Isaac reorganizing as it blows through the Lesser Antilles

By: Dr. Jeff Masters , 8:34 PM GMT on August 22, 2012

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Tropical Storm Isaac continues to maintain top winds of just 45 mph as its center prepares to move through the Lesser Antilles islands late this afternoon and early this evening. The entire Lesser Antilles chain of islands is receiving heavy rains from Isaac, with Martinique picking up 1.46" of rain as of 2 pm EDT, and St. Lucia receiving 1.49". However, Isaac is not yet generating much in the way of tropical storm-force winds, and none of the islands had received winds in excess of 30 mph as of 4 pm EDT. During their storm penetration to obtain their 2 pm EDT center fix, an Air Force Reserve aircraft measured top surface winds of just 40 mph, and a central pressure of 1004 mb. Top winds at their 5000 foot flight altitude were 49 mph. Isaac is undergoing significant changes to its structure. The plane found the center had become a broad, elongated oval that extended 40 miles from NW to SE. The old center, fixed at 2 pm near 16.1°N, and closer to the dry air to Isaac's north, is being challenged for dominance by a new center that is attempting to form near a burst of heavy thunderstorms at 15.5°N. The Hurricane Hunters' latest fix at 3:50 pm EDT put the center near 15.9°N, a southwards shift of about 17 miles. The resulting battle between centers is giving Isaac a rather odd spiral rectangular shape, as seen on visible satellite loops. The Hurricane Hunters did not observe an eyewall trying to form, and recent microwave satellite images also show no signs of an eyewall forming. A large area of dry air to the north of the storm, as seen on water vapor satellite loops, continues to interfere with development, and Isaac will not be able to begin strengthening until it resolves the battle between it two competing centers, and casts out the dry air infiltrating it. This is going to take at least a day, since Isaac is a very large storm, and it takes more time to spin up a big chunk of the atmosphere. Radar imagery from Barbados and Martinique show plenty of heavy rain showers, mostly on the south side of Isaac where it is moister. There has been a modest increase in spiral banding since this morning.


Figure 1. Afternoon satellite image of Isaac, showing its odd spiral rectangle shape.

Latest model runs for Isaac
The latest set of 12Z (8 am EDT) model runs are very similar to the previous set of runs, which I discussed in detail in this morning's post. The models show a westward track to a point on the south coast of Hispaniola. Isaac's center shift to the south may require some modest adjustments to the south and west for the models. This would result in the storm spending a few hours less time over Hispaniola, and more time over or just south of Cuba. This would slightly decrease the risk to the Dominican Republic, the east coast of Florida, and the Bahamas, but increase the risk to the west coast of Florida. The ECMWF--our best performing model over the past two years--continues to be an outlier among the models. It predicts that Isaac will track just south of Cuba, cross the western tip of Cuba on Monday, then head north towards an eventual landfall in Louisiana. However, this model is keeping Isaac weaker than the other models, and thus predicts the storm will have a weaker response to the trough of low pressure over the Southeast U.S. If the official NHC intensity forecast is right and Isaac becomes a hurricane on Thursday, the more southerly track of the ECMWF is not going to verify, and Isaac will spend considerable time over Cuba on Saturday and Sunday. Where Isaac pops off the coast of Cuba will be critical in determining its future path and intensity, and at this point, we don't know it its more likely that Isaac will go up the east coast of Florida, the west coast, or straight up the peninsula over land. At this point, I'd put the odds at:

40% chance of a track through the Gulf of Mexico, west of Florida
25% chance of a landfall in South Florida, and a track mostly over the Florida Peninsula
35% chance of a track along the east coast of Florida

