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Hawaiian Islands Synoptic Discussion and Guidance

073
FXHW60 PHFO 061938
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
940 AM HST FRI MAY 6 2016

.SYNOPSIS...
A PERIOD OF UNSETTLED WEATHER IS EXPECTED AS A LATE SEASON COLD
FRONT MAKES IT WAY DOWN THE ISLAND CHAIN. THE FRONT IS EXPECTED TO
REACH KAUAI BY THIS EVENING...OAHU OVERNIGHT...MAUI COUNTY SATURDAY
MORNING...AND THE BIG ISLAND BY SATURDAY NIGHT. RAINFALL ASSOCIATED
WITH THE FRONT WILL FOCUS ALONG WINDWARD AND NORTH FACING SLOPES AND
COASTS...ALTHOUGH A PERIOD OF CLOUDINESS WILL AFFECT ALL AREAS AS IT
PASSES. LOCALLY BREEZY NORTHEAST TRADE WINDS WILL INCREASE AFTER THE
FRONT PASSES...AND ARE EXPECTED TO CONTINUE INTO NEXT WEEK. THE
TRADE WINDS ARE EXPECTED TO DELIVER BRIEF PASSING SHOWERS TO
WINDWARD AREAS OF THE SMALLER ISLANDS FROM SATURDAY INTO NEXT WEEK.
HOWEVER...MOISTURE ASSOCIATED WITH THE STALLED AND DISSIPATING FRONT
IS EXPECTED TO FUEL PERSISTENT CLOUDS AND SHOWERS ALONG WINDWARD BIG
ISLAND AND EAST MAUI INTO NEXT WEEK.

&&

.DISCUSSION...
IN SUMMARY...A FRONT WILL MOVE DOWN THE ISLAND CHAIN FROM TONIGHT
INTO SUNDAY...BRINGING A PERIOD OF SHOWERS...MOST OF WHICH WILL FALL
OVER WINDWARD AND N FACING SLOPES AND COASTS. THE ASSOCIATED
MOISTURE IS THEN EXPECTED TO LINGER NEAR WINDWARD BIG ISLAND AND
EAST MAUI INTO EARLY NEXT WEEK. LIGHT WINDS TODAY WILL INCREASE AND
SHIFT TO THE NE TONIGHT AND SATURDAY OVER MOST AREAS EXCEPT THE BIG
ISLAND...WHERE THE BUILDING TRADE WINDS WILL MOST LIKELY NOT BE FELT
UNTIL SATURDAY NIGHT/SUNDAY.

CURRENTLY...LARGE-SCALE SURFACE ANALYSIS FEATURES A RIDGE EXTENDING
TOWARD THE BIG ISLAND FROM A SURFACE HIGH CENTERED FAR TO THE NE OF
THE ISLANDS...AND A FRONTAL BOUNDARY LOCATED ABOUT 125 MILES NW OF
KAUAI. AN AREA OF BROKEN TO OVERCAST SHOWERY LOW CLOUDS LIES BETWEEN
THE FRONT AND KAUAI...AND PREVAILS OVER WATERS OUT TO 400 MILES WSW
OF KAUAI. ANOTHER CLUSTER OF BROKEN TO OVERCAST SHOWERY LOW CLOUDS
IS CENTERED OVER MOLOKAI...AFFECTING MOST OF MAUI COUNTY AS WELL AS
THE NEAR SHORE WATERS SE OF OAHU. SE FLOW JUST S OF THE RIDGE AXIS
IS DELIVERING CLOUDS AND A FEW SHOWERS TO SE BIG ISLAND. MESOSCALE
ANALYSIS AND RADAR ANIMATIONS INDICATE A WEAK AND TINY BUBBLE HIGH
EXISTS JUST SW OF LANAI...AND THE WEAKLY CONVERGENT FLOW AROUND THIS
FEATURE IS LIKELY RESPONSIBLE FOR THE CLOUDS AND SHOWERS OVER MAUI
COUNTY. LATEST SOUNDINGS INDICATE A SUBSIDENCE INVERSION BASED
BETWEEN 7 AND 9 KFT...BUT THE INVERSION IS MUCH WEAKER AT LIHUE AS
COMPARED TO KAUAI.

DESPITE SUNNY SKIES THIS MORNING...CLOUDS AND SHOWERS WILL INCREASE
OVER KAUAI BY THIS AFTERNOON AS LOW LEVEL CONVERGENCE INCREASES
AHEAD OF THE APPROACHING FRONT. LIGHT WINDS OVER THE OTHER ISLANDS
ARE EXPECTED TO ALLOW SEA BREEZES TO DRIVE CLOUD AND SHOWER
DEVELOPMENT OVER ISLAND INTERIORS BY THIS AFTERNOON...AND THE
PASSAGE OF A WEAK TROUGH ALOFT MAY BE SUFFICIENT TO SUPPORT A FEW
LOCALLY HEAVY SHOWERS.

