Isaac lashing the Lesser Antilles; TD 10 forms

By: Dr. Jeff Masters , 3:06 PM GMT on August 22, 2012

Share this Blog
50
+

Tropical Storm Isaac is lashing the entire Lesser Antilles chain of islands with heavy rains this morning, and the winds will be on the increase this afternoon as the storm heads west at 19 mph. Isaac is still a weak and disorganized tropical storm, but that is changing. The Hurricane Hunters are in the storm, and have thus far found no increase in the storm's top surface winds, which remain near 45 mph. In their 7:44 am EDT center fix, an Air Force Reserve aircraft measured a rather unimpressive center pressure of 1007 mb, and top winds at their 1000 foot flight altitude of 56 mph. The plane 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 it is unlikely Isaac will become a hurricane today. Satellite loops, however, show that Isaac has developed a Central Dense Overcast (CDO) of high cirrus clouds, the hallmark of a developing storm. These clouds have very cold cloud tops, indicating that the updrafts creating them are quite strong. An analysis of upper level winds from the University of Wisconsin CIMSS shows that upper-level outflow is becoming well-established to the southwest and northwest, but outflow is restricted on the southeast side. A large clump of heavy thunderstorms several hundred miles southeast of the center continues to compete for moisture, and is interfering with the low level inflow and upper level outflow of the storm. The intensification rate of Isaac will increase if the storm is able to integrate this clump of heavy thunderstorms into its circulation, which satellite loops this morning suggest is now beginning to happen. Radar imagery from Barbados and Martinique show plenty of heavy rain showers, mostly on the south side of Isaac where it is moister, but little spiral banding. Hurricane hunter missions are scheduled for Isaac every six hours, and a NOAA hurricane hunter research aircraft will also be in the storm, with missions scheduled every 12 hours. The NOAA jet is first scheduled to fly into the storm on Thursday afternoon, to do a large-scale dropsonde mission to aid model forecasts.


Figure 1. Morning radar image of Isaac taken from the Barbados radar at 10:15 am EDT. Image credit: Barbados Weather Service.

Intensity forecast for Isaac
The latest 8 am EDT run of the SHIPS model shows that wind shear is moderate, 10 - 15 knots, but is expected to relax by this evening to a low 5 - 10 knots. Ocean temperatures have increased to a very warm 29°C, and the storm is now over waters with a high total heat content. The lowering wind shear and warm waters should allow the storm to wall off the dry air that has been interfering with development, and also allow the storm to integrate the thunderstorm clump on its southeast side that has been interfering with low level inflow and upper level outflow. It will take some time for the increase in organization to result in an increase in Isaac's winds, and I still expect top winds of 45 - 60 mph in the Lesser Antilles Islands this evening when the core of the storm moves through. On Thursday, when Isaac will be in the Eastern Caribbean, conditions should be favorable enough to allow steady strengthening to a Category 1 hurricane. The 11 am EDT wind probability forecast from NHC predicted a 47% chance that Isaac will become a hurricane by Friday morning, and a 16% chance it will be a Category 2 or stronger hurricane then. This is a reduction in the odds given in the 5 am advisory.

Impact of Isaac on the Islands
The entire Lesser Antilles Islands chain will have a three-day period of heavy weather Wednesday through Friday. Sustained tropical storm-force winds extend out about 50 miles to the north of the center and 30 miles to the south, so an 80-mile wide swath of the Lesser Antilles will potentially see tropical storm-force winds of 45 - 60 mph this Wednesday evening. Guadaloupe, Antigua and Barbuda, Dominica, Montserrat, and St. Kitts and Nevis at highest risk of these winds.

Winds in St. Croix in the Virgin Islands will likely rise above tropical storm force on Thursday morning, and the south coast of Puerto Rico should see tropical storm-force winds by Thursday afternoon. The San Juan airport may be able to stay open Thursday afternoon and evening, but I think it is more likely they will be forced to shut down.

On Thursday night, heavy rains and tropical storm-force winds should arrive on the southern coast of the Dominican Republic, and all airports in the D.R. will probably be closed on Friday. Rainfall amounts of 8 - 12 inches will likely affect the Dominican Republic Thursday through Saturday, creating dangerous flash floods and mudslides.

Isaac is potentially a very dangerous storm for Haiti, where 400,000 people still live outside underneath tarps in the wake of the 2010 earthquake. Heavy rains from Isaac will begin on Friday morning in Haiti, and last through Sunday. Rainfall amounts of 8 - 12 inches are possible, which will be capable of causing extreme flooding on the vegetation-denuded slopes of Haiti. It will be a major challenge to keep those Haitians living outside safe, if rainfall amounts of 5 - 10 inches occur.

