Dr. Jeff Masters' WunderBlog

Irene slightly weaker, but still very dangerous

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

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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 An upper-level outflow channel that was open to the south is gone, and has been replaced by shearing winds from the west and southwest that are ripping into the hurricane.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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1751. Patrap 03:09 GMT le 26 août 2011
Big Duke NOLA-7 Signing off at 22:09 CDT Member Since: 3 juillet 2005 Posts: 370 Comments: 111244

1752. AllyBama 03:10 GMT le 26 août 2011
Why does something so deadly and diasterous look so beautiful. Member Since: 3 août 2006 Posts: 131 Comments: 20499

1753. MIsland321 03:10 GMT le 26 août 2011
Going east of next point. Going out to sea. I am sure this is a near fish. I did not think that earlier. Will make people more skeptical next time. Hope I'm correct! Or not? Member Since: 22 mai 2007 Posts: 0 Comments: 3

1754. amd 03:10 GMT le 26 août 2011
Quoting atmosweather: Depends on if she can close her eyewall back up to the S and SW, it is still open according to the NOAA plane and a little ragged looking at satellite imagery but if she continues to improve in organization the winds could very well catch up to the low pressure. Both planes have consistently seemed to find very intense winds from 850mb to 925 mb which is an indication that an improvement in her internal core will allow those types of winds to reach the surface. yeah, and I also think intense convection forming along the eastern and northeastern eye-wall for the first time in a long while will finally begin the process of allowing stronger winds to concentrate back toward the center instead of extending out away from the center. Member Since: 29 août 2005 Posts: 0 Comments: 1024

1755. presslord 03:10 GMT le 26 août 2011
Quoting AllyBama: Why does something so deadly and diasterous look so beautiful. not at all unusual with women Member Since: 13 août 2007 Posts: 0 Comments: 10377

1756. westernmob 03:10 GMT le 26 août 2011
NE Turn, Here Fishy Fishy. Member Since: 6 avril 2004 Posts: 0 Comments: 71

1757. MZT 03:10 GMT le 26 août 2011
Clear, cool night air in Charlotte. Expect to wake up and see the outer cirrus tomorrow though. Member Since: 24 septembre 2005 Posts: 0 Comments: 775

1758. TampaSpin 03:10 GMT le 26 août 2011
Good nite everyone.......BE SAFE Member Since: 2 septembre 2007 Posts: 175 Comments: 19747

1760. TexasMariner 03:11 GMT le 26 août 2011
Hello everyone. I am knew to posting here, but by far not new to this blog or Tropical Weather. I have been lurking here since 2003. I live on the upper Texas coast, as my name suggests, and have weathered several recent storms, including Rita and Ike. Sadly, I am not a meteorologist, although at one point I considered that career path, I chose instead to become a Marine Engineer and am working toward that job. That said, I do hope people are taking Irene seriously. The storm has a comparable diameter to Ike and a comparable wind field (albeit with far better structure and higher intensity). The storm surge is going to be one of its biggest threats, especially as these areas along the east coast have not seen a storm like this in many years. Member Since: 25 août 2011 Posts: 0 Comments: 54

1761. tiggeriffic 03:11 GMT le 26 août 2011
Quoting presslord: there are ssoo many ways I can go with this...and not a one of them would be appropriate... boy you sure are full of piss and vinegar tonight... lol :P Member Since: 16 septembre 2007 Posts: 0 Comments: 3592

1762. angiest 03:11 GMT le 26 août 2011
Quoting wolftribe2009: I am finding it very ODD that Hurricane Irene's pressure has dropped to 942 MB which is the threshold for a Minimal CAT 4 Hurricane; however the storm remains at a Minimum CAT 3 The discussions were the same for Ike and Alex. Member Since: 26 août 2006 Posts: 16 Comments: 4757

1763. KoritheMan 03:11 GMT le 26 août 2011
Quoting charlottefl: Well that was kinda my point lol :p Touche. ;) Member Since: 7 Mars 2007 Posts: 408 Comments: 15418

