ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM NORMA DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 8 AM PDT SAT SEP 24 2005 SEVERAL MICROWAVE SATELLITE IMAGES DURING THE PAST 9 HOURS INDICATE NORMA HAS MOVED SLOWLY NORTHWEST AND THE CENTER IS LOCATED IN THE NORTHEASTERN PORTION OF THE DEEP CONVECTIVE CLOUD MASS AND NOT IN THE CENTER NEAR THE COLDER CLOUD TOPS. THE INITIAL INTENSITY OF 50 KT IS BASED ON A BLEND OF DVORAK CURRENT INTENSITY ESTIMATES OF 55 KT FROM TAFB... 45 KT FROM SAB AND AFWA... AND A 24/1029Z UW-CIMSS AMSU INTENSITY ESTIMATE OF 994 MB AND 50 KT. BASED ON THE MICROWAVE POSITIONS... THE INITIAL MOTION IS 340/05. THE MID-LEVEL RIDGE TO THE NORTH AND EAST OF NORMA IS FORECAST TO REMAIN WEAK... SO THE RESULTANT WEAK STEERING FLOW MAY CAUSE SOME ERRATIC MOTION FOR THE NEXT 36 HOURS OR SO. AFTERWARDS... STEERING CURRENTS ARE EXPECTED TO BECOME BETTER ESTABLISHED AS A STRONG UPPER-LEVEL TROUGH/LOW DIGS SOUTHWARD OFF THE CALIFORNIA COAST... WITH ASSOCIATED DOWNSTREAM RIDGING EXPECTED TO BUILD HIGH PRESSURE ACROSS THE SOUTHWESTERN U.S. AND MEXICO THROUGH 72 HOURS. BY DAYS 4 AND 5... THE FLOW IS ONCE AGAIN FORECAST TO WEAKEN AS THE FUTURE UPPER-LEVEL LOW OFF CALIFORNIA LIFTS OUT TO THE NORTH... WHICH ALLOWS WEAK RIDGING TO EXTEND WESTWARD TO THE NORTH OF NORMA. THE LATTER STEERING FLOW IS EXPECTED TO TURN THE CYCLONE SLOQLY WESTWARD AND EVENTUALLY WEST-SOUTHWESTWARD. CURRENT MODERATE EAST TO SOUTHEASTERLY VERTICAL SHEAR IS EXPECTED TO CONTINUE TO AFFECT NORMA THROUGHOUT THE FORECAST PERIOD. HOWEVER... THE SHEAR IS NOT FORECAST TO INCREASE ABOVE THE CURRENT 20 KT VALUE. THEREFORE... THE INTENSITY IS FORECAST TO REMAIN STEADY UNTIL NORMA REACHES COOLER WATER IN 48-72 HOURS... AFTER WHICH SLOW WEAKENING IS EXPECTED TO OCCUR. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE GFDL MODEL... BUT HIGHER THAN THE SHIPS INTENSITY MODEL... ESPECIALLY AT 96 AND 120 HOURS... WHICH IS WHEN THE SHIPS MODEL FORECASTS NORMA TO DISSIPATE. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 24/1500Z 16.4N 110.7W 50 KT 12HR VT 25/0000Z 16.9N 111.0W 50 KT 24HR VT 25/1200Z 17.6N 111.5W 50 KT 36HR VT 26/0000Z 18.5N 112.3W 50 KT 48HR VT 26/1200Z 19.5N 113.5W 45 KT 72HR VT 27/1200Z 20.5N 115.5W 45 KT 96HR VT 28/1200Z 21.0N 117.0W 40 KT 120HR VT 29/1200Z 20.0N 119.5W 35 KT $$ NNNN
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Page last modified: Saturday, 24-Sep-2005 14:40:23 UTC