Isaac reorganizing as it blows through the Lesser Antilles

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

Share this Blog
56
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 1901 - 1851

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71 | 72 | 73 | 74 | 75 | 76 | 77 | 78 | 79 | 80 | 81 | 82 | 83 | 84 | 85 | 86 | 87 | 88 | 89 | 90Blog Index

Quoting wunderkidcayman:
I think Isaac will end up tracking like what the CLIP CLP5 and the LBAR is showing

Isaac continues to look good and further S and W
last I heard even Jim Cantore was was just talking about this

but I certainly say its near 15.2N 63.3W

with possible relocation to where Jim was saying I think it was somewhere near 14N

I don't know but I will stick to 15.2N 63.3W


You know, throughout your long tenure here, not once have I ever heard you call for a center reformation that didn't put the cyclone closer to you... And you wonder why people don't take you seriously. It's your fault, and no one else's. Sorry if this seems mean, but enough is enough.
Member Since: March 7, 2007 Posts: 521 Comments: 19125
the sheer size of the broad low pressure this will consolidate together in addition to further signs of southern/western run makes me even more worried.....next 24 hrs this pulls away from the dry air and can build it's own environment.....not to mention the warmer waters from now on.....when i saw the euro run bomb this in combo with the size of the low pressure basin i was worried....i knew the intensity models were junk because it hadn't pulled together enough.....this could be catastrophic especially if Isaac completely avoids DR/Haiti.....
Member Since: Posts: Comments:
WV

Member Since: Posts: Comments:
1898. scott39
The NHC Cone will shift more W and then N. Isaac will then bomb in the GOM...IMHO :)
Member Since: June 13, 2009 Posts: 0 Comments: 6706
Quoting Dakster:


How are the pythons doing these days?
the only one ive seen was a big one hanging out of the mouth of a gator as the gator was crossing Tamiami trail. the gator had a strut like he was real proud of his "catch"
Member Since: Posts: Comments:
Junkie was talking with Brad miller earlier today with the setup for Hugo was there an ull in the gulf?
Member Since: August 19, 2011 Posts: 0 Comments: 131
Quoting StormJunkie:


Again, I am not "so" sure; but fairly certain.

1. Most model guidance keeps it close to Fl.
2. It is a badly decoupled system ATM and it is also a large system which means it has a lot of work to do in order to work that decoupling out.
3. Most models have it tangling with mountains in Haiti and Eastern Cuba. This would likely disrupt any stacking it attempted previously.
4. Very large systems take their time getting back together after being disrupted (mountains) typically.

Sure, there is always a chance the unexpected happens...But those chances are low in this case imho.


Great points...interesting thought, it seems like all the "I" storms are either very large and/or have huge windfields but are not extremely intense. This one seems headed down that road...
Member Since: Posts: Comments:
Quoting StormJunkie:
Rapid intensification can not possibly be underway since the system is not vertically stacked.


Exactly what the NOAA flight noted, this is a very shallow and primitive system.
Member Since: Posts: Comments:
I think Isaac will end up tracking like what the CLIP CLP5 and the LBAR is showing

Isaac continues to look good and further S and W
last I heard even Jim Cantore was was just talking about this

but I certainly say its near 15.2N 63.3W

with possible relocation to where Jim was saying I think it was somewhere near 14N

I don't know but I will stick to 15.2N 63.3W
Member Since: Posts: Comments:
Quoting Joshsen18:
2059. Joshsen18 4:02 AM GMT on August 22, 2012   +0
we leave Friday for cancun riviera are for our honeymoon....does anyone have advice are. We pretty safe there from issac? I would hate to cancel....any advice please I trust people who really know how to read storms? Or any ideas
Action: Quote | Modify Comment
Member Since: August 18, 2012 Posts: 0 Comments: 1


I think it's very unlikely the storm will hit Cancun. You might get some rip currents and moderate NW winds though.
Member Since: Posts: Comments:
this is a large storm reminds me of gilbert in that same area back in 1988...I think regardless of where he tracks alot of people in his path are gonna get drenched..I believe florida from miami to pensacola will feel some affects from this storm...just my personal thinking
Member Since: Posts: Comments:
Quoting chevycanes:

shift west?

latest runs at 00z.