Impact on Florida, Cuba, Jamaica, and the Bahamas
Florida, Cuba, Jamaica, and the Bahamas are all at high risk of receiving hurricane conditions from Isaac. The latest set of 06Z (2 am EDT) model runs for Isaac are fairly unified for the coming three days, showing a westward track to a point on the south coast of Hispaniola. All of the models then predict a more west-northwest track across the island and into eastern Cuba, as Isaac responds to a trough of low pressure over the Southeast U.S. Most of the models then predict a path for Isaac along the spine of Cuba, then into the Florida Straits off the coast of Miami by five days from now. A notable exception is our best-performing model, the ECMWF, which keeps Isaac just south of Cuba, and takes the storm more to the west between Jamaica and Cuba on Saturday, then into the Yucatan Channel between Mexico and Cuba by Monday. 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. Some models predict a more easterly exit point, allowing Isaac to move up the east coast of Florida, and potentially make landfall in the Southeast U.S. The latest 06Z GFS model run predicts a more westerly track, which would potentially allow Isaac to move up the west coast of Florida towards Tampa. Keep in mind that the average error in a 5-day forecast is 260 miles. The two most recent runs of the GFS model, at 00Z and 06Z (8 pm and 2 am EDT), gave positions for Isaac that were about 250 miles apart--the earlier run putting the center near West Palm Beach, and the more recent run giving a location between Key West and Havana, Cuba. While passage over the high mountains of Hispaniola and then Cuba will substantially disrupt Isaac and probably reduce it below hurricane strength, the storm is quite large, and should be able to re-intensify once it emerges over the Florida Straits. Waters will be very warm, near 30°C, wind shear is predicted to be light, and forecasts of the upper-level winds show the possibility of an upper-level outflow pattern very favorable for intensification. If Isaac spends a day over water, that should be enough time for it to intensify into a Category 1 hurricane, and if the storm takes a longer 2-day track over water up either the east or west coast of Florida, a Category 2 or stronger storm is possible.

Isaac is a threat to affect Tampa during the Republican National Convention, August 27 - 30, and the official NHC forecast now has Tampa in the 5-day cone of uncertainly. The latest 11 am EDT wind probability forecast from NHC gives Tampa a 9% chance of receiving tropical storm-force winds for the 24-hour period ending on the morning of first day of the convention (Monday). I blogged about the climatological chances of a hurricane causing an evacuation of Tampa during the convention in a post last week, putting the odds at 0.2%. I put the odds of an evacuation occurring during the convention in the current situation at 3%.


Figure 2. Morning satellite image of Tropical Depression Ten.

Tropical Depression Ten forms in the Eastern Atlantic
The large tropical wave in the Central Atlantic, midway between Africa and the Lesser Antilles Islands, has become Tropical Depression Ten. The depression has an impressive amount of spin and heavy thunderstorm activity, as seen on visible satellite loops, and should be Tropical Storm Joyce by Thursday. None of the models show that TD 10 will be a threat to the Lesser Antilles Islands.

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? Well, 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 3, 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 3. 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 this afternoon.

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: 143 - 93

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 | 32Blog Index

Quoting belizeit:
I stated in the last Blogg that Isaac is probably a open wave but they keep it as a TS because of the lives that were lost with degrading TD 7 earlyer this month


It is not an open wave.
Member Since: Posts: Comments:
Quoting Patrap:
Those are not "Blunder's"..that ridiculous, as track forecast early on are often and usually not the end solution, but they are the Best forecast with availible Data at that time.

.

Exactly my point. Freaking out over a 5-day forecast is silly. Just be prepared.
Member Since: Posts: Comments:

Quoting Patrap:
Fer snits and Giggles maybe?


NOT.  FUNNY.

I survived Gustav...I do NOT need Son of Lili over my house.

Take that back, Pat.

(OK, maybe a bit funny.)

Let's hope that the Euro remains an outlier, like it ultimately became with Ernesto.
Member Since: September 20, 2005 Posts: 0 Comments: 208
Quoting yoboi:


that's not the nhc chart.....


Agreeing with Pat's earlier post, and this justifies it. Personal forecasts can be confusing to other non-regulars searching for info on an official blog like this. Best to leave them to personal blogs.
Member Since: Posts: Comments:
Quoting pottery:

Where they flying from ?


From the Google Earth overlay, they left from St. Croix and they aren't too far from getting back there right now.
Member Since: Posts: Comments:
Quoting Patrap:
Those are not "Blunder's"..that ridiculous, as track forecast early on are often and usually not the end solution, but they are the Best forecast with availible Data at that time.

.


Exactly. That is why people need to relax and stop saying Florida is doomed when the storm has a ways to go before we know exactly where it is going
Member Since: Posts: Comments:
ok maybe you guys are right but if recon goes in and finds it near where I said then what hmm
Member Since: June 13, 2009 Posts: 2 Comments: 12180
Member Since: August 6, 2011 Posts: 4 Comments: 39690
Quoting 954Soxfan:


Based on the models and each update. This latest update shows the cone moved slightly west which is likely to cotinue.


