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 An upper-level outflow channel that was open to the south is gone, and has been replaced by shearing winds from the west and southwest that are ripping into the hurricane.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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1201. CarolinaHurricanes87 01:36 GMT le 26 août 2011
Quoting breald: I love Wilmington, NC. What an awesome place. I'll be there. Along with several other Wilmington NC residents on this blog. Should be interesting... a slight shift either way drastically changes the impacts for this area Member Since: 4 août 2011 Posts: 0 Comments: 471

1202. MZT 01:37 GMT le 26 août 2011
Quoting HiWay: this blog feels like it has gone from deep worry to resignation of the fact we're gonna get smacked hard and are just mesmerized by the size and power of her. People in coastal NC don't freak out so much, storms pass through quite often out there. What is less common is for storms to come directly ashore and affect the inland cities. The last one to really hit the interior hard was probably Fran in 1996 and Floyd in 1999. Although Ivan did some heavy flooding in the mountains by coming up the backside. Member Since: 24 septembre 2005 Posts: 0 Comments: 782

1204. robj144 01:37 GMT le 26 août 2011
Quoting weatherh98: whoa brian norcross just said that a jet streak* miight strengthen her before land fall in new york* Would that be a drunken fan at the Giants/Jets game? :) Member Since: 19 août 2008 Posts: 0 Comments: 820

1205. aspectre 01:37 GMT le 26 août 2011
H.Irene's_12amGMT_ATCF : Starting 25August_12amGMT and ending 26August_12amGMT The 4 shorter line-segments represent HurricaneIrene's path and the northernmost line-segment is the straightline projection. Using straightline projection of the travel-speed&heading derived from the ATCF coordinates spanning the 6hours between 6pmGMT then 12amGMT : H.Irene's travel-speed was 14mph(22.5k/h) on a heading of 351.6degrees(N) H.Irene was headed toward passage over SunsetBeach,NorthCarolina ~1day5hours from now Copy&paste tcb, mhh, 23.5n75.1w-24.1n75.9w, 24.1n75.9w-25.5n76.5w, 25.5n76.5w-26.5n77.2w, 26.5n77.2w-27.7n77.4w, jax, 26.5n77.2w-33.868n78.501w, cre into the GreatCircleMapper for more info The previous mapping (for 25August_6pmGMT) Member Since: 21 août 2007 Posts: 0 Comments: 4855

1206. Bluestorm5 01:37 GMT le 26 août 2011
Quoting ncstorm: Instead of an early dismissal tomorrow, they have closed schools all day tomorrow in New Hanover County and Brunswick County Johnston will not goes with early dismissal, because Irene is arriving at night. Football games COULD be moved up. Member Since: 1 août 2011 Posts: 12 Comments: 4305

1207. Tazmanian 01:37 GMT le 26 août 2011
Quoting TropicalAnalystwx13: Hurricane Irene's ATCF update - No change in strength: AL, 09, 2011082600, , BEST, 0, 277N, 774W, 100, 946, HU, 64, NEQ, 70, 60, 25, 50, 1008, 300, 30, 0, 0, L, 0, , 0, 0, IRENE, D, i think thats a little old? Member Since: 21 mai 2006 Posts: 5089 Comments: 111632

1208. charlottefl 01:37 GMT le 26 août 2011
Any change in wind speed is gonna lag the pressure drop a while, just because she has such a large area to spread that wind over... Member Since: 18 décembre 2006 Posts: 7 Comments: 2685

1211. LAnovice 01:38 GMT le 26 août 2011
Quoting TomTaylor: People have explained this several times now, but just to explain it one more time...winds are created by pressure gradients. The tighter/steeper the pressure gradient (the greater amount of change in pressure over a given area) the stronger the winds. Once you understand that, the reason behind Irene's relatively light winds despite a ~940mb pressure becomes clear; its because she is a large storm, and therefore, her pressure gradient isn't very steep. Ok got that - but the first question was why there were no vortex Member Since: 7 septembre 2007 Posts: 0 Comments: 356

