ZCZC MIATCDEP3 ALL TTAA00 KNHC DDHHMM TROPICAL STORM CALVIN DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 2 AM PDT MON JUN 27 2005 THE INITIAL POSITION IS BASED MAINLY ON CONTINUITY WITH THE PREVIOUS FORECAST TRACK AND EXTRAPOLATION OF MICROWAVE SATELLITE POSITIONS BETWEEN 00Z AND 05Z. A 27/0449Z AMSU OVERPASS INDICATED THE LOW-LEVEL CIRCULATION REMAINS TO THE SOUTHEAST OF THE MAIN CONVECTIVE CLOUD MASS AND THE WELL-DEFINED MID-LEVEL CIRCULATION CENTER. THE INTENSITY OF 35 KT AND THE DECISION TO NAME THE SYSTEM TROPICAL STORM CALVIN WAS BASED ON A CONSENSUS DVORAK SATELLITE CURRENT INTENSITY ESTIMATE OF T2.5/35 KT FROM TAFB...SAB...AND AFWA...PLUS A UW-CIMSS 3-HR AVERAGE AODT ESTIMATE OF T2.6/36 KT. THE INITIAL MOTION ESTIMATE IS NOW 330/04. THERE IS NO SIGNIFICANT CHANGE TO THE REASONING OF THE TWO PREVIOUS FORECAST TRACK DISCUSSIONS. NHC MODEL GUIDANCE REMAINS REASONABLY CONSISTENT ON GRADUALLY BUILDING THE MEXICAN SUBTROPICAL RIDGE WESTWARD OVER THE NEXT 2-3 DAYS...WHICH SHOULD ACT TO TURN CALVIN NORTHWESTWARD LATER TODAY AND THEN MORE WEST-NORTHWESTWARD AFTER 24 HOURS...ALONG WITH A GRADUAL INCREASE IN FORWARD SPEED UP TO ABOUT 10 KT. CALVIN IS EXPECTED TO REACH NEAR-26C SSTS BY 72 HOURS AND SLOWLY BEGIN TO WEAKEN...AND THEN BE FORCED WESTWARD BY THE LOW-LEVEL EASTERLIES. THE ENVIRONMENT SURROUNDING CALVIN IS STRIKINGLY SIMILAR TO THAT OF TS BEATRIZ JUST A FEW DAYS AGO. ANOTHER STRONG CONVECTIVE BURST WENT OFF NORTHWEST OF THE LOW-LEVEL CENTER BETWEEN 03Z-06Z...BUT HAS SINCE WEAKENED. OTHER BURSTS WILL LIKELY CONTINUE FOR THE NEXT FEW DAYS...WITH EACH ONE SLIGHTLY STRENGTHENING THE CYCLONE. HOWEVER...25 TO 30 KT 300-200 MB EASTERLY WINDS HAVE BEEN AND WILL LIKELY CONTINUE TO UNDERCUT THE OTHERWISE FAVORABLE OUTFLOW LAYER AND PRODUCE AT LEAST 15-20 KT OF SHEAR. THE GFDL MODEL IS MUCH LESS ROBUST THAN ITS PREVIOUS RUNS AND NOW ONLY BRINGS CALVIN UP TO 56 KT IN 24 HOURS. SINCE THIS IS SIMILAR TO THE SHIPS MODEL...THE INTENSITY FORECAST HAS BEEN TRIMMED BACK SLIGHTLY. HEAVY RAINS FROM CALVIN ARE ALREADY AFFECTING PORTIONS OF THE TROPICAL STORM WATCH AREA. SINCE THE CURRENT FORECAST KEEPS ANY TROPICAL STORM FORCE WINDS JUST OFFSHORE...THE EXISTING WATCH SHOULD SUFFICE FOR THIS FORECAST PACKAGE. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 27/0900Z 14.6N 98.4W 35 KT 12HR VT 27/1800Z 15.0N 99.5W 40 KT 24HR VT 28/0600Z 15.6N 101.0W 45 KT 36HR VT 28/1800Z 16.3N 103.1W 50 KT 48HR VT 29/0600Z 16.9N 105.4W 55 KT 72HR VT 30/0600Z 17.5N 109.0W 55 KT 96HR VT 01/0600Z 17.5N 111.5W 40 KT 120HR VT 02/0600Z 17.5N 114.5W 30 KT $$ NNNN
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Page last modified: Monday, 27-Jun-2005 08:40:03 UTC