1764. SouthDadeFish 03:11 GMT le 26 août 2011
Quoting wolftribe2009: I am finding it very ODD that Hurricane Irene's pressure has dropped to 942 MB which is the threshold for a Minimal CAT 4 Hurricane; however the storm remains at a Minimum CAT 3 That chart is a HUGE generalization and the reason they changed the Saffir-Simpson Hurricane Scale to the Saffir-Simpson Hurricane Wind Scale. Each storm is different, for example look at Ike. He caused surge damage nowhere near the category two range. Storm surge depends on many factors other than maximum sustained winds. Also pressure can be different for each storm, depending on the size of the storm. Member Since: 12 août 2007 Posts: 11 Comments: 2413

1765. bassis 03:12 GMT le 26 août 2011
Quoting Patrap: Big Duke NOLA-7 Signing off at 22:09 CDT Sleep well. see ya in the am Member Since: 8 septembre 2008 Posts: 0 Comments: 422

1766. BiloxiBlues 03:12 GMT le 26 août 2011
Turn NE you MoFo...Fish are waiting for you. Member Since: 8 juillet 2005 Posts: 0 Comments: 19

1767. KoritheMan 03:12 GMT le 26 août 2011
Quoting AllyBama: Why does something so deadly and diasterous look so beautiful. One of the many mysteries of life. Member Since: 7 Mars 2007 Posts: 408 Comments: 15418

1768. tornadolarkin 03:12 GMT le 26 août 2011
Irene is a time bomb pretty much waiting to go off. Member Since: 1 mai 2010 Posts: 0 Comments: 352

1769. bassis 03:12 GMT le 26 août 2011
Quoting MZT: Clear, cool night air in Charlotte. Expect to wake up and see the outer cirrus tomorrow though. Agreed, I'm in concord Member Since: 8 septembre 2008 Posts: 0 Comments: 422

1770. KEEPEROFTHEGATE (Mod) 03:12 GMT le 26 août 2011
Member Since: 15 juillet 2006 Posts: 143 Comments: 40398

1772. KEEPEROFTHEGATE (Mod) 03:13 GMT le 26 août 2011
Member Since: 15 juillet 2006 Posts: 143 Comments: 40398

1773. osuwxguynew 03:13 GMT le 26 août 2011
Quoting wolftribe2009: I am finding it very ODD that Hurricane Irene's pressure has dropped to 942 MB which is the threshold for a Minimal CAT 4 Hurricane; however the storm remains at a Minimum CAT 3 REPOST AS THE ANSWER TO SEVERAL OF THE SAME QUESTION: I need to clear something up. The reason that Irene's winds are lower than would be expected is because of the size of the storm and the relaxed pressure gradient within it. If you were following the storm on recon earlier this week, there would be a steep drop of pressure as the plane flew through the eye and then a sharp increase. This might have occurred over a single relayed message in the recon data. NOW however, the plane will fly in a direction for several messages and all the reading will be sub 980. The storm has removed a huge amount of mass from its center which will make her resistant to weakening much over the next couple days as she heads north. However it is the pressure GRADIENT force that drives winds. So the slow transition of pressure means that her winds are no longer 115mph even thoug her pressure is lower. The pressure GRADIENT force (pgf) is why a 1006 tropical storm can have 60mph winds when it's butting up against a strong Bermuda High, or a storm can have 990mb pressure and have the same 60 mph winds when it is in a larger region of low ambient pressure. The change in pressure over the distance is what drives wind speed. Member Since: 15 juin 2010 Posts: 0 Comments: 291

1774. MiamiHurricanes09 03:13 GMT le 26 août 2011
Extrap pressure already jacked up with Recon lol. Member Since: 2 septembre 2009 Posts: 129 Comments: 19976

1775. MelbourneTom 03:14 GMT le 26 août 2011
A big jog to the East. I hope it holds, would be a big dfference to NC. Member Since: 2 juin 2007 Posts: 0 Comments: 600

1777. crazywxguy 03:16 GMT le 26 août 2011
Quoting MelbourneTom: A big jog to the East. I hope it holds, would be a big dfference to NC. Looking at the latest image it appears to moving due north Member Since: 24 août 2011 Posts: 0 Comments: 2

1778. njdevil 03:16 GMT le 26 août 2011
Last 3 hour run was .6N .1E. Looks to be east of 8PM center cone at 2AM. If that's a trend and not just a wobble it might be headed more for a track like a couple of days ago Member Since: 9 juillet 2008 Posts: 0 Comments: 145