Depends on which model you think is hot i guess. I need to see multiple runs to verify. High pressure/strength of storm are not easy reads. Lots of percolating still to do. nobody is clear yet.
Member Since: Posts: Comments:
Quoting kshipre1:
can someone give their best educated answer and guess if they think it is possible this storm could miss florida to it's east or west? I think the intentsity forecast seems better for Florida compared to last night. someone please chime in on their predicted path east or west and possible intensity. thanks!
What does anyone's opinion matter? Only the offical NHC provides the plots which are GUESSED at by using all the scientific data they can get. My 50+ years of living in the Florida Keys has taught me to listen to the experts, prepare for the worst (direct hit, higher winds than anticipated) and hope for the best. A lot of people on here love to try and predict to see if they get it right. Not even the NHC gets it right all the time. Read the book "Phantom" to see what happens when forecasts are wrong.
Member Since: Posts: Comments:
Quoting Patrap:
Those are not "Blunder's"..that ridiculous, as track forecast early on are often and usually not the end solution, but they are the Best forecast with availible Data at that time.

.


Initial forecasts have a high chance of being incorrect. Many ever changing dynamics to consider, of which we can't precisely predict. That's what makes weather so fascinating, and at times, dangerous.
Member Since: Posts: Comments:
132. yoboi
Quoting grandmotherof6:


So its going to Savannah? Im confused


that's not the nhc chart.....
Member Since: August 25, 2010 Posts: 7 Comments: 2369

Quoting LargoFl:
I hope at this time, folks in Miami and ft Meyers and Sarasota should be preparing their hurricane things, could go up either coast but I wouldnt wait for an official warning to come..might be too late by then to buy things etc
One should always have hurricane kits every hurricane season already if you live in those areas, i would not panic yet as its still 5-6 days away and tracks can change 250+ miles.
Member Since: Posts: Comments:
JMA model at 144 hours

Member Since: August 19, 2006 Posts: 13 Comments: 15744
Quoting DavidHOUTX:


Don't forget this blunder either!



Good catch. I forgot about that particular "oops".
Member Since: Posts: Comments:
For those folks in Lee county in case you need this..lee county emergency operations center with tons of info for you in a hurricane............Link
Member Since: August 6, 2011 Posts: 4 Comments: 39690
Quoting Patrap:
Those personal Track forecast's and other Formatted looking Tracks are best suited for a Personal Blog as posting them here is like, well kinda distracting and confusing to the general Lurker.

My opine only.

Mine too.
Member Since: Posts: Comments:
My apologies if this has already been posted

Link
Member Since: Posts: Comments:
33hrs:
Member Since: Posts: Comments:
TS Isaac RainBow Top Loop

Member Since: July 3, 2005 Posts: 426 Comments: 128871
Maybe we will see the LLC reform in the new blowup to the east.
Member Since: Posts: Comments:
Quoting WxGeekVA:


here fishy fishy fishy...;P



Just for comparison:

Hurricane Frances of 2004



Track forecasts out to 5 days for tropical cyclones that have barely developed and matured are subject to HUGE changes.
Member Since: Posts: Comments:
Those are not "Blunder's"..that ridiculous, as track forecast early on are often and usually not the end solution, but they are the Best forecast with availible Data at that time.

.
Member Since: July 3, 2005 Posts: 426 Comments: 128871
Quoting 954Soxfan:


Based on the models and each update. This latest update shows the cone moved slightly west which is likely to cotinue.

lol@likely to continue. the GFS has been going back and forth with east coast and west coast landfalls in FL.
Member Since: Posts: Comments:
Those personal Track forecast's and other Formatted looking Tracks are best suited for a Personal Blog as posting them here is like, well kinda distracting and confusing to the general Lurker.

My opine only.
Member Since: July 3, 2005 Posts: 426 Comments: 128871
Quoting jeffs713:
For people freaking out about the cone basically destroying Florida... Just remember last year:

IRENE


ISSAC


Things can, and will change. How they will change, we don't know. But they will change.


Don't forget this blunder either!

Member Since: Posts: Comments:
almost here
Member Since: August 6, 2011 Posts: 4 Comments: 39690
Quoting ecupirate:


You, calling for it to be further south or heading SW? NO way....

Let him go! Let him go by his own thing.
Member Since: Posts: Comments:
21 hrs:

Member Since: Posts: Comments:
Quoting GetReal:
An observation with a question... After observing the Barbados radar loops it is clearly visible to anyone that the convection north of Barbados is moving EAST to
WEST. Now if the center of Isaac is currently located at 15.9N as NHC indicated on last advisory, shouldn't the convection on the Barbados radar be moving WEST to EAST. After all doesn't a cyclone rotate counter-clockwise in the N hemisphere?


