Tropical Storm Guillermo Update – noon

• A Flash Flood Watch is in effect for Hawaii Island and Maui until 6 p.m. Thursday. As abundant moisture from Tropical Storm Guillermo moves over the area, conditions may develop that lead to flash flooding. Total rainfall amounts of 1 to 3 inches are expected on Hawaii Island, with isolated maximum amounts near 7 inches mainly in higher terrain.
• A Tropical Storm Watch remains in effect for Hawaii Island, as well as the Islands of Maui, Molokai, Lanai and Kahoolawe. If the motion of the system continues, the watches may be cancelled later today.
• As of 11 a.m. HST Tropical Storm Guillermo was 395 miles east of Hilo, Hawaii. The storm is moving northwest at 10 mph. The National Weather Service says the center of Guillermo is expected to pass 230 miles northeast of Hilo Wednesday afternoon.
• Tropical Storm Guillermo is just below hurricane strength, with maximum sustained winds at 70 mph with higher gusts. Steady weakening anticipated.
• A High Surf Advisory is still in effect for east facing shores of all islands. Wave heights will be in the 5 to 8 ft. range.

National Weather Service – 11 a.m.

AFTER A BRIEF INCREASE IN DEEP CONVECTION LAST NIGHT… THE APPEARANCE OF GUILLERMO IN THE SATELLITE IMAGES HAS BECOME DEGRADED ONCE AGAIN. THE SYSTEM IS VERY ASYMMETRIC WITH THE COLDEST CLOUD TOPS MAINLY IN THE NORTHEAST QUADRANT AND SOME OF THE CIRRUS REACHING CALIFORNIA. A USAF RESERVE WEATHER RECON MISSION THIS MORNING REPORTED A MAXIMUM FLIGHT LEVEL WIND OF 65 KT AND A MAXIMUM SFMR VALUE OF 55 KT IN THE NORTHEAST QUADRANT. THE INBOUND LEG FROM THE NORTHWEST PICKED UP SFMR VALUES OF 65 AND 69 KT BUT THIS WAS THROUGH A BURST OF DEEP CONVECTION AND IS CONSIDERED NOT REPRESENTATIVE. BASED ON THE ADJUSTMENT TO THE FLIGHT LEVEL WINDS AND THE VALID SFMR VALUES… THE INITIAL INTENSITY WILL BE MAINTAINED AT 60 KT.

GUILLERMO HAS CONTINUED TO MOVE NORTHWEST THROUGH A BREAK IN THE RIDGE ALOFT WITH THE INITIAL MOTION FOR THIS PACKAGE AT 310/09 KT. THE RELIABLE OBJECTIVE AIDS HAS ONCE AGAIN SHIFTED NORTH A BIT FOR THIS PACKAGE… AND THE FORECAST TRACK HAS BEEN NUDGED NORTH SLIGHTLY FROM THE PREVIOUS FORECAST IN RESPONSE. THE CURRENT FORECAST IS CLOSELY ALIGNED WITH THE ECMWF FORECAST THROUGH 48 HOURS THEN SOUTH OF MOST OF THE DYNAMICAL GUIDANCE BEYOND THAT TIME FRAME. ON THE FORECAST TRACK… GUILLERMO IS FORECAST TO REMAIN WELL NORTHEAST OF THE MAIN HAWAIIAN ISLANDS AT ITS CLOSEST POINT OF APPROACH. IF THIS MOTION CONTINUES… AND THERE IS NO SIGNIFICANT DEVIATION TO THE LEFT OF THE FORECAST TRACK… THE TROPICAL STORM WATCH FOR THE BIG ISLAND AND MAUI COUNTY MAY BE CANCELED LATER TODAY OR TONIGHT.

THE CIMSS ANALYSIS AT 1800 UTC SHOWED OVER 26 KT OF VERTICAL SHEAR IMPACTING GUILLERMO. THE SYSTEM IS MOVING INTO AN AREA OF INCREASING VERTICAL SHEAR. IT IS ALSO MOVING TOWARD A DRIER AIRMASS. THESE FACTORS SHOULD STEADILY WEAKEN GUILLERMO EVEN THOUGH SEA SURFACE TEMPERATURES ARE ADEQUATE. SHIPS GUIDANCE SHOWS A SHARP WEAKENING WITH DISSIPATION BY 72 HOURS. HWRF MAINTAINS THE SYSTEM NEAR 50 KT FOLLOWED BY A SHARPER WEAKENING TREND. THE FORECAST FOLLOWS THE IVCN CONSENSUS WITH GUILLERMO STEADILY WEAKENING TO A TROPICAL DEPRESSION AFTER DAY 3.

Rain pours in Hilo just before noon.