Hurricane Irene Prepares to Leave the Bahamas and Head for the US

By: Dr. Jeff Masters , 7:51 AM GMT on August 25, 2011

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As of 2AM EDT, Hurricane Irene was located at 24.2N, 76.0W, 105 miles east-southeast of Nassau or 760 miles south of Cape Hatteras. It was moving northwest at 12 mph with maximum sustained winds of 115 mph, making it a Category 3 storm on the Saffir-Simpson scale. Irene has a minimum central pressure of 950 mb. Hurricane force winds can be found up to 70 miles from Irene's center, and tropical storm force winds can be found out to 255 miles from the storm's center.

Hurricane warnings are in effect for all of the Bahamas. Hurricane and tropical storm watches will likely be posted for the Carolina coastlines later this morning. At this time, Dare County Emergency Management has issued a mandatory evacuation order for all visitors in their county. Dare County Schools will also be closed Thursday and Friday.

Satellite Views
Figure 1 is the infrared satellite image of Irene at 135EDT. The convection is a bit unbalanced around the storm center, which is going to cause Irene to wobble like an unbalanced clothes washer (Analogy courtesy of Angela Fritz) over the next few hours. At the time this image was taken, the convection around Irene's center appears to be getting more vigorous, as cold cloudtops are starting to increase around the storm center. This is important to note because microwave satellite imagery from Wednesday evening suggested Irene was starting an eyewall replacement cycle. Figure 2 shows passive microwave imagery from a Air Force DMSP polar-orbiting satellite. The two concentric green/yellow bands in the image suggest that two eyewall features are present in Irene, and Hurricane Hunter observations confirm this. This has important consequences for Irene's intensity, because in an eyewall replacement cycle, as the inner eyewall weakens, the storm's intensity drops. However, once the inner eyewall is gone, and the outer eyewall contracts to replace it, the storm intensity will increase again.


Figure 1 IR satellite view of Irene taken at 113AM EDT, August 23, 2011


Figure 2 DMSP F18 microwave overpass of Irene at 824PM EDT, August 24, 2011. Image courtesy of the Naval Research Laboratory

Track Forecast

Irene is forecast to move to the northwest, passing over the northwest Bahamas by Thursday evening, then curving to the northeast. Irene then makes landfall in the US near or at the Outer Banks Saturday afternoon, then traveling along the mid-Atlantic coastline of the US. Sunday, Irene may make secondary landfall anywhere from New Jersey to Long Island and the southern New England coastline. In my opinion, New York City may be significantly impacted by Irene. It is also important to note that the windfield of Irene is expected to be large, affecting areas distant from the immediate track of Irene's center. Tropical storm forces winds are expected to be found out to at least 150 miles away from Irene's center on Friday afternoon.

NHC is forecasting for Irene to become a Category 4 storm (winds faster than 130 mph) by Thursday morning. As Irene moves northward into cooler water, the intensity is expected to drop slowly to a Category 2 storm before making landfall in the Outer Banks.


Figure 3 Official track forecast of Irene at 2AM EDT.

Forecast models and today's planned flights
The different forecast models are still in fairly good agreement about Irene's track through the Bahamas and along the east coast of the US. The 00Z GFS run is in close agreement with the 12Z ECMWF run, but the 00Z ECMWF run (shown in figure 4) is continuing the ECMWF's trend of shifting the track westward with each run. NHC forecasters have been placing emphasis on the ECMWF's forecast track when making their forecasts for IRene, so it is possible that the NHC track will shift westwards at the 5AM update.

Looking at the plan of the day valid for today, it will be a busy day for airborne reconnaissance. Three flights for the Air Force hurricane hunters, two flights for the Gulfstream IV (Gonzo), and two flights for NOAA 42, a WP-3D (Kermit). They may have to give NOAA a littering permit for all of the dropsondes used to monitor Irene and her environment, but the forecast improvements they generate are worth the effort.


Figure 4 Plot of the maximum sustained winds in mph over the next week from the 00Z ECMWF forecast.

Impacts

Hurricane force winds will arrive in the northwestern Bahamas today. Storm surge near the center of Irene will be 7-11 feet above tide level. The Bahamas can expect 6-12 inches of rain over the next day or so, and it looks like the Turks and Caicos islands will receive a total of 6-12 inches from Irene. Large, swells from Irene will start landing on the southeastern US coastline later today. Please don't go in the water, as these swells can cause dangerous rip currents. Dr. Masters has catalogued the worst-case storm surge surge scenarios as a function of storm intensity here.

