Irene's eyewall collapses; further intensification unlikely

By: Dr. Jeff Masters , 3:14 PM GMT on August 26, 2011

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Satellite data and measurements from the Hurricane Hunters show that Irene is weakening. A 9:21 am EDT center fix by an Air Force Reserve aircraft found that Irene's eyewall had collapsed, and the central pressure had risen to 946 mb from a low of 942 mb this morning. The highest winds measured at their flight level of 10,000 feet were 125 mph, which would normally support classifying Irene as a Category 3 hurricane with 115 mph winds. However, these winds were not mixing down to the surface in the way we typically see with hurricanes, and the strongest surface winds seen by the aircraft with their SFMR instrument were just 90 mph in the storm's northeast eyewall. Assuming the aircraft missed sampling the strongest winds of the hurricane, it's a good guess that Irene is a mid-strength Category 2 hurricane with 100 mph winds. 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 wind shear of 10 - 20 knots due to upper-level winds out of the southwest. 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 Wlimington, North Carolina, shows that the outermost spiral bands from Irene are now beginning to come ashore along the South Carolina/North Carolina border. Winds at buoy 41004 100 miles offshore from Charleston, SC increased to 36 mph as of 10 am, with significant wave heights of 18 feet.


Figure 1. Distribution of Irene's wind field at 9:30 am 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 and storm surge potential for Irene
With its eyewall collapsed and just 24 more hours over water before landfall, it is unlikely Irene will 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 Category 2 hurricane at landfall in North Carolina on Saturday, and a rapidly weakening Category 1 hurricane at its second landfall in New England on Sunday. 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 9:30am EDT this morning, a wind analysis from NOAA/HRD (Figure 1) indicated that the potential storm surge damage from Irene rated a 5.1 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 gradually decline as Irene moves northwards and weakens, we can still expect a storm surge one full Saffir-Simpson Category higher than Irene's winds. 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. A surge rivaling that experienced during Hurricane Isabel in 2003 is likely in northern NC, southern Maryland, and up Chesapeake Bay on Saturday night. Coastal New England from New York City to Massachusetts may also see storm surges characteristic of a Category 1 hurricane during Sunday morning's high tide, even if Irene has weakened to a tropical storm. I continue to give a 20% chance that a storm surge high enough to over-top the Manhattan flood walls and swamp the New York City subway system will occur on Sunday.

Wind damage
I don't think Irene is going to do a lot of wind damage to the mid-Atlantic states, since the eye of the storm will be just offshore, and the I-95 corridor from Virginia to New Jersey will be on the weak (left) side of the hurricane. The current wind distribution of Irene (Figure 1) shows almost all of the hurricane's winds are on the right side of the storm, and by the time the storm reaches Virginia, there will be likely be no hurricane-force winds on the left side of Irene. Sustained winds should stay below 74 mph (hurricane force), and wind damage will be similar to that wrought be some of the strongest Nor'easters of the past 20 years, from Virginia northwards to New York City. Since Irene will be steadily weakening as it approaches its second landfall on Long Island, I give a 50% chance that no mainland U.S. surface station in New England will record sustained hurricane-force winds. I do think it likely that one or more of the offshore islands--Block Island, Nantucket, and Marthas Vinyard--will get Category 1 hurricane winds. Though the wind damage to buildings will be similar to what the Northeast has seen during some of the more severe nor'easters of the past 20 years, tree damage will be much worse. The trees are in full leaf during hurricane season, and catch the wind much more readily than during the winter. Tree damage will very heavy, and we can expect trees in regions with saturated soils will fall over in high winds onto power lines. Irene is likely to cause one of the top-five most widespread power outages in American history from a storm. The record power outage from a Northeast storm was probably the ten million people that lost power during the great Blizzard of 1993. I don't think Irene's power outages will be quite that extensive, but several million people will likely lose power.

Irene likely to bring destructive fresh water flooding
In addition to storm surge, flash flooding and river flooding from Irene's torrential rains are the main threats. The hurricane is expected to bring rains in excess of 8" to a 100-mile-wide 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. New Jersey has had its 6th wettest August on record, with most of that rain falling in the past two weeks. Expect major river flooding throughout New Jersey the Delmarva Peninsula, and regions near New York City, as Irene's rains run off the saturated soils directly into the rivers. 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. I don't think flooding from heavy rains will be a huge concern in North Carolina, which is under moderate to severe drought. Irene's rains are likely to do some good in Southeast Virginia, where a fire triggered by lightning from a thunderstorm on August 4 sparked a fire in the Dismal Swamp that is burning out of control. 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 Wednesday August 31, as issued by NOAA/HPC.

