 mph winds. The eye of the storm was just off the coast of Abaco Island in the Bahamas. Note the rather squashed appearance of the hurricane, with less heavy thunderstorms on its southwest side. Upper level winds of 10 - 20 knots out of the southwest were eating away at the clouds on this side, and you can see that this shear helped drive some dry air into the hurricane, which can be seen as a darker strip of cloud spiraling into the center from the south, around the east side, then into the center along the northwest side of the storm. Image credit: a href=http://rapidfire.sci.gsfc.nasa.gov/gallery/ NASA.

Irene likely to bring destructive fresh water flooding
In this morning's post, I highlighted the threat from storm surge flooding, but flash flooding and river flooding from Irene's torrential rains are also a huge threat. The hurricane is expected to bring rains in excess of 12" to 100-mile swath from Eastern North Carolina northwards along the coast, through New York City. The danger of fresh water flooding is greatest in northern New Jersey, Southeast Pennsylvania, and Southeast New York, where the soils are saturated from heavy August rains that were among the heaviest on record. At Philadelphia, rainfall so far this August has been 13 inches, not far from the record for rainiest month of all-time, the 15.82" that fell in August 1867. This record will almost certainly be broken when Irene's rains arrive. In general, the heaviest rains will fall along the west side of the hurricane's track, and the greatest wind damage will occur on the east side. Right now, it does not appear that tornadoes will be a major concern, but there will probably be a few weak tornadoes. Hurricane Bob of 1991, the last hurricane to affect New England, spawned six tornadoes, most of them weak F-0 and F-1 twisters.

Figure 2. Predicted rainfall for the 5-day period ending at 8 am EDT Tuesday August 30, as issued by NOAA/HPC.

Latest forecast for Irene
The latest set of model runs don't show any major changes to Irene's track or intensity. Irene will bring damaging winds, torrential rains, and an extremely dangerous storm surge to the coast, affecting a huge area of the mid-Atlantic and New England. Take this storm seriously! Expect widespread disruptions to electric power, transportation, and water systems. Be prepared for many days without power, as utility crews will be overwhelmed with the damage. Irene is capable of inundating portions of the coast under 10 - 15 feet of water, to the highest storm surge depths ever recorded. I strongly recommend that all residents of the mid-Atlantic and New England coast familiarize themselves with their storm surge risk. The best source of that information is the National Hurricane Center's Interactive Storm Surge Risk Map, which allows one to pick a particular Category hurricane and zoom in to see the height above ground level a worst-case storm surge may go. If you prefer static images, use wunderground's Storm Surge Inundation Maps. If these tools indicate you may be at risk, consult your local or state emergency management office to determine if you are in a hurricane evacuation zone. Mass evacuations of low-lying areas along the entire coast of New Jersey, Delaware, Maryland, and Virginia are at least 50% likely to be ordered by Saturday. The threat to the coasts of New York, Connecticut, Rhode Island, Massachusetts, New Hampshire, and Maine is less certain, but evacuations may be ordered in those states, as well. Irene is a very dangerous storm for an area that has no experience with hurricanes, and I strongly urge you to evacuate from the coast if an evacuation is ordered by local officials. My area of greatest concern is the coast from Ocean City, Maryland, to Atlantic City, New Jersey. It is possible that this stretch of coast will receive a direct hit from a slow-moving Category 2 hurricane hitting during the highest tide of the month, bringing a 10 - 15 foot storm surge.

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.

Jeff Masters

Irene Rainband from downtown Ft. Lauderdale (pho)

8/25/11 0910 local time.

HurricaneIreneIsOutThere! (trigirl)

Early at the beach to snap the waves from Hurricane Irene east of our coast, the wind was unreal with thunderclouds rolling in with lots of rain for the day.

