ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM ISIS DISCUSSION NUMBER 23 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 2 PM PDT MON SEP 13 2004 VISIBLE ANIMATION DEPICTS THAT ISIS IS TRYING TO MAKE A COMEBACK. THE LOW-LEVEL CIRCULATION CENTER HAS TUCKED IN FURTHER BENEATH THE DEEP CONVECTION...JUST TO THE NORTHEAST OF A SMALL DEVELOPING CENTRAL DENSE OVERCAST. THE INITIAL POSITION HAS BEEN ADJUSTED FURTHER SOUTH BASED ON THIS RECENT DEVELOPMENT. IMAGERY ALSO REVEALS THE POSSIBILITY OF A BANDING FEATURE DEVELOPING OVER THE EASTERN PERIPHERY. WIND SHEAR ALSO APPEARS TO BE LESSENING...ACCORDING TO THE UW-CIMSS ANALYSIS. WIDESPREAD STRATOCUMULUS FORCING IN FROM THE NORTHWEST...RELATIVELY DRY STABLE AIR...IS POSSIBLY INHIBITING THE MOISTURE CONTENT OF ISIS WITHIN THE LOW AND MID LEVELS. THIS IS MORE THAN LIKELY THE ONLY MECHANISM THAT IS PREVENTING ISIS FROM INTENSIFYING SIGNIFICANTLY. CURRENT SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM SAB...45 KT FROM AFWA...AND 35 KT FROM TAFB. THE INITIAL INTENSITY WILL REMAIN AT 45 KT BASED ON THE CENTER'S CLOSE PROXIMITY TO THE DEVELOPING CDO USING THE SHEAR PATTERN. THE INTENSITY FORECAST FOLLOWS THE SHIPS AND THE GFDL THROUGH 48 HOURS. AFTERWARD...THE GFDL RUN INDICATES AN ABRUPT RECURVATURE TO THE NORTHEAST AND A DECREASE IN INTENSITY TO 34 KT OVER COOLER WATERS. OUR INTENSITY FORECAST FOLLOWS THE SHIPS GUIDANCE MORE CLOSELY BEYOND 48 AS THE TROPICAL CYCLONE SLOWS SIGNIFICANTLY WITHIN A DEVELOPING BREAK IN THE RIDGE. INITIAL MOTION IS 270/9 KT. A MID-LEVEL RIDGE TO THE NORTHWEST OF ISIS SHOULD GRADUALLY WEAKEN AND RETROGRADE WEST DURING THE NEXT 36 HOURS...IN RESPONSE TO AN APPROACHING MID-LATITUDE TROUGH. THROUGH THE REMAINDER OF THE FORECAST...ISIS SHOULD SLOW AND MEANDER AS STEERING CURRENTS DECREASE. AS PREVIOUSLY MENTIONED...THE 12Z GFDL RUN INDICATES A RECURVATURE SCENARIO AS OPPOSED TO A STAIR-STEP WITHIN THE DEVELOPING WEAKNESS...WHICH THE OTHER GLOBAL MODELS ARE SUGGESTING. THE OFFICIAL FORECAST IS BASICALLY AN UPDATE OF THE PREVIOUS ADVISORY AND IS BASED ON A BLEND OF THE GFS...UKMET AND NOGAPS GUIDANCE. FORECASTER ROBERTS/FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 13/2100Z 16.7N 128.4W 45 KT 12HR VT 14/0600Z 16.7N 129.6W 50 KT 24HR VT 14/1800Z 16.7N 130.7W 50 KT 36HR VT 15/0600Z 16.8N 131.3W 50 KT 48HR VT 15/1800Z 16.9N 131.8W 50 KT 72HR VT 16/1800Z 17.0N 132.0W 50 KT 96HR VT 17/1800Z 17.5N 132.0W 50 KT 120HR VT 18/1800Z 17.5N 132.0W 50 KT $$ NNNN
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Page last modified: Monday, 13-Sep-2004 20:44:36 UTC