Tropical Storm ISIS
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TROPICAL STORM ISIS DISCUSSION NUMBER 19
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2 PM PDT SUN SEP 12 2004
ISIS IS SHOWING SIGNS OF WEAKENING. VISIBLE ANIMATION DEPICTS A
POORLY DEFINED PARTIALLY EXPOSED LOW-LEVEL CENTER. OUTFLOW
BOUNDARIES APPEAR MORE ABUNDANT THAN LOW CLOUD LINES ASSOCIATED
WITH THE CENTER. IMAGERY ALSO REVEALS WIDESPREAD STRATOCUMULUS
FORCING IN FROM THE NORTH AND NORTHWEST. WHICH LEADS US TO BELIEVE
THAT THIS MAY BE RESTRICTING THE MOISTURE CONTENT IN THE LOW/MID
LEVELS. WATER VAPOR ANIMATION INDICATES THAT THE EASTERLY SHEAR
PERSISTS. SATELLITE CURRENT INTENSITY ESTIMATES FROM ALL AGENCIES
REMAIN AT 45 KT. THE INITIAL INTENSITY REMAINS AT 45 KT JUST IN
CASE THE CENTER HAS MOVED OR REDEVELOPED FURTHER BENEATH THE
CONVECTION. IF THIS IS NOT THE CASE AND THE CURRENTLY UNFAVORABLE
ENVIRONMENT CONTINUES...THE INTENSITY WILL HAVE TO BE DECREASED ON
THE NEXT ADVISORY. THE SHIPS MODELS HAS CONSISTENTLY BEEN TOO LOW
ON THE STRENGTH OF THE EASTERLY SHEAR. 10 TO 20 KT UPPER EASTERLIES
REMAIN OVER THE TROPICAL CYCLONE ACCORDING TO THE CIMSS SHEAR
ANALYSIS. THE INTENSITY FORECAST REMAINS UNCHANGED FOR NOW.
HOWEVER...THE SLOW INTENSIFICATION TREND TO 55 KT IN 48 HOURS MAY
BE TOO GENEROUS GIVEN THE CURRENT STATE OF THE ENVIRONMENT.
THE INITIAL MOTION IS WESTWARD OR 270/8...WHICH IS SLIGHTLY SLOWER
THAN THE PREVIOUS ADVISORY. THE FORECAST TRACK IS BASICALLY AN
UPDATE OF THE PREVIOUS FORECAST...AND AGREES WITH THE MODEL
CONSENSUS.
FORECASTER ROBERTS/BEVEN
FORECAST POSITIONS AND MAX WINDS
INITIAL 12/2100Z 17.4N 124.1W 45 KT
12HR VT 13/0600Z 17.4N 125.4W 45 KT
24HR VT 13/1800Z 17.4N 127.5W 50 KT
36HR VT 14/0600Z 17.4N 129.5W 50 KT
48HR VT 14/1800Z 17.4N 131.0W 55 KT
72HR VT 15/1800Z 17.4N 133.0W 55 KT
96HR VT 16/1800Z 17.4N 134.0W 55 KT
120HR VT 17/1800Z 17.4N 134.5W 55 KT
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