Funnel Cloud in Hawaii, June 1, 2005

HAWAIIAN ISLANDS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST WED JUNE 01 2005

.SYNOPSIS...
RECOVERING HIGH PRESSURE NORTH OF THE MAIN HAWAIIAN ISLANDS WILL
KEEP TRADE WINDS BLOWING THROUGH THE FORECAST PERIOD. IN
GENERAL...WE WILL SEE A TRADE WIND PATTERN OF CLOUDS AND SHOWERS
FAVORING WINDWARD AND MAUKA AREAS. LEEWARD AREAS OF THE BIG ISLAND
WILL SEE INCREASED AFTERNOON AND EARLY EVENING CLOUDS AND SHOWERS
WHICH CLEAR OUT OVERNIGHT. EAST SOUTHEAST WIND FLOW MAY TRIGGER
SHOWERS OVER SOME LEEWARD AREAS DURING THE AFTERNOON TODAY.

&&

.DISCUSSION...
THERE IS LITTLE CHANGE IN FORECAST PHILOSOPHY FROM SEVEN HOURS AGO.
WINDS ARE FROM THE EAST SOUTHEAST ACROSS THE WESTERN AND CENTRAL
ISLANDS THIS MORNING IN RESPONSE TO A WEAKNESS...OR TROUGH...IN THE
SUBTROPICAL RIDGE WEST OF THE STATE. THIS TROUGH IS A SURFACE
REFLECTION OF A BROADER MIDDLE AND UPPER LEVEL TROUGH NEAR THE
DATELINE. LATEST GFS75 SHOWS THIS UPPER TROUGH WILL STAY WEST OF THE
STATE THROUGH THURSDAY...THEN LIFT NORTHWARD LATE THURSDAY INTO THE
WEEKEND. THE SURFACE TROUGH WILL BEGIN TO FILL THURSDAY...ALLOWING
THE MAIN HIGH WITHIN THE RIDGE NORTHEAST OF HAWAII TO SPREAD
WESTWARD. THIS ACTION WILL REALIGN THE PRESSURE FIELD AND
GRADIENT...SWINGING TRADE WINDS BACK AROUND TO AN EAST OR EAST
NORTHEAST DIRECTION THURSDAY AND AFTERWARDS. MODELS SHOW THE
SUBTROPICAL RIDGE WILL THEN CONTINUE TO SPREAD WESTWARD AND
STRENGTHEN THROUGH THE REST OF THE FORECAST PERIOD.

OVERNIGHT SOUNDINGS SHOW A CONTINUED DAYTIME TREND OF INCREASING
INSTABLILITY TOWARDS THE WEST ACROSS THE ISLANDS. HOWEVER...AT LIHUE
INSTABILITY DECREASED SIGNIFICANTLY OVER THE PAST 12 HOURS WITH THE
ELIMINATION OF THE HEATED BOUNDARY LAYER. THERE IS NOW AN INVERSION
NOTED IN BOTH THE HILO AND LIHUE SOUNDINGS AT ABOUT 7700 FEET. THERE
IS SUFFICIENT MOISTURE UPWIND FROM THE ISLANDS TO TRIGGER SHOWERS
THROUGH THE FORECAST PERIOD. THE RATHER HIGH INVERSION HEIGHTS WILL
ALLOW ENOUGH VERTICAL CLOUD DEVELOPMENT FOR BRIEF HEAVY SHOWERS ONCE
AGAIN TODAY. THIS ENHANCEMENT WILL LESSEN AS THE TROUGH WEST OF THE
ISLANDS LIFTS OUT THURSDAY.

WINDS WILL LIKELY REMAIN FROM THE EAST SOUTHEAST ACROSS THE CENTRAL
AND WESTERN ISLANDS THROUGH THE DAY TODAY...SO SHOWERY CONVECTIVE
WEATHER MAY OCCUR AGAIN AS PLUME CLOUDS MOVE ACROSS THE ISLANDS. THE
ISLAND OF OAHU SEEMS TO BE PARTICULARLY VULNERABLE TO THIS TYPE OF
CONVECTIVE TRIGGER. HOWEVER...THE ATMOSPHERE IS TOO DRY AND NOT
UNSTABLE ENOUGH FOR THUNDERSTORMS. OUR WEATHER WILL DRY OUT AS WINDS
TAKE ON A SLIGHTLY MORE NORTHERLY COMPONENT THURSDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

POWELL