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Hawaiian Islands Synoptic Discussion and Guidance

251
FXHW60 PHFO 020651
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
850 PM HST MON SEP 1 2014

.SYNOPSIS...
LIGHT TRADE WINDS WILL STRENGTHEN SLIGHTLY ON TUESDAY...AND REMAIN
LIGHT TO MODERATE FOR MOST OF THE UPCOMING WEEK. THE LIGHT WINDS
WILL ALLOW LAND BREEZES TO DEVELOP OVER LEEWARD AREAS LATER TONIGHT
AS THE LAND COOLS...RESULTING IN CLEARING SKIES. MEANWHILE...THE
LIGHT TRADE WINDS WILL DELIVER A FEW SHOWERS TO WINDWARD AREAS.
WITH THE STRENGTHENING TRADES...EXPECT CLOUDS AND SHOWERS TO FAVOR
WINDWARD AREAS...ESPECIALLY DURING NIGHTS AND MORNINGS.

&&

.DISCUSSION...
LATEST SATELLITE AND RADAR ANIMATIONS SHOW THE LOW-LEVEL FLOW IS
FROM THE E...AT LEAST AT CLOUD LEVEL...PUSHING LIMITED CLOUDS AND
SHOWERS OVER NEAR SHORE WATERS TOWARD THE W. AN AREA OF ENHANCED
SHOWERS IS LINGERING OVER WINDWARD OAHU AND NEAR SHORE WATERS...AS
REMNANTS OF AFTERNOON CONVECTION INTERACT WITH THE LIGHT E WINDS.
THE WINDS ARE BEING SUPPORTED BY A DISTANT HIGH THAT IS RELATIVELY
WEAK...WITH WEAK TROUGHS BETWEEN THE HIGH AND THE ISLANDS
CONTRIBUTING TO A LOOSE PRESSURE GRADIENT...AS IS THE REMNANT
CIRCULATION OF MARIE ABOUT 1300 MILES NE OF THE ISLANDS. ALTHOUGH
SKIES IMMEDIATELY UPSTREAM OF THE ISLANDS ARE NEARLY CLEAR...AN AREA
OF SHOWERY LOW CLOUDS LIES 100 TO 300 MILES E OF WINDWARD BIG
ISLAND...MOVING W NEAR 10 MPH.

OVERNIGHT...LINGERING SEA BREEZE-DRIVEN CLOUDS AND SHOWERS OVER
KAUAI AND OAHU WILL GRADUALLY DIMINISH...WHILE THE LIGHT TRADE WINDS
DELIVER A FEW SHOWERS TO WINDWARD AREAS STATEWIDE. LEEWARD AREAS ON
ALL ISLANDS WILL SEE CLEAR SKIES DEVELOPING...WITH THE LIGHT TRADES
ALLOWING LAND BREEZES TO DEVELOP IN SHELTERED AREAS.

WINDS WILL SLOWLY STRENGTHEN ON TUESDAY AS THE TROUGHS NW OF THE
ISLANDS WEAKEN AND THE SURFACE RIDGE TO THE N STRENGTHENS SOMEWHAT.
THE OVERALL SYNOPTIC PATTERN DOES NOT SUPPORT A STRONG TRADE FLOW
THIS WEEK HOWEVER...BUT RATHER A LIGHT TO MODERATE FLOW. THE TRADE
WINDS WILL PUSH THE AREA OF MOISTURE E OF THE BIG ISLAND OVER THE
ISLAND CHAIN OVER THE 12 TO 36 HOURS...WITH LATEST GUIDANCE
SUGGESTING IT WILL MOVE OVER WINDWARD BIG ISLAND BY TUESDAY
MORNING...MAUI COUNTY DURING THE DAY...OAHU BY EVENING AND KAUAI BY
TUESDAY NIGHT BEFORE CLEARING TO THE W. AFTER THIS MODEST MOISTURE
SOURCE PASSES...LIMITED MOISTURE IS EXPECTED THROUGH THURSDAY.
INCREASED MOISTURE LOOSELY ASSOCIATED WITH THE REMNANT OF MARIE
PASSING FAR NE OF THE ISLANDS MAY INCREASE WINDWARD SHOWERS FROM
THURSDAY NIGHT THROUGH SATURDAY.

BIGGEST FORECAST QUESTION FOR THE NEXT COUPLE OF DAYS INVOLVES THE
STRENGTH OF THE TRADE WINDS...AND WHETHER OR NOR LEEWARD SEA BREEZES
WILL BECOME STRONG ENOUGH TO LEAD TO CLOUD AND SHOWER DEVELOPMENT
OVER LEEWARD AND INTERIOR AREAS...SIMILAR TO WHAT WE SAW ON KAUAI
AND OAHU TODAY. LATEST FORECAST GRIDS DO NOT INDICATE THAT THIS WILL
OCCUR...AND WILL MONITOR OVERNIGHT TRENDS AND MODEL GUIDANCE TO SEE
IF A CHANCE OF AFTERNOON LEEWARD SHOWERS SHOULD BE INCLUDED IN THE
FORECAST. NEEDLESS TO SAY...THE LEEWARD BIG ISLAND IS THE
EXCEPTION...WITH LEEWARD CLOUDS AND SHOWERS BE EXPECTED EVERY
AFTERNOON AND EVENING THROUGH THE FORECAST PERIOD.

&&

.AVIATION...
WINDWARD AND MOUNTAIN AREAS MAY EXPERIENCE ISOL MVFR CONDITIONS AS
WEAK TRADE WIND FLOW PUSHES A FEW SHRA ASHORE. THERE ARE NO AIRMETS
IN EFFECT.

&&

.MARINE...
ELEVATED SURF WILL CONTINUE ALONG S FACING SHORES THIS WEEK.
ALTHOUGH SURF IS CURRENTLY BELOW ADVISORY LEVELS...FORERUNNERS OF A
VERY LONG PERIOD S SWELL /20-25 SECONDS/ ARE EXPECTED TO BEGIN
ARRIVING OVERNIGHT...ALTHOUGH AT LOW HEIGHTS. AS THIS SWELL FILLS
IN...IT WILL PRODUCE SURF NEAR ADVISORY LEVELS ALONG S FACING
SHORES...LIKELY FROM EARLY WEDNESDAY INTO THURSDAY.

WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS
AT LEAST FOR THE NEXT SEVERAL DAYS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

BIRCHARD



Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office