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Hawaiian Islands Synoptic Discussion and Guidance

570
FXHW60 PHFO 281335
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST SAT MAR 28 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 NORTHEAST OF THE ISLANDS...AND AN ASSOCIATED
RIDGE ABOUT 500 MILES NORTH OF MAUI. A RIDGE ALOFT KEEPS OUR AIRMASS
STABLE...AND A MOSTLY DRY TRADE WIND WEATHER PATTERN IS IN PLACE
OVER THE ISLANDS. VERY LITTLE RAINFALL HAS BEEN OBSERVED
OVERNIGHT...BUT SATELLITE LOOP AND RADAR SHOWS AN AREA OF BROKEN LOW
CLOUDS MOVING INTO MAUI AND THE BIG ISLAND WITHIN EASTERLY TRADE
FLOW THIS MORNING. WE EXPECT A SLIGHT MOISTENING OF TRADE FLOW THIS
MORNING 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 TODAY.
AIRMET TANGO IS IN EFFECT FOR MODERATE TURBULENCE BELOW 6000 FEET
IMMEDIATELY SOUTH THROUGH WEST OF THE ISLANDS...BUT MAY BE
DISCONTINUED LATER THIS MORNING AS TRADE WINDS DECREASE. AIRMET
SIERRA FOR MOUNTAIN OBSCURATION MAY BE NEEDED LATER AS LOW CLOUDS
MOVE INTO MAUI AND THE BIG ISLAND.

&&

.MARINE...
WINDS AROUND THE BIG ISLAND HAVE DECREASED BELOW SMALL CRAFT
ADVISORY THRESHOLD...PROMPTING US TO CANCEL THE ADVISORY. 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 TODAY...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...
NONE.

&&

$$

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







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