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 An upper-level outflow channel that was open to the south is gone, and has been replaced by shearing winds from the west and southwest that are ripping into the hurricane.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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501. chicagowatcher 22:57 GMT le 25 août 2011
Quoting WthrBearSF: Being a total amateur, is there any possibility that wide swath of dry air will be able to affect Irene, or is the eye wall strengthening too quickly? Thanks! You know, I thought this was an interesting question. Many times we've seen a strong hurricane quickly drop in intensity when it approaches continental landfall as it entrains so much dry air (surge and flooding of course still a major danger). As Irene may spend so much time over land the next couple of days, I wonder if she'll drop in intensity and become massive, but disorganized storm? (but still providing surge and freshwater flooding concerns in at-risk areas) Member Since: 28 août 2005 Posts: 0 Comments: 153

502. Patrap 22:57 GMT le 25 août 2011
Storm Relative 1km Geostationary Visible Imagery Member Since: 3 juillet 2005 Posts: 377 Comments: 112981

503. wunderweatherman123 22:58 GMT le 25 août 2011
Quoting MississippiWx: Irene will have a limited amount of time to take advantage of leaving behind the upper level low. When she gets north of 30N, she'll start having to deal with southwesterly shear from the approaching trough, as well as continental air. However, she could be stronger than she is now by then and much less susceptible to those impediments. She most likely won't strengthen any when those issues begin to impact her, though. bascially if she gets to a high cat 3 low end cat 4 and mantains/slowly weakens she could still be a 3 at landfall remember larger storms can take more shear than smaller ones and irene is HUGE Member Since: 23 août 2011 Posts: 0 Comments: 843

504. crzyboutncweather 22:59 GMT le 25 août 2011
I have been looking around the forums today, I am currently near Charlotte but just moved my family to Camp Lejeune NC where I will be stationed. Does anyone know if Grandpato4 left and went to his daughters in Raleigh. I hope so because its going to be bad on Topsail Island. Just a little worried for him. Member Since: 5 septembre 2007 Posts: 0 Comments: 37

505. TampaSpin 22:59 GMT le 25 août 2011
Quoting angelafritz: I don't know if I'd want to be in Atlantic City this weekend! :) Might wanna go today or tomorrow.....it won't look the same come Saturday and Sunday i'm afraid! I think one can Bet on that! Member Since: 2 septembre 2007 Posts: 176 Comments: 19767

506. MississippiWx 23:00 GMT le 25 août 2011
Quoting wunderweatherman123: bascially if she gets to a high cat 3 low end cat 4 and mantains/slowly weakens she could still be a 3 at landfall remember larger storms can take more shear than smaller ones and irene is HUGE If she's going to become a low end Cat 4, tonight is the night to make those steps. If her core can stay together, it's possible. Member Since: 15 juillet 2006 Posts: 14 Comments: 8909

507. EYEStoSEA 23:00 GMT le 25 août 2011
Member Since: 16 septembre 2010 Posts: 0 Comments: 1491

509. taistelutipu 23:00 GMT le 25 août 2011
Quoting Titoxd: Fixed it. I replaced the direct link to the image with a link to the image source. You can click on it if you still want to see what the IKE values were. Thanks, I'll have a look at it now that it's safe to do so, lol. Member Since: 20 août 2007 Posts: 10 Comments: 578

510. MarcoIslandCat5 23:01 GMT le 25 août 2011
Eye's Closed let the fireworks begin!! Member Since: 26 octobre 2010 Posts: 0 Comments: 50

511. TomTaylor 23:01 GMT le 25 août 2011
Quoting gulfbreeze: Should that get better as it moves to the North? For a little while, yes. We should keep in mind that the ULL to the SW really isn't a very big issue at the moment. It's certainly not a big enough issue to prevent Irene from strengthening. Anyway, over the next 18-24 hours the limited outflow or upper divergence to the south west will improve as the ULL over the east Gulf backs away. Beyond the next day or so, the trough will approach Irene and begin inflicting more shear and upper convergence (which limits outflow) along the western side. Member Since: 24 août 2010 Posts: 18 Comments: 4053

512. Gatorxgrrrl 23:01 GMT le 25 août 2011
Hi Angela - You taken the night shift? I have enjoyed your updates. No free trip to Atlantic City for you??lol Member Since: 10 mai 2007 Posts: 70 Comments: 15596

