High Surf in Hawaii, September 10 to 13, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST THU SEP 10 2009

.SYNOPSIS...
A TROUGH WILL BRING ISOLATED SHOWERS TO LEEWARD SECTIONS OF THE
SMALLER ISLANDS THROUGH SATURDAY WITH SCATTERED SHOWERS ON WINDWARD
AND MOUNTAIN SLOPES. GENTLE TO MODERATE TRADE WINDS WILL CONTINUE
TODAY THROUGH FRIDAY...AND WEAKEN SATURDAY AND SUNDAY...AS THE
RIDGE FAR NORTH OF THE STATE MOVES SOUTH. TRADES WILL BE LIGHT NEXT
WEEK RESULTING IN HOT AND MUGGY CONDITIONS DURING THE AFTERNOON AND
CLEAR SKIES AT NIGHT WITH SEA BREEZE SHOWERS POSSIBLE IN LEEWARD
AREAS.

&&

.DISCUSSION...
A SUBTROPICAL RIDGE IS IN PLACE ABOUT 600 MILES NORTH OF THE STATE
WITH A TROUGH JUST SOUTH OF THE BIG ISLAND. THESE TWO FEATURES ARE
TIGHTENING THE PRESSURE GRADIENT JUST ENOUGH TO SUPPORT GENTLE TO
MODERATE TRADE WINDS TODAY THROUGH EARLY MONDAY MORNING. A
SOUTHEASTERLY MOVING COLD FRONT FROM AN INTENSE SURFACE LOW PRESSURE
SYSTEM JUST SOUTH OF ALASKA WILL WEAKEN AND PUSH THE SUBTROPICAL
RIDGE FURTHER TO THE SOUTH TO ABOUT 200 MILES NORTH OF OAHU. WITH
THE RIDGE SO CLOSE TO THE ISLANDS...THE TRADE WINDS WILL BE LIGHT TO
GENTLE ALL OF NEXT WEEK...RESULTING IN SEA BREEZES DOMINATING DURING
THE DAY AND LAND BREEZES AT NIGHT. THE WEAK TRADE WIND PATTERN NEXT
WEEK WILL CAUSE CONDITIONS TO BE CLOUDY...VERY MOIST...AND WARMER
DURING THE DAYTIME HOURS WITH CLEAR SKIES AT NIGHT.

THE TROUGH JUST SOUTH OF THE BIG ISLAND IS CAUSING ENHANCED SHOWER
ACTIVITY OVER THE SOUTHEAST PART OF THE ISLAND AND OVER WATERS SOUTH
OF IT. THE HILO SOUNDING SHOWS THIS INCREASED MOISTURE WITH A DEEPER
MOIST LAYER UP TO ABOUT 10000 FEET THIS MORNING AND GLENWOOD AND
MOUNTAIN VIEW RAIN GAGE SITES ON THE BIG ISLAND SHOW ACCUMULATIONS
OF 0.37 AND 0.50 INCHES RESPECTIVELY OVER THE PAST 6 HOURS. THIS
TROUGH WILL CONTINUE TO MOVE FROM EAST TO WEST POSSIBLY ADVECTING
INCREASED MOISTURE OVER THE REST OF THE HAWAIIAN ISLANDS THROUGH
SATURDAY. AFTER THIS MOISTURE PASSES THROUGH...PRECIPITABLE WATER
VALUES SHOW RELATIVE DRYNESS OVER THE ISLANDS THROUGH NEXT WEEK.
CONSIDERING THIS AND THE WEAK TRADE WINDS DURING THAT TIME...SEA
BREEZE SHOWERS ARE LIKELY ON LEEWARD SECTIONS OF THE ISLANDS DURING
THE AFTERNOON. SCATTERED SHOWERS ON WINDWARD AND MOUNTAIN SLOPES ARE
EXPECTED DURING THE ENTIRE FORECAST PERIOD.

&&

.MARINE...
THE FETCH PRODUCED BY A STRONG LOW FAR NORTH OF THE MAIN HAWAIIAN
ISLANDS HAS SENT A SIGNIFICANT EARLY SEPTEMBER SWELL TOWARD US. THIS
SWELL HAS ALREADY ARRIVED AT BUOY 1 THIS MORNING WITH A SWELL HEIGHT
OF 6 FEET AND A DOMINANT SWELL PERIOD OF 16 SECONDS. FORERUNNERS
HAVE ALSO ARRIVED AT THE WAIMEA BAY BUOY LOCATED A SHORT DISTANCE
OFFSHORE FROM THE NORTH SHORE OF OAHU. THIS SWELL WILL CONTINUE TO
FILL IN ALONG NORTH AND WEST FACING SHORES OF MOST OF THE SMALLER
ISLANDS FROM NIIHAU AND KAUAI TO MAUI TODAY. THE SURF PRODUCED BY
THIS SWELL WILL LIKELY APPROACH HIGH SURF ADVISORY THRESHOLD FOR
SEVERAL HOURS ALONG NORTH AND WEST FACING SHORES OF SOME OF THE
SMALLER HAWAIIAN ISLANDS LATER TONIGHT AND FRIDAY MORNING. THIS
SWELL...WHICH IS EXPECTED TO SHIFT TO A MORE NORTHERLY DIRECTION BY
SATURDAY...WILL MAINTAIN ELEVATED SURF ALONG NORTH FACING SHORES OF
MOST HAWAIIAN ISLANDS THROUGH THIS WEEKEND.

ELSEWHERE...A NEW SOUTH SWELL ARRIVING FRIDAY WILL PRODUCE SMALL TO
MODERATE SIZED SURF ALONG SOUTH FACING SHORES OF MOST HAWAIIAN
ISLANDS THROUGH THE FIRST FEW DAYS OF NEXT WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY FOR NORTH AND WEST FACING SHORES OF NIIHAU AND
KAUAI AND NORTH FACING SHORES OF OAHU THROUGH FRIDAY AFTERNOON.

&&

HARRISON/POWELL