Category 2 Irene Approaches The Bahamas

By: Dr. Jeff Masters , 7:51 AM GMT on August 23, 2011

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As of 2am EDT, Hurricane Irene was located at 20.1N, 69.7W, 135 miles southeast of Grand Turk Island. It was moving west-northwest at 12 mph with maximum sustained winds of 100 mph, making it a Category 2 storm on the Saffir-Simpson scale. Irene has a minimum central pressure of 978 mb. Hurricane warnings have been issued for the northern coast of the Dominican Republic from the Haiti board to Cabo Engano, the southeastern and central Bahamas, and the Turks and Caicos islands. Hurricane watches have been posted for the north coast of Haiti from Le Mole, St. Nicholas to the Dominican border and the northwestern Bahamas. Tropical storm warnings are in effect for all of Haiti and the southern coast of the Dominican Republic from Cabo Engano to Santo Domingo.

5AM Update
As of 5am EDT, Hurricane Irene was located at 20.3N, 70.1W, 105 miles southeast of Grand Turk Island. It was moving west-northwest at 12 mph with maximum sustained winds of 100 mph, keeping it a Category 2 storm on the Saffir-Simpson scale. Irene has a minimum central pressure of 978 mb.

Figure 1 shows that Irene is maturing into a vigorous storm, with apparent waves in the western edge of the cirrus outflow.


Figure 1 IR satellite view of Irene taken at 135AM EDT, August 22, 2011

Track Forecast

Irene is forecast to move to the north-northwest, passing over all of the Bahama islands by Thursday evening, at which points it starts curving to the north. Irene is forecast to make landfall in the US near Wilmington, NC Saturday evening. However, it is important to note that this is not a definitive forecast, the average forecast error for day 5 is 250 miles. The timing of Irene's recurvature depends on how quickly several small troughs of low pressure in the Northeastern US move to the east. After Saturday, Irene may pose a threat to the mid-Atlantic coastline and locations further north, but it is too early to make a skillful forecast for those regions.

NHC is forecasting for Irene to become a major hurricane (winds faster than 110 mph), within 24 hours, then reaching peak intensity at 130 mph (Category 4 storm) by 8pm EDT Thursday evening.

Forecast models and adaptive observations
The different forecast models are in rough agreement until Irene nears the Carolinas. The dynamical hurricane forecasting models, GFDL and HWRF, have Irene making landfall near Charleston, SC. NGFDL (a variant of the GFDL that uses NOGAPS for background conditions) has landfall near Morehead City, NC, and the GFS has Irene crossing the Outer Banks. The UKMET forecast track splits the difference, placing Irene near Myrtle Beach, SC at landfall.

To reduce the model spread, and improve the track forecast error, the NOAA Gulfstream IV and an Air Force WC-130J have been flying dropsonde missions north of Irene. A dropsonde is an meteorological instrument package dropped from a plane that can tell you the vertical profile of temperature, pressure, moisture, and winds. By flying these missions, the dropsondes can improve all of the numerical weather prediction models initial picture of the atmospheres, which improves the forecast. Also, NHC has asked NWS offices in the southeastern US that launch weather balloons to do so every 6 hours instead of the normal 12 hour frequency.


Figure 2 Official track forecast of Irene as of 2am.

5AM update
The 00Z ECMWF forecast is available and Figure 3 shows the maximum wind speed over the next week for the eastern coast of the US. Green indicates tropical storm force winds, while yellow and orange are hurricane-force winds. The important thing is not to fixate on the predicted landfall location, but to see that Irene's winds will affect areas far away from landfall. The GFS, not shown, agrees with ECMWF that Irene will have a large area of tropical-storm force winds associated with it.

Figure 3 Maximum wind-speed in mph from the 00Z August 23 ECMWF forecast for the next week.

Impacts

In the immediate future, Irene is expected to have a significant impact on the Bahamas and surrounding islands. Hurricane force winds are forecast to reach the southeastern Bahamas and the Turks and Caicos sometime this afternoon or evening. These locations can also expect 5-10 inches of rain. Three to six inches of rain are forecast over northern Hispaniola, with isolated areas receiving up to 10 inches. This could lead to flash flooding and mudslides in mountaineous terrain. NHC is predicting a storm surge of 9-13 feet above normal tide level for the southeastern Bahamas and the Turks and Caicos.

Outside of the islands immediately impacted by Irene, it is my judgement that everybody living on the eastern coast of the US should monitor Irene and review their hurricane preparations over the next few days.

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 cchsweatherman:
Right now based upon the latest Hurricane Hunter data, Hurricane Irene appears to have significantly weakened possibly back down to tropical storm strength given the max sustained surface wind measured at 71 mph. Also pressure is steadily rising once again inside the storm. Hispanola is having a much greater effect on Irene than anticipated, most likely due to the slower motion and wobble more west to west-southwestward given the past few recon fixes.