Which model should you trust?
Wunderground provides a web page with computer model forecasts for many of the best-performing models used to predict hurricane tracks. So which is the best? The best forecasts are made by combining the forecasts from three or more models into a "consensus" forecast. Over the past decade, NHC has greatly improved their forecasts by relying on consensus forecast models made using various combinations of the GFS, GFDL, NOGAPS, UKMET, HWRF, and ECMWF models. If you average together the track forecasts from these models, the NHC official forecast will rarely depart much from it, and the NHC forecast has been hard to beat over the past few years. The single best-performing model over the past two years has been the ECMWF (European Center model). The GFS model has been a close second. You can view 7-day ECMWF and 16-day GFS forecasts on our wundermap with the model layer turned on. Ten-day ECMWF forecasts are available from the ECMWF web site. The European Center does not permit public display of tropical storm positions from their hurricane tracking module of their model, so we are unable to put ECMWF forecasts on our computer model forecast page that plots positions from the other major models. As seen in Figure 2, the HWRF and GFDL were well behind the ECMWF and GFS in forecast accuracy in 2011, but were still respectable. The BAMM model did very well at 4 and 5-day forecasts. The UKMET, NOGAPS, and CMC models did quite poorly compared to the ECMWF, GFS, GFDL, and HWRF. For those interested in learning more about the models, NOAA has a great training video (updated for 2011.)


Figure 2. Skill of computer model forecasts of Atlantic named storms 2011, compared to a "no skill" model called "CLIPER5" that uses just climatology and persistence to make a hurricane track forecast (persistence=a storm will tend to keep going in the direction it's current going.) OFCL=Official NHC forecast; GFS=Global Forecast System model; GFDL=Geophysical Fluid Dynamic Laboratory model; HWRF=Hurricane Weather Research Forecasting model; NOGAPS=Navy Operational Global Prediction System model; UKMET=United Kingdom Met Office model; ECMWF=European Center for Medium Range Weather Forecasting model; TVCA=one of the consensus models that lends together several of the above models; CMC=Canadian Meteorological Center (GEM) model; BAMM=Beta Advection Model (Medium depth.) Image credit: National Hurricane Center 2011 verification report.

I'll have a new post in the morning.

Jeff Masters

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Quoting Tribucanes:
No, I'm nice to everyone except those who spread propaganda and lies. Those I eat, bones and all. Jerk to everyone much?


Hey, calm down. I was messing with you - sorry for not being clear and coming off as rude.
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Quoting Tribucanes:
No, I'm nice to everyone except those who spread propaganda and lies. Those I eat, bones and all. Jerk to everyone much?


Seems I'm not the only lightning rod on here. ;)
Member Since: March 7, 2007 Posts: 553 Comments: 19911
"I don't think it's going to be a factor in this particular convention."

No disrespect, but Famous last words? ^^^^

It's been 91 years too late since a significant hurricane hasn't been a factor for Tampa.
Member Since: May 12, 2012 Posts: 11 Comments: 2315
2147. Levi32
Quoting MiamiHurricanes09:
Sir Levi or Kori, I have a question for you. Should Isaac completely miss Cuba, and an essence only scrape the northeastern coast and remain over water, what type of implications would that have on the intensity and track?


I think that would almost guarantee a hurricane for Florida even if it went right for the southern peninsula. As for track this is a classic situation where any kind of significant strengthening could nudge it farther north.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
2146. LBAR
Hahaha. Jim Cantore said it's "basically an open wave". Yikes.
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Quoting Clearwater1:
Looks like he may get to keep his job, if the westward trend continues. Or maybe they won't chance it.


I really dont think the trend will continue, there is no evidence as Levi was saying that shows this system will go as far west as the Euro says it will, I think the track will be fairly close to what they have now

even if it goes further west, Isaac is and will be huge and will still dump tons of rainfall on Florida; which is really bad for areas already having flooding issues
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2144. JLPR2


The islands are going to end up as swamps soon. :\

Also a feeder band is currently over Pottery's area.
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felix....? tropics chat? or anyone for that matter? lot of crazyness on here right now!
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2142. scott39
Quoting KoritheMan:


My apologies. Just provide some clarification next time.
My apologies to you too.
Member Since: June 13, 2009 Posts: 0 Comments: 6732
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What a joke ISAAC was on the Lesser Antilles LOL big LOL
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Quoting opal92nwf:
What the... is that supposed to mean!?!?
img src="Image and video hosting by TinyPic">



I was confused, too. Isaac is moving west at 20, according to NHC...so..what IS that?
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Quoting HoustonTxGal:
Well, just for the record.. I am not here for recongnition. I am not here to downcast, wishcast, doomcast or any other casting maneuver.