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 there, and I will be available if my schedule permits. Listeners can email in or call in questions. The email address to ask questions is broadcast@wunderground.com.

Portlight mobilizes for Irene
The Bahamas have been hit hard by Irene, and unfortunately, it appears that the Northeast U.S. may have its share of hurricane victims before Irene finally dissipates. My favorite disaster relief charity, Portlight.org, is mobilizing to help, and has sent out their relief trailer and crew to North Carolina. Check out this blog to see what they're up to; donations are always needed.

Jeff Masters

Hurricane Irene's Wrath ! (MikeTheiss)
A shot of the Palm Trees at Nassau, Bahamas being thrashed by high winds during Irene's closest approach !
Hurricane Irene's Wrath !
Aftremath of Hurricane Irene in Nassau, Bahamas (ktbahamas)
Utility pole with street light snapped in half by Irene's winds on a busy street in New Providence.
Aftremath of Hurricane Irene in Nassau, Bahamas
Irene Response (presslord)
Portlight deploying to North Carolina
Irene Response

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329. MahFL
Bagdad Bob just told me "there is no eye in the hurricane".





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Quoting P451:


It is. It's clearing back out. See post 244 and watch the NAM imagery play out. It pegged this real well.





Please keep in mind, folks, that as any storm heads north and leaves the deep tropics, you will see the -70C cloud tops warm to the -60C ranges or even less. This is not an indication of a rapidly weakening cyclone. The higher latitudes don't support those colder convective cloud tops in large cyclones. You're dealing with a different atmosphere.

Some very intense nor'easters only have cloud tops in the -40C range - and they produce torrential rain.

Just because you no longer see a thick ring of reds and purples this is not to be considered a rapid weakening.

Her structure has improved quite well the past few hours now.


Glad I'm not the only one seeing all of this. Great analysis.
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Quoting EastTexJake:
What I'd be most worried about in NYC or any really big city, is the number of indigent, government dependant people, whom rarely plan for disaster. What's going to happen if they wake up to find the power out, no fresh water, the busses and trains don't run, and the streets are clogged with debris, making it impossible for law enforcement to respond, even if the police and fire crews weren't already all busy. The storm wont kill that many I think, but the aftermath might be a warzone.


New York City survived the largest blackout in history with zero problems. This post in completely inappropriate.
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Live broadcast by Ustream
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Quoting weatherb0y:
If Hurricane Irene's eyewall has collapsed, why is it that her eye is reappearing as per the RGB and visible channels?


there is a big difference between the center of circulation and an eye wall
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Quoting hurricanejunky:
The flood potential has always been the main concern and that threat isn't going away no matter how weak Irene gets.


+10 and I hope the newscasters are emphasizing that
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Quoting FLdewey:


Pressha be droppin!


The last frame of the loop Keep posted shows what looks to be a reformed eye popping out.
Member Since: August 29, 2010 Posts: 0 Comments: 5236
power company cut power to ecsurfing tournament they are operating on batteries 24 hrs as much money as they put into the community i would think they could wait a hr or more to finish it up
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Quoting PrivateIdaho:
Off shore from Edisto Island SC. 21' waves.

Link
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Surely some rebuilding to do.
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316. Gorty
Quoting hurricanejunky:
The flood potential has always been the main concern and that threat isn't going away no matter how weak Irene gets.


People keeps downplaying the LARGE wind field of damaging winds that will affect NE and New England.
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307. Will Robinson?
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313. Gorty
Wow her bands are getting far away from the center. Dry air is not affecting her much.
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Quoting surfsidesindy:


Sending her all the dry air we can from Florida and keeping all in harms way in our prayers.


Thank you! LOL.

Reds on IR have vanished and the convective appearance of Irene continuing to degrade.
Member Since: June 29, 2009 Posts: 13 Comments: 5300
The flood potential has always been the main concern and that threat isn't going away no matter how weak Irene gets.
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Quoting P451:


Where are you located?

I was in Jersey on Wednesday and by late afternoon the ocean changed and you could tell the first outer most swells were moving in.

If you're looking for storm surge then check the buoys and see what you find. It's out there.


Uhh i just went through the hurricane, Nassau Bahamas. Like.. when Igor passed to our northeast last year... it generated HUGE swells for me! this one was much closer, and not even a swell, just chop.
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This buoy is SE of Wrightville Beach NC. Should get some big swells here later on.

