Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 280133
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST MON JUL 27 2015

.SYNOPSIS...
EASTERLY TRADE WINDS WILL REMAIN IN THE GENTLE TO LOCALLY MODERATE
RANGE THROUGH TOMORROW...WEAK ENOUGH TO ALLOW AFTERNOON SEA BREEZES
TO SET UP ALONG MOST LEEWARD AREAS. SHOWERS WILL REMAIN FOCUSED
ACROSS WINDWARD AREAS...WITH SPOTTY AFTERNOON SHOWERS DEVELOPING
ACROSS LEEWARD AREAS. LOCALLY FRESH TRADE WINDS AND TYPICAL WINDWARD
AND MAUKA SHOWERS PATTERN WILL RETURN ON WEDNESDAY...WITH AN
INCREASE IN SHOWERS POSSIBLE DURING THE WEEKEND.

&&

.DISCUSSION...
EAST TO EAST-SOUTHEAST TRADE WINDS WILL REMAIN AT GENTLE TO LOCALLY
MODERATE STRENGTH THROUGH TUESDAY...WEAK ENOUGH FOR AFTERNOON SEA
BREEZES TO PRODUCE CLOUDS AND SPOTTY SHOWERS OVER MOST LEEWARD
AREAS. SURFACE HIGH PRESSURE WILL PERSIST ABOUT 1400 MILES NORTH OF
THE STATE...WHICH WOULD NORMALLY BE STRONG ENOUGH TO DRIVE LOCALLY
BREEZY TRADE WINDS LOCALLY. HOWEVER...A SERIES OF WEAK SURFACE
TROUGHS PASSING NORTH OF THE ISLANDS HAS BEEN WEAKENING THE TRADE
WINDS AND CAUSING THEM TO SHIFT OUT OF THE EAST TO EAST-SOUTHEAST.
THE RESULT HAS BEEN AFTERNOON SEA BREEZES OVER MOST LEEWARD
AREAS...PRODUCING CLOUDS AND SPOTTY SHOWERS. EXPECT A REPEAT THIS
AFTERNOON...AND POSSIBLY AGAIN ON TUESDAY AFTERNOON.

THE ATMOSPHERE IS SLIGHTLY UNSTABLE. THE ISLANDS LIE WITHIN A
TRANSITION ZONE BETWEEN MID TO UPPER LEVEL RIDGING TO THE SOUTH AND
AND TROUGHING TO THE NORTH...AND THE SOUNDINGS REVEAL NO INVERSION
AND PRECIPITABLE WATER VALUES RUNNING ABOUT 15 TO 25 PERCENT ABOVE
NORMAL. AS A RESULT...BRIEF ISOLATED HEAVY SHOWERS HAVE DEVELOPED ON
LEEWARD SECTIONS OF ALL ISLANDS THIS AFTERNOON AND MAY DEVELOP AGAIN
ON TUESDAY. LEEWARD SHOWER ACTIVITY WILL RAPIDLY DIMINISH BEFORE
SUN DOWN...ALLOWING RAINFALL TO BECOME FOCUSED OVER TYPICAL WINDWARD
SLOPES OVERNIGHT. IN ADDITION...AS THE UPPER TROUGH TO THE NORTH
DEEPENS SLIGHTLY TONIGHT...AN INCREASE IN HIGH CLOUDS AND A CHANCE
FOR A BRIEFLY HEAVY WINDWARD SHOWER IS POSSIBLE FOR THE WESTERN END
OF THE STATE TONIGHT.

TRADE WINDS WILL STRENGTHEN...AND A TYPICAL WINDWARD AND MAUKA
RAINFALL WILL BECOME ESTABLISHED BY WEDNESDAY. THE SURFACE TROUGHS
PASSING NORTH OF THE STATE WILL FINALLY MOVE OFF TO THE WEST...
ALLOWING THE PRESSURE GRADIENT TO TIGHTEN AND TRADES TO STRENGTHEN
OVER THE STATE. THE MID TO UPPER LEVEL RIDGE CURRENTLY TO THE SOUTH
WILL STRENGTHEN AND SETTLE OVER THE ISLANDS...BRINGING INCREASINGLY
STABLE CONDITIONS AND LIKELY LIMITING SHOWERS TO WINDWARD SLOPES.

UNCERTAINTY IS RATHER HIGH HEADED INTO THE WEEKEND. THE GFS AND
ECMWF ARE HINTING AT AN INCREASE IN MOISTURE ASSOCIATED WITH
TROPICAL DEPRESSION 08E MOVING OVER THE ISLANDS IN THE TRADE WIND
FLOW AS EARLY AS SATURDAY NIGHT. THE OFFICIAL FORECAST FROM THE
NATIONAL HURRICANE CENTER PLACES THE WEAKENING TROPICAL CYCLONE A
COUPLE HUNDRED MILES EAST-SOUTHEAST OF THE BIG ISLAND ON SATURDAY.
NOTE THAT TROPICAL CYCLONE FORECASTS THIS FAR OUT CONTAIN A HIGH
DEGREE OF UNCERTAINTY...SO THE FORECAST WAS BROADLY PAINTED WETTER
SUNDAY AND MONDAY.

&&

.AVIATION...
A HIGH PRESSURE RIDGE SITTING FAR TO THE NORTH WILL CONTINUE TO
YIELD LIGHT TO MODERATE TRADE WINDS ACROSS THE STATE THROUGH
TUESDAY. BOUTS OF SEA BREEZES DURING THE DAY MAY OVERRIDE THE TRADES
AT TIMES UNTIL THE TRADES STRENGTHEN LATER THIS WEEK.

MAINLY INTERIOR AND MOUNTAIN CLOUDINESS DURING THE AFTERNOONS WILL
RESULT FROM DAYTIME HEATING. AND SOME WINDWARD SECTIONS MAY
EXPERIENCE MVFR CONDITIONS AT TIMES FROM THE CLOUDS BROUGHT IN BY
THE TRADES. OTHERWISE...VFR CONDITIONS ARE EXPECTED TO PREVAIL OVER
MOST AREAS.

&&

.MARINE...
A HIGH SURF ADVISORY REMAINS POSTED FOR SOUTH FACING SHORES THROUGH
TONIGHT. BUOYS SOUTH OF THE ISLANDS ARE SHOWING A SLOW DECLINE IN
LONG PERIOD ENERGY...SIGNALING THAT THE SWELL IS ON A SLOW DECLINE.
ALTHOUGH THE ADVISORY IS CURRENTLY SET TO END TONIGHT...CONDITIONS
SHOULD REMAIN BORDER LINE THROUGH TUESDAY MORNING. THE SWELL WILL
SLOWLY SUBSIDE FOR SEVERAL DAYS...WITH NO OTHER SOURCES FOR
SIGNIFICANT SWELL DUE THIS WEEK.

WITH TRADE WINDS DUE TO BUILD ON WEDNESDAY...A SMALL CRAFT ADVISORY
/SCA/ FOR THE TYPICALLY WINDY WATERS AROUND THE BIG ISLAND AND MAUI
WILL LIKELY BE POSTED SOMETIME WEDNESDAY. ONCE UP...THE SCA SHOULD
REMAIN IN PLACE THROUGH THE WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST TUESDAY MORNING FOR SOUTH FACING
SHORES OF ALL HAWAIIAN ISLANDS.

&&

$$

DISCUSSION/MARINE...WROE
AVIATION...FUJII




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