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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it should be noted that the "westward" motion is taking Irene into much warmer water. The area just east of south florida is extremely hot compared to areas further to the east.
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I have a flight planned for 5pm Friday night out of Myrtle Beach.... Anyone have any ideas on if that will happen or not? Our local forcast states possible tropical weather for that time.
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Quoting TBird78:
I love watching people argue about the weather and predictions. It's like watching redneck cagefights!

It's ridiculous as hell but you can't turn away because it's hilarious!

LMAO
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1282. WxLogic
Wide open for any northerly fluctuations:

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tigger...it looks like a reasonably safe bet this won't be a Charleston event...in fact, I think the biggest impact we're gonna feel is some flooding...as we will have high astronomical tides this weekend...
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Quoting 7544:
looks like we have a new player in the field the new blob now shows on the surface map this could make things more interestin so what effect will this have irene is anyones guess hope some one here can give us a hint she hasnt pulled a surpise yet but now she just might


I think the most likely outcome is that Irene attempts to absorb the low pressure blob. This could do anything to the track, it's very difficult to forecast.
Member Since: August 10, 2010 Posts: 2 Comments: 1971
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.


They plot their track as a consensus of model track and model track changes as the conditions change; what were your thoughts on how they did it? Should they stick to a track despite the fact that it's wrong? Or do you have a way of making a storm conform to a specific track?
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NEW STEERING MAP:


The AB high has once again nosed W slightly as well as changing orientation a bit. The trough appears to be trying to flatten as well. Texas ridge is roughly the same. No major changes but:

Link
Member Since: December 18, 2006 Posts: 7 Comments: 2687
Quoting NICycloneChaser:


I think Irene may have weakened slightly, but it's still a hurricane IMO. Dropsonde in the NW eyewall found surface winds of 80mph. Will be interesting to see what is found in the NE eyewall. Not looking as impressive on satellite imagery.


Will be interesting to see what the NHC does with this new data showing significant weakening and deterioration of the inner structure of the hurricane in the next update.
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11:00am Advisory
Click image for enlarged view
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1274. TBird78
I love watching people argue about the weather and predictions. It's like watching redneck cagefights!

It's ridiculous as hell but you can't turn away because it's hilarious!

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Quoting Nolehead:
looks like it might hit just a tad to the south of the next nhc mark...just dont see that big turn happening anytime soon...but it's just me..
which big turn?left? right?
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Quoting rkay1:
SPECIAL UPDATE: The only way FLORIDA will be effected is if it detaches from America and floats about 250-300 miles East.


You never know... LOL!
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1271. Patrap
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"blob" not going to go north of Irene from what i see. It looks like the two will collide which that would be interesting. I think Irene would suck up the blob creature and eat it from dinner. Yet if the blob becomes a low and moves far enough west over Florida it would be the door open to turn the storm into the Carolinas.

That is what I am looking at. Wow the weather is unpredictable. Where was this blob yesterday lol?
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Quoting 69Viking:


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!


Posted that awhile back , looks like some just can't handle the truth, not sayin it won't go where the NHC has forecasted it to, but why not be truthful about the direction, simple as that!
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Quoting 7544:
looks like we have a new player in the field the new blob now shows on the surface map this could make things more interestin so what effect will this have irene is anyones guess hope some one here can give us a hint she hasnt pulled a surpise yet but now she just might


Isn't that what happend to Jeanne, and what caused her to do the loop d loop.
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1266. 900MB
Quoting scCane:
Take note that Hispaniola most mountainous region is directly south of the center which is cutting off Irene's inflow. Once it passes the island it should start strengthening again.


Agree.
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Quoting RussianWinter:


I can understand the wobble and the dry air in the center....

But how come the other stuff wasn't picked up like the blob and the trough speed?


Sorry, "picked up" by what?
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1264. Buhdog
Quoting rkay1:
Give the West casting a break.  That horse is dead.  Move on.




uhm did you see the latest fix? clearly you did not..if so you would agree wobble wobble. I just call it like i see it...don't get mad.
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Quoting tiggeriffic:


not if hispanolia weakens her a bit...could cause a slight shift back to the west...sorry...


I live in CHS and I'm still a bit nervous...
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1262. dmh1026
Quoting cloudburst2011:



WELL SIR according to your definition of a fish storm we would never have one...if a storm stays out in the atlantic its going to hit land somewhere down the road whether it will be the azores or england its going to happen...so you better come up with a proper definition of a fish storm regarding the united states mainland...

Have you never seen a tropical cyclone stay in the Atlantic with no land interaction? I've seen plenty of them. I call them FISH storms as do most other's here.
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Quoting TropicalXprt:


Wow.....You have zero knowledge of fluid dynamics.
Here you go...

Exactly fits my description to a tee.

http://www.nhc.noaa.gov/surge/

I have seen the difference personally.

Why am I replying to a troll??
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Quoting zoomiami:


Just because you are reading all of the posts does not mean that others who can only check in once and a while can go back hundreds of posts to see whats going on.

Especially for those of us who sometimes can only use our phones to see what is going on.

