Isaac remains disorganized
Tropical Storm Isaac has strengthened slightly, data from the hurricane hunters show, but the storm remains disorganized and difficult to forecast. If you have to make decisions based upon what Isaac will do, I highly recommend that you wait until at least Friday morning to make a decision, if at all possible, as the forecasts then should be of significantly higher accuracy. Isaac continues to have a large area of light winds about 50 miles across near its center. This makes the storm subject to reformations of the center closer to areas of heavy thunderstorms that form, resulting in semi-random course changes. Until Isaac consolidates, the lack of a well-defined center will make forecasts of the storm's behavior less accurate than usual. An Air Force Reserve hurricane hunter aircraft is in Isaac this afternoon, and has found that surface tropical storm-force winds on the east side of the storm, south of Puerto Rico, have undergone a modest expansion. These winds were mostly in the 40 mph range, with a few areas of 45 mph winds. The surface pressure remained fairly high, at 1004 mb. Infrared and visible satellite loops show that Isaac has fairly symmetric circular cloud pattern, with developing spiral bands that are contracting towards the center, which suggests intensification. However, the storm has a very clumpy appearance, and is a long way from being a hurricane. Given the storm's continued reluctance to organize, Isaac is unlikely to reach hurricane strength before encountering Haiti and Cuba. An analysis of upper level winds from the University of Wisconsin CIMSS shows an upper-level outflow channel well-established to the north, and an intermittent outflow channel to the south. Radar imagery from Puerto Rico shows some weak low-level spiral bands that haven't changed much in intensity or organization this afternoon. NOAA buoy 42060 reported 1-minute mean winds of 35 mph and a wind gust of 40 early this afternoon. At St. Thomas in the Virgin Islands, wind gusts up to 45 mph were observed early this afternoon. Isaac's rains caused major flooding last night in Trinidad and Tobago, the southernmost islands of the Lesser Antilles chain, according to the Trinidad Express. Isaac's rains have not been heavy enough today to cause flooding problems on other islands.
Figure 1. True-color MODIS image of Isaac taken at 1:40 pm EDT August 23, 2012. Image credit: NASA.
Latest model runs for Isaac
The latest set of 12Z (8 am EDT) model runs have shifted to the west compared to the previous set of runs. The models continue to show a west-northwestward track to a point on the south coast of Hispaniola, then across eastern Cuba and into the Florida Straits between Florida and Cuba. A trough of low pressure is then expected to pull Isaac to the northwest and then north, towards the Florida Panhandle. The big news in this model cycle is that both of our top models--the GFS and ECMWF--predict that 5 - 6 days from now, the trough of low pressure pulling Isaac to the north may not be strong enough to finish the job. These models predict that the trough will lift out and a ridge of high pressure will build in, forcing Isaac more to the west. The GFS predicts this will occur after Isaac makes landfall in the Florida Panhandle, resulting in Isaac moving slowly to the west over land, from Georgia to Alabama. The ECMWF predicts the westward motion will happen while Isaac is in the northern Gulf of Mexico, resulting in an eventual landfall near the Louisiana/Texas border on Thursday. There are some huge issues to resolve to make an accurate long-range track forecast for Isaac. Where will its center consolidate? How will the interaction with the mountains of Hispaniola and Cuba will affect it? Where will Isaac pop off the coast of Cuba? Hopefully, the data being collected by the NOAA jet this afternoon will give us a more unified set of model forecasts early Friday morning. For now, pay attention to the cone of uncertainty. If you're in the cone, you might get hit.
Figure 2. Predicted 5-day rainfall total ending at 8 am EDT Tuesday August 28 from Tropical Storm Isaac. Graphics were generated from the 12Z (8 am EDT) August 23, 2012 run of the HWRF model (top) and GFDL model (bottom). The heaviest rainfall is expected to occur in a 50 - 80 wide wide swath along and to the right of where the center tracks. Amounts in excess of 8 inches (yellow colors) are predicted for portions of the Dominican Republic and Haiti from the HWRF model, but not the GFDL model. Given the current disorganization of Isaac, these rainfall amounts are probably at least 20% too high. Image credit: Morris Bender, NOAA/Geophysical Fluid Dynamics Laboratory.
Jeff Masters
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Not unexpected here ... more will follow.