You can probably throw upwelling into the mix considering it's been over fairly shallow waters in the same area for a long period of time.
Member Since: December 18, 2006 Posts: 7 Comments: 2685
Quoting TropicalXprt:


Wow.....You have zero knowledge of fluid dynamics.
LOL

That is funny...
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The COC of Irene is looking ragged. This is great news for the Turk and Caicos because Irene could be easily going under RI right now.

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Quoting SPLbeater:
I am getting fed up with the NHC, all this shifting. go from South Florida to barely scraping the NC coast! really wish they would admit they dont know where its going, geez...Irene is looking good though.
'


Clouds are pointing west in front-she's going West!!
Member Since: August 14, 2007 Posts: 0 Comments: 535
Quoting Abacosurf:
That confirms the wobble to the WSW.


How does a storm go from 20.6N to 20.5N and the NHC in their advisory still says it's moving WNW??? Even if it's a wobble the movement from one advisory to the next was to the WSW, why lie about that? I'm goint to laugh if Irena misses the next trough, then who knows where she would end up. Not to mention that "thing" off the coast of Georgia, yep, this is getting to be a fun one to track!
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Quoting wolftribe2009:


WE DON'T WANT IT BECOMING A LOW PRESSURE SYSTEM. That would sling shot Irene right into the North East and that would be brutal. The storm looking like it wants to go out to sea and a low develops behind it and sling shots it right back into the US.
,actually would send her out to sea quicker imo,if it formed it should move ne stregthening the trough and pulling irene noth and then nne away from the northeast bahamas imo
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Is it me, or visible satellite is showing that Irene is developing eye? It's still open to the SE.
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Quoting cchsweatherman:
Right now based upon the latest Hurricane Hunter data, Hurricane Irene appears to have significantly weakened possibly back down to tropical storm strength given the max sustained surface wind measured at 71 mph. Also pressure is steadily rising once again inside the storm. Hispanola is having a much greater effect on Irene than anticipated, most likely due to the slower motion and wobble more west to west-southwestward given the past few recon fixes.


If this is true, will this bring a further west movement bringing the storm closer to our coast down the road?
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Old timers down here in Key West (I'm a newby...only have 25yrs of hurricanes here in KW) are telling me to pay attention. And I am, seeing that "blob" off the coast of FL/GA. We don't like storms "coming up the alley" - and looking at radar (not models) - it's not looking like FLA is "hoof the hook" by a long shot. Prayers for our people in Turks/Bahamas. Mind you, if Irene sucks up the alley, it will be too late to evacuate.
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Irene seems to be making a pretty decent jog to the west...it may have lost some latitude also...
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Quoting alvarig1263:
Latest TWD for 12Z shows LOW off shore of GA, SC



That low is expected to dissipate...
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Quoting CajunCrawfishhunter:
FISH


Tell that to the people who have already been creamed... or have got it coming in the next few days... or even few hours.
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I am getting fed up with the NHC, all this shifting. go from South Florida to barely scraping the NC coast! really wish they would admit they dont know where its going, geez...Irene is looking good though.
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Right now based upon the latest Hurricane Hunter data, Hurricane Irene appears to have significantly weakened possibly back down to tropical storm strength given the max sustained surface wind measured at 71 mph. Also pressure is steadily rising once again inside the storm. Hispanola is having a much greater effect on Irene than anticipated, most likely due to the slower motion and wobble more west to west-southwestward given the past few recon fixes.
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something happening off GA/Fla coast?? hmmmm
Member Since: August 14, 2007 Posts: 0 Comments: 535
Quoting E46Pilot:
Florida officially out of the cone of confusion.




I just don't see how they are plotting the next point that much further north than what Irene is currently positioned at and heading towards.

Think about it this way, yesterday the XTRP had the straight tajectory aimed at Miami-Dade county. Today, the XTRP is south of that. It leads me to beleive that its forward motion is slightly more West than WNW. Maybe somewhere in between. However, according to their next forcast point, they have it maving in between WNW and NW. I agree it is still generally moving WNW, but closer to West than NW.

Hope it makes sense. Until I see that turn more the NW, I still beleive the models should be slighlty West of their current positions.
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Quoting CaicosRetiredSailor:
My only "good" aspect of the 11Am advisory is that
she is not forecast to be a Major prior to being closest to Provo

still looking for any positives I can!


you have WU mail
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Latest TWD for 12Z shows LOW off shore of GA, SC

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1214. BrandiQ
Quoting alvarig1263:
Everything going crazy! A wobble WSW, possible stalling, trough may not have enough time to pick Irene up, dry air affecting the center, RI still possible, and a blob off of NE FL. This is why I keep saying S FL your not in the clear yet. So many thing can change with these crazy tropical systems. Just sayin...

