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Hawaiian Islands Synoptic Discussion and Guidance

710
FXHW60 PHFO 280630
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST FRI MAR 27 2015

.SYNOPSIS...
MODERATE TO LOCALLY FRESH TRADE WINDS WILL CONTINUE OVER THE WEEKEND
AND EARLY NEXT WEEK...BEFORE DIMINISHING TUESDAY. MOSTLY DRY WEATHER
WILL CONTINUE FOR MOST OF THE WEEKEND...WITH A SLIGHT INCREASE IN
WINDWARD SHOWERS EXPECTED LATE SUNDAY AND MONDAY...ESPECIALLY ON
KAUAI AND OAHU. A DISTURBANCE PASSING NORTH OF THE ISLANDS ON
TUESDAY WILL WEAKEN THE TRADE WINDS...AND MAY BRIEFLY LEAD TO
INCREASED WINDWARD SHOWERS. THE DISTURBANCE WILL MOVE EAST OF THE
AREA ON WEDNESDAY AND THURSDAY...WITH TYPICAL TRADE WIND WEATHER
EXPECTED THROUGH THE END OF NEXT WEEK.

&&

.DISCUSSION...
MODERATE TO LOCALLY FRESH TRADE WINDS ARE BEING SUPPLIED BY A 1031
MB SURFACE HIGH FAR NE OF THE ISLANDS...AND AN ASSOCIATED RIDGE
ABOUT 500 MILES N OF MAUI. A RIDGE ALOFT KEEPS OUR AIRMASS
STABLE...AND A MOSTLY DRY TRADE WIND WEATHER PATTERN IS IN PLACE
OVER THE ISLANDS. LATEST SOUNDINGS SHOW A STRONG SUBSIDENCE
INVERSION AND PW VALUES NEAR 0.8 INCHES. AS A RESULT VERY LITTLE
RAINFALL HAS BEEN OBSERVED TODAY. WE EXPECT A SLIGHT MOISTENING OF
TRADE FLOW OVERNIGHT TO ALLOW FOR A FEW WINDWARD SHOWERS...BUT THEY
ARE EXPECTED TO BE BRIEF AND LIGHT.

A MOSTLY DRY TRADE WIND WEATHER PATTERN IS EXPECTED THROUGH MOST OF
THE WEEKEND AS A MID LEVEL RIDGE REMAINS OVERHEAD. TRADE WINDS WILL
GRADUALLY DIMINISH AS THE SURFACE RIDGE NORTH OF THE ISLANDS
RETREATS EASTWARD. A NEW HIGH BUILDING NORTHWEST OF THE AREA ON
SUNDAY WILL PUSH REMNANT FRONTAL MOISTURE TOWARD THE ISLANDS FROM
THE NORTH ON SUNDAY AND MONDAY. ALTHOUGH THIS MOISTURE IS NOT
EXPECTED TO MAKE IT AS FAR SOUTH AS THE ISLANDS...WEAKLY CONVERGENT
LOW LEVEL FLOW WILL LEAD TO INCREASED TRADE WIND SHOWERS...MAINLY
OVER KAUAI AND OAHU...FROM LATE SUNDAY INTO MONDAY. THE ATMOSPHERE
WILL CONTINUE TO BE RELATIVELY STABLE SO THESE SHOWERS ARE NOT
EXPECTED TO BE HEAVY.

THE TRADE WIND FLOW COULD BE DISRUPTED AROUND TUESDAY AS A MID-LEVEL
TROUGH PASSES NORTH OF THE ISLANDS AND INDUCES THE FORMATION OF A
SURFACE TROUGH NEAR THE ISLANDS. HOWEVER...MODELS DISAGREE ON THE
STRENGTH OF THE TROUGH. EITHER WAY...TRADES COULD BE LIGHT ENOUGH ON
TUESDAY FOR SEA BREEZES TO DRIVE AFTERNOON LEEWARD CLOUD
FORMATION.

&&

.AVIATION...
PREDOMINANTLY VFR CONDITIONS ARE EXPECTED AT ALL TERMINALS
OVERNIGHT. AIRMET TANGO IS IN EFFECT FOR MODERATE TURBULENCE BELOW
6000 FEET IMMEDIATELY SOUTH THROUGH WEST OF THE ISLANDS.

&&

.MARINE...
LATEST MODELS SHOW THAT WINDS NEAR 25 KT WILL CONTINUE OVER WATERS
NORTH AND SOUTH OF THE BIG ISLAND OVERNIGHT...WHERE A SMALL CRAFT
ADVISORY IS IN EFFECT THROUGH 6 AM SATURDAY. TRADE WINDS ARE STILL
EXPECTED TO GRADUALLY EASE THROUGH SATURDAY...AND WHILE A SLIGHT
INCREASE IN WIND SPEEDS IS EXPECTED SUNDAY AND MONDAY...WE EXPECT
WINDS WILL REMAIN BELOW SMALL CRAFT ADVISORY SPEEDS BEFORE WINDS
DIMINISH AGAIN SOMEWHAT TUESDAY.

LINGERING SOUTH SOUTHWEST AND NORTH NORTHWEST SWELLS WILL GRADUALLY
FADE AWAY THROUGH SATURDAY...AND A SMALL LONG-PERIOD SOUTH SOUTHEAST
SWELL WILL BUILD. A LONG-PERIOD NORTHWEST SWELL WILL BUILD AND PEAK
ON SUNDAY...WITH PEAK SURF HEIGHTS NEARING ADVISORY LEVELS ALONG
EXPOSED NORTH AND WEST SHORES. THIS SWELL WILL GRADUALLY DIMINISH IN
HEIGHT AND PERIOD THROUGH TUESDAY. AT ITS PEAK...THIS SWELL WILL
BRING COMBINED SEAS CLOSE TO THE 10 FT THRESHOLD FOR SMALL CRAFT
ADVISORY ISSUANCE. SWELLS ARRIVING FROM THE SOUTH WILL BE RELATIVELY
LOW IN MAGNITUDE...BUT SUFFICIENTLY LARGE TO KEEP SOME SURF ALONG
SOUTH FACING SHORES THROUGH THE PERIOD...WITH THE STRONGEST SOURCE
BEING A SOUTH SOUTHEAST SWELL THAT IS CURRENTLY ON THE RISE.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 AM HST SATURDAY FOR ALENUIHAHA
CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.

&&

$$

DISCUSSION/MARINE...POWELL
AVIATION...DONALDSON






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