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Hawaiian Islands Synoptic Discussion and Guidance

697
FXHW60 PHFO 240128
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST SAT MAY 23 2015

.SYNOPSIS...A WEAK FRONT CURRENTLY NEAR THE BIG ISLAND WILL FOCUS
SHOWERS ACROSS WINDWARD BIG ISLAND BEFORE PUSHING SOUTH OF THE STATE
ON SUNDAY. COOL AND RATHER DRY NORTHEASTERLY WINDS IN PLACE OVER
THE WESTERN HALF OF THE STATE WILL GRADUALLY FILL IN OVER THE ENTIRE
ISLAND CHAIN ON SUNDAY AND PERSIST THROUGH THE HOLIDAY WEEKEND...
CONFINING LIGHT SHOWERS TO NORTHEAST FACING SLOPES. LIGHTER WINDS
ARE EXPECTED DURING THE NEW WORK WEEK.

&&

.DISCUSSION...
A RARE LATE MAY FRONT NEAR THE BIG ISLAND WILL MOVE SOUTH TONIGHT...
WITH AN ATYPICAL LATE MAY WEATHER PATTERN EXPECTED THROUGH MUCH OF
THE UPCOMING WEEK.

THE FRONT IS CURRENTLY LOCATED OVER THE BIG ISLAND AND CONTINUES TO
DRIFT SOUTHWARD AT LESS THAN 10 MPH. RAINFALL HAS BEEN UNIMPRESSIVE
ACROSS WINDWARD BIG ISLAND SO FAR...GENERALLY LESS THAN ONE HALF OF
AN INCH...WHILE THE KONA SLOPES HAVE NOT RECEIVED MUCH ENHANCEMENT
FROM THE FRONTAL MOISTURE. EXPECT CONTINUED MODEST SHOWERS ACROSS
WINDWARD SLOPES TONIGHT WITH THE DISSIPATING FRONT STALLING JUST
SOUTH OF THE BIG ISLAND ON SUNDAY.

A COOL AND RATHER DRY NORTHEASTERLY IN PLACE ACROSS THE WESTERN HALF
OF THE STATE WILL FILL IN ACROSS ALL OF THE SMALLER ISLANDS TONIGHT.
DEW POINTS FROM KAUAI TO MOLOKAI ARE HOVERING IN THE UPPER 50/S TO
LOW 60/S...QUITE DRY BY LATE MAY STANDARDS. MODELS ARE HINTING AT A
SLIGHT INCREASE IN LOW LEVEL MOISTURE WITHIN THE NORTHEAST FLOW LATE
TONIGHT AND EARLY SUNDAY MORNING...BUT WE EXPECT MAINLY AN INCREASE
IN LOW CLOUDS AND ONLY MEAGER RAINFALL ALONG WINDWARD AND NORTHERN
SLOPES...WHILE LEEWARD AREAS REMAIN DRY. EXPECT SOMEWHAT COOL
CONDITIONS TONIGHT WITH OVERNIGHT LOW TEMPS RUNNING AROUND 3 TO 5
DEG F BELOW NORMAL.

THE LARGE SCALE PATTERN RESPONSIBLE FOR THIS UNUSUAL LATE MAY SET UP
CONSISTS OF A DEEP TROUGH TO THE NORTHEAST OF THE ISLANDS ALONG 150W
AND SURFACE HIGH PRESSURE DISPLACED SOUTHWEST OF ITS TYPICAL LATE
MAY POSITION TO NEAR 30N175W. THE ISLANDS LIE BETWEEN THESE FEATURES
WITHIN A RATHER DRY AND STABLE NORTHEAST FLOW BEHIND THE ABOVE
MENTIONED FRONT. ONCE THE FRONT PUSHES SOUTH OF THE BIG ISLAND...THE
ENTIRE ISLAND CHAIN WILL EXPERIENCE MODERATE AND RATHER DRY
NORTHEAST FLOW THROUGH THE REMAINDER OF THE HOLIDAY WEEKEND.
RAINFALL WILL REMAIN MODEST AND CONFINED TO NORTHEAST SLOPES AS WELL
AS THE KONA SLOPES EACH AFTERNOON.

