ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM HURRICANE DARBY DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 2 AM PDT WED JUL 28 2004 SSMI MICROWAVE DATA AT 28/0336Z AND 28/0507Z CLEARLY INDICATE THAT DARBY HAS DEVELOPED A 20-25 NMI DIAMETER EYE...WHICH MAKES CENTER PLACEMENT FAIRLY STRAIGHTFORWARD. HOWEVER...THE INTENSITY ESTIMATE IS SOMEWHAT PROBLEMATIC GIVEN THE LARGE VARIANCE IN THE SATELLITE INTENSITY ESTIMATES...WHICH RANGE FROM 77 KT FROM TAFB TO 65 KT FROM SAB...AND 55 KT FROM AFWA. IN ADDITION...AUTOMATED ODT VALUES FROM UW-CIMSS ARE AROUND 69 KT WITH A COUPLE OF RAW VALUES OF 77 KT. BASED ON A BLEND OF THE ODT VALUES...A ROUND CDO FEATURE...AND THE WELL-DEFINED EYE NOTED IN THE MICROWAVE IMAGES...THE INITIAL INTENSITY IS INCREASED TO 70 KT AND DARBY IS UPGRADED TO THE SECOND HURRICANE OF THE 2004 EASTERN NORTH PACIFIC HURRICANE SEASON. THE INITIAL MOTION IS 290/12. THE LATEST NHC MODEL GUIDANCE IS IN MUCH BETTER AGREEMENT ON DARBY MAINTAINING A WEST-NORTHWESTWARD MOTION FOR THE NEXT 36-48 HOURS ACCOMPANIED BY A GRADUAL DECREASE IN FORWARD SPEED. BY 72 HOURS...A MORE WESTWARD TURN IS EXPECTED AFTER THE CYCLONE MOVES OVER COOLER WATER AND THE DOMINANT STEERING FLOW IS THE STRENGTHENING LOW-LEVEL RIDGE TO THE NORTH. SINCE THE LATEST SATELLITE FIXES HAVE BEEN BASICALLY COMING IN ON TRACK...THE OFFICIAL TRACK IS JUST AN UPDATE OF THE PREVIOUS FORECAST TRACK AND IS IN CLOSE AGREEMENT WITH THE GUNA MODEL CONSENSUS. NOW THAT DARBY HAS DEVELOPED A WELL-DEFINED EYE...SOME ADDITIONAL SIGNIFICANT STRENGTHENING IS STILL POSSIBLE BEFORE THE HURRICANE MOVES OVER SUB-26C SSTS IN 36-48 HOURS SINCE DARBY REMAINS IN A LOW SHEAR ENVIRONMENT AND OVER 27.5 SSTS. ALTHOUGH THE CYCLONE HAS BEEN RAPIDLY INTENSIFYING FOR THE PAST 30 HOURS...SUCH PHASES RARELY EXCEED 36 HOURS. AS SUCH... THE CURRENT INTENSITY TREND IS BEING LEVELED OFF SOMEWHAT. THIS IS CONSISTENT WITH THE SHIPS INTENSITY MODEL. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 28/0900Z 14.8N 122.3W 70 KT 12HR VT 28/1800Z 15.4N 123.9W 75 KT 24HR VT 29/0600Z 16.0N 125.9W 80 KT 36HR VT 29/1800Z 16.5N 127.8W 80 KT 48HR VT 30/0600Z 17.0N 130.0W 70 KT 72HR VT 31/0600Z 17.6N 134.3W 60 KT 96HR VT 01/0600Z 18.0N 139.0W 50 KT 120HR VT 02/0600Z 18.5N 143.0W 40 KT $$ NNNN
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Page last modified: Wednesday, 28-Jul-2004 08:42:26 UTC