WINDS WILL SHIFT TO THE N AND THEN NE AS THE FRONT MOVES DOWN THE
ISLAND CHAIN...AND HIGH PRESSURE BUILDS TO THE NW OF THE ISLANDS.
CLOUDS AND SHOWERS ASSOCIATED WITH THE FRONT WILL THEREFORE FOCUS
ALONG N AND NE FACING SLOPES AND COASTS...BUT MOISTURE WILL BE
SUFFICIENTLY DEEP TO BRING CLOUDS AND A FEW SHOWERS TO LEEWARD AREAS
AS WELL. THE BULK OF THE SHOWERS ARE EXPECTED ON KAUAI THIS
AFTERNOON AND EVENING ON KAUAI...AND OVERNIGHT TONIGHT ON OAHU. THE
MOISTURE IS EXPECTED TO ARRIVE IN MAUI COUNTY LATE TONIGHT AND
SATURDAY...AND THE BIG ISLAND BY SATURDAY NIGHT. UNLIKE THE SMALLER
ISLANDS...WHERE SOME CLEARING IS EXPECTED IN FAIRLY SHORT ORDER
AFTER THE FRONT PASSES...WINDWARD MAUI AND BIG ISLAND ARE EXPECTED
TO REMAIN CLOUDY AND WET WELL INTO NEXT WEEK AS THE FRONT STALLS AND
DISSIPATES...LEAVING BEHIND AN AREA OF INCREASED MOISTURE THAT WILL
BE FORCED OVER THE WINDWARD SLOPES. IN ADDITION...A MID-LEVEL TROUGH
MOVING OVER THE AREA FROM LATE MONDAY INTO WEDNESDAY WILL LIKELY
ENHANCE THIS LINGERING MOISTURE. AFTER THE MOISTURE MOVES S OF THE
BIG ISLAND AFTER MID-WEEK...WINDWARD MAUI AND BIG ISLAND WILL JOIN
THE REMAINDER OF THE STATE IN A FAIRLY TYPICAL TRADE WIND WEATHER
PATTERN.

&&

.AVIATION...
A FRONT NORTHWEST OF KAUAI WILL CONTINUE TO ADVANCE TOWARDS THE
STATE...REACHING KAUAI LATER THIS AFTERNOON AND OAHU LATE TONIGHT. A
CONVERGENCE BAND AHEAD OF THE FRONT IS PRODUCING SCATTERED SHOWERS
OVER MAUI COUNTY...HOWEVER MOST CIGS/VIS REMAIN VFR. EXPECT THIS
BAND TO LINGER OVER AND NEAR THE EASTERN PORTION OF THE STATE
THROUGHOUT THE DAY. LIGHT SOUTHEAST FLOW WILL ALLOW FOR SEA BREEZES
TO DEVELOP TODAY...HELPING TO SUPPORT INTERIOR CLOUDS AND SHOWERS
THIS AFTERNOON. SOME SHOWERS MAY BE POTENTIALLY HEAVY AT TIMES AND
CARRY PASSING PERIODS OF MVFR TO ISOLATED IFR.

THERE ARE NO AIRMETS IN EFFECT AS OF 2000Z. AIRMET SIERRA FOR
MOUNTAIN OBSC WILL BE ISSUED AS NEEDED. ADDITIONALLY...EDDIES...
MOSTLY NEAR MAUI...MAY INTRODUCE INTERMITTENT LIGHT TURBULENCE.

&&

.MARINE...
A SMALL WNW SWELL WILL GRADUALLY DIMINISH TODAY...WITH A NEW
RELATIVELY SHORT-PERIOD NNW SWELL BUILDING TONIGHT AND SATURDAY.
THIS SWELL WILL PERSIST INTO NEXT WEEK AS IT SHIFTS TO THE N...WITH
A PERSISTENT BUT WEAK LOW TO THE DISTANT NNE MAINTAINING SOME
SEMBLANCE OF N SWELL THROUGH MID-WEEK. PEAK SURF HEIGHTS ALONG N
FACING SHORES ARE EXPECTED TO REMAIN BELOW ADVISORY LEVELS. A S
SWELL IS EXPECTED TO BUILD OVER THE NEXT 24 HOURS OR SO...PEAKING
THIS WEEKEND NEAR ADVISORY LEVELS ALONG S FACING SHORES. LATEST BUOY
OBSERVATIONS SHOW A MIX OF SWELLS...WITH LINGERING LOWER-PERIOD WNW
SWELL AND LONG PERIOD ENERGY OF MUCH LOWER MAGNITUDE ARRIVING FROM
THE S. LATEST SURF CAM OBSERVATIONS INDICATE INCONSISTENT SMALL SURF
ALONG S FACING SHORES OF OAHU.

HIGH PRESSURE BUILDING TO THE DISTANT NW OF THE ISLANDS OVER THE
NEXT 24 HOURS WILL PUSH A FRONT DOWN THE ISLAND CHAIN...WHILE ALSO
BRINGING INCREASING NNE WINDS. WINDS MAY GET STRONG ENOUGH TO
SUPPORT THE ISSUANCE OF A SMALL CRAFT ADVISORY /SCA/ THIS WEEKEND
WHERE WINDS ARE MOST ACCELERATED BY ISLAND TERRAIN. THE INITIAL AREA
OF CONCERN WOULD BE LEEWARD KAUAI WATERS TONIGHT AND SATURDAY...WITH
WINDS INCREASING FROM NW TO SE ACROSS THE CHAIN FROM TONIGHT THROUGH
SATURDAY NIGHT.

&&

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

&&

$$

DISCUSSION/MARINE...BIRCHARD
AVIATION...EATON

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



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