Hurricane ISAAC

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HURRICANE ISAAC DISCUSSION NUMBER  33
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
400 AM CDT WED AUG 29 2012
 
AFTER REMAINING QUASI-STATIONARY FOR SEVERAL HOURS...AIRCRAFT AND
RADAR DATA INDICATE THAT THE CENTER OF ISAAC MADE A SECOND LANDFALL
NEAR PORT FOURCHON LOUISIANA AND IS BEGINNING TO MOVE INLAND OVER
SOUTHEAST LOUISIANA.  OBSERVATIONS FROM THE HURRICANE HUNTER
AIRCRAFT INDICATE THAT THE EYE IS OPEN OVER THE WESTERN PORTION OF
THE CIRCULATION...AND THE RADAR PRESENTATION HAS BECOME MORE
ASYMMETRIC OVER THE PAST COUPLE OF HOURS.  HOWEVER...THE RADAR
REFLECTIVITIES INDICATE THAT CONVECTION HAS BECOME STRONGER OVER
THE NORTHERN AND EASTERN PORTIONS OF THE CYCLONE...AND THE AIRCRAFT
REPORTED THAT THE CENTRAL PRESSURE REMAINS QUITE LOW.  THE CURRENT
INTENSITY IS HELD AT 70 KT...BUT WEAKENING IS IMMINENT NOW THAT THE
CENTER HAS BEGUN TO MOVE OVER LAND.  FOR THE NEXT 24 HOURS OR
SO...THE OFFICIAL INTENSITY FORECAST SHOWS A SOMEWHAT SLOWER RATE
OF WEAKENING THAN THAT GIVEN BY THE INLAND DECAY MODEL DUE TO THE
SWAMPY TERRAIN THAT THE SYSTEM WILL TRAVERSE. 

SINCE THE SYSTEM HAS ONLY BEGUN TO MOVE RECENTLY...THE INITIAL
MOTION IS AN UNCERTAIN 300/7.  ISAAC IS CURRENTLY MOVING THROUGH A
WEAKNESS IN THE SUBTROPICAL RIDGE.  OVER THE NEXT FEW DAYS...A
MID-LEVEL ANTICYLONE SHIFTS EASTWARD OVER THE CENTRAL AND EASTERN
UNITED STATES.  AS A RESULT...ISAAC SHOULD GRADUALLY TURN TOWARD
THE NORTH AND NORTHEAST DURING THE FORECAST PERIOD.  NEAR THE END
OF THE PERIOD...POST-TROPICAL ISAAC SHOULD MOVE EAST-NORTHEASTWARD
IN THE FLOW BETWEEN THE MID-LATITUDE WESTERLIES AND THE
AFOREMENTIONED ANTICYLONE.  THE OFFICIAL TRACK FORECAST IS SIMILAR
TO THE PREVIOUS ONE AND CLOSE TO THE MODEL CONSENSUS.

SINCE THE SYSTEM IS LIKELY TO MOVE SLOWLY OVER THE NEXT 24 HOURS OR
SO...THERE IS A CONTINUED THREAT OF FLOODING FROM HEAVY RAINS OVER
THE NORTHERN GULF COAST AREA.

NATIONAL OCEAN SERVICE TIDE GAUGES INDICATE THAT STORM SURGE HEIGHTS
OF 6 TO 10 FEET ARE STILL OCCURRING ALONG PORTIONS OF THE COAST OF
SOUTHEASTERN LOUISIANA AND MISSISSIPPI.  GIVEN THE LONG DURATION
OF ONSHORE FLOW IN THESE AREAS...WATER LEVELS ARE EXPECTED TO REMAIN
HIGH THROUGH TODAY.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  29/0900Z 29.2N  90.5W   70 KT  80 MPH...INLAND
 12H  29/1800Z 29.7N  91.1W   65 KT  75 MPH...INLAND
 24H  30/0600Z 30.5N  91.8W   50 KT  60 MPH...INLAND
 36H  30/1800Z 31.8N  92.8W   30 KT  35 MPH...INLAND
 48H  31/0600Z 33.6N  93.7W   25 KT  30 MPH...INLAND
 72H  01/0600Z 37.5N  93.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  02/0600Z 39.5N  90.0W   15 KT  15 MPH...POST-TROP/REMNT LOW
120H  03/0600Z 40.5N  86.0W   15 KT  15 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER PASCH/ROBERTS
 
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