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 dan77539:
Let's just say that at least Haiti is finally catching a break! Another natural disaster would have just added insult to injury.


With all of the rain they are getting right now.. Im not really sure they are catching a break. From the winds probably and surge probably... But the rain in the mountains is going to be a real problem with flash flooding and mud slides.
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E-Fly, I got mines. Got 300gals. ready to go and another (6) 5 gal. cans we fill when one approaches.
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283. wpb
hmrf 6z is east of 00z latitude of miami
same with gfs
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Quoting LightningCharmer:


Good Point. Florida Keys and southeast Florida peninsular residents might want to make sure their boats are tied well, likely rough surf and gusty winds.

Swimmers and beach goes this also means stronger rip tides. Swimming and playing in high surf may be fun but be careful.

Interested to see the interaction of Irene with the front in a day or two. Weakening front meets strengthening cyclone sounds like a headliner.

If Irene takes her projected parabola path there will be a good chance the storm will drag in dryer air and the Lower Keys will experience a beautiful sunny day. I've seen it happen many times.

Showers and thunder storms in Key West this AM
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Let's just say that at least Haiti is finally catching a break! Another natural disaster would have just added insult to injury.
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Quoting msgambler:
Until they run out of gas.


Very true... So wear a rain jacket and fill that thing back up or its back to the candles! :)
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Quoting CBJeff:
All the 4-5 day track caveats from the NHC got me thinking of something a veteran 'caster told me back in my Navy days:

"Once a storm gets big enough, she can steer herself."


That's what I'm afraid of.
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Quoting lennykat4:




Okay, so on here early with lots of good explanations for us learning/lurkers....

...I have to ask a real rookie question.

How, specifically, does that subtropical ridge control the steering of the storm either east or west? Also, if the storm slows or stalls and doesn't encounter the ridge what does that do to the forecasted track?

My apologies for the freshman like questions- just trying to learn how these things work. Thanks for all the great explanations from you guys.


Tropical cyclones are steered around the southern and western edge of the subtropical ridge.. Think of it as a big blanket. Storms cannot move "through the ridge"...They follow the path of least resistance. Sometimes the ridge "bridges" with the High pressure system over the center of the country which is sometimes referred to as the "Rockies High." When you see due west runners, this is typically the reason why. Troughs act to weaken and erode High pressure, which creates a weakness between the two highs. Simply, the storm will follow the weakness.
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Quoting msgambler:
Until they run out of gas.

LOL
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All the 4-5 day track caveats from the NHC got me thinking of something a veteran 'caster told me back in my Navy days:

"Once a storm gets big enough, she can steer herself."
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Quoting earthlydragonfly:


Most generators will run fine in the rain anyway.
Until they run out of gas. Just sayin'
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Quoting nash28:
Just did a quick look at the 400-850mb steering layer and noticed that the subtropical ridge over the last few hours has ever so slightly nudged a bit further westward.

We'll see if this is a sign of the trough not amplifying enough to cause the sharp turn. This is a tricky one to forecast because even a difference of 100 miles in either direction has massive implications.


I saw this also. I also thought this would be happening sooner. But I guess not. Hopefully it won't be too big of a nudge and keep the Irene 100 miles or so off our coast. Still bears watching.
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Well, Irene grows in size

11 PM last night


5 AM this morning


Kinda reminds me of Ike
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Quoting snotly:
Remember if you use a generator DO NOT start it in a garage with the doors closed (to stay out of the rain). Many people die each power outage when the fail to understand the dangers of carbon monoxide


Most generators will run fine in the rain anyway.
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Quoting lennykat4:




Okay, so on here early with lots of good explanations for us learning/lurkers....

...I have to ask a real rookie question.

How, specifically, does that subtropical ridge control the steering of the storm either east or west? Also, if the storm slows or stalls and doesn't encounter the ridge what does that do to the forecasted track?

My apologies for the freshman like questions- just trying to learn how these things work. Thanks for all the great explanations from you guys.