1213. wunderweatherman123 01:38 GMT le 26 août 2011
Quoting TropicalAnalystwx13: Hurricane Irene's ATCF update - No change in strength: AL, 09, 2011082600, , BEST, 0, 277N, 774W, 100, 946, HU, 64, NEQ, 70, 60, 25, 50, 1008, 300, 30, 0, 0, L, 0, , 0, 0, IRENE, D, does that mean the nhc at 11pm wont bump irene back to a 120mph cat 3? because on satalite she sure looks like one... Member Since: 23 août 2011 Posts: 0 Comments: 843

1214. HurricaneStriker 01:38 GMT le 26 août 2011
Link Member Since: 21 juillet 2011 Posts: 0 Comments: 10

1215. MississippiWx 01:38 GMT le 26 août 2011
Quoting FLdewey: Big waves out there today... Surfers out in full force. Lol...Smoooooth... Member Since: 15 juillet 2006 Posts: 14 Comments: 8925

1216. Chucktown 01:38 GMT le 26 août 2011
Quoting chsstormgirl: Good to know... Schools in Charleston are still open... just hoping we don't get any tropical storm winds, because if they close the bridges I don't know how I would get home! If it happens, it won't be until after dark tomorrow. Winds are not expected to be sustained over TS force, just in the feeder bands that survive onshore. Member Since: 27 août 2006 Posts: 0 Comments: 1411

1218. RedrumATL 01:39 GMT le 26 août 2011
Quoting WeatherNerdPR: Meanwhile in Puerto Rico, images from the flooding on Tuesday: Wow - do you have power now? Member Since: 17 août 2011 Posts: 0 Comments: 106

1219. HiWay 01:39 GMT le 26 août 2011
Quoting MZT: People in coastal NC don't freak out so much, storms pass through quite often out there. What is less common is for storms to come directly ashore and affect the inland cities. The last one to really hit the interior hard was probably Fran in 1996. Although Ivan did some heavy flooding in the mountains by coming up the backside. Oh yeah, I'm in Raleigh myself. I'm glad to get back to talking about the actual storm stats instead of all the other mess. Member Since: 17 août 2007 Posts: 0 Comments: 55

1220. Levi32 01:39 GMT le 26 août 2011
Quoting NCSCguy: Levi, if your on here, what do you think of the way the trough is shaping up? You can see the base of it is already starting to lift out over Pennsylvania. It leaving will help Irene move right up the coast before the next trough comes in behind it. Member Since: 24 novembre 2005 Posts: 593 Comments: 25612

1221. TropicalAnalystwx13 01:39 GMT le 26 août 2011
Quoting Tazmanian: i think thats a little old? No, it says the 8/26/11. Member Since: 6 juillet 2010 Posts: 92 Comments: 25992

1222. Remek 01:39 GMT le 26 août 2011
Quoting CarolinaHurricanes87: If it doesnt increase the winds, are there any other effects a lower pressure can cause? Storm surge height. Member Since: 29 août 2005 Posts: 0 Comments: 118

1223. redwagon 01:39 GMT le 26 août 2011
Quoting TampaSpin: I am not here to scare of frighten anyone......but, i just tell ya what i see and my thoughts.....i am NO MET! These tracks moving more and more west.. I expect thousands of people to pop in saying my met just said so and so, is it true? They're not, which worries me. Member Since: 4 août 2007 Posts: 0 Comments: 1487

1224. 900MB 01:39 GMT le 26 août 2011
Quoting NoVaForecaster: J-E-T-S JETS JETS JETS!!!! Yes a Jets fan in Northern Virginia. And not a bandwagoner either. Now back to the storm. Wind probabilities from NHC. Still a 10% chance it is still a Cat 3 when it approaches NYC, and that is not good. More like 5% (Sun 2pm), but what's 5% between friends (except the Giants rule)? Might be 10% by tomorrow morning though. Member Since: 11 juin 2006 Posts: 0 Comments: 615

