Heavy Rain in Hawaii, February 4, 2005

HAWAIIAN ISLANDS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1135 AM HST FRI FEB 4 2005

.SYNOPSIS...
A TROUGH OVER THE ISLANDS WILL SLOWLY WEAKEN THROUGH THE WEEKEND.
THE THREAT OF HEAVY SHOWERS AND THUNDERSTORMS WILL CONTINUE FOR
MAUI AND THE BIG ISLAND DUE TO INSTABILITY ASSOCIATED WITH THE
TROUGH. CLOUD COVER AND THE LIKELIHOOD OF HEAVY SHOWERS WILL
GRADUALLY DECREASE AS THE TROUGH WEAKENS. WITH THE TROUGH
WEAKENING...TRADE WINDS MAY RETURN EARLY NEXT WEEK.
&&

.UPDATE...
COLD TEMPERATURES AT THE SUMMITS...COMBINED WITH LAYERED CLOUDS
MOVING OVER THE BIG ISLAND WILL BRING SNOW SHOWERS TO THE SUMMITS
ABOVE 12000 FEET TODAY AND TONIGHT. HAVE ISSUED A WINTER WEATHER
ADVISORY AS A RESULT. UPDATED GRIDS/ZONES WILL GO OUT WITHIN THE
NEXT 30 MINUTES.
&&

.DISCUSSION...
MUCH OF THE HEAVY RAIN HAS ENDED OVER THE ISLANDS FOR THE TIME
BEING. RAIN CONTINUES OVER THE BIG ISLAND...WHICH RECEIVED A LOT OF
RAIN OVERNIGHT. THE MOST RAIN OVERNIGHT WAS RECORDED AT A RAIN GAGE
IN MOUNTAIN VIEW...WHICH HAD 11.26 INCHES BETWEEN 8 PM AND 8 AM.

NO MAJOR CHANGES ARE EXPECTED AT THIS TIME. SHOWERS WILL CONTINUE
THROUGH THE WEEKEND. THE PREVIOUS DISCUSSION FOLLOWS.
&&

.PREV DISCUSSION...
ISSUED AT 400 PM
A STUBBORN AND SHARP TROUGH OVER THE ISLANDS BOTH AT THE SURFACE AND
ALOFT CONTINUES TO PRODUCE LOCALLY HEAVY RAINFALL AND ISOLATED
THUNDERSTORMS THIS MORNING...CONCENTRATED MAINLY OVER MAUI COUNTY
AND THE BIG ISLAND. OVER THE PAST TWO HOURS...RAINFALL HAS STARTED
TO AFFECT OAHU...THOUGH COMING FROM A DIFFERENT DIRECTION. WITH THE
TROUGH AXIS IN THE KAIWI CHANNEL...SHOWERS ARE HITTING MAUI COUNTY
AND THE BIG ISLAND FROM THE SOUTH...THEN REVERSING COURSE NORTHEAST
OF THE STATE AND RETURNING TO HIT KAUAI AND OAHU. THE BULK OF
MOISTURE BEING RECYCLED AND REDIRECTED IS MAINLY FOCUSED ON OAHU AT
THE MOMENT...CREATING CONDITIONS SIMILAR TO WET TRADES.

EARLY THIS MORNING...ROAD CLOSURES IN THE KAU DISTRICT ON THE BIG
ISLAND PROMPTED THE ISSUANCE OF A FLASH FLOOD WARNING. AS SHOWERS
CONTINUE TO FORM TO THE SOUTH AND MOVE ONSHORE...THE FLASH FLOOD
WARNING WILL LIKELY REMAIN IN PLACE THROUGH THE MORNING HOURS...AND
MAY EVEN NEED TO BE EXPANDED TO OTHER AREAS. OTHER AREAS OF CONCERN
THIS MORNING IS THE EASTERN TIP OF MAUI FROM KIPAHULU THROUGH HANA.
UP TO THIS POINT...THE FORECAST REASONING WAS TO ASSOCIATE THE HEAVY
SHOWERS WITH THE AREAS ALONG AND EAST OF THE TROUGH AXIS...BUT WITH
WHAT WE ARE SEEING ON OAHU...THIS PHILOSOPHY NO LONGER HOLDS.

THE PAST COUPLE OF DAYS HAVE BEEN A TOUGH FORECAST...AND THE CURRENT
SCENARIO IS NOT DIFFERENT. MODELS DO NOT HAVE A GOOD HANDLE ON
THINGS...AND ARE LACKING RUN TO RUN CONSISTENCY. WITH TRADES EARLIER
EXPECTED BY THE WEEKEND...IT NOW APPEARS THAT THE TROUGH WILL LINGER
OVER THE ISLANDS A BIT LONGER IN A WEAKENED STATE...RATHER THAN
DRIFT OFF TOWARD THE EAST. IN FACT...GFS IS NOW ADVERTISING THE
TROUGH TO SHIFT WESTWARD...ESSENTIALLY SHUTTING OFF THE TRADES OVER
THE WEEKEND. THE TROUGH AXIS HAS DEMONSTRATED A SLIGHT WESTWARD
DRIFT OVERNIGHT...BUT WHETHER THIS TREND WILL CONTINUE IS QUITE
UNCERTAIN. WITH AMPLE LOW LEVEL MOISTURE AROUND...CHANCE FOR FOR
LOCALLY HEAVY SHOWERS AND THUNDERSTORMS WILL CONTINUE FOR THE
EASTERN HALF OF THE CHAIN AT LEAST THROUGH TODAY....AND WE MIGHT BE
IN FOR A MUGGY COUPLE OF DAYS OVER THE WEEKEND. AS SUCH...OUR DATE
WITH THE TRADEWINDS IS STILL UP IN THE AIR...BUT WE ARE CURRENTLY
SHOOTING FOR EARLY NEXT WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FOR OAHU MAUI MOLOKAI LANAI KAHOOLAWE AND THE BIG
ISLAND THROUGH TONIGHT.
WINTER WEATHER ADVISORY FOR SUMMITS OF THE BIG ISLAND ABOVE 12000 FT.
&&

M BALLARD