000 WTPZ45 KNHC 140237 TCDEP5 TROPICAL STORM GUILLERMO DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP102009 800 PM PDT THU AUG 13 2009 EVEN THOUGH VISIBLE IMAGERY SHOWS THAT AN EYE-LIKE FEATURE DEVELOPED EARLIER TODAY...INFRARED IMAGERY SHOWS A MORE RAGGED APPEARANCE WITH ONE WELL-DEFINED CONVECTIVE BAND TO THE SOUTHWEST OF THE LOW-LEVEL CENTER. A RECENT PARTIAL SSMI PASS SUGGESTS THAT A CONVECTIVE RING HAS ENCIRCLED THE CENTER...AND THIS COULD BE A SIGN THAT GUILLERMO IS READY TO STRENGTHEN. DVORAK FINAL T-NUMBERS ARE T4.0 FROM TAFB AND T3.5 FROM SAB...SO THE INITIAL INTENSITY IS KEPT JUST BELOW HURRICANE STATUS AT 60 KT. VERTICAL SHEAR IS EXPECTED TO REMAIN LOW FOR ANOTHER 48 HOURS OR SO...BUT SEA SURFACE TEMPERATURES ALONG THE FORECAST TRACK ARE EXPECTED TO FALL FROM 27C TO NEAR 24C OVER THE NEXT 3 DAYS. THE OFFICIAL FORECAST STILL SHOWS GUILLERMO BECOMING A HURRICANE SOON...BUT THEN SHOWS STEADY WEAKENING AFTER 36 HOURS. THIS SCENARIO IS VERY CLOSE TO THE INTENSITY CONSENSUS. THE INITIAL MOTION IS 275/13. GUILLERMO IS EXPECTED TO TURN TOWARD THE WEST-NORTHWEST OVER THE NEXT DAY OR SO ONCE IT BECOMES POSITIONED ON THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE EXTENDING WESTWARD FROM NORTHERN MEXICO. ALL OF THE NUMERICAL MODELS...AS WELL AS BAM SHALLOW...INDICATE THAT THIS MOTION WILL CONTINUE THROUGH THE FORECAST PERIOD EVEN AFTER GUILLERMO WEAKENS AND BECOMES A SHALLOW SYSTEM. THIS IS LIKELY THE RESULT OF A WEAKNESS IN THE SUBTROPICAL RIDGE FORECAST TO DEVELOP JUST NORTH OF THE HAWAIIAN ISLANDS BY DAY 4. THE OFFICIAL TRACK FORECAST IS THEREFORE SHIFTED A LITTLE NORTHWARD ON DAYS 4 AND 5 TOWARDS THE TIGHT MODEL CLUSTERING. FORECAST POSITIONS AND MAX WINDS INITIAL 14/0300Z 17.2N 124.5W 60 KT 12HR VT 14/1200Z 17.6N 126.5W 65 KT 24HR VT 15/0000Z 18.2N 129.2W 65 KT 36HR VT 15/1200Z 18.8N 131.9W 60 KT 48HR VT 16/0000Z 19.3N 134.6W 55 KT 72HR VT 17/0000Z 20.5N 140.0W 45 KT 96HR VT 18/0000Z 21.5N 145.0W 35 KT 120HR VT 19/0000Z 22.0N 150.0W 30 KT $$ FORECASTER BERG