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401. Orcasystems 22:34 GMT le 25 août 2011
Complete Update TS BUSTED FORECAST ALIBI Member Since: 1 octobre 2007 Posts: 77 Comments: 26077

402. rmbjoe1954 22:34 GMT le 25 août 2011
Hi Angela- I am Joe from Port St. Lucie, FL and am very glad Irene avoided Florida. But looking at what awaits us in September it would be prudent to maintain vigilence and be ready to act upon any tropical threat. Member Since: 16 juin 2005 Posts: 0 Comments: 733

403. Patrap 22:34 GMT le 25 août 2011
unenhanched IR Member Since: 3 juillet 2005 Posts: 372 Comments: 111641

404. petewxwatcher 22:34 GMT le 25 août 2011
Quoting jazzygal: Is everyone getting that username and password thing every time you reload. Does anyone know how to get rid of it? Flag and minus comment 252 please. Member Since: 24 Mars 2011 Posts: 3 Comments: 392

405. TomTaylor 22:35 GMT le 25 août 2011
Quoting GTcooliebai: Do you think the eye will get wider? Nope, don't think so. On radar, it looks like the EWRC cycle is very near completed, if not already completed. Which means the eye should contract if anything. Pressures are also falling, which would tend to cause the eyewall to contract, rather than expand. Member Since: 24 août 2010 Posts: 18 Comments: 3914

406. PELSPROG 22:36 GMT le 25 août 2011
Hi NUR, sorry you had to cancel you trip NC. Member Since: 3 septembre 2008 Posts: 0 Comments: 65

407. malaclypse 22:36 GMT le 25 août 2011
Quoting GTcooliebai: I thought the eye would've been wider, but these pin-hole eyes can ramp up quickly, I think Wilma had a pin-hole eye. Only looks like a pinhole becasue Irene is over 500 miles across Member Since: 20 octobre 2005 Posts: 0 Comments: 3

408. quante 22:36 GMT le 25 août 2011
Headed to the North, and on satellite, RGB, it looks to be expanding in overall size. NHC has strength down, but going to be a large storm in size for sure. Member Since: 2 août 2006 Posts: 0 Comments: 328

409. bwat 22:37 GMT le 25 août 2011
Quoting AVL: Bullets... Dude, I live in NC, that should of been a gimmie. :) More important things to discuss, I'll go back to lurking now, my appologies. Member Since: 18 août 2009 Posts: 0 Comments: 338

410. 800733 22:37 GMT le 25 août 2011
are the modles showing anything out there to watch in the next few weeks or so? Member Since: 10 août 2011 Posts: 0 Comments: 8

411. Gorty 22:37 GMT le 25 août 2011
TWC has me for widespread wind damage in western Mass. Member Since: 8 novembre 2008 Posts: 11 Comments: 1058

414. Titoxd 22:38 GMT le 25 août 2011
Fixed it. I go away for a little bit and a link I put causes all sorts of issues, lol. It wasn't asking me for a password, so I was just confused as to what was going on. Member Since: 28 juin 2010 Posts: 0 Comments: 242

415. Patrap 22:38 GMT le 25 août 2011
Member Since: 3 juillet 2005 Posts: 372 Comments: 111641

416. hurricanehunter27 22:38 GMT le 25 août 2011
Quoting TomTaylor: Nope, don't think so. On radar, it looks like the EWRC cycle is very near completed, if not already completed. Which means the eye should contract if anything. Pressures are also falling, which would tend to cause the eyewall to contract, rather than expand. Lets see te pressure HH about to make center pass. Member Since: 22 juillet 2010 Posts: 1 Comments: 3474

417. MiamiHurricanes09 22:38 GMT le 25 août 2011
Quoting TomTaylor: The eye isn't a pinhole eye. Recon and radar confirms this. The reason it looks so small on satellite is due to cirrus clouds over top covering up the sides of the eye, and not because the eyewall is contracted so tightly that the eye looks like a "pinhole". But anyway, yea, ADT numbers should pick up big time now Lol, pinhole on the satellite image. Shoulda clarified. Member Since: 2 septembre 2009 Posts: 129 Comments: 19976

418. JRipswx27 22:38 GMT le 25 août 2011
Recon is heading back in... I expect to see a drop in the pressure at the very least. Member Since: 31 mai 2011 Posts: 3 Comments: 8

419. Mucinex 22:39 GMT le 25 août 2011
CBS Evening News: Hurricane Watches and Warnings go out across the eastern U.S. The big question; Will cell phones work in a Hurricane? Seriously! That's the big question. Let the media chaos begin. Member Since: 23 mai 2011 Posts: 0 Comments: 254