1225. weatherh98 01:39 GMT le 26 août 2011
Quoting SCwannabe: would that be people streaking at a Jets game... lol who knows just kidding its like a pulse in the jetstream that will suck air out of iit temporairily increasing the wind Member Since: 17 juin 2011 Posts: 11 Comments: 6302

1226. chsstormgirl 01:40 GMT le 26 août 2011
Quoting Chucktown: If it happens, it won't be until after dark tomorrow. Winds are not expected to be sustained over TS force, just in the feeder bands that survive onshore. Yeah.... I was just hoping for an extra day of planning tomorrow, that's all. Students are not the only ones who want a hurricane day! Member Since: 20 septembre 2007 Posts: 0 Comments: 118

1227. TropicalAnalystwx13 01:40 GMT le 26 août 2011
Quoting Levi32: You can see the base of it is already starting to lift out over Pennsylvania. It leaving will help Irene move right up the coast before the next trough comes in behind it. Levi, what is the latest in terms of your projected path. I know I asked this yesterday, and the day before, but I am going to ask tomorrow too. LOL. Member Since: 6 juillet 2010 Posts: 92 Comments: 25992

1228. aasmith26 01:40 GMT le 26 août 2011
Getting dry on the shelves here in VA... Member Since: 30 juin 2006 Posts: 5 Comments: 226

1229. TomTaylor 01:40 GMT le 26 août 2011
Quoting LAnovice: Ok got that - but the first question was why there were no vortex not sure, that's up to recon to make the vortex messages Member Since: 24 août 2010 Posts: 18 Comments: 4053

1230. IceCoast 01:41 GMT le 26 août 2011
Quoting TampaSpin: I'm not sure now a Cat.5 might not look impossible.....Conditions are very good. I strongly disagree. Conditions need to be perfect for a Cat 5. Irene is still under a little shear from the SW which although is not detrimental, will not allow her to intensify to Cat5. Could also be dealing with some dry air on the western side. I say there's about a 1% chance of Cat5 status just as the NHC says, although Cat4 is still a possibility. Member Since: 17 octobre 2010 Posts: 0 Comments: 1260

1231. WeatherNerdPR 01:41 GMT le 26 août 2011
Quoting RedrumATL: Wow - do you have power now? I was spared - the Northeastern Half wasn't. Member Since: 7 juillet 2010 Posts: 0 Comments: 5490

1232. RedrumATL 01:41 GMT le 26 août 2011
Quoting GeoffreyWPB: OK - that's NOT GOOD! RI expected IMO. Member Since: 17 août 2011 Posts: 0 Comments: 106

1234. wunderweatherman123 01:42 GMT le 26 août 2011
Quoting TropicalAnalystwx13: No, it says the 8/26/11. well actually, it shows the same exact coordinates from the 8pm advisory 27.7N and 77.4W so it doesnt look new to me Member Since: 23 août 2011 Posts: 0 Comments: 843

1235. MississippiWx 01:42 GMT le 26 août 2011
Irene doesn't have the appearance of a hurricane that wants to rapidly intensify. Gradual strengthening is more likely because of the shear and dry air issues. While they aren't significant, they are enough to keep her from rapidly intensifying. Member Since: 15 juillet 2006 Posts: 14 Comments: 8925

1236. TropicalAnalystwx13 01:43 GMT le 26 août 2011
Quoting MississippiWx: Irene doesn't have the appearance of a hurricane that wants to rapidly intensify. Gradual strengthening is more likely because of the shear and dry air issues. While they aren't significant, they are enough to keep her from rapidly intensifying. Since when did rapid intensification have a look? :P Member Since: 6 juillet 2010 Posts: 92 Comments: 25992

1237. Brock31 01:43 GMT le 26 août 2011
Super fun waves here at Wrightsville Beach. Making final preparations. Moving vehicles to a "less flood prone" location. We'll see what Irene has for us tomorrow. Member Since: 22 août 2011 Posts: 0 Comments: 95

