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Hawaiian Islands Synoptic Discussion and Guidance

302
FXHW60 PHFO 271958
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM 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.

&&

.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 SOMEWHAT STABLE...AS THE ISLANDS LIE WITHIN A
TRANSITION ZONE BETWEEN MID TO UPPER LEVEL RIDGING TO THE SOUTH AND
AND TROUGHING TO THE NORTH...BUT THE SOUNDINGS REVEAL PRECIPITABLE
WATER VALUES RUNNING ABOUT 15 TO 20 PERCENT ABOVE NORMAL. AS A
RESULT...WE CANNOT RULE OUT A BRIEF HEAVY SHOWER OVER LEEWARD AREAS
THIS AFTERNOON. LEEWARD SHOWER ACTIVITY WILL RAPIDLY DIMINISH LATE
IN THE AFTERNOON...ALLOWING RAINFALL TO BECOME FOCUSED OVER TYPICAL
WINDWARD SLOPES OVERNIGHT. IN ADDITION...AN INCREASE IN HIGH CLOUDS
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.
THE NEXT INCREASE IN MOISTURE COULD OCCUR NEXT WEEKEND...BUT
UNCERTAINTY REMAINS HIGH AT THIS TIME.

&&

.AVIATION...
A HIGH PRESSURE RIDGE SITTING FAR TO THE NORTH WILL CONTINUE TO
YIELD LIGHT TO MODERATE TRADE WINDS ACROSS THE STATE THROUGH
TUESDAY. DAYTIME HEATING WILL ALLOW SEA BREEZES TO KICK IN AT TIMES
DUE TO THE LIGHT WIND REGIME. BUT DO NOT EXPECT LAND BREEZES AT
NIGHT TO BE AS SIGNIFICANT AS THE DAYTIME SEA BREEZES WITH LIGHT
TRADES PREVAILING IN MOST AREAS AT NIGHT.

THUS EXPECT SOME CLOUDS AND POSSIBLE SHOWERS TO BUILD PRIMARILY
ACROSS THE INTERIOR AND LEEWARD SECTIONS WITH SOME MVFR CIGS
OCCURING. OTHERWISE...VFR CONDITIONS ARE EXPECTED TO PREVAIL.

NO AIRMETS ARE CURRENTLY IN EFFECT.

&&

.MARINE...
A HIGH SURF ADVISORY REMAINS POSTED FOR SOUTH FACING SHORES THROUGH
TONIGHT. BUOYS 51002 AND 51003 SHOWED A MODEST PULSE OF RENEWED
SWELL ENERGY IN THE 15 TO 16 SECOND RANGE DURING THE OVERNIGHT
HOURS. THIS SHOULD MAINTAIN SURF AT CURRENT LEVELS...WELL ABOVE THE
HIGH SURF ADVISORY THRESHOLD OF 8 FT...AND CONTINUE THE THREAT FOR
SOME BREAKING WAVE AT HARBOR ENTRANCES THROUGH THE DAY. THE SWELL
WILL BEGIN A GRADUAL DECLINE TONIGHT...AND ALTHOUGH THE ADVISORY IS
CURRENTLY SET TO END BY TUESDAY MORNING...CONDITIONS SHOULD REMAIN
BORDER LINE FOR TUESDAY. 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



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