There are different steering layers, or (heights) for different strengths of storms. High pressure systems always steer storms in a clockwise flow. If you look at the image below. Irene is at the Western periphery of the AB ridge over the Atlantic. The flow there changes from due West to between WNW-NW. She should continue moving WNW-NW until she reaches the end of the ridge where the gap between the two highs in. The exception to this would be if the AB Ridge would build West, or if the trough was deeper than expected, forcing either a more westward track, or a sharper turn N, and then E. Hope that helps ;)

Link
Member Since: December 18, 2006 Posts: 7 Comments: 2687
Remember if you use a generator DO NOT start it in a garage with the doors closed (to stay out of the rain). Many people die each power outage when the fail to understand the dangers of carbon monoxide
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How did we put it last year, she's "pumpin'" the ridge?

Actually, I'm not sure who's pumpin' who?

Anyone believe this next trough could possibly be strong enough to turn this thing?

Not me, and that's not wishful thinking. I'm looking at it. There's no way that little tiny trough will turn this big top.

Tell me I'm wrong ...

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Quoting HurricaneDevo:
Good Morning, Irene!




And let there be light!
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Quoting lennykat4:




Okay, so on here early with lots of good explanations for us learning/lurkers....

...I have to ask a real rookie question.

How, specifically, does that subtropical ridge control the steering of the storm either east or west? Also, if the storm slows or stalls and doesn't encounter the ridge what does that do to the forecasted track?

My apologies for the freshman like questions- just trying to learn how these things work. Thanks for all the great explanations from you guys.


Those are good questions and never apologize for asking and wanting to learn. Most of us here have done the same thing at one time or another. Sorry I'm not knowledgeable enough to answer your question though.
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As of the last observation at 11:04:30Z, the plane's...

Direction of Travel: WNW (289°)
Location: 72 miles (115 km) to the W (271°) from San Juan, Puerto Rico (USA).
Member Since: December 18, 2006 Posts: 7 Comments: 2687
Quoting nash28:
Just did a quick look at the 400-850mb steering layer and noticed that the subtropical ridge over the last few hours has ever so slightly nudged a bit further westward.

We'll see if this is a sign of the trough not amplifying enough to cause the sharp turn. This is a tricky one to forecast because even a difference of 100 miles in either direction has massive implications.




Okay, so on here early with lots of good explanations for us learning/lurkers....

...I have to ask a real rookie question.

How, specifically, does that subtropical ridge control the steering of the storm either east or west? Also, if the storm slows or stalls and doesn't encounter the ridge what does that do to the forecasted track?

My apologies for the freshman like questions- just trying to learn how these things work. Thanks for all the great explanations from you guys.
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Quoting DookiePBC:


Mornin Dewey...

I think you and I were on the same page on this one yesterday...just seemed like the trend was gonna be to continue shifting the cone eastward. And the only thing keeping the cone as far west as it was was the NHC not wanting to discard the GFDL. Sure enough, once it fell in line with the others, the cone took a major jump to the east. Again...would love to see it keep moving east and avoid land and the Bahamas all together.


I noticed that as well. Does anyone know enough about the GFDL to know why it was such an outlier to the west?

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Good Morning, Irene!



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Quoting weatherguy03:


Nothing for Florida as far as Watches or Warnings go. Expect some Gusty winds along the immediate coast and probably the biggest factor with Irene will be beach erosion and high surf.


Good Point. Florida Keys and southeast Florida peninsular residents might want to make sure their boats are tied well, likely rough surf and gusty winds.

Swimmers and beach goes this also means stronger rip tides. Swimming and playing in high surf may be fun but be careful.

Interested to see the interaction of Irene with the front in a day or two. Weakening front meets strengthening cyclone sounds like a headliner.

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Quoting oakland:


Not impossible but not likely.


ok thanks
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259. bwi
Good morning. Looks like while the NHC has shifted the black line slightly to the right overnight, HPC prelims have moved left a little, with the southern middle atlantic states and Chesapeake Bay possibly in the higher wind zone.