1779. Vero1 03:16 GMT le 26 août 2011
Quoting presslord: there are ssoo many ways I can go with this...and not a one of them would be appropriate... We will leave in the context of "disaster relief". Member Since: 21 juillet 2008 Posts: 4 Comments: 2233

1780. 996tt 03:16 GMT le 26 août 2011
NE turn coming. Stay off shore baby. Waves will be good tomorrow. Member Since: 5 septembre 2008 Posts: 0 Comments: 308

1781. Maryland1 03:17 GMT le 26 août 2011
early today, helped my friends down on the South River near Annapolis. Tomorrow, people will suddenly get what is about to go down here. I've live through a few and this one I am legitimately scared of. Member Since: 26 août 2008 Posts: 0 Comments: 122

1782. FlyingScotsman 03:17 GMT le 26 août 2011
Just checked CNN's home page, and couldn't find a single mention of Irene! Now that's just irresponsible... For once, Fox is actually the reliable one (they have a big home page headline about it). Member Since: 1 septembre 2010 Posts: 5 Comments: 125

1783. crazywxguy 03:18 GMT le 26 août 2011
Quoting njdevil: Last 3 hour run was .6N .1E. Looks to be east of 8PM center cone at 2AM. If that's a trend and not just a wobble it might be headed more for a track like a couple of days ago It's getting tugged by the trough moving by....then it will get pushed back west a little then go back to due north till nc Member Since: 24 août 2011 Posts: 0 Comments: 2

1784. KoritheMan 03:18 GMT le 26 août 2011
Quoting Tazmanian: POOF bye bye Quoting BiloxiBlues: Turned north to soon for you wishcaster. I am ordinarily not one to get involved in petty skirmishes, but the both of you just need to calm down. No one wants Irene to cause destruction or death, but arguing about this isn't helping. People come here for valuable information, and in cases where a landfall is imminent, bickering will only serve to dissuade those people. Member Since: 7 Mars 2007 Posts: 408 Comments: 15418

1786. StlChrispy 03:19 GMT le 26 août 2011
Quoting FlyingScotsman: Just checked CNN's home page, and couldn't find a single mention of Irene! Now that's just irresponsible... For once, Fox is actually the reliable one (they have a big home page headline about it). That's kinda disgusting! Member Since: 23 août 2011 Posts: 0 Comments: 9

1787. Hibiscus07 03:19 GMT le 26 août 2011
uhhhhh...Irene is looking pretty darn far east of the tracking points here: http://www.ssd.noaa.gov/goes/flt/t2/flash-rb-s.htm l Good for NC, bad for us New Englanders. Thoughts on this? Think she will getback on track or is this a permanent eastward shift? Member Since: 30 juillet 2010 Posts: 0 Comments: 10

1788. charlottefl 03:19 GMT le 26 août 2011
Thought this was interesting. Superimposed Irene's wind field on Irene's 11AM Advisory from this past Sunday: Member Since: 18 décembre 2006 Posts: 7 Comments: 2672

1789. TexasMariner 03:19 GMT le 26 août 2011
"Last 3 hour run was .6N .1E. Looks to be east of 8PM center cone at 2AM. If that's a trend and not just a wobble it might be headed more for a track like a couple of days ago" Seems like its just a wobble. These things tend to do alot of that especially when they become as large (in terms of overall circulation) as Irene is. Ike did quite a bit of stair-step type wobbling prior to its landfall. That's not to say, it would be really great if something changed and this thing was able to turn out to sea a bit, but right now just don't see that in the cards. Member Since: 25 août 2011 Posts: 0 Comments: 54

1790. IFuSAYso 03:19 GMT le 26 août 2011
Quoting AllyBama: Why does something so deadly and diasterous look so beautiful. Sounds like my last marriage. Member Since: 8 Mars 2011 Posts: 0 Comments: 112

1792. houstongator 03:20 GMT le 26 août 2011
Quoting SouthDadeFish: Yeah but why use Isabel's data when she was not at her largest? Because the discussion was that Isabel was very big, but still at high winds. I didn't know the whole data - but I find it interesting that Isabel was much smaller (half the size) while at "Ludicrous" speed (160 mph) and then as it got bigger, the wind speeds slowed (or it could be the other way around). But the gist of the discussion was that large hurricanes can still have high wind speeds and while Isabel was of significant size while at 160 mph, Irene covers twice the area right now as Isabel when she was at that speed. Member Since: 28 août 2005 Posts: 0 Comments: 109

