High Surf in Hawaii, November 21 to 24, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST WED NOV 21 2007

.SYNOPSIS...
LIGHT NORTHERLY WINDS WILL BECOME STRONGER NORTHEAST TRADE WINDS BY
THURSDAY AS THE LOW NORTHEAST OF THE ISLANDS LIFTS TO THE NORTH.
THIS LOW MAY TRIGGER THUNDERSTORMS ACROSS WATERS JUST UPWIND FROM
THE ISLANDS TODAY AND TONIGHT. A TRADE WIND DISTRIBUTION OF CLOUDS
AND SHOWERS IS EXPECTED FROM LATE TODAY THROUGH THE HOLIDAY
WEEKEND...FAVORING WINDWARD AND MAUKA AREAS. AN UPPER TROUGH MAY
BRING UNSETTLED WEATHER LATE SUNDAY THROUGH TUESDAY.

&&

.DISCUSSION...
A DEEP LOW NORTHEAST OF THE MAIN HAWAIIAN ISLANDS CONTINUES TO
INDUCE WEAK NORTHERLY FLOW ACROSS LOCAL WATERS THIS MORNING. AN
UPPER TROUGH ASSOCIATED WITH THIS LOW HAS ALSO TRIGGERED
THUNDERSTORMS JUST OUTSIDE LOCAL WATERS...PROMPTING A GRIDDED
DATABASE CHANGE TO INCLUDE THESE THUNDERSTORMS OVER AREAS UPWIND
FROM OAHU AND THE ISLANDS OF MAUI COUNTY THROUGH WEDNESDAY NIGHT.
OVERNIGHT SOUNDINGS SHOW THAT THE AIRMASS ACROSS THE WESTERN ISLANDS
HAS MOISTENED AND DESTABILIZED SLIGHTLY...WITH PRECIPITABLE WATER
NOW AT 1.13 INCHES AND THE K-INDEX AT 28 AT LIHUE. ALSO...THE
INVERSION THERE HAS RISEN TO ABOUT 6000 FEET.

THE DEEP LOW IS MOVING TOWARDS THE NORTH...MOTION THAT MODELS SAY
WILL CONTINUE THROUGH THE NEXT 24 HOURS. BY WEDNESDAY EVENING...THE
LOW WILL BE NORTH OF 40N AND SURFACE HIGH PRESSURE NORTHWEST OF THE
MAIN ISLANDS WILL BEGIN BUILDING EASTWARD IN ITS WAKE. THE
ASSOCIATED UPPER TROUGH SHOULD REMAIN OVER THE ISLANDS FOR THE NEXT
FEW DAYS...DESTABILIZING THE AIRMASS KEEPING THE THREAT OF
THUNDERSTORMS ALIVE ACROSS WINDWARD LOCAL WATERS AT LEAST THROUGH
WEDNESDAY NIGHT. THE AIRMASS ACROSS THE EASTERN ISLANDS WILL DRY OUT
TOWARDS THE WEEKEND AND WINDS WILL VEER TO NORTHEASTERLY TRADE
WINDS. A TIGHTER PRESSURE GRADIENT WILL CAUSE WINDS TO STRENGTHEN
BACK INTO THE MODERATE TO FRESH RANGE BY TONIGHT AND THURSDAY.
SEASONAL MOISTURE WILL RETURN TO THE WESTERN ISLANDS THROUGH THE
NEXT 48 HOURS AND A TRADE WIND DISTRIBUTION OF CLOUDS AND
SHOWERS...FAVORING WINDWARD AND MAUKA AREAS...WILL RESUME.

IT REMAINS A BIT UNCLEAR WHAT THE UPPER TROUGH WILL DO EARLY NEXT
WEEK. ALTHOUGH TRADE WIND FLOW WILL CONTINUE AT THE SURFACE THROUGH
THE FORECAST PERIOD...LATEST GFS SHOWS THE UPPER TROUGH DRIFTING
JUST EAST OF THE ISLANDS BY LATE FRIDAY...THEN PINCHING OFF INTO AN
UPPER LOW SOUTH OF THE BIG ISLAND SUNDAY. THE UPPER LOW THEN SLOWLY
FILLS BY MIDWEEK NEXT WEEK...BRINGING LOTS OF RAINFALL TO THE
EASTERN ISLANDS LATE SUNDAY THROUGH TUESDAY. NOGAPS ALSO DEVELOPS A
PINCHED OFF UPPER LOW AT ABOUT THE SAME TIME...BUT ONLY AFTER
PUSHING THE UPPER TROUGH EAST TO 140W...CONSIDERABLY FARTHER TO THE
EAST THAN GFS AND RESULTING IN LESS RAINFALL FOR THE ISLANDS. WE
WILL STICK WITH THE RAINIER SOLUTION FOR NOW.

&&

.MARINE...
FORERUNNERS OF A NORTH NORTHWEST SWELL GENERATED ON MONDAY NEAR THE
ALEUTIANS HAS ARRIVED AND IS EXPECTED TO BUILD TODAY AND CONTINUE
INTO EARLY THURSDAY. THIS LONG PERIOD SWELL WILL GENERATE HIGH SURF
ADVISORY CONDITIONS ON NORTH FACING SHORES.

MODELS CONTINUE TO INDICATE A LARGE NORTHWEST SWELL FOR THURSDAY
NIGHT AND FRIDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY FOR NORTH FACING SHORES OF NIIHAU KAUAI OAHU
MOLOKAI MAUI THROUGH 10 AM THURSDAY.

&&

POWELL