T.S. Isaac Discussion #19 (25/2100 AUG UTC)

000
WTNT44 KNHC 252102
TCDAT4

TROPICAL STORM ISAAC DISCUSSION NUMBER  19
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
500 PM EDT SAT AUG 25 2012

THE CENTER OF ISAAC IS CURRENTLY MOVING
ALONG THE NORTH COAST OF EASTERN CUBA.
THE SATELLITE APPEARANCE IS SOMEWHAT
DISORGANIZED... WITH THE MAIN CONVECTIVE
MASS 50 N MI OR MORE EAST OF THE LOW-LEVEL
CENTER.  AN AIR FORCE RESERVE HURRICANE
HUNTER AIRCRAFT HAS REPORTED 850 MB FLIGHT-
LEVEL WINDS OF 56 KT TO THE NORTHEAST OF
THE CENTER...WITH RELIABLE-LOOKING SFMR
SURFACE WIND DATA NEAR 50 KT. BASED ON 
THIS...THE INITIAL INTENSITY REMAINS 50 KT.
THE CENTRAL PRESSURE OF 997 MB IS BASED ON
A COMBINATION OF AIRCRAFT DATA AND
CUBAN SURFACE OBSERVATIONS.

THE INITIAL MOTION IS NOW 310/18.  
ISAAC IS CURRENTLY PART OF A LARGE 
LOW/MID-LEVEL LOW PRESSURE SYSTEM 
COVERING THE NORTHWESTERN CARIBBEAN SEA
AND THE ADJACENT LAND AND OCEAN AREAS.  
THIS LOW PRESSURE AREA HAS A SECOND 
VORTICITY CENTER BETWEEN JAMAICA AND 
THE CAYMAN ISLANDS...AND FOR THE NEXT 
24-36 HR ISAAC AND THIS CENTER WILL 
LIKELY ROTATE AROUND EACH OTHER.  
BASED ON THIS EXPECTATION... THE 
FORECAST TRACK SHOWS ISAAC MOVING
NORTHWESTWARD FOR 12 HR OR SO...
FOLLOWED BY A TURN TOWARD THE WEST-
NORTHWEST.  IT IS POSSIBLE THE STORM 
COULD MAKE A SHARPER TURN THAN FORECAST...
AS THE UKMET IS SHOWING AN ALMOST DUE WEST
MOTION BETWEEN THE FLORIDA KEYS AND CUBA
NEAR THE 36 HR POINT.  THE EARLY PART OF
THE FORECAST TRACK IS SHIFTED A LITTLE TO
THE LEFT OF THE PREVIOUS FORECAST...BUT 
STILL LIES TO THE RIGHT OF THE CONSENSUS
MODELS AND THE BULK OF THE DYNAMICAL
MODELS.  AFTER 36 HR...ISAAC SHOULD BREAK
FREE OF OR ABSORB THE REST OF THE LOW...
WITH THE SUBTROPICAL RIDGE TO THE EAST
BECOMING THE DOMINANT STEERING INFLUENCE.
THIS SHOULD ALLOW THE STORM TO GRADUALLY 
TURN TOWARD THE NORTHWEST AND NORTH OVER 
THE EASTERN AND NORTHERN GULF OF 
MEXICO...WITH AN EVENTUAL LANDFALL
ALONG THE NORTHERN GULF COAST IN 72-96
HR.  WHERE THIS MIGHT OCCUR IS STILL 
RATHER UNCERTAIN...WITH THE TRACK GUIDANCE
SPREAD BETWEEN SOUTHEASTERN LOUISIANA AND
THE CENTRAL FLORIDA PANHANDLE.  THIS PART
OF THE TRACK FORECAST LIES IN THE CENTER
OF THE GUIDANCE ENVELOPE NEAR THE 
CONSENSUS MODELS AND IS SIMILAR TO THE
PREVIOUS FORECAST.

A COMBINATION OF LIGHT WESTERLY VERTICAL
WIND SHEAR AND LAND INTERACTION SHOULD AT 
LEAST SLOW INTENSIFICATION FOR THE NEXT 12
HR.  AFTER THAT...THE SHEAR SHOULD DIMINISH 
WHILE THE CYCLONE REACHES OPEN WATER.  
THIS SHOULD ALLOW ISAAC TO GRADUALLY 
STRENGTHEN INTO A HURRICANE NEAR THE 
FLORIDA KEYS OR OVER THE SOUTHEASTERN GULF
OF MEXICO.  THE NEW INTENSITY FORECAST IS
SIMILAR TO THE PREVIOUS FORECAST AND IS
NEAR OR A LITTLE ABOVE THE INTENSITY
CONSENSUS.  IT SHOULD BE NOTED THAT THE 
GLOBAL MODELS ARE FORECASTING A VERY 
FAVORABLE PATTERN OF UPPER-LEVEL WINDS 
OVER THE NORTHERN GULF OF MEXICO BY 72 HR.
SHOULD THIS VERIFY AND SHOULD ISAAC 
ESTABLISH AN INNER CORE...THE CYCLONE 
COULD BE SIGNIFICANTLY STRONGER THAN
CURRENTLY FORECAST.

IT IS IMPORTANT NOT TO FOCUS ON THE 
EXACT TRACK OF ISAAC DUE TO THE
UNCERTAINTIES IN THE FORECAST AND THE
FACT THAT ISAAC HAS A LARGE AREA OF 
TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT.


FORECAST POSITIONS AND MAX WINDS

INIT  25/2100Z 21.3N  76.0W   50 KT  60 MPH
 12H  26/0600Z 22.6N  78.0W   55 KT  65 MPH
 24H  26/1800Z 24.1N  80.6W   60 KT  70 MPH
 36H  27/0600Z 25.2N  82.7W   65 KT  75 MPH
 48H  27/1800Z 26.5N  84.3W   75 KT  85 MPH
 72H  28/1800Z 29.0N  86.0W   85 KT 100 MPH
 96H  29/1800Z 31.5N  86.0W   55 KT  65 MPH...INLAND
120H  30/1800Z 33.5N  85.5W   25 KT  30 MPH...INLAND

$$
FORECASTER BEVEN