Severe Thunderstorm Warning 1, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
700 AM HST SUN DEC 20 2009

.SYNOPSIS...
THUNDERSTORMS AND HEAVY SHOWERS ARE EXPECTED FROM OAHU TO THE BIG
ISLAND TODAY DUE TO AN UPPER LEVEL TROUGH PASSING OVER THE ISLANDS.
THE TRADE WINDS WILL BE TURNING LIGHT AND VARIABLE TONIGHT. ASIDE
FOR A BRIEF RETURN TUESDAY NIGHT...THE LIGHT AND VARIABLE WINDS WILL
BE THE RULE UNTIL THURSDAY NIGHT WHEN THE A COLD FRONT MOVES THROUGH
THE ISLAND CHAIN. MODERATE TO LOCALLY STRONG TRADES WILL FOLLOW IN
BEHIND THE FRONT AND WEEKEND DURING THE UPCOMING WEEKEND.

&&

.DISCUSSION...
A SHORT WAVE TROUGH MOVING OVER OAHU THIS MORNING IS HELPING TO
TRIGGER THUNDERSTORMS AND HEAVY SHOWERS FROM OAHU EAST.
THUNDERSTORMS ARE EXPECTED TO CONTINUE TO DEVELOP IN THIS UNSTABLE
AIRMASS THROUGHOUT THE DAY TODAY. AS THE SHORT WAVE ROTATES TO THE
EAST...THE FOCUS OF THE THUNDERSTORMS SHOULD SHIFT EASTWARD AS WELL.
EXPECT THUNDERSTORMS...AND THE HEAVY SHOWERS...TO DIE OFF LATER THIS
AFTERNOON AS MID LEVEL RIDGING WEST OF THE IMPULSE SHOULD BE
BUILDING ACROSS THE AREA. THE GFS MODEL POINTS TO A STRONGER
INVERSION FROM 9 THOUSAND FEET ON THE KAUAI END TO 12 THOUSAND OVER
THE BIG ISLAND BY MONDAY MORNING.

AT THE SURFACE...THE TRADES WILL BE GIVING WAY TO A LIGHT AND
VARIABLE WIND REGIME THAT WILL FAVOR LOCAL DAYTIME SEA BREEZES
ESPECIALLY ALONG THE LEEWARD BEACHES. THIS WILL LEAD TO SOME
AFTERNOON INTERIOR CLOUDINESS. LOW LEVEL MOISTURE IS MARGINAL AND
THE INVERSION SLIGHT WEAKER AND HIGHER AT 12 THOUSAND FEET. SO DO
EXPECT SOME ISOLATED SHOWERS STATEWIDE. MODERATE TRADE MAY MAKE A
BRIEF RETURN TUESDAY NIGHT BUT IT IS LIGHT AND VARIABLE UNTIL A
FRONT PUSHES THROUGH THE MAIN HAWAIIAN ISLANDS THURSDAY.

&&

.MARINE...
THE LATEST BUOY REPORTS SHOWS A RISE IN THE NORTH SWELL AT THE
KAILUA BUOY THE PAST FEW HOURS AND HOLDING AT 8 TO 9 FEET. THE
PERIOD IS SHOWING SIGNS OF BECOMING SHORTER...FLUCTUATING BETWEEN 13
TO 11 SECONDS. THE THE HIGH SURF ADVISORY STILL LOOKS GOOD FOR AN
EXPIRATION OF 6 PM THIS EVENING. ADDITIONALLY...THE CONDITIONS
PERSIST FOR POTENTIAL MODERATE SURGES FOR NORTH FACING HARBORS
SUCH AS KAHULUI AND HILO.

LOOKING AHEAD...A LARGER NORTHWEST SWELL MAY PRODUCE SURF AROUND
WARNING LEVELS FOR NORTH AND WEST FACING SHORES DURING THE MIDDLE OF
NEXT WEEK. THE SYSTEM THAT WILL SEND THE FRONT TOWARD THE ISLANDS
DURING THE END OF NEXT WEEK MAY ALSO DELIVER AN EVEN LARGER
NORTHWEST SWELL LATE IN THE WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY EAST FACING SHORES OF NIIHAU KAUAI OAHU MOLOKAI
MAUI AND THE BIG ISLAND UNTIL 6 PM HST.

FLASH FLOOD WATCH OAHU...MAUI COUNTY AND THE BIG ISLAND UNTIL 6 PM
TODAY.

&&