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: 393 - 343

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 yoboi:


did not do so well with debby....
They seem to have more problems with the TSs than the hurricanes... wonder why that is...
Quoting mcluvincane:
I don't understand why people post the precipitation map instead of the vorticity map when posting model runs
Precip maps work for me because it gives some idea how much rain we're likely to see, which could inform re: flooding potential...
Member Since: Posts: Comments:
What happens to this thing after the turn North? Does it just shoot straight up into the Gulf Coast and wear out over land or does it have the ability to turn West?
Member Since: Posts: Comments:
Quoting LargoFl:


I'm sure you know, but the 0z is out, past 144 hour and has it closer to the coast, near us.
Member Since: Posts: Comments:
390. wpb
Quoting KEEPEROFTHEGATE:


sorry
i follow NHC consenus on the storm
as to not cause confusion to official forecasts
and models speak for themselves

do not take offense to comment
a ok
Member Since: Posts: Comments:
Quoting alvarig1263:
GFS Model at 114 Hours:

you know it COULD do that, sit off the sw tip of florida, then cross over the tip of florida to the east, hit miami etc then back into the atlantic and up the coast, would that..shock all the experts
Member Since: August 6, 2011 Posts: 4 Comments: 41842
Quoting CajunCrawfishhunter:
Will the blob in the Gulf ever go away. It appeared to be moving West at one point but now seems to stall or move east. I think it is making the ocean rise!



I LIKE that blob in the Gulf! It's got to be pulling some measure of warmth from our waters, and at this point I'd like to mess up Isaac's welcome mat as much as possible!
Member Since: Posts: Comments:
Florida Gulf Coast
Maximum Of the Maximum Envelope Of Waters
Member Since: July 3, 2005 Posts: 427 Comments: 129449
Quoting Tropicsweatherpr:



Nice post looks like it is there..
Member Since: Posts: Comments:
Doesn't look bad to me...

Member Since: Posts: Comments:
384. wpb
Quoting wpb:
gfs has a 993 mb tropical storm off s tip of fla.this am 5am stewart discussion was for doom and gloom with outflow channels most of nhc forecasters have a even keel pen. stewart is too must and the wrong message is sent to the public.stacey calm down
so true
Member Since: Posts: Comments:
From Levi
Member Since: Posts: Comments:
Quoting Tropicsweatherpr:

That seems to be the center. I'm wondering if the little bits of convection just to its south will expand.
Member Since: Posts: Comments:
Quoting LargoFl:


Places Issac in the Sweet spot of the SE gulf... can you name me the 3 storms that come to mind that REALLY liked it there?

C, K, R were the letters.
Member Since: Posts: Comments:
Quoting serialteg:


thanks


Good try but you know that wasn't for you!
Member Since: Posts: Comments:
Quoting Clearwater1:
Yep, a lot of distance between there and Tampa with a whole lot of mess in between. Each report changes a little, but seems like it's back and forth, all ending with a FL hit.
yeah i am worried about it coming up the coast then making that turn eastward, if that happens, we could see alot of flooding as it pushes the water in front of it onland
Member Since: August 6, 2011 Posts: 4 Comments: 41842
Quoting LargoFl:
now would be a good time to check out what tidal surges we might expect from this storm
I saw someone post a graphic concerning that with a past storms. Maybe that person or someone else can post a link or chart.
Member Since: Posts: Comments:
GFS Model at 114 Hours:

Member Since: Posts: Comments:
Quoting wpb:
can you comment on run from prior and your thoughts


sorry
i follow NHC consenus on the storm
as to not cause confusion to official forecasts
and models speak for themselves

do not take offense to comment
Member Since: Posts: Comments:
this is the 12z precip map for the GFS through 120 hours

Member Since: Posts: Comments:
Quoting LargoFl:
stay tuned just in case


No please all take this one! I don't have the time to start up disaster recovery at work.
Member Since: Posts: Comments:
NOGAPS shifts west.
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Okay, so if this high pressure weakens that will allow Isaac to run up the east coast of Florida, if it stays strong enough it will pull Isaac towards the west coast of FL? But either way, Fl will get something?
Member Since: Posts: Comments:
Storm Surge in no way can be predicted without a Landfall Point,

Also, the Local Coastline and Storm Strength, and tides need to be accounted for to make that Variable better known or resolved, beforehand.

