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Hawaiian Islands Synoptic Discussion and Guidance

779
FXHW60 PHFO 220631
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
820 PM HST THU MAY 21 2015

.SYNOPSIS...
THE AFTERNOON CLOUDS WILL GIVE WAY TO FAIR SKIES OVERNIGHT.
THEN A DISSIPATING FRONT WILL MOVE DOWN THE ISLAND CHAIN BETWEEN
FRIDAY THROUGH SATURDAY...BRINGING WITH IT SOME SCATTERED SHOWERS.
IN THE WAKE OF THE FRONT...LIGHT TO MODERATE NORTHEAST WINDS WILL
SETTLE IN LINGERING INTO NEXT WEEK...AND RESUME A TRADE WIND REGIME
WITH SHOWERS FAVORING THE WINDWARD AND MOUNTAIN AREAS.



&&

.DISCUSSION...
A LIGHT NW WIND FLOW HAS SPREAD DOWN TO MOLOKAI FROM THE W THIS
EVENING AHEAD OF A DISSIPATING FRONT. THIS FLOW HAS EITHER THINNED
OR CHASED AWAY ANY AFTERNOON CLOUDS AND SHOWERS THAT FORMED ON KAUAI
OAHU AND MOLOKAI. THE FLOW PATTERN HAS ALSO PREVENTED ANY VOG FROM
REACHING ANY OF THE SMALLER ISLANDS. THIS NW FLOW WILL BECOME MORE
NORTHERLY AS THE NIGHT PROGRESSES WHERE IT MAY CARRY IN A STRAY
LIGHT SHOWER OR TWO ONTO THE WINDWARD AND MAUKA AREAS OF THESE
ISLANDS. LIGHT AND VARIABLE WINDS WILL CONTINUE OVERNIGHT OVER MAUI
AND LANAI AS THEY ARE NEAR A LOW LEVEL TROUGH. LIGHT WEST TO
NORTHWEST WINDS WILL EASE IN AHEAD OF THE FRONT FRIDAY. AS FOR THE
BIG ISLAND...LIGHT SOUTHERLY WINDS WILL PERSIST INTO FRIDAY.

AT 7 PM HST...THE FRONT IS 100 MILES NORTH NORTHWEST OF KAUAI. IT IS
FORECAST TO REACH KAUAI BY NOON FRIDAY FOLLOWED BY OAHU AT MID
AFTERNOON...THEN DRAG ACROSS MAUI COUNTY FRIDAY NIGHT...DISSIPATING
ALONG THE WAY. THE REMNANTS OF THE FRONT ARE EXPECTED TO REACH THE
BIG ISLAND SATURDAY WHERE IT WILL LINGER THROUGH THE WEEKEND WITH
THE WINDWARD SIDE GETTING THE BRUNT OF IT. THE FRONT WILL USHER IN
NOT ONLY A MODERATE NORTHEASTERLY WIND FLOW BUT A SLIGHTLY DRIER AIR
MASS MOSTLY FELT ON KAUAI AND OAHU.

NO UPPER LEVEL SUPPORT FOR THE FRONT AS THE UPPER TROUGH WILL BE
RUNNING OUT AHEAD OF IT. SO NO EXCESSIVE RAINFALL EXPECTED. THE
DEPTH OF THE MOISTURE ASSOCIATED WITH THE FRONT WILL BE CONFINED TO
NO HIGHER THAN 12K FEET.

THE LOW THAT HELPED TO PUSH THE FRONT DOWN THE CHAIN IS FORECAST TO
LINGER 900 MILES NE OF THE ISLANDS THROUGH AT LEAST THE MIDDLE OF
NEXT WEEK WHILE HIGH PRESSURE BUILDS NW OF THE ISLANDS. THIS
JUXTAPOSITION OF FEATURES WILL LEAD TO UNSEASONABLE N/NE WINDS FOR
THE BULK OF THE FORECAST PERIOD...ALTHOUGH SPEEDS WILL BE LIGHT TO
LOCALLY MODERATE. AS THE LOW MAKES A JOG TO THE S EARLY NEXT
WEEK...WINDS MAY BECOME LIGHT ENOUGH TO ALLOW LOCAL LAND/SEA BREEZES
TO DOMINATE THE ISLAND WEATHER PATTERN. OTHERWISE...SHALLOW BANDS OF
MOISTURE ROTATING AROUND THE LOW MAY FAVOR THE N AND E FACING
SLOPES...BUT THE ATMOSPHERE WILL REMAIN RELATIVELY STABLE THROUGH
THE PERIOD. THE LOW WILL EXIT TO THE NE BY THE SECOND HALF OF NEXT
THE WEEK ALLOWING THE RETURN OF LIGHT TO MODERATE TRADE WINDS.

&&

.AVIATION...
A WEAKENING COLD FRONT NW OF KAUAI WILL MOVE THROUGH KAUAI LATE
FRIDAY MORNING AND PUSH SOUTHWARD THROUGH OAHU FRIDAY AFTERNOON AND
INTO MAUI COUNTY FRIDAY NIGHT. CAN/T RULE OUT A FEW ISOLATED SHOWERS
ALONG AND IN ADVANCE OF THE COLD FRONT...BUT PREDOMINANTLY VFR
CONDITIONS ARE EXPECTED AT ALL TAF SITES THROUGH 23/06Z.

NO AIRMETS ARE IN EFFECT AND NONE ARE ANTICIPATED THROUGH THE NIGHT.

&&

.MARINE...
WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA FOR
ALL WATERS INTO NEXT WEEK. AN EXTENDED RUN OF S SWELL...GENERATED BY
SEVERAL LOWS IN THE DEEP S PACIFIC OVER THE LAST WEEK...WILL BRING
A SLIGHT RISE IN THE SURF FOR THE S FACING SHORES INTO THE MIDDLE OF
NEXT WEEK. SURF HEIGHTS ARE EXPECTED TO REMAIN BELOW ADVISORY LEVELS
FOR THE BULK OF THE TIME...BUT OVERLAPPING SWELLS SUNDAY/MONDAY
COULD BRING ADVISORY LEVEL SURF TO EXPOSED S FACING SHORES. A COUPLE
OF SMALL SWELLS FROM THE NNW AND WNW ARE EXPECTED OVER THE WEEKEND
AND EARLY NEXT WEEK...WITH RESULTANT SURF WELL BELOW ADVISORY LEVELS.

&&

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

&&

$$

DISCUSSION/MARINE...LAU
AVIATION...JELSEMA




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