ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM NORMA DISCUSSION NUMBER 10 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 2 AM PDT SUN SEP 25 2005 SHORTWAVE INFRARED IMAGERY AND A SERIES OF MICROWAVE SATELLITE OVERPASSES INDICATE THAT THE CENTER OF NORMA IS EXPOSED TO THE NORTHEAST OF A STRONG CONVECTIVE CLUSTER. SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM TAFB...45 KT FROM AFWA...AND 35 KT FROM SAB. THE INITIAL INTENSITY IS REDUCED TO 45 KT BASED ON A BLEND OF THESE ESTIMATES AND THE EXPOSED CENTER. THIS INTENSITY IS IN GOOD AGREEMENT WITH THE LATEST QUIKSCAT OVERPASS. THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 325/5. WATER VAPOR IMAGERY SHOWS A MID/UPPER-LEVEL RIDGE EXTENDING WESTWARD FROM MEXICO ALONG 24N 120W...WITH A DIGGING MID/UPPER-LEVEL TROUGH EXTENDING FROM CALIFORNIA SOUTHWESTWARD TO NEAR 27N130W. THIS COMBINATION SHOULD STEER NORMA GENERALLY NORTHWESTWARD IN THE SHORT TERM. AFTER 48 HR OF SO...THE TROUGH SHOULD WEAKEN... ALLOWING THE RIDGE TO BUILD WESTWARD AND TURN NORMA WESTWARD OR WEST-SOUTHWESTWARD. THE LARGE-SCALE MODELS ALL SHOW THIS SCENARIO...AS DOES THE OFFICIAL FORECAST. THE NEW TRACK FORECAST IS SIMILAR TO...BUT NORTH OF AND A LITTLE FASTER THAN...THE PREVIOUS FORECAST BASED MAINLY ON THE INITIAL POSITION AND MOTION. IT IS MORE OR LESS DOWN THE MIDDLE OF THE ENVELOPE OF GUIDANCE. NORMAL IS IN AN ENVIRONMENT OF 20-25 KT EASTERLY SHEAR ACCORDING TO ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN. LARGE-SCALE MODELS FORECAST THE SHEAR TO CONTINUE FOR 48-72 HR...WHICH SHOULD PREVENT INTENSIFICATION AND POSSIBLY CAUSE FURTHER WEAKENING. THE SHEAR WILL LIKELY DECREASE AFTER 72 HR...BUT BY THAT TIME NORMA SHOULD HAVE MOVED NORTH OF THE 26C SEA SURFACE TEMPERATURE ISOTHERM. THE INTENSITY FORECAST WILL CALL FOR SLOW WEAKENING FOR THE FIRST 48 HR...FOLLOWED BY A FASTER WEAKENING OVER THE COOLER WATERS. THIS FORECAST IS A BLEND OF THE WEAKER SHIPS AND THE STRONGER GFDL. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 25/0900Z 17.4N 111.5W 45 KT 12HR VT 25/1800Z 18.0N 111.9W 45 KT 24HR VT 26/0600Z 18.9N 112.6W 45 KT 36HR VT 26/1800Z 19.9N 113.6W 40 KT 48HR VT 27/0600Z 20.7N 114.8W 40 KT 72HR VT 28/0600Z 21.0N 116.5W 30 KT 96HR VT 29/0600Z 20.5N 118.5W 25 KT...DISSIPATING 120HR VT 30/0600Z 20.0N 121.0W 20 KT...REMNANT LOW $$ NNNN
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Page last modified: Sunday, 25-Sep-2005 08:55:20 UTC