That looks more east to me than west but maybe I am not seeing everything right...
Member Since: Posts: Comments:
Quoting carlos1986:
Is this considered an indirect death related to Isaac? A 75 years old woman died today at Bayamon Puerto Rico, while she was taking preparations for TS Isaac.


Link


Yes.
Member Since: March 7, 2007 Posts: 521 Comments: 19125
1888. trey33
Quoting floridaT:
that kid that got his arm bit off by a gator a couple years ago. a block from my house


eek! gotta be careful. we have a few in my lake. thankfully all are smart here not to feed them so they stay away from us and we never see them, well mostly never.
Member Since: Posts: Comments:
i guess the texas coast is safe
Member Since: Posts: Comments:
No shift E
Quoting chevycanes:

shift west?

latest runs at 00z.

Member Since: Posts: Comments:
Rapid intensification can not possibly be underway since the system is not vertically stacked.
Member Since: August 17, 2005 Posts: 26 Comments: 15472
Quoting serialteg:


ok, i'll do it



There seems to be a radar "swirl" east of Dominica and another west of St. Vincent.
Member Since: Posts: Comments:
Quoting intampa:
Met on channel 13 says he is "optimistic "that Isaac going further out in the gulf and we will dodge this one again
Gusty for a Tampa met to say he was "optimistic", unless he has the inside scoop on the 11 o'clock report.
Member Since: Posts: Comments:
Is this considered an indirect death related to Isaac? A 75 years old woman died today at Bayamon Puerto Rico, while she was taking preparations for TS Isaac.


Link
Member Since: Posts: Comments:




Member Since: Posts: Comments:
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting Jwd41190:
So there is still a chance that the models can shift to the east?


If tonight's relative increase in organization finally heralds the beginnings of an inner core and some substantial intensification occurs, then yes, I can see that happening. Still a bit unsure though, as Ernesto looked good for a time at a similar location, and then struggled continuously later on.
Member Since: March 7, 2007 Posts: 521 Comments: 19125
Quoting Abacosurf:
we'll whose we'll
Highlands County employees along with Red Cross open and run the shelters here. It is really kind of fun...firefighters, emcs, librarians, county officials, it's a real leveler...We have nice shelters (animal shelters too) and
Quoting trey33:


Agreed and thanks!

When the RNC collided with my 15th wedding anniversary I made very early evacuation plans...

Vegas!!! (sad to miss prince harry by a few days)
Quoting Abacosurf:
we'll whose we'll
Us Highlands County employees have mandatory shelter duty. We partner with the Red Cross to make your stay nearly delightful! LOL...
Member Since: Posts: Comments:
From me
Member Since: Posts: Comments:
Will Isaac start pulling north because of that ULL over Cuba?

Member Since: Posts: Comments:
1873. sar2401
Quoting Jwd41190:
So there is still a chance that the models can shift to the east?


There's an excellent chance the models will shift all over the place during the three or four days. We won't get reliable model runs until Isaac develops a real COC.
Member Since: Posts: Comments:
Not liking the shape it's beginning to take on.

Member Since: Posts: Comments:
Dam poor Taiwan thought they were going to escape with a managable storm Temblim not anymore projected cat 4 at land fall wave heights 32 feet at last forecast,how high of a stormsurge would that bring to the coast and how much rain inland u guys think will come from this storm?My prayers go out to those that will be victimized by this monster.
Member Since: Posts: Comments:
Quoting MrstormX:


Of course, it all depends on the ridge. The current trend is obviously West however.

shift west?

latest runs at 00z.

Member Since: Posts: Comments:
1869. Dakster
Quoting floridaT:
that kid that got his arm bit off by a gator a couple years ago. a block from my house


How are the pythons doing these days?
Member Since: Posts: Comments:
1868. scott39
Quoting StormJunkie:


Again, I am not "so" sure; but fairly certain.