513. TampaSpin 23:02 GMT le 25 août 2011
I know the NHC is currently not Forecasting a CAT 4 but, Irene sure looks to be on her way now......DANG! Member Since: 2 septembre 2007 Posts: 176 Comments: 19767

514. HurricaneDean07 23:02 GMT le 25 août 2011
Irene should likely be 120 to 125 Mph at Intermediate advisory, Pressure of 946 MB. moving NNW... Member Since: 3 octobre 2010 Posts: 40 Comments: 4129

515. mbphoto 23:02 GMT le 25 août 2011
Weather guy here in Myrtle Beach said pretty much a non event. A little wind but not enough to do anything. Said don't evacuate and don't board up window. Member Since: 3 septembre 2008 Posts: 0 Comments: 0

516. Gatorxgrrrl 23:02 GMT le 25 août 2011
Ironically the rainbands are going way inland in florida and missing the coast now. Member Since: 10 mai 2007 Posts: 70 Comments: 15596

517. redwagon 23:03 GMT le 25 août 2011
Quoting violet312s: Inverse situations: a) Snow forecasted for NC: mass panic and clearing of grocery store shelves of items needed to make french toast (milk, bread and eggs) You can actually make a pretty good french toast with power out using 3 or 4 Sternos. Stuff it with cream cheese and top with blueberries and syrup for extra AM energy. I'd go ahead and take a big jar of instant coffee, add sugar and water to make a liquid for iced coffee. And get all your laundry done now. Member Since: 4 août 2007 Posts: 0 Comments: 1487

518. MississippiWx 23:04 GMT le 25 août 2011
To get an idea of how much Irene has grown today, click the link below. Stop the loop on the first frame, then click the back button and it will take you to the last frame. It's pretty amazing. Link Member Since: 15 juillet 2006 Posts: 14 Comments: 8909

519. Patrap 23:04 GMT le 25 août 2011
Member Since: 3 juillet 2005 Posts: 377 Comments: 112981

520. fortpiercecane1 23:04 GMT le 25 août 2011
We had some decent squalls in Stuart,Fl, but it looks like the most of the rest is going to stay offshore. Member Since: 22 août 2011 Posts: 0 Comments: 35

522. TampaSpin 23:05 GMT le 25 août 2011
The BAM MODELS and BAMD are keeping Irene just off shore. Member Since: 2 septembre 2007 Posts: 176 Comments: 19767

523. Gatorxgrrrl 23:05 GMT le 25 août 2011
She looks to being going due north now Member Since: 10 mai 2007 Posts: 70 Comments: 15596

524. Elena85Vet 23:05 GMT le 25 août 2011
Interesting intensity downgrade prior to NC landfall. I hope folks don't let their guards down and realize there is still going to be storm surge and the potential for inland flooding. Member Since: 18 août 2008 Posts: 0 Comments: 619

525. nrtiwlnvragn 23:05 GMT le 25 août 2011
Quoting scotths: I'm trying to learn more about the models that are used for hurricane prediction. Reading through the various information it appears that some models are called "late" as they are not available at the time of the nhc update. I notice that at least at the present time this site is showing interpolated models and models from the last set of runs for the late models. When the new model runs become available will they be posted on this site, is there another site that provides such information, or will we generally have to wait for the next nhc update to see the information? (I'm particularly interested due to the apparent push to the west) The models on WU and other sites are generally updated within an hour of synoptic time, 06Z (2AM EDT), 12Z (8AM EDT), 18Z (2PM EDT) and 00Z (8PM EDT). Another site to use is here, where you can choose which of the early or late models you want to see. Member Since: 23 septembre 2005 Posts: 12 Comments: 9094

526. Joshfsu123 23:06 GMT le 25 août 2011
Quoting P451: As we continue to pull from the islands, and the core continues to organize and deepen, the wobbles will probably smooth out. As you can see it's still wobbling but the storm continues west of north. One thing to note for the WobbleWatchers is that there are two types. There is the curly cue wobble which Irene has had since before it was even declared a storm - and if you watch a long term loop you can place a fairly straight line and watch the eye wobble around it...yet the storm will keep that same steady heading over time. There is a stairstep wobble when Earl did last summer which can have an effect on an overall course of a storm over time. Just keep this in mind. Irene's wobbles have not affected the overall outcome of her heading. Earl's wobbles did - they brought him closer to the coast than forecasted. great post! Member Since: 6 juillet 2005 Posts: 5 Comments: 575