Alex I


I hear that! I am still keeping an eye on this one...!
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Quoting alvarig1263:


Not really, yes we're out of the cone, but more things are affecting Irene's future which may not put S FL in the clear yet.


I HATE night storms. Frances was a real pain--and she lingered for so long. Imagine, sitting in a 100 yr. old wood house (up off the ground) that snaps, creaks, pops and shutters with every gust--and leaks like an old ship? AND being in the dark--trying to get towels under these leaks. The only good thing is that over time, wood swells, and many of the leaks stop!

So, I will probably be up ALL Thurs. Nite on leak patrol. Better than putting up all the shutters, tho!
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1210. Buhdog
She is dubstepping left. wobble woble

hmmmmmmmmmmm.
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Shear must be hard to predict. now its 15-20 kts and hindering strengthening.. all talk has been ideal conditionins and a cat 4 on the way. one of the mysteries of these magnificent storms..
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My only "good" aspect of the 11Am advisory is that
she is not forecast to be a Major prior to being closest to Provo

still looking for any positives I can!
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Everything going crazy! A wobble WSW, possible stalling, trough may not have enough time to pick Irene up, dry air affecting the center, RI still possible, and a blob off of NE FL. This is why I keep saying S FL your not in the clear yet. So many things can change with these crazy tropical systems. Just sayin...

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Trough split?



If this did anything it could throw the track out the window. Probably won't come to much though.
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Quoting Drakoen:


You're still in the cone so no.


had not seen the cone when I asked
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Pretty good link on storm surge:

THANKS! Yes,it is the increased friction of the bottom on the shallow water that stops it from moveing and Allows it to Stack Higher! gottcha.

Lesson for the day.
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Quoting stillwaiting:
that blob off jax looks like its starting to orgaize,man that would be a HUGE fly in the ├┤ntment and if it develops throw all the models out and start over,it would be unpresidented,it sure looks highly suspect on high res loop from cod


WE DON'T WANT IT BECOMING A LOW PRESSURE SYSTEM. That would sling shot Irene right into the North East and that would be brutal. The storm looking like it wants to go out to sea and a low develops behind it and sling shots it right back into the US.
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1200. BA
Quoting cloudburst2011:
hey when we first had irene reach tropical storm i was on board with everyone here...it looked like to me IRENE was going to be a hum dinger for florida ...however i have to go by what i see and conditions change as time goes on..i forecast on the atmospheric conditions not by the computers..so whatever i see happening whether its good or bad im going to state my opnion whether the blog likes it or not..I SEE IRENE BEING PICKED UP BY THIS DEEPENING TROF COMING DOWN THE EAST COAST AND WHISKED OUT TO SEA...A 70% CHANCE OF THAT HAPPENING...LIKE I SAID IF YOU GUYS CANT TELL FLORIDA IS 100% OFF THE HOOK THEN YOU ARE ONLY IN A FANTASY WORLD..


if you think anything is 100% in hurricane forecasting you are in fantasy world
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Quoting stillwaiting:
that blob off jax looks like its starting to orgaize,man that would be a HUGE fly in the ˘ntment and if it develops throw all the models out and start over,it would be unpresidented,it sure looks highly suspect on high res loop from cod


Noticed that a few minutes back was well. Very interesting.

NOAA SSD Tropical Atlantic Wide
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Quoting biff4ugo:
How does shallow water allow for larger storm surges?
Shallow water moves less due to increased bottom friction, unless you know something I am missing.
It may be more damaging in shallow areas because the coast isn't prepared for waves of any size.
Yes?

Does the cone include the width of the storm or just uncertainty about the path of the eye?


I believe it has to do with the absence of the continental shelf in the gulf which allows greater flow...
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Quoting surferjoe5899:
11am advisory = big relief for S. Florida


Not really, yes we're out of the cone, but more things are affecting Irene's future which may not put S FL in the clear yet.
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WRAL in Raleigh is saying Triangle will get TS Force, while area on I-95 will get hurricane force if Irene follows 11 am NHC track... I'm in I-40/I-95, soooo yikes.
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Quoting stillwaiting:
that blob off jax looks like its starting to orgaize,man that would be a HUGE fly in the ├┤ntment and if it develops throw all the models out and start over,it would be unpresidented,it sure looks highly suspect on high res loop from cod


Any idea how this would affect irene?
Member Since: August 14, 2007 Posts: 0 Comments: 535
Quoting biff4ugo:
How does shallow water allow for larger storm surges?
Shallow water moves less due to increased bottom friction, unless you know something I am missing.
It may be more damaging in shallow areas because the coast isn't prepared for waves of any size.
Yes?

Does the cone include the width of the storm or just uncertainty about the path of the eye?