We are no where near that point for any where...CONUS wise.

Member Since: July 3, 2005 Posts: 427 Comments: 129449
Quoting Tropicsweatherpr:


You pegged the center on the nose.
Member Since: Posts: Comments:
Quoting KEEPEROFTHEGATE:
this will be ugly for a lot before it even gets to tampa


Just had that conversation with my mother who lives in Sarasota. Wanted to make sure she is aware of the storm and is getting extra water and batteries, ect. just in case.
Member Since: Posts: Comments:
366. wpb
gfs has a 993 mb tropical storm off s tip of fla.this am 5am stewart discussion was for doom and gloom with outflow channels most of nhc forecasters have a even keel pen. stewart is too must and the wrong message is sent to the public.stacey calm down
Member Since: Posts: Comments:
I wonder if that band to the east is going to wrap around the center, or if it's just going to wane. The bursting pattern with Isaac's bands worries me a little.

Member Since: Posts: Comments:
Quoting KEEPEROFTHEGATE:
this will be ugly for a lot before it even gets to tampa
Yep, a lot of distance between there and Tampa with a whole lot of mess in between. Each report changes a little, but seems like it's back and forth, all ending with a FL hit.
Member Since: Posts: Comments:
Quoting DavidHOUTX:


Don't forget this blunder either!

Listen: the 3-day forecast point was less than 50 miles from the actual storm track...
Quoting matilda101:
Have any of you noticed how much smaller the 5 day cone of uncertainly has been shrunked since Ike came thru a couple of years ago...looks like a about a 1/3 smaller.... NHC said that their ability of forecasting that far out has improved remarkably!
Still not perfect, but some improvements have definitely been seen. I'm looking forward to the shrink in the 5 day track... Then they can add a 7-day bulb...

Quoting RufusBaker:
go watch the local news now.......
Thanks, Rufus, you reminded me to listen to mine...
Member Since: Posts: Comments:
Quoting Patrap:


Actually the last 4 Days GFS has pinged Tampa.

So it bears scrutiny ,,but the end lines and such on the Forecast ensembles will be affected West, if the trend West continues.


It's been flipping from west coast to east coast for the past four days. Ultimately very consistent for the long range, but certainly not just targeting Tampa.
Member Since: Posts: Comments:
Member Since: August 6, 2011 Posts: 4 Comments: 41842
Will the blob in the Gulf ever go away. It appeared to be moving West at one point but now seems to stall or move east. I think it is making the ocean rise!
Member Since: Posts: Comments:
Quoting KEEPEROFTHEGATE:
this will be ugly for a lot before it even gets to tampa
its GONNA get ugly for where ever it hits
Member Since: Posts: Comments:
Quoting CJ5:
In looking at the models here Link

It seems they all initialize Isaac further north that he is currently tracking. It appears to me that if there is to be any strike on Haiti/DR he will have to be pulled North pretty strongly in the next 24/36 hours.



Looks that way, but the received wisdom is that the COC is farther north than you'd think from looking at it, at 15.9N.
Member Since: Posts: Comments:
TS Issac RGB Loop

Member Since: July 3, 2005 Posts: 427 Comments: 129449
Quoting schistkicker:
Are there any historical storms that would be an analog to those models showing a hurricane basically strafing the entire W coast of Florida?
Having Ft Myers, Naples, AND the Tampa area all under the front-right quadrant gun seems pretty close to a doomsday scenario--if it pans out (plenty of time for other things to happen)...
now would be a good time to check out what tidal surges we might expect from this storm
Member Since: August 6, 2011 Posts: 4 Comments: 41842
no.personal.forecast???...write.about.the.birds.and .the.bees?..come.on.now
Member Since: Posts: Comments:


Member Since: July 3, 2005 Posts: 427 Comments: 129449
Quoting KEEPEROFTHEGATE:
144hr final