527. MississippiWx 23:06 GMT le 25 août 2011
@reedtimmerTVN Reed Timmer Irene looks to be the strongest it's ever been. Not good timing for U.S. Member Since: 15 juillet 2006 Posts: 14 Comments: 8909

528. redux 23:06 GMT le 25 août 2011
so what would happen if Irene did go up the chesapeake? could she maintain cat 2 strength? Member Since: 28 juin 2010 Posts: 0 Comments: 183

529. cg2916 23:06 GMT le 25 août 2011
Oh no, Sunset Beach! Dang it, Irene! Member Since: 21 décembre 2007 Posts: 13 Comments: 2955

530. Stormchaser2007 23:07 GMT le 25 août 2011
I should be in NE NJ by noon tomorrow. Member Since: 9 juin 2007 Posts: 4 Comments: 15295

531. MrMixon 23:07 GMT le 25 août 2011
Quoting HurricaneDean07: Wow, a lot of Flight level winds at 130 mph Maybe jets heading through the area could use Irene to get a little boost and save some fuel. Hey, if you hit it just right it could work... Member Since: 26 Mars 2006 Posts: 40 Comments: 1090

532. TampaSpin 23:07 GMT le 25 août 2011
Quoting P451: As we continue to pull from the islands, and the core continues to organize and deepen, the wobbles will probably smooth out. As you can see it's still wobbling but the storm continues west of north. One thing to note for the WobbleWatchers is that there are two types. There is the curly cue wobble which Irene has had since before it was even declared a storm - and if you watch a long term loop you can place a fairly straight line and watch the eye wobble around it...yet the storm will keep that same steady heading over time. There is a stairstep wobble when Earl did last summer which can have an effect on an overall course of a storm over time. Just keep this in mind. Irene's wobbles have not affected the overall outcome of her heading. Earl's wobbles did - they brought him closer to the coast than forecasted. Its the Wobble just before coming ashore that is the bad wobble for some and good wobble for others. Member Since: 2 septembre 2007 Posts: 176 Comments: 19767

534. petewxwatcher 23:07 GMT le 25 août 2011
Quoting Stormchaser2007: Should be in NE NJ by noon tomorrow. Since you modified your comment I will modify mine :) Member Since: 24 Mars 2011 Posts: 3 Comments: 392

535. Hurricanes12 23:08 GMT le 25 août 2011
Quoting P451: As we continue to pull from the islands, and the core continues to organize and deepen, the wobbles will probably smooth out. As you can see it's still wobbling but the storm continues west of north. One thing to note for the WobbleWatchers is that there are two types. There is the curly cue wobble which Irene has had since before it was even declared a storm - and if you watch a long term loop you can place a fairly straight line and watch the eye wobble around it...yet the storm will keep that same steady heading over time. There is a stairstep wobble when Earl did last summer which can have an effect on an overall course of a storm over time. Just keep this in mind. Irene's wobbles have not affected the overall outcome of her heading. Earl's wobbles did - they brought him closer to the coast than forecasted. I always enjoy your drawings and explanations. Keep it up. :-) Member Since: 21 juin 2010 Posts: 0 Comments: 528

536. beell 23:08 GMT le 25 août 2011
Quoting twincomanche: Irene is not going to spend a lot of time over land unless it goes West and if you look at the CONUS radar* you will see a lot of moisture coming at here, not dry air.* Water vapor loops probably work a little better. Eastern US Water Vapor Loop Member Since: 11 septembre 2007 Posts: 126 Comments: 13069

537. Stormchaser2007 23:08 GMT le 25 août 2011
Member Since: 9 juin 2007 Posts: 4 Comments: 15295

538. cjswilmingtoneye 23:08 GMT le 25 août 2011
I'm in Kure Beach, NC(southern New Hanover county) can see the upper level cloudiness building in and getting thicker, just had a sprinkle. The ocean has become a little more excite but still pretty calm. The latest NWS forecast is calling for sustained winds between 55-65 mph with gusts to 80 mph on Saturday. We're stocked and ready to go. As of now, we're under a voluntary evacuation, we'll see what happens tomorrow. Member Since: 1 juin 2009 Posts: 0 Comments: 107

539. Stormchaser2007 23:08 GMT le 25 août 2011
Quoting petewxwatcher: More like noon Sunday. "I should be in NE NJ by noon tomorrow." Member Since: 9 juin 2007 Posts: 4 Comments: 15295