421. Thunderpig75 22:39 GMT le 25 août 2011
Quoting P451: Damn the floater relocations. Still..gives a look into the convective structure. And the fading VIS: OMG FLORIDA JUST WENT 400 MILES EAST! Member Since: 4 août 2011 Posts: 0 Comments: 98

422. wolftribe2009 22:39 GMT le 25 août 2011
Storm looks like it is moving towards the NE now. This should get interesting. Some might start considering if the storm will move out to sea afterall. I stick to the west track I have been stating would occur since the beginning. \ 950 MB storm with winds 115MPH That pressure is pretty low to me for a 115 MPH storm. I am thinking this storm will become a CAT 4 Hurricane and I just wonder how low the pressure will go? Member Since: 22 juillet 2010 Posts: 6 Comments: 752

423. Vero1 22:39 GMT le 25 août 2011
My wife was watching the National Broadcast Committee's TWC and NYC is going to wait till Sat afternoon before calling for evacuations. Shoot it takes 4 hrs to drive to work on a sunny day. Member Since: 21 juillet 2008 Posts: 4 Comments: 2233

424. Squid28 22:39 GMT le 25 août 2011
The national news is heavily featuring Irene tonight with a very strong emphasis on impcats to the N.E. I hope no harm comes to anyone, but I really hope those on the fence or in denial start to listen. Member Since: 23 mai 2006 Posts: 0 Comments: 343

425. cheetaking 22:39 GMT le 25 août 2011
Irene just decided to wake up... I expect some significant strengthening by the 8:00 update, and the Gulf Stream is dead-ahead. On a positive note, though, it just took a huge jog to the east. Member Since: 18 août 2009 Posts: 0 Comments: 162

426. Patrap 22:39 GMT le 25 août 2011
Storm Relative 1km Geostationary Visible Imagery Member Since: 3 juillet 2005 Posts: 372 Comments: 111641

429. MiamiHurricanes09 22:40 GMT le 25 août 2011
Next center fix likely to find another 1-2mb dip. Member Since: 2 septembre 2009 Posts: 129 Comments: 19976

430. AVL 22:40 GMT le 25 août 2011
Quoting bwat: Dude, I live in NC, that should of been a gimmie. :) More important things to discuss, I'll go back to lurking now, my appologies. LOL...Me to and in the Mountains... Member Since: 23 août 2011 Posts: 0 Comments: 15

431. Angela Fritz, Atmospheric Scientist (Admin) 22:40 GMT le 25 août 2011
Still concerned about the weak outflow on the southwest side. That whole quadrant looks like it's struggling. I think the Hurricane Center's intensity forecast is wise.

432. taistelutipu 22:40 GMT le 25 août 2011
Quoting atmoaggie: Was it? Fixed, though I didn't see it (maybe one of a lucky few that got through on the anonymous ID). Why would WU have the quoted post with an img tag open the connection to a server when it doesn't intend to show the image? Quick work atmoaggie, thanks a lot, 'tis highly appreciated. I still have the window with the source code open. If you are interested I can WUmail you the code - wouldn't dare to post it here. I might trigger another login pop-up. lol. I don't know why the entire code of the quoted post is copied into the quote box although it is not visible. You have to check the source code to see it. Nor do I know what could be done about it - I only know some basic html. Member Since: 20 août 2007 Posts: 10 Comments: 566

433. Patrap 22:40 GMT le 25 août 2011
Member Since: 3 juillet 2005 Posts: 372 Comments: 111641

434. TomTaylor 22:40 GMT le 25 août 2011
Quoting taistelutipu: Re #348 TomTaylor. Thanks for bringing that to our attention. Wow, what a buzzsaw, beautiful representation on sat images, but I'm very worried for the landmass to its left (Luzon, Philippines, if my geography doesn't desert me) - the coast is in the cone. As far as I know it's also densely populated. I hope the people there will be warned adequately to minimize loss of life. Two very dangerous storms threatening two densely populated coastlines simultaneously - this season is definitely no bust. Yea the northeastern side of Luzon (the largest island of the Philippines) will take a beating from Nanmadol. Rainfall/flooding will be a big issue with this storm (aside from the winds) since Nanmadol has been sitting off their coast for the last couple of days now and is forecasted to make landfall (or just graze the coast) in a day from now before slowly moving out. Member Since: 24 août 2010 Posts: 18 Comments: 3914