WU saved my family and I from getting caught with our pants down during Katrina when we lived on the MS gulf coast. Due to the combined knowledge of all here, we were VERY WELL prepared.

When I moved to Houston and IKE headed our way.. WU gave me the knowledge I needed to once again prepare and to get my in-laws and my husbands grandmother off Galveston Island, in which all of them live.

I have learned some over the years I have been visiting this site but am no expert, nor do I claim to be. But I do have a much better understanding of these storms than I did pre-Katrina and I thank all of you for that.

End of speech :o)


Amen
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Quoting galvestonhurricane:


Kissing up much?
No, I'm nice to everyone except those who spread propaganda and lies. Those I eat, bones and all. Jerk to everyone much?
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Quoting galvestonhurricane:


Wow. I didn't even make the thing. It seems like everyone is trying to complain or argue about every little thing on the blog tonight. Honestly, I'm sick of it and going to bed.


Never said you did...but the graphic could've been prepared better by whatever source designed it.
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Quoting Chicklit:
15.8N 60.2W 1006mb at 8 p.m. and
15.8N 63.0W 1003mb at 11 p.m.

it was at 62.2 at 8pm 60.2 at 5pm.
Member Since: August 6, 2007 Posts: 0 Comments: 693
Quoting aasmith26:


You know I was gonna say the same thing. They could spice that map up a little bit at least...doesn't look very professional at all.


Wow. I didn't even make the thing. It seems like everyone is trying to complain or argue about every little thing on the blog tonight. Honestly, I'm sick of it and going to bed.
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Quoting Clearwater1:
That's a pretty good shift and I think the trend will continue a little further west from central FL. Still not good for the Keys and of course Haiti.
I noticed the middle of the cone is line with the last GFS run.



Member Since: August 31, 2009 Posts: 0 Comments: 5628
2132. airmet3
Quoting MrstormX:


It goes deeper then that, for one the DHS should stay out of the emergency management aspect of "homeland security" leave that to FEMA. If the government is serious about protecting people in disasters then they will let FEMA be an independent agency again, with a director in a cabinet level position as it was pre 9/11. Bottom line is that the government should rely on the NHC as the law, and they can use other services as supporting material but nothing more.

Above all else though, people need to take responsibility for themselves. They also need to monitor weather forecasts and plan accordingly, FEMA can't hold everybody's hands. People need to look out for themselves, and let the government help them do it.


If I remember correctly, that was about the time Rick Santorum was trying to privitize the forecasting functions of the NWS. Santorum was a Senator from PA. and Accu Weather was one of his largest contributors.
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Quoting HrDelta:


Because of them, the DHS mis-deployed their resources, lengthening the amount of time to get to New Orleans.


Then the lesson is to not count on the feds to save you. DHS, the same dept that likes to fondle wheelchair bound kids going through the airport, is the last agency I want trying to coordinate a relief effort after a major disaster.
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2130. scott39
Quoting MysteryMeat:


Putting a smiley on a post that predicts a rapidly intensifying hurricane in the GOMEX where it will cause significant damage and loss of life.

I'm woozy from the class being shown.
The smiley fast is for IMHO. Your are twisting it for your own pleasure.
Member Since: June 13, 2009 Posts: 0 Comments: 6732
Well, just for the record.. I am not here for recongnition. I am not here to downcast, wishcast, doomcast or any other casting maneuver.

WU saved my family and I from getting caught with our pants down during Katrina when we lived on the MS gulf coast. Due to the combined knowledge of all here, we were VERY WELL prepared.

When I moved to Houston and IKE headed our way.. WU gave me the knowledge I needed to once again prepare and to get my in-laws and my husbands grandmother off Galveston Island, in which all of them live.

I have learned some over the years I have been visiting this site but am no expert, nor do I claim to be. But I do have a much better understanding of these storms than I did pre-Katrina and I thank all of you for that.

End of speech :o)
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Quoting CaneHunter031472:
LOL!! I bet the person who chose Tampa for the Republican National Convention must be kicking his own butt!! What a logistical nightmare. Couldn't they choose Arkansas or somewhere more stable?
Looks like he may get to keep his job, if the westward trend continues. Or maybe they won't chance it.
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15.8N 60.2W 1006mb at 8 p.m. and
15.8N 63.0W 1003mb at 11 p.m.
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Quoting MiamiHurricanes09:
Sir Levi or Kori, I have a question for you. Should Isaac completely miss Cuba, and an essence only scrape the northeastern coast and remain over water, what type of implications would that have on the intensity and track?


