000 WTPZ45 KNHC 240845 TCDEP5 TROPICAL STORM DARBY DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP052010 200 AM PDT THU JUN 24 2010 ACCORDING TO A 0156 UTC TRMM PASS...A PINHOLE EYE FEATURE APPEARED TO HAVE DEVELOPED IN THE MIDDLE OF THE SMALL CENTRAL DENSE OVERCAST OVER DARBY. THIS TINY FEATURE HAS NOT BEEN EVIDENT IN INFRARED SATELLITE IMAGERY...AND DVORAK CLASSIFICATIONS FROM TAFB AND SAB REMAIN AT T3.5...55 KT. HOWEVER...THE SAB CLASSIFICATION DID YIELD A DATA T-NUMBER OF 4.5...77 KT...USING THE EMBEDDED CENTER PATTERN. IT IS NOT OUT OF THE ORDINARY FOR SMALL TROPICAL CYCLONES TO BE STRONGER THAN THE DVORAK TECHNIQUE WILL ALLOW...AND IT IS ASSUMED THAT DARBY MAY HAVE STRENGTHENED A LITTLE. MORE RECENTLY...THE CENTRAL DENSE OVERCAST HAS BECOME SOMEWHAT RAGGED...BUT A CURVED BAND HAS DEVELOPED AND IS NOW CONNECTED TO THE CENTRAL CONVECTION. THE INITIAL INTENSITY IS SET AT 60 KT. THE INITIAL MOTION REMAINS 285/10 AS DARBY IS STEERED TO THE WEST BY A LOW/MID-LEVEL RIDGE OVER MEXICO. THE RIDGE IS EXPECTED TO WEAKEN WITHIN THE NEXT 48 HOURS OR SO DUE TO THE COMBINED EFFECTS OF A DISTURBANCE OVER THE WESTERN CARIBBEAN AND A DEEP MID/UPPER-LEVEL TROUGH MOVING INTO CALIFORNIA. AS A RESULT...DARBY IS FORECAST TO SLOW DOWN CONSIDERABLY AND MAY ATTAIN SOME EASTWARD MOTION BY DAY 5 WITH THE DEVELOPMENT OF LOW-LEVEL SOUTHWESTERLY FLOW. THE TRACK GUIDANCE IS IN FAIRLY GOOD AGREEMENT OVER THE NEXT 36 HOURS BUT THEN DIVERGES...AND HAS ALSO SHIFTED A LITTLE BIT TO THE WEST COMPARED TO THE PREVIOUS PACKAGE. THE NHC FORECAST FOLLOWS THIS JOG TO THE WEST AND INDICATES A SLOW TURN TOWARD THE NORTHEAST BY DAY 5. THE TRACK AND INTENSITY FORECASTS ARE BOTH COMPLICATED BY THE FACT THAT MOST OF THE GLOBAL MODELS DISSIPATE DARBY BY DAYS 4 AND 5 DUE TO A DECOUPLING OF THE LOW- AND MID-LEVEL CIRCULATIONS. THE HURRICANE MODELS DO HOLD ON TO THE CYCLONE THROUGH THE FORECAST PERIOD...BUT BOTH WEAKEN DARBY TO ABOUT 20-30 KT IN 120 HOURS. THE STATISTICAL SHIPS AND LGEM MODELS ARE THE ONLY ONES TO KEEP DARBY AS A SIGNIFICANT TROPICAL CYCLONE AT THAT TIME. REGARDLESS OF THE MODEL...ALL ARE SIGNIFICANTLY LOWER AT DAYS 4 AND 5 COMPARED TO THE PREVIOUS FORECAST...AND THE NEW OFFICIAL FORECAST INDICATES MORE RAPID WEAKENING AT THE END OF THE FORECAST PERIOD...ENDING CLOSE TO THE UPPER END OF THE INTENSITY GUIDANCE. FORECAST POSITIONS AND MAX WINDS INITIAL 24/0900Z 12.6N 98.0W 60 KT 12HR VT 24/1800Z 12.9N 99.2W 65 KT 24HR VT 25/0600Z 13.2N 100.6W 70 KT 36HR VT 25/1800Z 13.4N 101.7W 80 KT 48HR VT 26/0600Z 13.6N 102.6W 80 KT 72HR VT 27/0600Z 14.0N 103.5W 70 KT 96HR VT 28/0600Z 14.5N 103.5W 65 KT 120HR VT 29/0600Z 15.0N 103.0W 55 KT $$ FORECASTER BERG