WTPA44 PHFO 170908 TCDCP4 TROPICAL STORM GUILLERMO DISCUSSION NUMBER 21 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP102009 1100 PM HST SUN AUG 16 2009 SHEAR CONTINUES TO WEAKEN GUILLERMO. THE LOW LEVEL CENTER IS PARTLY EXPOSED ON THE SOUTHWEST SIDE OF THE SYSTEM. INFRARED SATELLITE IMAGERY SHOWS ONLY A SMALL AMOUNT OF DEEP CONVECTION...AND THAT IS DISPLACED ABOUT 60 NM NORTHEAST OF THE CENTER. THE REMAINING HIGH CLOUDS ARE BECOMING STRETCHED OUT ALONG A NORTH SOUTH AXIS. GUILLERMO IS CLEARLY WEAKENING RATHER QUICKLY DUE TO STRONG WEST SOUTHWEST SHEAR. SUBJECTIVE DVORAK ANALYSES KEPT GUILLERMO ABOVE HURRICANE STRENGTH...BUT THE DVORAK CONSTRAINTS MAY MAKE INTENSITY ESTIMATES TOO HIGH IN A RAPIDLY SHEARING SYSTEM. GIVEN THE RAPID DETERIORATION OF THE CLOUD PATTERN IT SEEMS REASONABLE TO DOWNGRADE GUILLERMO TO TROPICAL STORM STRENGTH. THE HIGH CLOUDS HAVE NOT YET SHEARED FAR ENOUGH AWAY TO GIVE A CLEAR VIEW OF THE LOW LEVEL CENTER...SO THE SATELLITE POSITION ESTIMATES AT 0600 UTC WERE A BIT UNCERTAIN. MICROWAVE PASSES AT 0255 AND 0325 UTC SUGGEST THAT THE CENTER MAY HAVE BEEN FARTHER SOUTH THAN THE 0600 UTC FIXES INDICATED AND OUR 0000 UTC POSITION MAY HAVE BEEN TOO FAR NORTH. I HAVE RE-BESTED THE 0000 UTC POSITION AND SHIFTED THE TRACK SLIGHTLY TO THE LEFT. THE TRACK CONTINUES CLOSE TO A CONSENSUS OF THE DYNAMIC MODELS. WE WILL BE WATCHING TO SEE IF THE TRACK WILL NEED TO BE SHIFTED FARTHER TO THE LEFT IF GUILLERMO BECOMES A SHALLOW SYSTEM MORE QUICKLY THAN WE HAVE FORECAST. GUILLERMO REMAINS OVER COOL...24.5 DEGREES CELSIUS... WATER. GUILLERMO WILL MOVE OVER WARMER WATER AFTER ABOUT 36 HOURS...BUT IT MAY NOT MATTER. THERE IS STRONG WEST SOUTHWEST SHEAR ACROSS THE SYSTEM AND THE SHEAR WILL BECOME EVEN STRONGER OVER THE NEXT 48 HOURS. THIS STRONG SHEAR SHOULD STEADILY WEAKEN GUILLERMO. ONCE GUILLERMO HAS BEEN REDUCED TO A SHALLOW LOW...WARMER WATER IS UNLIKELY TO BE ENOUGH TO ALLOW THE SYSTEM TO REGENERATE. FORECAST POSITIONS AND MAX WINDS INITIAL 17/0900Z 20.8N 142.6W 60 KT 12HR VT 17/1800Z 21.5N 144.8W 50 KT 24HR VT 18/0600Z 22.8N 147.8W 40 KT 36HR VT 18/1800Z 24.4N 150.7W 35 KT 48HR VT 19/0600Z 26.2N 154.0W 35 KT 72HR VT 20/0600Z 28.9N 161.1W 30 KT...REMNANT LOW 96HR VT 21/0600Z 29.6N 167.8W 25 KT...REMNANT LOW 120HR VT 22/0600Z 29.5N 173.3W 20 KT...REMNANT LOW $$ FORECASTER DONALDSON