Tropical Storm ISAAC

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TROPICAL STORM ISAAC DISCUSSION NUMBER  16
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
1100 PM EDT FRI AUG 24 2012
 
SATELLITE IMAGERY AND RECONNAISSANCE AIRCRAFT DATA INDICATE THAT THE
CIRCULATION AND CONVECTIVE ORGANIZATION OF ISAAC HAS CONTINUED TO
IMPROVE SINCE THE PREVIOUS ADVISORY. INFRARED AND MICROWAVE
SATELLITE IMAGERY SUGGEST THAT AN EYE IS FORMING...AND THIS IS THE
BASIS FOR INCREASING THE INTENSITY TO 60 KT. 
 
THE INITIAL MOTION ESTIMATE IS 315/12 BASED ON RECON AND MICROWAVE
FIXES. ALTHOUGH THE TRACK FORCAST WAS ADJUSTED SLIGHTLY TO THE
RIGHT THROUGH 48 HOURS...NO OTHER SIGNIFICANT CHANGES WERE MADE TO
THE PREVIOUS ADVISORY TRACK. RECENT UPPER-AIR DATA AND NOAA G-IV
AIRCRAFT DROPSONDE DATA INDICATE THE TROUGH THAT HAS CREATED THE
BREAK IN THE SUBTROPICAL RIDGE ACROSS FLORIDA HAS SHIFTED TO A
POSITION JUST EAST OF THE FLORIDA PENINSULA. THE 18Z GFS MODEL...
WHICH SHIFTED TO THE RIGHT OF ITS 12Z TRACK...CAPTURED THIS FARTHER
EAST POSITION...WHEREAS THE 18Z UKMET AND 12Z ECMWF KEPT THE TROUGH
ACROSS THE WESTERN FLORIDA PENINSULA VALID AT 00Z THIS EVENING.
BASED ON THE GFS VERIFYING BETTER THAN THE OTHER MODELS AT 00Z THIS
EVENING...THE NHC TRACK HAS BEEN SHIFTED A LITTLE TO THE RIGHT.
AFTER 48 HOURS...THE RIDGE IS EXPECTED TO BUILD BACK WESTWARD
ACROSS FLORIDA AND KEEPING ISAAC ON A MOSTLY NORTHWESTWARD HEADING
ACROSS THE EASTERN AND NORTH-CENTRAL GULF MEXICO. THE OFFICIAL
FORECAST TRACK IS CLOSE TO THE CONSENSUS MODELS TVCA AND TV15
THROUGH 48 HOURS...AND THEN IS A LITTLE TO THE RIGHT OF THOSE
MODELS AFTER THAT.

WITH THE INNER CORE CONVECTION IMPROVING...THERE IS STILL THE
POSSIBILITY THAT ISAAC COULD REACH HURRICANE INTENSITY BEFORE
REACHING HAITI TONIGHT. THE INTENSITY FROM 12-24 HOURS WILL BE
DETERMINED BY THE AMOUNT OF LAND INTERACTION WITH HAITI AND EASTERN
CUBA. AFTER THAT...THE SLIGHT EASTWARD SHIFT IN THE FORECAST TRACK
IS ENOUGH TO PLACE ISAAC OVER WATER LONGER THAN WHAT WAS INDICATED
IN THE PREVIOUS INTENSITY FORECAST REQUIRED AN INCREASE IN THE
INTENSITY FORECAST. THE EASTWARD TRACK SHIFT AND A LARGER INITIAL
AND FORECAST WIND FIELD TO THE NORTH ARE WHAT NECESSITATED THE
CHANGES IN THE WATCHES AND WARNINGS FOR FLORIDA.
 
IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK 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  25/0300Z 17.7N  72.5W   60 KT  70 MPH
 12H  25/1200Z 19.4N  74.1W   50 KT  60 MPH
 24H  26/0000Z 21.7N  76.7W   50 KT  60 MPH
 36H  26/1200Z 23.4N  79.4W   55 KT  65 MPH
 48H  27/0000Z 24.9N  81.6W   60 KT  70 MPH
 72H  28/0000Z 27.1N  84.6W   70 KT  80 MPH
 96H  29/0000Z 30.0N  86.5W   80 KT  90 MPH
120H  30/0000Z 32.5N  86.5W   40 KT  45 MPH...INLAND
 
$$
FORECASTER STEWART
 
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