Member Since: August 29, 2010 Posts: 0 Comments: 5236
305. Vero1
As Hurricane Irene Moves Closer to East Coast, FEMA Continues Urging All Residents to Be Prepared
FEMA and Federal Partners Moving Teams and Commodities Throughout East Coast to Support States and Cities

Release Date: August 25, 2011
Release Number: HQ-11-137


...FEMA encourages everyone, regardless of whether they live in a hurricane-prone area, to take steps to ensure their families, homes and businesses are prepared for a possible emergency. As a reminder, the month of September is designated as National Preparedness Month (NPM), an opportunity to encourage Americans to be prepared for disasters or emergencies in their homes, businesses, and communities. Individuals and families can learn about events and activities, and groups can register to become a NPM Coalition Member by visiting community.fema.gov. NPM is sponsored by the Ready Campaign in partnership with Citizen Corps and The Ad Council.

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Quoting TideWaterWeather:
Latest Dvorak looking pretty weak

Link


Agreed that they aren't the strongest of the strong BUT much stronger on that south side than she's been - and that's what had been dragging Irene down to a 2.
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fading fading fading
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting AllStar17:


Keep swallowing up that dry air, Irene!


Sending her all the dry air we can from Florida and keeping all in harms way in our prayers.
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Irene is the prettiest she's ever been. Even the S/SW sides are fleshing out.

Yet her core is the weakest since early yesterday, or moreso.

Not much time for a comeback, but historically she build in the afternoons.
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Quoting SPLbeater:


Why are you posting pictures from yesterday?

Ooops, sorry, misread the date. Now I have my glasses on.
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Quoting MahFL:
Irene is like the Rocky films....she's on about the 5th re-make already ! And looking good too....must be all the plastic surgery......
Irene is the Joan Rivers of hurricanes?
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Quoting flcoopercrew:


oh wow, that certainly changes things. thanks
NYC will have experienced similar force winds from NorEasteners. I personally do not foresee extensive wind damage in the city proper. (Lived in lower Manhattan almost 3 yrs.) As Dr Jeff points out the larger issue will be downed trees due to the larger wind profile due to being in full leaf and the saturated soils.
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295. wpb
Quoting P451:
Looking improved for certain. The NAM (see post 244) accurately predicted the system weakening and then strengthening before NC.

same as gfdl
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Eye becomes visible on radar from: https://twitter.com/#!/wunderground/status/1071299 91141142528
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293. 900MB
Quoting P451:
Looking improved for certain. The NAM (see post 244) accurately predicted the system weakening and then strengthening before NC.



It "looks better", but if you look at the water vapor, funktop, or rainbow it is clear that the tops are warming significantly. It is gonna take alot of work for Irene to intensify. If anything it is deteriorating quickly over the past 2 hours.
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Quoting P451:
Looking improved for certain. The NAM (see post 244) accurately predicted the system weakening and then strengthening before NC.



Contrast values on vis sat images are changing constantly with sun angle. Using the visible shot for evaluation is problematic.
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291. TX2FL
Wow seems like the storm is now being downplayed for PA, NJ, NYC..alot of people will probably not evacuate now. What if it strengthens again??
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Quoting mojofearless:


This kind of smacks of condescension. I don't know if that was your intention - agreed that the aftermath could be very difficult. But indigent people in Manhattan? Have you been there lately?


In fact the closest I've been was a trip through JFK airport in the 80's. But the storm isn't going to only effect Manhatten.

Condescension wasn't my intention, I tried to make the wording as politically neutral as I could.
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Quoting weatherb0y:
If Hurricane Irene's eyewall has collapsed, why is it that her eye is reappearing as per the RGB and visible channels?


Yes, its obvious on that last frame.....
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287. Jax82
Looks like the eye is trying to clear out but she has dry air on the W and NW side of her. Lets hope she continues to weaken.
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Quoting ecupirate:
Isnt the NE quadrant the one that has the most issues with tornados from a land falling Hurricane?


Correct
Member Since: June 29, 2009 Posts: 13 Comments: 5300
Folly Island, In the dunes.

Member Since: August 29, 2010 Posts: 0 Comments: 5236
are hurricane hunters going into irene now?
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Quoting KEEPEROFTHEGATE:
09L/MH/I/C2
RI FLAG (off)
RD FLAG (flag)
MARK
30.48n/76.98w







ALWAYS FOLLOW NHC/TPC FORECASTS FOR ALL WARNINGS REGARDING THIS STORM

Am I wrong or does that look like an eye forming in the last few frames?
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281. wpb
gfdl had intensity down but shows increase prior to crossing the cost. check it out
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Isnt the NE quadrant the one that has the most issues with tornados from a land falling Hurricane?
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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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