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Hawaiian Islands Synoptic Discussion and Guidance

548
FXHW60 PHFO 210601
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST WED AUG 20 2014

.SYNOPSIS...
TRADE WINDS WILL CONTINUE WITH MINOR CHANGES IN SPEED THROUGH THE
WEEKEND. A BATCH OF SHOWERS MOVING IN FROM THE EAST WILL DAMPEN
MAUI AND HAWAII COUNTIES TONIGHT...AND THE REST OF THE STATE FROM
THURSDAY INTO FRIDAY. GENERALLY LIGHTER SHOWERS THEN WILL PREVAIL
OVER LEE SLOPES OF THE BIG ISLAND EACH AFTERNOON...AND WINDWARD
SLOPES ACROSS THE STATE ALL DAY.

&&

.DISCUSSION...
A MASS OF NIMBOSTRATUS WITH EMBEDDED TOWERING CUMULI APPROACHED THE
STATE FROM THE EAST. THIS FEATURE LIKELY CONSISTED OF MOISTURE DRAWN
UP FROM THE DEEP TROPICS BY THE DISTURBANCES NEAR 140W EARLIER IN
THE WEEK. GUIDANCE REALLY EMPHASIZED THE DEVELOPMENT OF THIS SHOWER
CLUSTER EARLY ON...BUT MORE RECENT SOLUTIONS GENERALLY HAVE
DOWNPLAYED ITS SIGNIFICANCE. IN ANY CASE...THIS FEATURE LIKELY WILL
ENHANCE SHOWER ACTIVITY OVER WINDWARD SLOPES OF MAUI AND HAWAII
COUNTIES TONIGHT INTO THURSDAY. EFFECTS ON KAUAI COUNTY...OAHU...AND
LEE SLOPES OF THE BIG ISLAND WILL BE LESS...BUT THE PROBLEM OF THE
NIGHT MAY WELL CONSIST OF DETERMINING JUST HOW MUCH ENHANCEMENT WILL
OCCUR OVER THESE MARGINAL AREAS.

OTHERWISE...GUIDANCE PREDICTED THE SUBTROPICAL RIDGE TO THE NORTH TO
REMAIN IN PLACE THROUGH THE FORECAST PERIOD...KEEPING THE TRADE
WINDS BLOWING OVER THE ISLANDS. RIDGING ALOFT WILL VARY IN STRENGTH
ALMOST RANDOMLY WITH TIME...AND THE SUBTROPICAL RIDGE WILL REACT
ACCORDINGLY...BUT THE OSCILLATIONS SHOULD REMAIN CLOSE TO
CLIMATOLOGY.

SIMILARLY...AFTER THE PATCH OF ENHANCED SHOWERS MOVES WEST OF THE
STATE...PRECIPITATION WILL FOCUS OVER SLOPES WHERE OROGRAPHIC
FORCING IS STRONGEST. CHANGES FROM DAY TO DAY WILL AFFECT MAINLY THE
AMOUNT OF ACCUMULATION...AND LIKELY WILL BE SMALLER IN AMPLITUDE
THAN THE MODELS SUGGEST. A BLEND OF MODEL OUTPUT PREDICTED THAT
PRECIPITABLE WATER WILL PEAK FROM SUNDAY INTO MONDAY...AND SHOWER
ACTIVITY PROBABLY SHOULD FOLLOW THIS TREND AS WELL.

&&

.AVIATION...
AN AREA OF ENHANCED TROPICAL MOISTURE MOVING ACROSS THE EASTERN
PARTS OF THE STATE WILL PRODUCE INCREASED SHOWERS AND CLOUDS
TONIGHT INTO THURSDAY. AIRMET SIERRA HAS BEEN ISSUED FOR THE
WINDWARD SECTIONS OF THE BIG ISLAND AND MAUI...WHERE MOUNTAIN
OBSCURATION AND PERIODS OF MVFR CONDITIONS ARE LIKELY. PHTO
TERMINAL WILL ALSO SEE LONG PERIODS OF MVFR THROUGH THE NIGHT AND
THURSDAY MORNING...WITH BRIEF IFR POSSIBLE. FURTHER WEST...PASSING
SHOWERS AND ISOLATED MVFR CONDITIONS WILL BE POSSIBLE ON THE
WINDWARD SLOPES OF OAHU AND KAUAI.

VFR CONDITIONS WILL PREVAIL ELSEWHERE...INCLUDING THE REMAINING
TERMINALS.

&&

.MARINE...
WINDS LIKELY WILL PERSIST JUST BELOW THE THRESHOLD FOR A SMALL CRAFT
ADVISORY THROUGH THE REST OF THE WEEK.

A NEW SSW SWELL BUILDING TONIGHT AND THURSDAY IS EXPECTED TO
CONTINUE THROUGH FRIDAY...PRODUCING SURF JUST UNDER THE THRESHOLD
FOR A HIGH SURF ADVISORY. A SERIES OF SOUTH SWELLS WILL CONTINUE
THROUGH EARLY NEXT WEEK...BUT SHOULD REMAIN BELOW ADVISORY LEVELS.
SHORT-PERIOD TRADE-WIND SWELL WILL CONTINUE ALONG EAST-FACING
SHORES. NO SIGNIFICANT NORTHWEST SWELL IS EXPECTED THROUGH THE
WEEKEND.

&&

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

&&

$$

DISCUSSION/MARINE...RYSHKO
AVIATION...JACOBSON



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