Flash Flood Warning 8, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST TUE NOV 27 2007

.SYNOPSIS...
HEAVY SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED ACROSS KAUAI
AND OAHU TONIGHT AND WEDNESDAY...WITH LOCALLY HEAVY SHOWERS POSSIBLE
ELSEWHERE. LIGHT SOUTH TO SOUTHEAST WINDS WILL CONTINUE THROUGH THE
NEXT SEVERAL DAYS...ALONG WITH UNSETTLED WEATHER AND THE THREAT OF
LOCALLY HEAVY RAINFALL.

&&

.DISCUSSION...
RADAR SHOWS AN ACTIVE AREA OF HEAVY SHOWERS ACROSS KAUAI AND THE
KAUAI CHANNEL THIS EVENING...EXTENDING SOUTH SOUTHEAST ACROSS OAHU
LEEWARD WATERS. SMALLER AREAS OF MODERATE TO HEAVY SHOWERS ARE
DEVELOPING SOUTH OF THE REMAINING ISLANDS...WITH PORTIONS OF
WINDWARD MAUI AND THE KONA SLOPES OF THE BIG ISLAND STILL AFFECTED
BY MODERATE SHOWERS WHICH FORMED A FEW HOURS AGO. A FLOOD WATCH IS
IN EFFECT FOR KAUAI AND OAHU THROUGH WEDNESDAY AFTERNOON AS THE
THREAT OF FLOODING...GREATEST ON THOSE ISLANDS...INCREASES.

GENERAL STEERING FLOW IS FROM THE SOUTH SOUTHEAST...SO ANYTHING THAT
DEVELOPS SOUTH OF THE ISLANDS STANDS A GOOD CHANCE OF AFFECTING US.
SO FAR...THE BULK OF SHOWER ACTIVITY HAS BEEN OVER WATER AND ACROSS
KAUAI THIS EVENING. HOWEVER...GIVEN THE NUMBER OF DEVELOPING SHOWER
AREAS WITHIN 100 MILES SOUTH OF THE ISLANDS...HEAVY SHOWERS COULD
OCCUR ANYWHERE ACROSS THE MAIN HAWAIIAN ISLANDS THROUGH THE NEXT 24
HOURS OR SO.

A SHARP UPPER TROUGH NORTHWEST OF KAUAI HAS TAPPED INTO MOISTURE
BROUGHT UP FROM THE DEEP TROPICS WITHIN SOUTHERLY FLOW TO GENERATE
THIS CURRENT BOUT OF UNSETTLED WEATHER. AFTERNOON SOUNDINGS SHOW A
MOIST AIRMASS BELOW 500 MB...WITH LITTLE OR NO SUBSIDENCE INVERSION.
PHLI SOUNDING SHOWS OVER 1300 J/KG OF CONVECTIVE ENERGY...WITH PHTO
SHOWING OVER 700 J/KG. THESE SOUNDINGS ALSO SHOW 1.67 INCHES OF
PRECIPITABLE WATER...WHILE AFTERNOON AMSU/SSMI PASSES SHOW A TONGUE
OF HIGH PRECIPITABLE WATER ACROSS THE STATE. THE GREATEST VALUES
EXTEND FROM SOUTH OF THE BIG ISLAND TO KAUAI AND OAHU...WITH VALUES
NEAR 1.9 INCHES.

MODELS SHOW BROAD SOUTHEASTERLY SURFACE FLOW WILL CONTINUE ACROSS
THE MAIN HAWAIIAN ISLANDS THROUGH MUCH OF THE WORK WEEK...BETWEEN A
HIGH FAR TO THE NORTHEAST AND A STALLED FRONT TO THE NORTHWEST. THIS
FLOW OUT OF THE TROPICS WILL CONTINUE TO BRING ABOVE NORMAL MOISTURE
ACROSS THE STATE. CONTINUED TROUGHING ALOFT WILL KEEP INVERSIONS
WEAK TO NON-EXISTENT AND THE ATMOSPHERE RATHER UNSTABLE FOR THE NEXT
FEW DAYS. THIS WILL KEEP THE THREAT OF HEAVY SHOWERS ALIVE THROUGH
FRIDAY.

LATEST GFS SHOWS A PAIR OF COLD FRONTS REACHING THE ISLANDS THIS
WEEKEND...WITH THE SECOND FRONT STALLING OVER THE CENTRAL ISLANDS
EARLY NEXT WEEK. WEAK SOUTHERLY FLOW WILL PERSIST SOUTH OF THESE
FRONTS AND THE CURRENT FORECAST PACKAGE KEEPS WEAK SOUTHERLY FLOW
ACROSS THE MAIN ISLANDS THROUGH THE FORECAST PERIOD. IF FUTURE MODEL
RUNS SHOW THESE FRONTS PUSHING FARTHER TO THE SOUTH...WE WILL HAVE
TO CHANGE OUR DAY 6 AND 7 FORECAST. FOR NOW...WE WILL KEEP THINGS AS
THEY ARE.

&&

.MARINE...
SURF IS CURRENTLY RUNNING NEAR ADVISORY LEVELS FOR NORTH FACING
SHORES. THE NORTHWEST SWELL WILL REMAIN NEAR CURRENT LEVELS OR
SUBSIDE A BIT OVERNIGHT...BUT WILL BUILD AGAIN ON WEDNESDAY. SURF
WILL INCREASE ABOVE ADVISORY LEVELS ON WEDNESDAY.

THUNDERSTORMS CONTINUE TO DEVELOP AND AFFECT COASTAL AND OFFSHORE
WATERS ALONG AND TO THE WEST OF OAHU. PLEASE SEE THE LATEST MARINE
WEATHER STATEMENT...ISSUED UNDER AWIPS HEADER MWSHFO AND WMO HEADER
FZHW70 PHFO...FOR THE LATEST INFORMATION ON THUNDERSTORM COVERAGE
AND MOVEMENT.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH WEDNESDAY AFTERNOON FOR NIIHAU-KAUAI-
OAHU.

HIGH SURF ADVISORY FROM 4 AM WEDNESDAY TO 4 PM HST THURSDAY FOR
NIIHAU-KAUAI WINDWARD-KAUAI LEEWARD-WAIANAE COAST-OAHU NORTH
SHORE-OAHU KOOLAU-MOLOKAI-MAUI WINDWARD WEST-WINDWARD HALEAKALA.

&&

POWELL