In my opinion, people living from the Carolinas to Cape Cod should pay close attention to Irene and prepare for a wide range of impacts. I think that there is a 75% chance of Irene's secondary landfall will be somewhere between JFK airport and Cape Cod. That said, Irene's size will cause significant impacts for people living far from it's center.

Dr. Masters will have a new blog entry this morning, and Angela Fritz will be covering the afternoon. I'll be back on third shift tonight.

Thanks for reading,

Dr. Rob Carver

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Quoting FLdewey:
Maybe we'll get some spouts...



woot woot

Did you ever see and/or use this NWS waterspout activity calculator (or one like it), Dewey? It works. I used it one day last summer, saw things were favorable, and went to the beach one afternoon and set up my camera while just a short line of cumulus drifted offshore. A curious passerby asked what I was shooting, and I said "waterspouts". Literally as he noted there were none, one started snaking down just a mile offshore. I think he thought I was magic... ;-)

- - - - - - - - - - - - - -
Note: The waterspout calculations do not include stability or moisture parameters. Before using make sure stability and moisture parameters are high enough to support at least widely scattered showers over the coastal waters.
ACARS / Sounding mean wind speed and direction______________

1.) If mean wind below 15,000 feet is (equal to or less than) 8 knots
and max layer wind speed 12 kt or below then.........................add 1.0
(If max layer wind is between 12 kt and 15 kt then only add 0.5)
If mean wind below 15,000 feet is between 9 and 11 kt and
max layer wind speed 15 kt or less then............................add 0.5
(If max layer wind above 15 kt then add 0)

If mean wind below 15,000 feet is greater 12 kt or greater then..add 0
Wind Speed Factor_________
2.) If mean wind direction below 15,000 feet is:

Between 010-069 degrees.............................add 0.5
Between 070-209 degrees.............................add 1.0
Between 210-289 degrees.............................add 0.5
Between 290-360 degrees.......................subtract 0.5

Wind Direction Factor_________
3.) If previous day had waterspout activity and no major synoptic
change expected then.............................................. ...............add 1.0
(Treat waterspouts in Keys and SE Coast Seperately)
Persistence Factor_________

TOTAL WATERSPOUT POTENTIAL________
If total equals 2.0 then waterspouts are possible.
If total equals 2.5 or 3.0 then waterspouts potential is high.
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http://radar.weather.gov/radar.php?product=N0Z&rid= amx&loop=yes
Member Since: June 16, 2010 Posts: 0 Comments: 86
The last averaged 4......12Zs for Irenes movement are, starting with the most recent..... 1) NW or 314 degrees 2)NW or 314 degrees 3)NW or 310 degrees 4) NW or 305 degrees........ Per Tropical Atlantic....... As you can see Irene has not continued a trend to the N, to make the current 12z stay the same . In fact she would have had to trended back to the W a little in the last 6 hours according to the current average 12Z.
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Just started to get a downpour here in So. Florida....
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Quoting nrtiwlnvragn:
NWS is going all out for the models. Normally on the 06Z and 18Z model runs very few upper air obs are included. A few days ago they requested obs at those times in the eastern region.

18Z obs yesterday:




Last night NWS requested more stations, 06Z obs this morning:



That's a lot of sounding...
Member Since: August 14, 2008 Posts: 4 Comments: 4881
Quoting liljade:
Could share the link please?


Link

The 06Z run is now out too. Pick the run you want at the top, then select which parameter you want half way down, then which hour/loop you want at the bottom.
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NOAA are really going all out for this one.

Seems pretty bad in the Bahamas, just hope there's no fatalities. If buildings are lost, they can be replaced; if lives are lost, they can't.

Big heatwave in some parts of Europe, first really all year. It's been a quiet summer. It's mainly in the Med though, northern areas not getting a thing. Been quite a few storms apparently though, looks like that will continue.