MODELS HINT AT THE TROUGH SHIFTING WESTWARD TOWARD THE STATE LATE
TUESDAY OR WEDNESDAY. THIS SHOULD LEAD TO A DECREASE IN WINDS ALONG
WITH A CONVECTIVE LAND AND SEA BREEZE PATTERN. THE FORECAST
CURRENTLY CALLS FOR A LIGHT TRADE WIND PATTERN DURING THE SECOND
HALF OF THE WORK WEEK...BUT RECENT RUNS OF THE GFS AND ECMWF SUGGEST
TRADE WINDS COULD BECOME DISRUPTED AS A TROUGH FORMS TO THE
NORTHEAST OF THE ISLANDS.

&&

.AVIATION...
THE DISSIPATING FRONT IS NOW JUST NE OF THE BIG ISLAND. EXPECT N
THRU E SLOPES OF THE BIG ISLAND TO SEE ENHANCEMENT IN CLOUDS AND
SHOWERS AS THE FRONT...OR WHAT IS LEFT OF THE FRONT...PUSHES S INTO
SUNDAY. PERIODS OF MVFR AND POSSIBLE ISOL IFR WILL LIKELY BE ALONG
THESE SLOPES OVERNIGHT...INCLUDING PHTO. AIRMETS FOR MOUNTAIN OBSC
WILL BE ISSUED AS NEEDED. THE BROKEN TO OVERCAST CLOUDS ALONG
LEEWARD AREAS OF THE BIG ISLAND SHOULD SCATTER OUT WITH SUNSET AND
VFR WILL PREVAIL.

OVER THE SMALLER ISLANDS...MODERATE N TO NE WINDS WILL CONTINUE
THROUGH THE PERIOD...AND CLOUDS AND MINIMAL SHOWERS WILL FAVOR THE
N THRU E SECTIONS. VFR WILL PREVAIL.

&&

.MARINE...
MODERATE TO FRESH NORTHEASTERLY WINDS WILL PERSIST BEHIND A SLOWLY
SOUTHWARD MOVING FRONT CURRENTLY NEAR THE BIG ISLAND. A SMALL CRAFT
ADVISORY /SCA/ IS CURRENTLY POSTED FOR KAUAI LEEWARD WATERS...MAINLY
DUE TO ACCELERATION OF NORTHEAST WINDS WITHIN THE CHANNEL BETWEEN
KAUAI AND NIIHAU. THE BARKING SANDS OBSERVATION AND A RECENT ASCAT
PASS SUGGEST BORDER LINE CONDITIONS ARE IN PLACE...SO WE WILL LET
THE SCA CONTINUE THROUGH THE AFTERNOON. BORDER LINE CONDITIONS MAY
ALSO BE EXPERIENCED AROUND MAUI COUNTY AND THE BIG ISLAND AS THE
FRONT CONTINUES ITS PUSH TO THE SOUTH TONIGHT. EXPECT ALL WATERS TO
BE BELOW SCA CRITERIA TONIGHT THROUGH MUCH OF THE UPCOMING WEEK.

AN EXTENDED RUN OF SOUTH SWELL...GENERATED BY SEVERAL LOWS IN THE
DEEP SOUTH PACIFIC OVER THE LAST WEEK...WILL BRING SOMEWHAT ELEVATED
SURF TO SOUTH FACING SHORES THROUGH THE WEEK AND BEYOND. SURF
HEIGHTS ARE EXPECTED TO REMAIN BELOW ADVISORY LEVELS FOR THE BULK OF
THE TIME...BUT OVERLAPPING SWELLS FROM SUNDAY INTO TUESDAY COULD
BRING SURF TO NEAR ADVISORY-LEVELS ALONG EXPOSED SOUTH FACING
SHORES. A SMALL NNE SWELL IS EXPECTED TO ARRIVE ON SUNDAY AND LINGER
THROUGH MONDAY. OTHERWISE...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. SEE THE LATEST OAHU SURF
DISCUSSION /SRDHFO/ FOR MORE DETAILS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING FOR KAUAI LEEWARD
WATERS.

&&

$$

DISCUSSION/MARINE...WROE
AVIATION...EATON



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