Link hit the 400km loop.


If the low level center is that far north, Isaac is not stacked, and that is a stronger mid level circulation the Barbados radar is picking up.


GR, yes, good obs. I think we're still seeing a disorganized system. Disjointed. LLC slightly more north, MLC more southwards as evidenced by your radar loop. Vorticity charts also verify that with the 200 mb levels trying to gain some intensity north of the MLC. The MLC is clearly shown in your loop and may become the dominate element as it matures. Radar best defines it rather than sat images - too bad we can't see radar a bit further out to see what was happening with the smaller llc.

Current speed and motion likely to continue and tracks will likely shift a bit further westwards gradually. He may have a name, but he's not there yet,and has a considerable ways to go yet to become a maturing system.

Later, geeks! ;)
Member Since: July 9, 2006 Posts: 184 Comments: 29610
Quoting BTRWeather:

Thanks, it would be neat if there was an archive somewhere.



Here ya go: Tropical Cyclone Advisory Archive
Member Since: Posts: Comments:


Link
hit 400km loop.
Member Since: Posts: Comments:
Quoting WxLogic:
12Z GFS Init:



About right.
Pretty solidly still in the easterlies without much room to move N with current flow regime in place.
Member Since: Posts: Comments:
I hope at this time, folks in Miami and ft Meyers and Sarasota should be preparing their hurricane things, could go up either coast but I wouldnt wait for an official warning to come..might be too late by then to buy things etc
Member Since: August 6, 2011 Posts: 4 Comments: 39690
Quoting BTRWeather:

Anyone have a link to past NHC official tracks? If not, I would like to copy these images if you don't mind?


Link
Member Since: Posts: Comments:
Quoting Patrap:
Fer snits and Giggles maybe?



I hope not for you guys,course i dont want it to come up the east coast either.We are way over due on the DelMarVa peninsula.Irene just grazed us last year with some rain and a little wind.
Member Since: Posts: Comments:
Quoting hydrus:
Thank you Dr..The different path scenario,s for Haiti are frightening. The unlikely path to the north would probably be the most forgiving, a pass to the south would still bring high winds and heavy rain, but not as bad as a direct hit. It appears that Hispaniola is to big for Isaac to miss, and there will be some type of tragedy. Not to sound prophetic, just a quick look at this regions history provides one with enough reason to be troubled.


Excellent point here. It seems the blog is more caught up with U.S. impact now, little thought has been given to Haiti. We know from previous storms that Haiti has suffered from hurricanes moreso than other countries due to it's topography (human caused sadly). Haiti should take notice now, and we should be more mindful of what impacts could be had there.I've had experience in disaster relief there in the Navy as apart of ACU-2 in 2010, though I can't precisely remember the storm. You lose track of such things being so busy. Point is, think of those in immediate danger first and foremost.
Member Since: Posts: Comments:
Quoting jeffs713:

Go ahead. The first one I pulled off a google search. The other one I pulled directly from the "printer friendly" version at the NHC website.

Thanks, it would be neat if there was an archive somewhere.
Member Since: Posts: Comments:
15hrs
Member Since: Posts: Comments:
Quoting wunderkidcayman:
hey guys I don't know but I don't take the 11am fix for Isaac to be at 15.9 N
well Sattelite radar and surface obs do kinda suggest that the LLC is quite abit S of 16N more like near 15.5N or even further S

anyway we should have a much better idea when recon flys in
by the way recon takeoff in about 3 hours I think


You, calling for it to be further south or heading SW? NO way....
Member Since: Posts: Comments:
Quoting grandmotherof6:


So its going to Savannah? Im confused


THAT IS NOT AN OFFICIAL ITEM.
It is produced by a blogger.
Member Since: Posts: Comments:
RECON info and POD's can be found by clicking Aircraft recon on the NHC Home page menu.

Member Since: July 3, 2005 Posts: 426 Comments: 128871
Quoting pottery:

OK, I wondered if it was BDos.
Thinking about it, I wouldn't be shocked if they leave from Barbados (which is where NOAA42 is right now), and land in St. Croix.
Member Since: Posts: Comments:
Quoting Patrap:
Fer snits and Giggles maybe?


What an ugly picture..:
Member Since: September 27, 2007 Posts: 1 Comments: 21492
Member Since: August 6, 2011 Posts: 4 Comments: 39690
hey guys I don't know but I don't take the 11am fix for Isaac to be at 15.9 N
well Sattelite radar and surface obs do kinda suggest that the LLC is quite abit S of 16N more like near 15.5N or even further S

anyway we should have a much better idea when recon flys in
by the way recon takeoff in about 3 hours I think
Member Since: June 13, 2009 Posts: 2 Comments: 12180

Viewing: 143 - 93

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 | 32Blog Index

Top of Page

About

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

Local Weather

Overcast
52 °F
Overcast