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recent recon data

Time: 11:01:30Z
Coordinates: 25.25N 75.7833W
Acft. Static Air Press: 750.5 mb (~ 22.16 inHg)
Acft. Geopotential Hgt: 2,291 meters (~ 7,516 feet)
Extrap. Sfc. Press: 978.0 mb (~ 28.88 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 168° at 114 knots (From the SSE at ~ 131.1 mph)
Air Temp: 12.3°C* (~ 54.1°F*)
Dew Pt: -*
Peak (10s) Flt. Lvl. Wind: 116 knots (~ 133.4 mph)
SFMR Peak (10s) Sfc. Wind: 83 knots (~ 95.4 mph)
SFMR Rain Rate: 51 mm/hr (~ 2.01 in/hr)
(*) Denotes suspect data
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Link


Miami radar
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Ok I see it getting awfully close to South Florida. I still don't have to worry about it right? I gotta make the call if I should take my daughter to school. Are you still "Confident" the turn is going to happen soon?
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From 168° at 114 knots
(From the SSE at ~ 131.1 mph) 12.3°C*
(~ 54.1°F*) -* 116 knots
(~ 133.4 mph)
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Well, my classroom is calling me, full of IEPs and little angels. Everyone have a great Thursday. Those who need to prepare or think they might need to, do it. Those who need to evacuate, make your plans. Better safe than sorry.
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Quoting tpabarb:


I'm surprised too. I'm close to downtown Wilmington and I think I might leave anyway, is that weird? The storm is passing by in the middle of the night, and what if it does jog west and I'm sitting here in the dark w/my dog, w/stuff flying around outside. My landlord wouldn't board the windows up anyway.


Id consider it, you have to do what you feel comfortable with. However, I would keep a very close eye on this one and wait it out for now. Be ready to evacuate, but by early tomorow you will have a much better idea if it is necessary- and still time to leave (albeit not much. you need to be ready to go, but have time to make the final decision tomorow AM).

Just my 2 cents. As of now were still predicted only to receive tropical storm force winds, and a 2-4 ft surge. If you live in low lying flood prone areas downtown, I'd maybe consider evacuating a little more. I personally live in a very safe spot (from flooding) and no trees... so I'll be staying
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Quoting NICycloneChaser:
Morning/Evening all.

Thought I'd start the day with a little picture of the 00Z GFS at 384 hours.



Just for giggles.
Could share the link please?
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Quoting ProgressivePulse:



Negative NAO favors east coast troughing like we seen at the beginning of the season. NAO was a record 68 days negative. Positive NAO favors east coast ridging.


Ah, okay. Getting mixed up lol.
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Quoting whepton3:


If that's where we think the center is, looks like the storm is just a tick east of forecast track.

And I do mean a tick... barely.


Still wobbling a lot. Took a wobble Nward earlier, still seems on track however.
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227. MahFL
If the weakness is over GA, then why has the track not changed to GA ?
Member Since: June 9, 2004 Posts: 0 Comments: 2905
Quoting NICycloneChaser:


And also stronger and more frequent troughs.



Negative NAO favors east coast troughing like we seen at the beginning of the season. NAO was a record 68 days negative. Positive NAO favors east coast ridging.
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Quoting ProgressivePulse:
Indeed just west of central Eluthera, whom is taking a beating it the eastern eyewall right now.

25.1333N 76.3W


If that's where we think the center is, looks like the storm is just a tick east of forecast track.

And I do mean a tick... barely.
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First band associated with irene moving in through portions of South Florida!
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Quoting ProgressivePulse:
Anyone notice this in the latest center fix?

D. Estimated (by SFMR or visually) Maximum Surface Wind: 55kts (~ 63.3mph)


Yes, but I also noticed this:

Maximum Flight Level Wind: 112kts (~ 128.9mph) in the northeast quadrant at 10:32:00Z

There's no way that 130mph flight level winds support 65mph at the surface lol
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Quoting beell:
Selected dropsonde locations and 500mb heights from the current NOAA Gulfstream flight with an amateur guess at the current western edge of the A/B ridge indicated by the 5890 meter heights. Lower heights to the east of this line.

For today-on track for a northward movement.

click to enlarge.

Beell: Could you please explain what your map represents? What is A/B ridge and its importance? Thank you.
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going to get it again http://en.wikipedia.org/wiki/Hope_Town
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the NHC on GMA just said that they expect Irene to only be going 15-20 mph which is much slower than normal for NE. longer periods of wind and rain but maybe knock her down a bit over the cooler waters?
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Quoting ProgressivePulse:
Anyone notice this in the latest center fix?

D. Estimated (by SFMR or visually) Maximum Surface Wind: 55kts (~ 63.3mph)


SFMR has been malfunctioning.
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NWS is going all out for the models. Normally on the 06Z and 18Z model runs very few upper air obs are included. A few days ago they requested obs at those times in the eastern region.

18Z obs yesterday:




Last night NWS requested more stations, 06Z obs this morning:

Member Since: September 23, 2005 Posts: 13 Comments: 10458
Quoting wxobsvps:


steering maps just a snapshot...they update every 3 hrs and you may see the atl high back off, allowing the weakness to migrate off-shore.


