ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM TROPICAL STORM DARBY DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP052010 200 AM PDT SUN JUN 27 2010 DEEP CONVECTION ASSOCIATED WITH DARBY HAS BEEN BURSTING INTERMITTENTLY THIS MORNING...BUT IS DISPLACED TO THE WEST OF THE CIRCULATION CENTER. UW-CIMSS SHEAR PRODUCT INDICATES 30 KT OF EASTERLY SHEAR AFFECTING THE OUTFLOW OVER THE EASTERN HALF OF THE CYCLONE. THIS STRONG UPPER LEVEL FLOW IS ASSOCIATED WITH THE OUTFLOW PATTERN OF TROPICAL STORM ALEX. THE INITIAL INTENSITY IS BASED ON A FEW INTENSITY ESTIMATES FROM CIMSS...AN AMSU ESTIMATE OF 38 KT...A SATELLITE CONSENSUS MEASUREMENT OF 53 KT...AND CONSTRAINED BY RULES...DVORAK SATELLITE ESTIMATES OF 66 KT AND 55 KT FROM TAFB AND SAB RESPECTIVELY. BASED ON THESE DATA...THE INITIAL INTENSITY IS LOWERED TO 50 KT. THE SHIPS MODEL...LGEM...AND FSU SUPERENSEMBLE ALL SUGGEST THAT THE EASTERLY SHEAR AFFECTING DARBY WILL INCREASE THROUGH THE PERIOD...RESULTING IN A CONTINUED WEAKENING TREND. THE INTENSITY FORECAST FOLLOWS SUIT AND IS BASED ON A BLEND OF THE AFOREMENTIONED MODELS REDUCING DARBY TO A REMNANT LOW SWIRL OF CLOUDS IN 3 DAYS OR LESS. INITIAL MOTION IS ESTIMATED AT 270/3...WITHIN THE LIGHT EASTERLY LOW TO MID-LEVEL FLOW GENERATED BY A RIDGE EXTENDING TO THE NORTH OF DARBY FROM CENTRAL MEXICO. SINCE DARBY IS EXPECTED TO WEAKEN CONSIDERABLY DURING THE NEXT COUPLE OF DAYS...THE DECAYING CYCLONE SHOULD MAKE A TURN NORTHEASTWARD AROUND THE 24 HR PERIOD IN RESPONSE TO THE RATHER LARGE LOW-LEVEL CIRCULATION OF TROPICAL STORM ALEX CURRENTLY MOVING OVER YUCATAN. THE OFFICIAL NHC FORECAST IS CLOSE TO THE PREVIOUS FORECAST BUT A LITTLE SLOWER ON THE TURN TO THE NORTHEAST...AND HEDGES TOWARD THE TVCN MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INITIAL 27/0900Z 13.5N 103.3W 50 KT 12HR VT 27/1800Z 13.5N 103.4W 40 KT 24HR VT 28/0600Z 13.9N 103.0W 35 KT 36HR VT 28/1800Z 14.2N 102.5W 25 KT 48HR VT 29/0600Z 14.5N 101.9W 25 KT 72HR VT 30/0600Z 14.9N 100.9W 20 KT...POST-TROP/REMNT LOW 96HR VT 01/0600Z...DISSIPATED $$ FORECASTER ROBERTS/STEWART NNNN
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