Very close call for us in the DC/Baltimore/Philly area for whether Irene will affect with damaging winds or just a blustery day. A 6z GFS track would be the latter -- looks like a miss for those of us inland. ECMWF 0z looks more like the former would be a possibility.

Tree damage and extensive power outages the big concern, with some coastal flooding also a concern. It doesn't look like Irene would be likely to stall long enough here either way for extensive freshwater flooding, unless the track shift way to the west in to the mountains.

So far, our locals are not raising the alarm, which is probably fine, since it looks like a good chance of only small impact. However, I'm gassing up the generator just in case. Don't want another Isabel with week long power out.
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Quoting Bassfishing123:
Morning guys and gals...Does anyone think this big girl could shift the tracks back a little west..


Not impossible but not likely.
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Quoting weatherguy03:


Highly doubtful on the Westside.


She would have to come closer to the coast for that to happen.
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Morning guys and gals...Does anyone think this big girl could shift the tracks back a little west..
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Quoting charlottefl:


Not to mention, depending on how close she get's short lived tornadoes in outer rain bands.


Highly doubtful on the Westside.
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Irene seems to have slowed down a bit. Is this because of land friction, or because it is fixing to start taking the expected turn?
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Quoting tpabarb:
I'm in Wilmington, NC - as of right now, this isn't looking very good! I'm totally leaving.


Wise choice. Material stuff can always be replaced. If you have important documents such as property deed, insurance papers birth certificates ss cards medical ins card don't forget to take them with you. Also gather as many photos and things you deem irreplaceble. My experience is that the biggest hit I had from Katrina wasnt loosing my property, but loosing those items I mentioned before. But most importantly your life and the life of your family.
Member Since: August 1, 2007 Posts: 0 Comments: 202
So if I am reading right, the NW turn should start to happen on Thursday???
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Quoting nash28:
Just did a quick look at the 400-850mb steering layer and noticed that the subtropical ridge over the last few hours has ever so slightly nudged a bit further westward.

We'll see if this is a sign of the trough not amplifying enough to cause the sharp turn. This is a tricky one to forecast because even a difference of 100 miles in either direction has massive implications.



Yeah, that's probably part of the reason the NHC cone is closer to the left side of the guidance envelope. (erring on the side of caution)
Member Since: December 18, 2006 Posts: 7 Comments: 2687
Quoting FLdewey:
This is going to be a mess for the Bahamas.

Keep on moving cone... keep on moving.
It's good to know the Keys are completely out of the 'cone' I feel for the Bahamian folks. As for your picture of the woman sitting in a bathtub of cheetos..wicked awesome!!!
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Wind Field Details:
The radius of 64 knot (74 mph | 119 km/h | 33 m/s) winds is:
45 nautical miles (52 miles | 83 kilometers) in the northeast quadrant.
30 nautical miles (35 miles | 56 kilometers) in the southeast quadrant.
20 nautical miles (23 miles | 37 kilometers) in the southwest quadrant.
35 nautical miles (40 miles | 65 kilometers) in the northwest quadrant.

The radius of 50 knot (58 mph | 93 km/h | 26 m/s) winds is:
90 nautical miles (104 miles | 167 kilometers) in the northeast quadrant.
60 nautical miles (69 miles | 111 kilometers) in the southeast quadrant.
60 nautical miles (69 miles | 111 kilometers) in the southwest quadrant.
70 nautical miles (81 miles | 130 kilometers) in the northwest quadrant.

The radius of 34 knot (39 mph | 63 km/h | 17 m/s) winds is:
180 nautical miles (207 miles | 333 kilometers) in the northeast quadrant.
120 nautical miles (138 miles | 222 kilometers) in the southeast quadrant.
120 nautical miles (138 miles | 222 kilometers) in the southwest quadrant.
130 nautical miles (150 miles | 241 kilometers) in the northwest quadrant.
Member Since: December 18, 2006 Posts: 7 Comments: 2687
Just did a quick look at the 400-850mb steering layer and noticed that the subtropical ridge over the last few hours has ever so slightly nudged a bit further westward.

