High Surf in Hawaii, August 18 to 19, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
320 AM HST TUE AUG 18 2009

.SYNOPSIS...
LIGHT WINDS ARE EXPECTED OVER THE STATE TODAY THROUGH WEDNESDAY AS
A TROPICAL CYCLONE PASSES NORTH OF THE ISLANDS. LOCAL LAND AND SEA
BREEZES WILL BE DOMINANT...WITH CLOUDS AND SHOWERS DEVELOPING OVER
LEEWARD AND INTERIOR AREAS DURING THE AFTERNOONS. TRADE WINDS WILL
RETURN THURSDAY AND STRENGTHEN INTO NEXT WEEKEND AS HIGH PRESSURE
BUILDS FAR NORTH OF THE ISLANDS.

&&

.DISCUSSION...
THE TRADES HAVE CONTINUED TO DECREASE OVERNIGHT...WITH MOST STATIONS
NOW SHOWING A LIGHT LAND BREEZE. THESE LIGHT WINDS WILL BE WITH US
FOR THE NEXT FEW DAYS AS GUILLERMO MOVES BY FAR TO THE NORTH OF THE
STATE. LITTLE IN THE WAY OF RAINFALL WAS MEASURED OVERNIGHT AS THE
LAND BREEZE RESULTED CLEARING SKIES OVER THE LAND MASSES. HOWEVER
SHOWERS HAVE INCREASED OVER THE WINDWARD COASTAL
WATERS...PARTICULARLY FROM MAUI NORTHWARD...WITH A FEW ENHANCED
COLD CLOUD TOPS SHOWING UP ON IR SATELLITE AND EVEN ISOLATED
THUNDERSTORMS JUST OUTSIDE OF THE WINDWARD OAHU COASTAL WATERS
EARLY THIS MORNING.

AN UPPER LEVEL TROUGH IS POSITIONED OVER THE ISLANDS...WITH THE
COLDEST AIR ALOFT JUST NORTH OF KAUAI...BRINGING A VERY UNSTABLE
AIRMASS ALOFT. A LOW LEVEL CAPPING INVERSION WAS IN PLACE YESTERDAY
AND THIS KEPT THE CONVECTION TO A MINIMUM EVEN WITH INSTABILITY
ALOFT. THIS CAP...ALBEIT WEAK...IS STILL IN PLACE IN THE LATEST
EARLY MORNING SOUNDINGS. THE CONVECTIVE INDICES ARE IMPRESSIVE IF
THE CAP CAN BE BROKEN...2000+ J/KG CAPE AND A LIFTED INDEX AT -6.
AS LOCAL AFTERNOON SEA BREEZES DEVELOP THIS AFTERNOON AND WEDNESDAY
AFTERNOON AND THESE WILL BE A FOCUSING MECHANISM FOR SHOWERS OVER
THE ISLAND INTERIORS. LOCALLY HEAVY RAINFALL IS POSSIBLE IF THIS
CONVECTION IS STRONG ENOUGH TO BREAK THROUGH THE WEAK CAP.

AS GUILLERMO CONTINUE TO PUSH FURTHER TO THE NORTH AND NORTHWEST OF
THE STATE...THE TRADES ARE EXPECTED TO RETURN WEDNESDAY NIGHT AND
THURSDAY. THE MODELS SHOW A PLUME OF VERY MOIST AIR ALONG THE AREA
OF CONVERGENCE WHERE THE TRADES ARE PUSHING WEST...AND AN INCREASE
IN SHOWER ACTIVITY IS EXPECTED AS THIS PLUME MOVES THROUGH WEDNESDAY
NIGHT THROUGH LATE THURSDAY. THEN DECREASING THURSDAY NIGHT AND
FRIDAY AS DRIER AND MORE STABLE AIR SPREADS OVER THE AREA.

FROM FRIDAY THROUGH THE WEEKEND...THE FORECAST IS FOR A RETURN TO
MODERATE TO FRESH TRADES AS THE RIDGE BUILDS BACK IN NORTH OF THE
STATE.

&&

.MARINE...
AN EAST NORTHEAST SWELL FROM GUILLERMO WILL AFFECT EXPOSED EAST
FACING SHORES TODAY THROUGH WEDNESDAY. LATEST BUOY DATA SHOWS THIS
SWELL JUST REACHING THE STATE WITH READINGS INDICATIVE OF 6 TO 8
FOOT SURF HEIGHTS ALONG THE EAST FACING SHORES AS EARLY AS THIS
MORNING. HAVE EXPANDED THE HIGH SURF ADVISORY TO INCLUDE THE EAST
FACING SHORES OF OAHU...KAUAI AND NIIHAU AS THE SWELL READINGS AT
MOKAPU POINT BUOY ARE ALREADY AT 4 FEET 13 SECONDS. THE SURF IS
EXPECTED TO PEAK TONIGHT AND EARLY WEDNESDAY...THEN TAPER OFF SLOWLY
TO BELOW ADVISORY LEVELS LATE WEDNESDAY.

AN UNSTABLE AIRMASS WILL BRING ISOLATED THUNDERSTORMS TO THE
COASTAL WATERS NEAR KAUAI AND WINDWARD OAHU TODAY...AND POSSIBLY
TONIGHT.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY FOR EAST FACING SHORES TODAY THROUGH WEDNESDAY.

&&

BRENCHLEY