540. GTcooliebai 23:09 GMT le 25 août 2011
Quoting P451: As we continue to pull from the islands, and the core continues to organize and deepen, the wobbles will probably smooth out. As you can see it's still wobbling but the storm continues west of north. One thing to note for the WobbleWatchers is that there are two types. There is the curly cue wobble which Irene has had since before it was even declared a storm - and if you watch a long term loop you can place a fairly straight line and watch the eye wobble around it...yet the storm will keep that same steady heading over time. There is a stairstep wobble when Earl did last summer which can have an effect on an overall course of a storm over time. Just keep this in mind. Irene's wobbles have not affected the overall outcome of her heading. Earl's wobbles did - they brought him closer to the coast than forecasted. Physics 101 right here, thanks for the explanation and drawings. Member Since: 31 août 2009 Posts: 0 Comments: 5460

541. HurricaneDean07 23:10 GMT le 25 août 2011
Could see a lower pressure than the last past from the second recon... This is still east of the center, Time: 23:05:00Z Coordinates: 27.45N 77.2667W Acft. Static Air Press: 696.6 mb (~ 20.57 inHg) Acft. Geopotential Hgt: 2,680 meters (~ 8,793 feet) Extrap. Sfc. Press: 946.4 mb (~ 27.95 inHg) D-value: - Flt. Lvl. Wind (30s): From 189° at 22 knots (From the S at ~ 25.3 mph) Air Temp: 15.8°C (~ 60.4°F) Dew Pt: 5.5°C (~ 41.9°F) Peak (10s) Flt. Lvl. Wind: 25 knots (~ 28.7 mph) SFMR Peak (10s) Sfc. Wind: 33 knots (~ 37.9 mph) SFMR Rain Rate: 0 mm/hr (~ 0 in/hr Member Since: 3 octobre 2010 Posts: 40 Comments: 4129

542. wn1995 23:11 GMT le 25 août 2011
If anyone is interested, my tropical update for today: http://www.youtube.com/watch?v=Z6FONaPBFoc Member Since: 17 juillet 2011 Posts: 1 Comments: 207

543. MississippiWx 23:11 GMT le 25 août 2011
Quoting Stormchaser2007: "I should be in NE NJ by noon tomorrow." If you're flying from Florida, you should bring the camera on the plane and take some pictures to your east. You'll probably have a pretty awesome view. Member Since: 15 juillet 2006 Posts: 14 Comments: 8909

544. Elena85Vet 23:12 GMT le 25 août 2011
"528. redux 6:06 PM CDT on August 25, 2011 so what would happen if Irene did go up the chesapeake? could she maintain cat 2 strength?" Yep. Particularly if moving fast. Member Since: 18 août 2008 Posts: 0 Comments: 619

545. TampaSpin 23:12 GMT le 25 août 2011
Member Since: 2 septembre 2007 Posts: 176 Comments: 19767

546. petewxwatcher 23:12 GMT le 25 août 2011
Quoting MississippiWx: To get an idea of how much Irene has grown today, click the link below. Stop the loop on the first frame, then click the back button and it will take you to the last frame. It's pretty amazing. Link Part of that is because it's a visible shot. Thin cirrus that are mostly transparent or translucent become more opaque as the sun approaches the horizon. Member Since: 24 Mars 2011 Posts: 3 Comments: 392

547. Bielle 23:13 GMT le 25 août 2011
Quoting P451: Everyone preparing big time up north here. Stores in NJ, NY, CT are just flooded like crazy. And it will just get worse. "Flooded"? From what? Member Since: 18 septembre 2008 Posts: 0 Comments: 603

549. Patrap 23:13 GMT le 25 août 2011
Storm Relative 1km Geostationary Visible Imagery Member Since: 3 juillet 2005 Posts: 377 Comments: 112981

550. Stormchaser2007 23:13 GMT le 25 août 2011
946.4 mb (~ 27.95 inHg) Member Since: 9 juin 2007 Posts: 4 Comments: 15295

551. MiamiHurricanes09 23:14 GMT le 25 août 2011
Still haven't reached the circulation. Wouldn't be too surprised to see Irene enter a phase of rapid intensification with a solid core taking shape. Additionally, upper-level winds should be pretty favorable and cyclone will be above the Gulf Stream. 230500 2727N 07716W 6966 02680 9464 +158 +055 189022 025 033 000 00 Member Since: 2 septembre 2009 Posts: 129 Comments: 20011

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