We'll see if this is a sign of the trough not amplifying enough to cause the sharp turn. This is a tricky one to forecast because even a difference of 100 miles in either direction has massive implications.
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Quoting FLdewey:
This is going to be a mess for the Bahamas.

Keep on moving cone... keep on moving.


Mornin Dewey...

I think you and I were on the same page on this one yesterday...just seemed like the trend was gonna be to continue shifting the cone eastward. And the only thing keeping the cone as far west as it was was the NHC not wanting to discard the GFDL. Sure enough, once it fell in line with the others, the cone took a major jump to the east. Again...would love to see it keep moving east and avoid land and the Bahamas all together.
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245. MahFL
The North turn is supposed to be Friday. NW Thursday.
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I'm in Wilmington, NC - as of right now, this isn't looking very good! I'm totally leaving.
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243. CapnK
Until the track changes east (if it does), the Hugo remembrances and references are going to be thick and frequent. We stayed 2 blocks off the beach through landfall, donning foul weather gear and hardhats to go down to waters edge every 30 minutes or so. Stayed in the wind shadow of buildings, peeping around the corners like we were under sniper fire fire when it came to crossing between them. On the beach, you could lean 45 degrees from the vertical, into the wind, and the sea was as nasty as I've ever seen it, a cross current running down the beach that must have been greater than 5 knots. The marina where I live now was wiped out completely when the concrete docks of the Coast Guard station bulldozed through from upwind...

Stay away, Irene. Feel free to recurve E. :) Praying for my friends in the Abacos.
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Quoting oceanblues32:


Thank you timewise does anyone know when aprox it is suppose to start taking that northward turn am in ft lauderdale so am a bit concerned have a midterm on monday i do not need any loss of power!!!


Here you go on track:

6 Hour Average Movement (About):
Toward the WNW or 293° at 10.2 knots (11.8 mph | 19.0 km/h)

12 Hour Average Movement (About):
Toward the WNW or 297° at 9.0 knots (10.3 mph | 16.6 km/h)
Member Since: December 18, 2006 Posts: 7 Comments: 2687
Quoting FLdewey:
This is going to be a mess for the Bahamas.

Keep on moving cone... keep on moving.


Ya, blogger CRS is first in line in the Turks & Caicos
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Yeahhhhh!!!AS PER THE LATEST OFFICIAL NHC TRACK...SUPPORTED BY A
REASONABLY WELL CLUSTERED TRACK GUIDANCE SUITE. THE KEYS ARE NOW
ENTIRELY OUTSIDE OF THE FORECAST ERROR CONE...WITH THE FORECAST TRACK
KEEPING THE HURRICANE EAST OF ANDROS ISLAND.
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Quoting nrtiwlnvragn:
Almost complete on the eyewall




Great capture, nrtiwlnvragn.
Looks like the tail is pulling through the Mona Passage on that image. Maybe Irene will pull her anticyclone along with her. She sure has been enveloping the Dominican Republic for quite a while, with the COC is on the north side of the island and the anticyclone on the south side.



(Great Blog Dr. Carver, thanks for the update!!)
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Quoting charlottefl:


All true, we've all seen em change tracks before. I think generally a good rule of thumb is to keep a close eye on them until they clear your latitude. (Now there are a few exceptions to that i.e. Jeanne), but for the most part.


Agree 100%
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Quoting nash28:


She has slowed. Many times, this indicates the beginning of a turn around the ridge. However, looking at the steering maps this morning, she should still be on the WNW heading.
Yeah, agreed. the latest maps show the weakness in the ridge so she might be on her way NW soon. It seems that recent forecasting models had her much farther to the W by this date and time though
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Check out Irene's beauty spots.

Member Since: August 10, 2010 Posts: 2 Comments: 1971

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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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