First of all, I don't see it taking that path unless it deepens significantly over the next day or so. It appears to be organizing now, but we'll see if that is just a hiccup or not. Furthermore, even if he does organize, I still think the trough over the eastern US is weakening a little based on water vapor loops. UW-CIMSS data seemed to support this idea as well.

But assuming he did take that track, that would likely mean a much stronger storm for Florida, and possibly the Carolinas as well (but more so Florida since the pattern doesn't appear amplified enough for a sharp recurve after landfall).
Member Since: March 7, 2007 Posts: 553 Comments: 19911
2125. K8eCane

Tropical Storm Isaac is a concern as GOP convention nears
By the CNN Wire Staff
updated 10:58 PM EDT, Wed August 22, 2012
STORY HIGHLIGHTS

Hurricane watch is in effect for Haiti, Puerto Rico and the U.S. Virgin Islands
The storm could become a hurricane Thursday night or Friday, hurricane center says
It's unclear whether the storm will affect the GOP convention in Florida next week

(CNN) -- Tropical Storm Isaac continued its westward path Wednesday, placing officials on alert from Puerto Rico to Guantanamo Bay to Florida, where it could pose a threat to the GOP convention next week.

It's too early to tell what effects Isaac will have on the U.S. mainland. But several computer models bring the storm into the Gulf of Mexico, while others move it farther east over Florida.

With roughly 50,000 people headed to Tampa for the Republican National Convention starting Monday, there is heightened interest in the path of the storm.

"We're monitoring the situation very closely," convention spokesman Kyle Downey said. "We are working closely with state, federal and local officials and plan on putting on a great convention."

Tampa Mayor Bob Buckhorn said his city is prepared.

"We have contingency plan after contingency plan," he said. "We are ready in the event that it happens. I don't think it's going to be a factor in this particular convention. But we are prepared in the event that it is."

At the U.S. naval base at Guantanamo Bay, Cuba, officials canceled the pretrial arguments scheduled to get under way in the trial of Khalid Sheikh Mohammed and four others.

Mohammed -- who has been held since 2006 -- is facing charges related to the September 11, 2001, terrorist attacks.

Pentagon officials said all court events at Guantanamo were canceled becaus
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Quoting Clearwater1:
That's a pretty good shift and I think the trend will continue a little further west from central FL. Still not good for the Keys and of course Haiti.


Not good for anyone really, especially the US. With more time in the GOM, Isaac could easily strengthen into a Cat. 2 storm.
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Quoting scott39:
The shear is lessoning on the N side of Isaac. Bottom line if Isaac takes a track over mountains we will see a weaker storm. If Isaac takes a route with less land interaction, then we will see a stronger storm. Based on most of the models now, we should see a weaker storm.


Therefore we can assume that Dr. Masters odds of it shifting west toward Louisiana might increase.
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Quoting opal92nwf:

Looks like someone had fun with Paint. lol


You know I was gonna say the same thing. They could spice that map up a little bit at least...doesn't look very professional at all.
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2121. GetReal
Quoting Chiggy:
Don't freaking believe the center is at 15.8N - I think NHC just sticking to the previous advisory in light of recon's failure to conclude on a LLC...


It is currently probably more like an educated best guess at this point, and sticking to continuity.
Member Since: July 4, 2005 Posts: 204 Comments: 8806
Quoting galvestonhurricane:


Pretty good agreement for S. Florida or farther west.

Looks like someone had fun with Paint. lol
Member Since: May 12, 2012 Posts: 11 Comments: 2315
Mission #3 is out early.

FLIGHT THREE --TEAL 71--
A. 23/0600Z, 1200Z
B. AFXXX 0509A CYCLONE
C. 23/0400Z
D. 16.0N 63.0W
E. 23/0530Z TO 23/1200Z
F. SFC TO 15,000 FT



Product: Air Force Temp Drop (Dropsonde) Message (UZNT13 KNHC)
Transmitted: 22nd day of the month at 21:56Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 307)
Storm Number: 09
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 3
Observation Number: 11
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Quoting GTcooliebai:
Slight shift westward, but would still give the west coast of FL. bad weather.