Cone based strictly on center position. The Mariner's 1-2-3 rule uses the radius of tropical storm force winds plus the cone radius.
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1193. kap333
Ya never know Wolftribe. Im wondering what that blob is off NE FL. What is that all about!

The models are so insistent about a curve, but Irene obviously has not felt any influence yet. If the trough is gonna do its thing, it better get a move on!


Quoting wolftribe2009:
ok time to consider this

It looks like Irene is jogging a bit to the West and the forecast is for her to turn more northward. Now who is in agreement with me that this storm might move WNW right above Eastern Cuba and towards the Western Bahamas? This is what I think she will do and so I am now on the "Westward" boat track for the short term. I still am thinking of a landfall in South Carolina since she is so far south.

Link
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Quoting Orcasystems:
That confirms the wobble to the WSW.
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Quoting Skyepony:
Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 23rd day of the month at 15:06Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 302)
Storm Number & Year: 09L in 2011
Storm Name: Irene (flight in the North Atlantic basin)
Mission Number: 8
Observation Number: 05
A. Time of Center Fix: 23rd day of the month at 14:38:20Z
B. Center Fix Coordinates: 20┬░31'N 70┬░57'W (20.5167N 70.95W)
B. Center Fix Location: 66 miles (107 km) to the S (170┬░) from Cockburn Town, Turks and Caicos Islands (GBR).
C. Minimum Height at Standard Level: 2,918m (9,573ft) at 700mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 62kts (~ 71.3mph)
E. Location of the Estimated Maximum Surface Wind: 11 nautical miles (13 statute miles) to the E (92┬░) of center fix
F. Maximum Flight Level Wind Inbound: From 193┬░ at 67kts (From the SSW at ~ 77.1mph)
G. Location of Maximum Flight Level Wind Inbound: 13 nautical miles (15 statute miles) to the E (98┬░) of center fix
H. Minimum Sea Level Pressure: 980mb (28.94 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 9┬░C (48┬░F) at a pressure alt. of 3,040m (9,974ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 14┬░C (57┬░F) at a pressure alt. of 3,107m (10,194ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 11┬░C (52┬░F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Open in the southwest
M. Eye Shape & Diameter: Circular with a diameter of 25 nautical miles (29 statute miles)
N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature
N. Fix Level: 700mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 2 nautical miles
Remarks Section - Remarks That Were Decoded...
Maximum Flight Level Wind: 67kts (~ 77.1mph) in the east quadrant at 14:34:30Z
Maximum Flight Level Wind Outbound: 68kts (~ 78.3mph) in the northwest quadrant at 14:44:00Z
Remarks Section - Additional Remarks...
SFC CTR NOT VISIBLE
BKN CLOUDS BLO



Definitely supports significant weakening with Irene as dry air and disrupted inflow over Hispanola continue to be a problem.
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1190. 7544
Quoting stillwaiting:
that blob off jax looks like its starting to orgaize,man that would be a HUGE fly in the ├┤ntment and if it develops throw all the models out and start over,it would be unpresidented,it sure looks highly suspect on high res loop from cod


yeap asked about that this am just came into play could it effect the path as the models didnt see this before the new ones came in you think irene can meet the blob or verser tia
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Quoting Abacosurf:

Go to the kitchen and get a plate and a bowl.

Fill them with water.

Blow on them.

Which one is easier to displace the water out of??

There you go.


Think of it like a Tsunami too. When a Tsunami comes in the water rises quickly whereas if you are out to sea the water rises much slower. The shallow water gets displaced quicker than deeper water. Rivers and Bays can see the worst rise during Tropical Storms and Hurricanes. I know that a TS moving into a Bay can cause more damage than if it just hit a regular landmass without one. It tends to push the water inward using the bay itself to maximize inflow.
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Florida officially out of the cone of confusion.


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Quoting whepton3:
11A advisory out... not gonna post it... assuming by being here you have the internet.
Yeah, don't. Patrap will probably post it several times anyway. LOL
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Quoting biff4ugo:
How does shallow water allow for larger storm surges?
Shallow water moves less due to increased bottom friction, unless you know something I am missing.
It may be more damaging in shallow areas because the coast isn't prepared for waves of any size.
Yes?

Does the cone include the width of the storm or just uncertainty about the path of the eye?


Wide shallow continental shelf offshore.The surge is directly proportional to the width of the shallow water, and inversely proportional to the depth. Essentially, hurricane force winds blowing onshore across tens of kilometers of shallow water pile up water along coasts. The stronger the wind, the shallower the water, and the greater the extent of shallow water, the higher the pile of water. In some cases it can exceed 2-5 meters. In Galveston, Isaac Cline, the chief meteorologist, measured a rise of sea level greater than 16 feet above mean sea level.
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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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