1793. 996tt 03:20 GMT le 26 août 2011
Quoting crazywxguy: Looking at the latest image it appears to moving due north Wobbly, but NE looking to me which is great news, especially for the surf. Swell should be clean tomorrow, especially the further east this thing turns. Models maybe following BAM. Nonetheless, wave are huge and should be epic when winds shift offshore tomorrow he in East Florida. Member Since: 5 septembre 2008 Posts: 0 Comments: 308

1794. CloudGatherer 03:20 GMT le 26 août 2011
Quoting charlottefl: NOAA BUOY 41010 LOCATED ABOUT 140 MILES...220 KM EAST OF CAPE CANAVERAL FLORIDA RECENTLY REPORTED A SUSTAINED WIND OF 49 MPH...79 KM/H... AND A WIND GUST OF 65 MPH...104 KM/H. And it's currently finding waves of 34.8 ft - this is some storm. Member Since: 18 août 2009 Posts: 0 Comments: 453

1795. ncstorm 03:21 GMT le 26 août 2011
Member Since: 19 août 2006 Posts: 7 Comments: 8350

1796. wolftribe2009 03:21 GMT le 26 août 2011
Quoting P451: Thanks, Taz, there it is folks the 937mb extrapolation is tossed out as suspect. I haven't been comfortable with the westward model tracks from earlier this afternoon and still am not. I continue to maintain and repeat we will have no handle on this storm's track until it crosses the outer banks. Until the those of us up in the NYC area just do not know what exactly to expect. Any shifts east down south yield a huge change to the weather up north here. Seen it so many times. I could see hurricane conditions or I could see absolutely nothing come Sunday. Won't really know until Saturday early morning IMO. Well, with the 11pm in, time to knock off and let Irene head to her peak over night. See what we got in the AM. That is true but the NE turn is probably your WORST enemy right now (Sorry North Carolina) but NY/RI/NJ ETC wants this storm to have some time over the land of the Outerbanks. If she stays just off shore it isn't going to be good. The models all are showing a sharp left turn once she gets north of NC I do hope she continues NE and spares the US her right side of her fury. Member Since: 22 juillet 2010 Posts: 6 Comments: 752

1797. violet312s 03:21 GMT le 26 août 2011
Greg Fishel on WRAL rocks. I'm off to bed now. Member Since: 1 juin 2007 Posts: 0 Comments: 769

1798. atmosweather 03:21 GMT le 26 août 2011
Quoting SouthDadeFish: That chart is a HUGE generalization and the reason they changed the Saffir-Simpson Hurricane Scale to the Saffir-Simpson Hurricane Wind Scale. Each storm is different, for example look at Ike. He caused surge damage nowhere near the category two range. Storm surge depends on many factors other than maximum sustained winds. Also pressure can be different for each storm, depending on the size of the storm. Hurricanes are like human beings, no one is exactly alike and they all behave differently. Member Since: 24 septembre 2005 Posts: 33 Comments: 9255

1799. TheF1Man 03:21 GMT le 26 août 2011
Quoting TexasMariner: Hello everyone. I am knew to posting here, but by far not new to this blog or Tropical Weather. I have been lurking here since 2003. I live on the upper Texas coast, as my name suggests, and have weathered several recent storms, including Rita and Ike. Sadly, I am not a meteorologist, although at one point I considered that career path, I chose instead to become a Marine Engineer and am working toward that job. That said, I do hope people are taking Irene seriously. The storm has a comparable diameter to Ike and a comparable wind field (albeit with far better structure and higher intensity). The storm surge is going to be one of its biggest threats, especially as these areas along the east coast have not seen a storm like this in many years. Welcome to the madness! Member Since: 23 février 2010 Posts: 0 Comments: 571

1800. houstongator 03:22 GMT le 26 août 2011
Quoting presslord: not at all unusual with women Where's the "Like" button? Member Since: 28 août 2005 Posts: 0 Comments: 109

1801. Melagoo 03:22 GMT le 26 août 2011
I think it is pretty apparent that Irene will hit the USA/Canada ... it is just where exactly will it hit Member Since: 31 juillet 2006 Posts: 19 Comments: 1510

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