435. Ryuujin 22:40 GMT le 25 août 2011
Quoting angelafritz: Hi all, how's it going this afternoon? Hey Angela! Exciting and scary times at the moment, huh? Member Since: 20 août 2010 Posts: 0 Comments: 364

437. tornadolarkin 22:41 GMT le 25 août 2011
Im still quite surprised that NYC has no hurricane watches yet. Member Since: 1 mai 2010 Posts: 0 Comments: 352

438. TomTaylor 22:41 GMT le 25 août 2011
Quoting MiamiHurricanes09: Lol, pinhole on the satellite image. Shoulda clarified. Yea, I figured that's what you meant since I know you aren't no fool, but I thought I'd clear it up for the rest on here anyway. Member Since: 24 août 2010 Posts: 18 Comments: 3914

439. Patrap 22:42 GMT le 25 août 2011
Member Since: 3 juillet 2005 Posts: 372 Comments: 111641

441. beell 22:42 GMT le 25 août 2011
Quoting charlottefl: Analyzed differently here: We did lose the delicate cirrus outflow on the west side. Still-not a factor as of yet. I do think the dry air will continue to wrap in as the shear increases before landfall. Got some doubts about a CAT 4. But Irene is certainly looking good right now and a serious 3 will be bad enough. Member Since: 11 septembre 2007 Posts: 125 Comments: 12894

443. TampaSpin 22:43 GMT le 25 août 2011
Member Since: 2 septembre 2007 Posts: 175 Comments: 19747

444. tpabarb 22:43 GMT le 25 août 2011
UNC-Wilmington is having voluntary evacuations tomorrow (noon or 1, I forgot). Also Sam Champion just said that one hurricane track goes right over the empire state building?! Member Since: 20 octobre 2005 Posts: 0 Comments: 52

445. hurricanehunter27 22:43 GMT le 25 août 2011
Quoting angelafritz: Still concerned about the weak outflow on the southwest side. That whole quadrant looks like it's struggling. I think the Hurricane Center's intensity forecast is wise. Starting to look a little better. Member Since: 22 juillet 2010 Posts: 1 Comments: 3474

446. weatherdogg 22:43 GMT le 25 août 2011
Is it just me or does she still look pretty lopsided? Member Since: 5 septembre 2005 Posts: 0 Comments: 59

447. Fotograffa 22:44 GMT le 25 août 2011
Quoting angelafritz: Hi all, how's it going this afternoon? Doing pretty good so far Angela..waiting here in Atlantic City... How are you? Member Since: 6 juin 2005 Posts: 0 Comments: 50

448. jazzygal 22:44 GMT le 25 août 2011
Whoever fixed it. Thank you! Member Since: 2 juin 2008 Posts: 0 Comments: 155

449. charlottefl 22:44 GMT le 25 août 2011
Quoting Mucinex: CBS Evening News: Hurricane Watches and Warnings go out across the eastern U.S. The big question; Will cell phones work in a Hurricane? Seriously! That's the big question. Let the media chaos begin. LOL. That depends on a lot of different things. I know Verizon worked down here when Charley took everything out. Sprint was very spotty probably cause it was using a tower from the next city up. A lot of the cell towers in FL now have backup generators, not sure about the NE. Member Since: 18 décembre 2006 Posts: 7 Comments: 2672

450. 53rdWeatherRECON 22:44 GMT le 25 août 2011
Quoting angelafritz: Still concerned about the weak outflow on the southwest side. That whole quadrant looks like it's struggling. I think the Hurricane Center's intensity forecast is wise. Angela, please don't take this as disrespect. But are you sure your sure? Member Since: 5 août 2005 Posts: 2 Comments: 74

451. petrichor 22:44 GMT le 25 août 2011
Quoting angelafritz: Hi all, how's it going this afternoon? We seem to be getting along well, mostly. How are you doing? Thanks for the good work here! Member Since: 18 mai 2007 Posts: 0 Comments: 14

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