1. Most model guidance keeps it close to Fl.
2. It is a badly decoupled system ATM and it is also a large system which means it has a lot of work to do in order to work that decoupling out.
3. Most models have it tangling with mountains in Haiti and Eastern Cuba. This would likely disrupt any stacking it attempted previously.
4. Very large systems take their time getting back together after being disrupted (mountains) typically.

Sure, there is always a chance the unexpected happens...But those chances are low in this case imho.
EURO is based on the more Southern track...time will tell
Member Since: June 13, 2009 Posts: 0 Comments: 6706
Member Since: Posts: Comments:
1866. Michfan
Quoting KoritheMan:
It would sure be nice to get a new microwave pass. Most recent one was near 2300 UTC.


If there is any time we need microwave it is now.
Member Since: Posts: Comments:
Quoting MrstormX:


Of course, it all depends on the ridge. The current trend is obviously West however.


Ok, thanks, I assume we will just have to wait and see what happens when it hits Hispaniola?
Member Since: Posts: Comments:
Quoting Jwd41190:
So there is still a chance that the models can shift to the east?


Still

Member Since: Posts: Comments:
1863. GetReal
Member Since: July 4, 2005 Posts: 204 Comments: 8802
It would sure be nice to get a new microwave pass. Most recent one was near 2300 UTC.
Member Since: March 7, 2007 Posts: 521 Comments: 19125
1861. trey33
Quoting matilda101:


He actually said "convection wrapping around the center" LOL it looks like a tongue to me though!!


ok good i feel better
you wouldn't believe the thoughts that ran thru my brain
Member Since: Posts: Comments:
Quoting trey33:


Wow you are in the glades
that kid that got his arm bit off by a gator a couple years ago. a block from my house
Member Since: Posts: Comments:
OK!!! Power is back!!! Let's see for how long though.
Member Since: Posts: Comments:
Quoting Jwd41190:
So there is still a chance that the models can shift to the east?


Of course, it all depends on the ridge. The current trend is obviously West however.
Member Since: Posts: Comments:
Member Since: Posts: Comments:
1856. sar2401
Quoting weatherganny:


Jim Cantore just said on the weather channel that he expected the models move more west.


Once again, the CME model is shifting to a trip through the central Gulf. Wholesale gasoline is up to more than $3.13 a gallon, over a dime's rise since yesterday. That's a big jump. Lots of people betting their money on a major disruption to production in the Gulf.
Member Since: Posts: Comments:
1855. wpb
Quoting Tribucanes:
Rapid organization is now underway with Isaac, he may be pushing cat2 strength before he hits any mountainous regions in the coming days imo. If somehow Isaac misses a direct strike with the mountainous regions of Eastern Cuba, that would bode poorly for everyone in his path. Can't wait for what NHC has to say in their 11PM update.
it will be a mellow there dealing with a system that news a day or two to get its core together. it's a recon headache now
Member Since: Posts: Comments:
So there is still a chance that the models can shift to the east?
Member Since: Posts: Comments:
1853. JLPR2
Quoting Levi32:
The ridge to the northwest of Isaac is starting to weaken a bit. 500mb geopotential height is down from 5900m at 12z to 5880m at 00z at Santo Domingo, DR.


Don't just say it (XD), and it means?
Member Since: September 4, 2007 Posts: 7 Comments: 8459
Quoting trey33:


he really said tongue wrap?


He actually said "convection wrapping around the center" LOL it looks like a tongue to me though!!
Member Since: Posts: Comments:
Quoting StormJunkie:
What's up WCSC, good to see you. Yeah, I know it's a dangerous game to play trying to keep level heads prevailing around here...lol


im good man just doing chyron for the fox 24 news at 10 but watching blog at same time lol
Member Since: August 19, 2011 Posts: 0 Comments: 131

Viewing: 1901 - 1851

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71 | 72 | 73 | 74 | 75 | 76 | 77 | 78 | 79 | 80 | 81 | 82 | 83 | 84 | 85 | 86 | 87 | 88 | 89 | 90Blog Index

Top of Page

About JeffMasters

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