Remind anyone of any recent events ?
Tropical Storm Fay.
500 PM EDT FRI AUG 15 2008
THE INITIAL MOTION IS 275/12. FAY IS ON THE SOUTH SIDE OF A
LOW/MID-LEVEL RIDGE...WITH THE LARGE-SCALE MODELS FORECASTING A
WEAKNESS TO DEVELOP IN THE RIDGE OVER THE EASTERN GULF OF MEXICO
OR FLORIDA DURING THE NEXT 48-96 HR. WHILE ALL THE TRACK GUIDANCE
AGREES THAT THIS WEAKNESS WILL CAUSE FAY TO TURN NORTH-
NORTHWESTWARD TO NORTHWARD BY THE END OF THE FORECAST PERIOD...THIS
IS A CONSIDERABLE SPREAD IN THE GUIDANCE ON JUST WHERE FAY WILL
TRACK. THE NAM CALLS FOR FAY TO PASS EAST OF THE FLORIDA
PENINSULA...WHILE THE HWRF CALLS FOR LANDFALL IN SOUTHEASTERN
FLORIDA. THE GFDL AND NOGAPS FORECAST A MORE WESTWARD TRACK TOWARD
THE NORTHERN GULF COAST...WHILE THE GFS...ECMWF...AND THE MODEL
CONSENSUS FORECASTS FAY TO TRACK NEAR OR OVER THE WEST COAST OF
FLORIDA. COMPLICATING MATTERS IS THE POSSIBILITY OF LAND
INTERACTION CAUSING ERRATIC MOTION AND REFORMATION OF THE CENTER.
THE FORECAST TRACK WILL FOLLOW THE MODEL CONSENSUS AND CALL FOR FAY
TO CROSS HISPANIOLA AND THE EASTERN PORTION OF CUBA...THEN PASS
NEAR OR OVER THE FLORIDA KEYS AND THE WEST COAST OF FLORIDA.
i only seen navy during irene....wonder who made the call to get them in there...
interesting - will be watching that one .... don't like it but ...
Ah, did not know that. Thanks.
Data is assimilated into the 00Z GFS up untill about 10 PM EST.
U think? Interesting....
Katrina Hit florida....
http://www.weather.unisys.com/satellite/sat_wv_ea st_loop-12.gif
Puts it in motion for you.
Thank u.
yes it did. i live in broward but the worst side was the south side when it rolled thru.
that other poster must be confused.
Guess it depends on the area. Water pipelines frequently burst here for no reason, imagine with a storm.
I'm calling it a night, I have to wake up early for school tomorrow. It would have been nice if they just left Friday off, but nope. Probably the one time no one will yell out "TGIF" during class.
Night everyone.
will do
- good to see Ike back btw - later - out.
Yes, the favored EURO goes more west than the other models. The EURO is no. 1 statistically. However, the best model can be off as well.
that is not possible, whens the last time missouri got rain from a dying tropical cyclone...its ridiculous....storms dont just plow into ridges like that i dont care how hard the hump/pump the ridge...i just dont see how its going to go west of NOLA...meteorlogically its almost impossible, i dont care what the models say.
yes I like that track too, which means to me that the keys, south florida and the west coast of FL from tampa southward are still in for some nasty weather from Isaac
i meant after that...lol
Exactly. All that black stuff. Convection can make determining motion very difficult, especially without the assistance of visible imagery. Radar rixes from San Juan is a bit of a better tool, and shows that Isaac is moving generally WNW.
Like I said, getting Bob Rose down with anything coming to TX is a miracle in itself, and he's pretty confident the weakness in the ridge will permit Isaac to go TX/LA.
Apparently that's the Euro's driver, too.
The result of a clash between Isaac's outflow on the western side with an old upper trough over eastern Cuba.
There is fatigue in GFS.... Ernesto has been so umpredictable, that it forgot to dissipate it after getting into land...
Except that Katrina when right through Florida.
We're up in Lantana. NHC kept saying Katrina was headed west (straight towards us) when it was obviously going SW. I never have figured that one out. Incidently, Hurricane Warnings weren't posted until 18 hours before landfall. Not a perfect world.
He's talking about when Katrina was forecast to hit the Panhandle after initially coming off Florida.
Also, not sure what straight on that map means in the real world. Maps distort.
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