000 WTPZ45 KNHC 080235 TCDEP5 TROPICAL STORM LINDA DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP152009 800 PM PDT MON SEP 07 2009 THE SATELLITE PRESENTATION OF LINDA HAS BECOME SOMEWHAT RAGGED...AND DVORAK ESTIMATES FROM TAFB AND SAB ARE 35 AND 45 KT...RESPECTIVELY. HOWEVER...AN 1841 UTC ASCAT PASS OVER THE WESTERN HALF OF THE CYCLONE INDICATED THAT MAXIMUM WINDS WERE 45 KT...AND IT IS POSSIBLE THAT THERE COULD BE 50 KT WITHIN THE EASTERN SEMICIRCLE. THE INITIAL INTENSITY IS THEREFORE HELD AT 50 KT. A 2119 UTC TRMM AND A 2217 UTC AMSU PASS WERE HELPFUL IN LOCATING THE LOW-LEVEL CENTER AT THOSE TIMES. HOWEVER...THE RECENT CLOUD MOTIONS HAVE NOT MATCHED THE EXTRAPOLATED MOTION...AND THIS COULD BE A SIGNAL THAT THE LOW- AND MID-LEVEL CIRCULATIONS ARE BECOMING A LITTLE DISPLACED FROM EACH OTHER. THE INITIAL POSITION...AND THE INITIAL MOTION OF 275/6...ARE THEREFORE A LITTLE UNCERTAIN. THE MID-LEVEL RIDGE NORTH OF LINDA IS EXPECTED TO BREAK DOWN OVER THE NEXT DAY OR SO AND WILL CAUSE THE STORM TO TURN TOWARD THE NORTHWEST IN ABOUT 48 HOURS. HOWEVER...THERE IS SOME SIGNIFICANT SPREAD IN THE MODEL GUIDANCE. THE UKMET AND NOGAPS ARE ON THE SOUTHERN SIDE OF THE ENVELOPE WHILE THE GFS...GFDL...AND HWRF MAINTAIN A DEEP SYSTEM AND TURN LINDA TOWARD THE NORTH. THE OFFICIAL FORECAST IS VERY CLOSE TO THE PREVIOUS FORECAST AND TVCN...AND ENDS UP NEAR THE BAM SHALLOW MODEL BY DAY 5 WHEN LINDA SHOULD BE A REMNANT LOW. VISIBLE IMAGERY SHOWS THAT LINDA IS INGESTING DRIER AND MORE STABLE AIR FROM THE NORTH INTO THE WESTERN SIDE OF ITS CIRCULATION...AND THE CYCLONE HAS BEEN PRODUCING SOME ARC CLOUDS TO ITS SOUTH. IN ADDITION...WATER VAPOR IMAGERY SHOWS NO EXPANSION OF THE MOISTURE CANOPY THAT SHOULD BE MOVING WESTWARD IN TANDEM WITH THE STORM. ALL THIS LEADS ME TO BELIEVE THAT ANY SHORT-TERM STRENGTHENING WILL BE LIMITED. THE SHIPS...LGEM...AND GFDL MODELS FOLLOW THIS TREND AND SHOW LINDA REACHING HURRICANE STRENGTH...OR JUST BELOW HURRICANE STRENGTH...IN ABOUT 36-48 HOURS. THEREFORE...THE NEW OFFICIAL FORECAST SHOWS SLOWER STRENGTHENING THAN PREVIOUSLY INDICATED...BUT STILL SHOWS LINDA BECOMING A HURRICANE IN 36 HOURS. INCREASING SOUTHERLY TO SOUTHWESTERLY SHEAR AND DECREASING SEA SURFACE TEMPERATURES ARE THEN EXPECTED TO WEAKEN THE SYSTEM BEYOND 48 HOURS. FORECAST POSITIONS AND MAX WINDS INITIAL 08/0300Z 15.3N 127.8W 50 KT 12HR VT 08/1200Z 15.4N 128.6W 55 KT 24HR VT 09/0000Z 15.7N 129.3W 60 KT 36HR VT 09/1200Z 16.3N 129.9W 65 KT 48HR VT 10/0000Z 17.3N 130.6W 60 KT 72HR VT 11/0000Z 19.5N 132.0W 45 KT 96HR VT 12/0000Z 21.5N 133.5W 30 KT 120HR VT 13/0000Z 23.5N 134.0W 20 KT...REMNANT LOW $$ FORECASTER BERG