That's a pretty good shift and I think the trend will continue a little further west from central FL. Still not good for the Keys and of course Haiti.
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LOL!! I bet the person who chose Tampa for the Republican National Convention must be kicking his own butt!! What a logistical nightmare. Couldn't they choose Arkansas or somewhere more stable?
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2116. scott39
The shear is lessoning on the N side of Isaac. Bottom line if Isaac takes a track over mountains we will see a weaker storm. If Isaac takes a route with less land interaction, then we will see a stronger storm. Based on most of the models now, we should see a weaker storm.
Member Since: June 13, 2009 Posts: 0 Comments: 6732
2115. HrDelta
Quoting islander101010:
storm.is.going.to.be.bigger.than.the.cone


Could you stop with the period thing? It is a little aggravating. Though I agree with what you are saying.
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2114. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 169 Comments: 53296
2113. trey33
Quoting RitaEvac:
He's deep down in the Caribbean at current location





Thanks Rita!

Member Since: August 16, 2007 Posts: 0 Comments: 499
Quoting Tribucanes:
I think your wrong HoustonTxGal!! Wrong wrong wrong, lets fight about it! :) Kori's a lightening rod what can I say? Weather guru that he is. JK Kori. You put a lotta Alphas in the room together and they're bound to try and eat each other sometimes. Awesome to have you here HoustonTxGal you have a lot to offer.


Kissing up much?
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Quoting KoritheMan:


I don't charge for forecasting lessons, dear.

And yes, dear me. How dare I suggest we use science on a weather blog. How thoughtless of me!

This is comical.
Wait. She was being serious? -____-
Member Since: September 2, 2009 Posts: 130 Comments: 21091
Quoting angiest:
Can someone post the advisory? I don't think we've seen it yet.




This look down the page we dont need this blog filled with 100s of updates from the nhc
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What the... is that supposed to mean!?!?
img src="Image and video hosting by TinyPic">
Member Since: May 12, 2012 Posts: 11 Comments: 2315
2108. ncstorm
A NOAA research plane is just leaving Isaac. Standing by for the 11 pm ET advisory. No doubt the NHC is struggling with the data trying to pick the center. It looks like lower pressure farther south, but is that real?

From Facebook-Bryan Norcross
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Quoting GTcooliebai:
30 minutes until GFS begins its run.


Don't think I can make it. =(
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2106. Chiggy
Don't freaking believe the center is at 15.8N - I think NHC just sticking to the previous advisory in light of recon's failure to conclude on a LLC...
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2105. LBAR
Isaac is moving too fast to wrap himself up.
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Pretty good agreement for S. Florida or farther west.
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Quoting Tribucanes:
I like the wunderkidcayman quite a bit, and his forecasting bothers me none. That being said, ya'll complaining about his very consistent trend of wishcasting are valid and understandably annoying to some if not many. Isaac coming together nicely now, three to five hours from now Isaac should be one nice solid ball of convection with an easily distinguishable center. I'm not calling you a wishcaster wunderkidcayman, but I understand completely why some do.


ok and really I am not wish casting

11pm update is out interesting they put it at 15.8N 63W ok I still rather waith till next hunter recon flys in to determine if this is so HH recon takes off in about 3 hours (1am) I think
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Quoting scott39:
The NHC Cone will shift more W and then N. Isaac will then bomb in the GOM...IMHO :)


Putting a smiley on a post that predicts a rapidly intensifying hurricane in the GOMEX where it will cause significant damage and loss of life.

I'm woozy from the class being shown.
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Quoting HoustonTxGal:
Wow, what just happened? One minute we are all discussing and share info on Isaac and then next minute and half a dozen arguments have broken out.
I think your wrong HoustonTxGal!! Wrong wrong wrong, lets fight about it! :) Kori's a lightening rod what can I say? Weather guru that he is. JK Kori. You put a lotta Alphas in the room together and they're bound to try and eat each other sometimes. Awesome to have you here HoustonTxGal you have a lot to offer.
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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.