High Surf in Hawaii, September 9 to 12, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST FRI SEP 9 2011

.SYNOPSIS...
GENTLE TO MODERATE TRADE WINDS WILL CONTINUE THROUGH TUESDAY WITH AN
INCREASE IN WINDS EXPECTED AROUND WEDNESDAY. THE STABLE AND SOMEWHAT
DRY TRADE WIND FLOW WILL PRODUCE MODEST SHOWER ACTIVITY OVER MAINLY
WINDWARD AREAS FOR THE NEXT FEW DAYS...THOUGH AFTERNOON CLOUDS MAY
DELIVER ISOLATED SHOWERS OVER LEEWARD TERRAIN. AN INCREASE IN MAINLY
WINDWARD SHOWERS IS POSSIBLE MONDAY THROUGH WEDNESDAY.

&&

.DISCUSSION...
A QUIET WEATHER PATTERN IS IN STORE FOR THE WEEKEND FEATURING
GENTLE TO LOCALLY MODERATE TRADES AND BELOW NORMAL SHOWER ACTIVITY.

TRADE WINDS INCREASED A NOTCH TODAY AND SHOULD REMAIN MORE OR LESS
UNCHANGED THROUGH MONDAY. A RATHER DEEP...EARLY SEPTEMBER UPPER
LEVEL TROUGH AND A SERIES OF ASSOCIATED SURFACE FRONTS OVER THE
GULF OF ALASKA AND CENTRAL NORTH PACIFIC HAVE KEPT THE SUBTROPICAL
RIDGE WEAKENED AND DISPLACED TO THE SOUTH FOR MUCH OF THE PAST WEEK.
THE SURFACE RIDGE STRENGTHENED SLIGHTLY TODAY...CAUSING THE INCREASE
IN THE TRADES. THE STRENGTH OF THE RIDGE WILL CHANGE LITTLE THROUGH
MONDAY...LEADING TO GENTLE TO LOCALLY MODERATE TRADES. UNDER THIS
FLOW...AFTERNOON SEA BREEZES ON THE SMALLER ISLANDS WILL BE CONFINED
TO AREAS TO THE LEE OF THE HIGH TERRAIN.

THE ATMOSPHERE WILL BE STABLE AND SOMEWHAT DRY THIS WEEKEND.
RIDGING ALOFT IS FIRMLY IN PLACE OVER THE ISLANDS WITH STRONG
SUBSIDENCE ALOFT NOTED ON WATER VAPOR IMAGERY...AND THE UPPER RIDGE
WILL CONTINUE TO PRODUCE STABLE CONDITIONS THIS WEEKEND.
MEANWHILE...THE TRADE WIND FLOW IMMEDIATELY UPWIND OF THE STATE IS
RATHER DRY WITH PRECIPITABLE WATER /PW/ VALUES RUNNING 10 TO 20
PERCENT BELOW SEPTEMBER NORMS. AS A RESULT...MODEST SHOWER ACTIVITY
WILL BE CONFINED MAINLY TO WINDWARD SLOPES WHILE SEA BREEZES WILL
PRODUCE AFTERNOON CLOUDS AND ISOLATED SHOWERS FOR LEEWARD TERRAIN.

AN INCREASE IN SHOWERS IS POSSIBLE DURING THE FIRST HALF OF THE WORK
WEEK. A WEAK MID LEVEL TROUGH CURRENTLY ABOUT 950 MILES EAST OF THE
STATE NEAR 20N140W IS EXPECTED TO MOVE OVER THE ISLANDS MONDAY INTO
WEDNESDAY. THE GFS SHOWS PRECIPITABLE WATER VALUES INCREASING BACK
AROUND SEASONAL NORMS AS THIS WEAK FEATURE TRAVELS ACROSS THE
ISLANDS. THUS...AN INCREASE IN SHOWERS IS POSSIBLE...MAINLY FOR
WINDWARD AREAS.

TRADE WINDS ARE EXPECTED TO STRENGTHEN DURING THE SECOND HALF OF THE
WORK WEEK. THE UPPER LEVEL TROUGH CURRENTLY IN PLACE OVER THE
CENTRAL NORTH PACIFIC WILL FLATTEN OUT...BECOMING ZONAL...OR WEST TO
EAST FLOWING. SURFACE HIGH PRESSURE WILL STRENGTHEN ALONG 32N...
LEADING TO A SLIGHT STRENGTHENING OF THE TRADE WINDS.

&&

.MARINE...
WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY /SCA/ CRITERIA
INTO EARLY NEXT WEEK. SCA WINDS MAY DEVELOP BY WEDNESDAY OVER THE
TYPICALLY WINDY WATERS AND CHANNELS AROUND THE BIG ISLAND AND MAUI.

THE NEW SOUTH SWELL HAS BEEN SLOW TO BUILD TODAY. HOWEVER...THERE
HAS BEEN AN INCREASE IN SWELL ENERGY IN THE 16 TO 18 SECOND RANGE ON
THE BARBERS POINT AND LANAI BUOYS IN THE PAST FIVE HOURS. WE WILL
CONTINUE TO MONITOR THE BUOYS TONIGHT...AND IF CURRENT TRENDS HOLD
SOUTH SHORE SURF WILL BE MARGINALLY HIGH TOMORROW. A HIGH SURF
ADVISORY REMAINS IN PLACE THROUGH SATURDAY AFTERNOON. THE SWELL IS
EXPECTED TO PRODUCE ELEVATED SURF NEAR THE ADVISORY LEVEL ON SUNDAY
THEN GRADUALLY LOWER THROUGH WEDNESDAY.

A MODERATE NORTH-NORTHWEST SWELL IS CURRENTLY PEAKING. THIS SWELL
WILL SLOWLY DECREASE THROUGH MONDAY.

&&

.AVIATION...
AN INCREASE IN CLOUDS WITHIN THE TRADE WIND FLOW IS EXPECTED
TONIGHT...BRINGING ISOL MVFR CIGS AND VIS IN SHRA TO WINDWARD
SLOPES. VFR CONDITIONS WILL DOMINATE ACROSS LEEWARD AREAS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST SATURDAY FOR ALL SOUTH FACING
SHORES ALL HAWAIIAN ISLANDS.

&&

WROE