So am I correct in reading it though? If the maps stayed the same it would head NNW right into the coast... but the trough is supposed to erode away the high back to the east a bit?
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Anyone notice this in the latest center fix?

D. Estimated (by SFMR or visually) Maximum Surface Wind: 55kts (~ 63.3mph)
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Quoting ProgressivePulse:



NAO was trending positive yesterday at -.1 should switch positive today which will result in a stronger Bermuda high.


And also stronger and more frequent troughs.
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Quoting oceanblues32:
getting our first feeder bands coming through wind picked up and it is raining very hard right now in dania beach florida just south of ft lauderdale!!

Here on Florida's southwest coast, the air is crystal clear and nearly calm. There is, however, a line of cirrus to the east running from the southern horizon to the northern, clearly the tops of the thunderstorms making up the westernmost fringe of Irene's. So thankful she won't be coming any closer to us...
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Quoting islander101010:
hopefully get on the east side hope town taking a direct hit again



Me too, never like to see folks in the NE eyewall.
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209. beell
Selected dropsonde locations and 500mb heights from the current NOAA Gulfstream flight with an amateur guess at the current western edge of the A/B ridge indicated by the 5890 meter heights. Lower heights to the CORR: west of this line.

For today-on track for a northward movement-or perhaps slightly W of N.

click to enlarge.

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Quoting ProgressivePulse:



That's too bad, they got a pounding in the NE eyewall. Looks like it will past just west of Great Abaco next.
hopefully get on the east side hope town taking a direct hit again the economy has given these folks a good beating the past few yrs
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Quoting WxLogic:
Pretty strong Bermuda High:



You can see that the weakness sure have displaced W some from a previous E Coast position.



NAO was trending positive yesterday at -.1 should switch positive today which will result in a stronger Bermuda high.
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Quoting FLdewey:
Maybe we'll get some spouts...



woot woot


I wish I didn't have to work... I'd heard down near Deerfield Beach pier and get some pics.

Also probably stop at Whale's Rib for the oysters.
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Quoting SCwannabe:


you got to watch it like a hawk today...


I know, its crazy... tropical storm conditions om the left side of the storm... or if it pushes idk, 20, 30, 50 miles west? We would be getting the eye/eyewall of a major hurricane. Weird setup, hope the NHC is right... Im sure they must be or theyd have put us in the hurricane watch to be safe
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Quoting CarolinaHurricanes87:
No hurricane watch for Wilmington. A little surprised given how close Irene is predicted to be off our coast.... I guess this means the NHC is pretty confident the models wont shift much further (if any) west than they already have...


I'm surprised too. I'm close to downtown Wilmington and I think I might leave anyway, is that weird? The storm is passing by in the middle of the night, and what if it does jog west and I'm sitting here in the dark w/my dog, w/stuff flying around outside. My landlord wouldn't board the windows up anyway.
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TWC strong language?
but no storm alert
http://www.weather.com/weather/videos/news-41/top -stories-169/forbes-first-thunderstorms-then-irene -21670

what the heck??
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Quoting oceanblues32:
not to take interest off irene but does anyone know what the blob is that sits over florida next friday through wednesday on the gfs?

getting our first feeder bands coming through wind picked up and it is raining very hard right now in dania beach florida just south of ft lauderdale!!
cool1 Thanks for the update! The storm will most likely draw in dry air for us and give us a beautiful sunny day in Key West. It happens quite often with north moving storms that are east of us.
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Quoting wxobsvps:


Similar set up, with the ULL over the GoM, that tracked Hugo into the SC coast. Difference here is the Bermuda high isn't oriented se/nw into the midatlantic states.


I didn't know that...an ULL was in play with Hugo? We have an ULL in the GOM now that looks to be retrograding SW a bit
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Quoting KeyWestwx:
06Z GFS at 384 hours. Of course, it is a very long way out and doesn't necessarily mean anything, but looks like we may have a 1-2 pattern, first recurves, next heads west.

This is what the GFDL predicted 12 hours ago, now the GFS. That last minute hook to the West in Southern NY could be bad news. I hope the news hypes this up soon. I never like hype but people in Eastern NY/NJ area need to know all the possibilities of the storm and not get caught off guard


I wasn't referring to Irene, I was referring to two possible storms at 384 hours.

That's 2 weeks out, Irene is long gone by then.
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Good morning all!!!

Including Irene!

She just heralded in the day here in Boca with a pretty sporty li'l squall passing through as I type.
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.