First of all it wasn't "hundreds" of posts ago. Post 795, then again around 875. So I guess it is ok for someone to just "pop" in and ask a legitamate question and not run the risk of being sarcastically reamed by some dork on here to read the posts to find out! You're damned if you do and your damned if you don't!
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1258. Vero1
Quoting rkay1:
FLORIDIANS OF THE BLOG! Give it a damn rest.  It's over. There is no West movement, no matter how much you pray to your raingods.  Get over the denial already, its tiresome. Your like that team behind by 10 runs in the 9th inning with 2 outs and still thinking you have a shot.



It is not over until it dissipates!
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Quoting GoWVU:
I am guessing by 5pm today Charleston will be out of the cone... Which is a good thing!!!


not if hispanolia weakens her a bit...could cause a slight shift back to the west...sorry...
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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 things can change with these crazy tropical systems. Just sayin...



I can understand the wobble and the dry air in the center....

But how come the other stuff wasn't picked up like the blob and the trough speed?
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Quoting Abacosurf:
LOL

That is funny...


Thought so too.. I liked the thing with the bowl... pretty good.
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1253. scCane
Take note that Hispaniola most mountainous region is directly south of the center which is cutting off Irene's inflow. Once it passes the island it should start strengthening again.
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69Viking

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
!


yes it does!!
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Quoting palmbaywhoo:


If this is true, will this bring a further west movement bringing the storm closer to our coast down the road?


Hard to say really.

Quoting charlottefl:


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.


Good point there. Goes hand in hand with the slower motion of the storm.
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Quoting rkay1:
FLORIDIANS OF THE BLOG! Give it a damn rest.  It's over. There is no West movement, no matter how much you pray to your raingods.  Get over the denial already, its tiresome. Your like that team behind by 10 runs in the 9th inning with 2 outs and still thinking you have a shot.


We'll see.... ;-)
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Quoting Nolehead:


SCwannabe
something happening off GA/Fla coast?? hmmmm


it just seems to get better and beter...now watch this be our next invest..geez..


Yeah, I just don't know how it will effect Irene... we need Levi for this one
Member Since: August 14, 2007 Posts: 0 Comments: 535
1247. A4Guy
Amazing how the blog settles down the more FL is out of the cone.

It still seems like there are a few people "concered" enough to think that SoFla is not basically in the clear...but other than some heavy surf and squally weather, we should be just fine. Always a slim chance of something unexpected happening (I have seen unexpected atmosphereic shift in the past with tropical systems), but it's as very low likelihood. I have impact windows, but my parents have shutters - and I am advising them not to close the shutters or pull in the paio furniture.
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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.


I think Irene may have weakened slightly, but it's still a hurricane IMO. Dropsonde in the NW eyewall found surface winds of 80mph. Will be interesting to see what is found in the NE eyewall. Not looking as impressive on satellite imagery.
Member Since: August 10, 2010 Posts: 2 Comments: 1971
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.


If the computer models got it right from the outset, we would not need the NHC, we could just load the model program on our smart-phones, and know weeks in advance if we had to prepare.

Just because the forecast changes doesn't mean the don't know what they're doing, it simply means technology and science is just not there yet when it comes to weather and climate.

I have noticed that over the years, the folks at the NHC have gotten a h*ll of a lot better.
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1244. GoWVU
I am guessing by 5pm today Charleston will be out of the cone... Which is a good thing!!!
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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.



she sucked in dry air from the mtns of Hispanola...possibly going to change things for the future
Member Since: August 14, 2007 Posts: 0 Comments: 535


SCwannabe
something happening off GA/Fla coast?? hmmmm


it just seems to get better and beter...now watch this be our next invest..geez..
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1240. 7544
looks like we have a new player in the field the new blob now shows on the surface map this could make things more interestin so what effect will this have irene is anyones guess hope some one here can give us a hint she hasnt pulled a surpise yet but now she just might
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Looks like Kill Devil Hills is out of luck (Again). Jim Cantore heading there?
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Quoting JimboUSMC17:


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.


Don't expect to see the turn until tomorrow. That is when the storm will be influenced by the trough.
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Quoting 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!




Well there is a lot of talk about Irene "weakening" due to Dry Air and interaction with Hispaniola. We know that a storm weaker would move more westward. Now if a Low does develop north of Irene it changes everything because she might be sheared by the easterly winds around the low which then in turn causes her to weak more and there you go: Westward right in Florida.

I am not saying this will happen but that all cars should now be on the table. The westward card should not be removed until she shows us that she wants to move NW. I am going to be skeptical of an eastward turn until she starts moving NW

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I for one am glad they have all these data planes and fancy computers because from a satellite view point this looks like a nightmare. I see the troughs coming down but there is a ull closing in from the east of the storm and interaction from Hispaniola. Not to mention what ever is off the coast of central Fl. and all other radar from Fl. showing west or s.w. motion.Well that's enough of my observations for today. Sincerely wishing everyone in the Bahamas the best esp. Baha,Caicos and the rest. In closing the big boys at the NHC earn their money this time of year even if they can't or don't want to sleep.
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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: 2687

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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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