High Surf in Hawaii, December 7 to 10, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST WED DEC 7 2011

.SYNOPSIS...
TRADE WIND WEATHER WILL CONTINUE ACROSS THE MAIN HAWAIIAN ISLANDS
THROUGH THE FORECAST PERIOD AS A RIDGE OF HIGH PRESSURE REMAINS
NORTH OF THE ISLANDS. WINDS WILL INCREASE BEGINNING WEDNESDAY AS
THIS HIGH PRESSURE CONSOLIDATES AND DRIFTS SOUTHWARD. CLOUDS AND
SHOWERS WILL FAVOR WINDWARD AND MAUKA AREAS. SHOWERS WILL INCREASE
OVER THE WEEKEND AND INTO NEXT WEEK AS MOISTURE FROM AN OLD SURFACE
TROUGH MOVES IN.

&&

.DISCUSSION...
A RIDGE OF HIGH PRESSURE EXTENDS SOUTHWESTWARD FROM A 1037 MB HIGH
NEAR 47N138W THROUGH 38N150W AND 30N170W. THE PRESSURE GRADIENT
BETWEEN THIS RIDGE AND EQUATORIAL LOW PRESSURE IS STEEP ENOUGH TO
SUPPORT MODERATE TRADE WINDS ACROSS LOCAL WATERS THIS MORNING.
SATELLITE LOOP SHOWS A MIXTURE OF PATCHY LOW CLOUDS MOVING ACROSS
THE CHAIN WITHIN TRADE FLOW...AND SCATTERED HIGH CLOUDS WITHIN AN
UPPER TROUGH MOVING EASTWARD ACROSS THE BIG ISLAND. OVERNIGHT
SOUNDINGS SHOW OUR AIRMASS IS A BIT MORE MOIST THAN 12 HOURS
AGO...WITH 1.1 TO 1.3 INCHES OF PRECIPITABLE WATER. BOTH SOUNDINGS
SHOW A BIT OF UPPER TROUGH-INDUCED INSTABILITY...WITH CAPE BETWEEN
700 AND 900 COMBINED WITH LIFTED INDEX VALUES RANGING FROM MINUS 1.8
TO MINUS 3.2. CLOUD DEVELOPMENT SEEMS CAPPED BY A WEAK INVERSION AT
ABOUT 7800 FEET...YET THE ISOLATED TO SCATTERED SHOWERS NOTED ON
RADAR ARE REACHING MODERATE INTENSITY AT TIMES.

MODELS SHOW THE UPPER TROUGH OVER US WILL MOVE EASTWARD OVER THE
NEXT FEW DAYS AS A SECOND UPPER TROUGH APPROACHES US FROM THE
NORTHWEST. WHILE LITTLE OR NO DIRECT INFLUENCE ON ISLAND WEATHER IS
EXPECTED FROM THESE UPPER TROUGHS...GFS HAS THE FIRST UPPER TROUGH
INDUCING A WEAK SURFACE TROUGH BETWEEN 140W AND 150W LATER IN THE
WEEK. THIS WOULD HELP TO POOL MOISTURE WHICH WOULD THEN BE PUSHED
ACROSS THE ISLANDS OVER THE WEEKEND WITHIN TRADE FLOW AS THE SURFACE
TROUGH WEAKENS. SINCE GFS PERSISTS WITH THIS SCENARIO FOR ITS 06Z
RUN...THE FORECAST HAS BEEN ALTERED BEGINNING SATURDAY NIGHT FOR
MORE SHOWERS...MAINLY ACROSS WINDWARD AREAS. POP...SKY...WX AND QPF
GRIDS HAVE ALL BEEN TWEAKED THROUGH EARLY NEXT WEEK TO ACCOUNT FOR
THIS ALTERATION.

THE RIDGE NORTH OF THE ISLANDS WILL STAY INTACT THROUGH THE
FORECAST PERIOD...SO TRADE WINDS WILL CONTINUE THROUGH THE WEEKEND
AND BEYOND. SLIGHTLY STRONGER TRADE WINDS ARE EXPECTED BEGINNING
WEDNESDAY AS A CENTER OF HIGH PRESSURE CONSOLIDATES TO OUR NORTH
AND DROPS SOUTHWARD. CLOUDS AND SHOWERS WILL FAVOR WINDWARD AND
MAUKA AREAS.

&&

.MARINE...
SURF HAS DECREASED BELOW ADVISORY LEVEL...SO THE HIGH SURF ADVISORY
IS CANCELLED. ANOTHER LARGER NORTHWEST SWELL WILL PRODUCE A MORE
SOLID HIGH SURF ADVISORY EVENT IN THE 24 TO 48 HOURS. SURF WILL
BUILD LATE TODAY AND THURSDAY ON NORTH AND WEST FACING
SHORES...REACHING UP TO 20 FOOT FACE HEIGHTS AS IT PEAKS LATE
THURSDAY AND EARLY FRIDAY...FOLLOWED BY A GRADUAL DECLINE INTO THE
WEEKEND. A HIGH SURF ADVISORY FOR THIS UPCOMING EVENT WILL BE ISSUED
LATER TODAY.

TRADE WINDS HAVE ALREADY INCREASED ABOVE ADVISORY THRESHOLD OVER THE
TYPICALLY WINDIER WATERS SURROUNDING MAUI AND THE BIG ISLAND THIS
MORNING...SO SMALL CRAFT ADVISORIES FOR THESE AREAS ARE NOW IN
EFFECT. THIS ADVISORY WILL LIKELY NEED TO BE EXPANDED TO INCLUDE
MORE AREAS FOR COMBINED SEAS REACHING 10 FEET OR MORE WITH THE
INCOMING NORTHWEST SWELL THURSDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY FROM 6 AM HST WEDNESDAY THROUGH 6 PM HST
THURSDAY FOR PAILOLO AND ALENUIHAHA CHANNELS...MAALAEA BAY AND THE
LEEWARD AND SOUTHEASTERN BIG ISLAND WATERS.

&&

POWELL