1238. Hou77083 01:43 GMT le 26 août 2011
Quoting lottotexas: Let me see if I understand this; Giants/Jets game to be played at 2pm on Sat. Game over around 6pm. Massive traffic jams with people leaving NY and at least a cat1 bearing down and weather already deteriorating. Whats wrong with this picture??? Is the NFL stupid. not stupid, just money hungry. Member Since: 5 juillet 2010 Posts: 0 Comments: 86

1239. presslord 01:43 GMT le 26 août 2011
Quoting FLdewey: Big waves out there today... Surfers out in full force. nice swells Member Since: 13 août 2007 Posts: 0 Comments: 10407

1240. wunderweatherman123 01:43 GMT le 26 août 2011
Quoting MississippiWx: Irene doesn't have the appearance of a hurricane that wants to rapidly intensify. Gradual strengthening is more likely because of the shear and dry air issues. While they aren't significant, they are enough to keep her from rapidly intensifying. yeah well if she takes her time she could still get up to 125 to 135mph. not RI but slow steady intensification and after that slow weakining Member Since: 23 août 2011 Posts: 0 Comments: 843

1241. jdjnola 01:44 GMT le 26 août 2011
Quoting HiWay: Just an observation, but since land fall seems to be a done deal now; the mood of this blog feels like it has gone from deep worry to resignation of the fact we're gonna get smacked hard and are just mesmerized by the size and power of her. Agreed. Things have slowed down considerably since the NHC track narrowed. Love your goggle cat avatar btw. Member Since: 4 août 2008 Posts: 0 Comments: 238

1242. Mikla 01:44 GMT le 26 août 2011
Member Since: 13 octobre 2006 Posts: 0 Comments: 227

1243. weatherh98 01:44 GMT le 26 août 2011
is it safe to saythe eyewall is back Member Since: 17 juin 2011 Posts: 11 Comments: 6302

1244. HurricaneStriker 01:44 GMT le 26 août 2011
Has anyone been hearing about the rip currents in Florida? Normally they mention a lot about them in coast storms like Earl but so far I havent heard anything "rip current" on Irene. Member Since: 21 juillet 2011 Posts: 0 Comments: 10

1245. owntime 01:44 GMT le 26 août 2011
Quoting HurricaneDean07: Thinking NYC will be spared, NC probably going to take the brunt, and kick Irene down a knotch(Weak Cat2, Strong Cat 1), after landfall as Weak Cat 3/Strong Cat 2. Then Irene will be 75 mph Cat 1, near NYC Jim Cantore is in NYC so look out. I wish this thing would just go out to sea, it is huge. Member Since: 28 septembre 2007 Posts: 0 Comments: 87

1246. MississippiWx 01:45 GMT le 26 août 2011
Quoting TropicalAnalystwx13: Since when did rapid intensification have a look? :P Since it was easy to tell when a hurricane is suffering from shear and dry air...lol. Member Since: 15 juillet 2006 Posts: 14 Comments: 8925

1247. MrstormX 01:45 GMT le 26 août 2011
Irene is not under RI, just gradual intensification Member Since: 27 mai 2009 Posts: 0 Comments: 4312

1248. jascott1967 01:45 GMT le 26 août 2011
IMHO, I think the CONUS will be spared. I've been consistent on this. It would not be at all unusual for this storm to curve north east and out to sea. Member Since: 16 août 2007 Posts: 0 Comments: 516

1249. 1900hurricane 01:45 GMT le 26 août 2011
Latest pass indicates continued organization: Member Since: 2 août 2006 Posts: 43 Comments: 10456

1250. chelseag 01:46 GMT le 26 août 2011
From Williamsburg, Va. Friends say shelves are emptying. We went through Isabel and are "I hope" prepared for Irene. Will try to provide pics/video, but worst is expected in the dark. Stay safe!!! Member Since: 15 octobre 2007 Posts: 0 Comments: 6

1251. Vero1 01:46 GMT le 26 août 2011
Quoting owntime: Jim Cantore is in NYC so look out. I wish this thing would just go out to sea, it is huge. Somebody tweet him to Bermuda. Member Since: 21 juillet 2008 Posts: 4 Comments: 2233

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