I recall asking you about the "final" thing you typed and relating the idea that after 144 hours the data is not too accurate. Seems reasonable, but sadly for me and others along it's path it does not look good. Oh well.
Member Since: Posts: Comments:
Quoting LargoFl:
this could get very ugly for the Tampa area
this will be ugly for a lot before it even gets to tampa
Member Since: Posts: Comments:
However, I would anticipate the outer convection to slowly pull toward the center over the next 24 hours, and think we'll get a HU sometime tomorrow.
Member Since: Posts: Comments:
Quoting HuracanTaino:
Don't say that loud, there is a Kidcayman there, that might faint of joy...


hey huracan, where are you going to ride this out
Member Since: Posts: Comments:
Tropical Storm 09L

UW-CIMSS Automated Satellite-Based
Advanced Dvorak Technique (ADT)
Version 8.1.3
Tropical Cyclone Intensity Estimation Algorithm

Current Intensity Analysis



UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 22 AUG 2012 Time : 151500 UTC
Lat : 15:54:17 N Lon : 59:22:07 W


CI# /Pressure/ Vmax
3.9 / 992.1mb/ 63.0kt


Final T# Adj T# Raw T#
3.8 3.4 2.9

Center Temp : -46.6C Cloud Region Temp : -56.4C

Scene Type : CURVED BAND with 0.50 ARC in LT GRAY
Maximum CURVED BAND with 0.76 ARC in LT GRAY
at Lat: 15:18:00 N Lon: 58:57:35 W

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : ATLANTIC
Dvorak CI > MSLP Conversion Used : ATLANTIC

Tno/CI Rules : Constraint Limits : 0.5T/hour
Weakening Flag : ON
Rapid Dissipation Flag : OFF

C/K/Z MSLP Estimate Inputs :
- Average 34 knot radii : 43km
- Environmental MSLP : 1014mb

Satellite Viewing Angle : 25.9 degrees

************************************************* ***



Member Since: July 3, 2005 Posts: 427 Comments: 129449
Quoting TheMom:
So I know I know I'm such an UNfair weather friend.. Hey to the old timers that sorta kinda remember me and my gagillions of cherry questions. Nice to see some fresh eyes that are not just playing troll. So here we are again playing monkey in the middle of the East or West track sayers. Are we allowed to do the reverse fanatics thing and say that a hurricane hitting Tampa would be punishment for Republicans creating the tea-party? or would that get me in the time out chair even though we aren't in panic mood yet?
*runs around room and hugs all my old timer favs*


Next it will be obama inherited this hurricane from Bush.
Member Since: Posts: Comments:
Quoting Chucktown:
Just my take on everything, especially sitting here in Charleston, the trough just doesn't look very deep to me, it is NOT a full latitude trough that will completely turn the system out to sea. However, since Isaac is still struggling, it will continue to gain more longitude than latitude for at least the next 48 hours. This kind of motion could increase time over the islands and therefore keep Isaac from exploding and hence, a more westerly track. I'm still in the eastern Gulf camp, but any quick strengthening could alter the track east and quite significantly at that.


Afternoon CT, good to see ya and thanks for the update. It is a pretty rough looking system right now. Will be interesting to see what recon finds.
Member Since: Posts: Comments:
Quoting GOLSUTIGERS:
Sorry, I don't like the ECMWF model, that would put it around the first kick off for LSU. Sorry to say but Florida can have this one!
stay tuned just in case
Member Since: August 6, 2011 Posts: 4 Comments: 41842
Quoting VirginIslandsVisitor:


The action's picking up over here in St. Thomas too!


oh yes it is. for me canes are very very exciting and i welcome the challenge. it's a way of life for the islanders.
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting clwstmchasr:


Two runs in a row up the west coast. Getting interesting for Tampa.


Actually the last 4 Days GFS has pinged Tampa.

So it bears scrutiny ,,but the end lines and such on the Forecast ensembles will be affected West, if the trend West continues.
Member Since: July 3, 2005 Posts: 427 Comments: 129449

Viewing: 393 - 343

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
26 °F
Overcast