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Hawaiian Islands Synoptic Discussion and Guidance

681
FXHW60 PHFO 310557
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST WED JUL 30 2014

.SYNOPSIS...
HIGH PRESSURE FAR NORTH OF THE STATE WILL KEEP TRADE WINDS BLOWING
THROUGH THE WEEKEND AND INTO NEXT WEEK. MOST SHOWERS WILL BE
LIGHT...AND LIMITED TO WINDWARD SLOPES...BUT A VERY MOIST AIR MASS
FROM THE DEEP TROPICS WILL BRING MORE WIDESPREAD RAIN TO THE BIG
ISLAND...AND POSSIBLY MAUI COUNTY...MAINLY FROM FRIDAY INTO SATURDAY.

&&

.DISCUSSION...
SURFACE OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS REPORTED LIGHT
TO MODERATE TRADE WINDS...THOUGH SPEEDS REMAINED HIGHER WHERE THE
FLOW ACCELERATED AROUND HEADLANDS AND BETWEEN ISLANDS. PRECIPITATION
WAS QUITE SPARSE IN AN UNSEASONABLY DRY AIR MASS UNDER A SOMEWHAT
LOW...IF WEAK...INVERSION. BROAD BUT SHALLOW TROUGHING PREVAILED
ALOFT TO THE NORTH OF THE STATE...WHILE A MID-LEVEL RIDGE GREW
TOWARD THE ISLANDS SLOWLY FROM THE EAST. BITS OF CIRRUS FOLLOWED A
JET STREAM OUT OF THE ITCZ...PASSING OVER THE STATE AT TIMES.

SOME MODELS STILL PREDICTED THE ACTIVE ITCZ TO SPOUT A DEEP PLUME OF
ENHANCED MOISTURE OVER SEVERAL ISLANDS FROM FRIDAY INTO THE
WEEKEND...BUT RECENT TRENDS SUGGESTED A SMALLER EFFECT ON THE STATE
THAN EXPECTED EARLIER. A FEW SOLUTIONS EVEN SUGGESTED THAT THE BULK
OF THE MOIST AIR MASS WOULD REMAIN SOUTH OF THE BIG ISLAND.
HOWEVER...CONSENSUS AND CONTINUITY STILL PREDICTED AN INCREASE IN
SHOWER ACTIVITY FROM FRIDAY INTO SATURDAY OVER THE BIG ISLAND AT
LEAST...AND THIS INCREASE IN PRECIPITATION EASILY COULD REACH MAUI
COUNTY AS WELL. GUIDANCE ALSO PREDICTED THE MID-LEVEL RIDGE TO
EXPAND OVER THE STATE FROM THE EAST DURING THIS TIME...SO SUBSIDENCE
WILL LIMIT CLOUD DEVELOPMENT TO SOME DEGREE...THOUGH PROBABLY NOT
ENOUGH TO COUNTERACT COMPLETELY THE INFLUENCE OF PLENTIFUL WATER
VAPOR.

TEMPERATURES ALOFT APPEARED TOO WARM TO SUPPORT DEEP CONVECTION...
SO FOR NOW IT WAS BEST TO LEAVE THUNDERSTORMS OUT OF THE OFFICIAL
FORECAST. HOWEVER...THE CHANCE FOR THUNDER REMAINED NON-TRIVIAL...
IF STILL QUITE LOW. LEE SLOPES OF THE BIG ISLAND...AND WATERS TO
EAST THROUGH SOUTH OF IT...WOULD BE THE MOST LIKELY CANDIDATES FOR
DEEP CONVECTION TO DEVELOP FROM FRIDAY NIGHT INTO SATURDAY.

THE SUBTROPICAL RIDGE SHOULD KEEP THE TRADE WINDS BLOWING THROUGH
THE FORECAST PERIOD...AND MAY SUPPORT SLIGHTLY INCREASED SPEEDS FROM
FRIDAY INTO SATURDAY AS WELL. BY LATE IN THE WEEKEND...SOLUTIONS
STARTED TO TREND TOWARD CLIMATOLOGY AGAIN. WIND SPEEDS SHOULD
DIMINISH SLIGHTLY...WHILE THE MOIST AIR MASS DEPARTS TOWARD THE
WEST...AND DRIER AIR ADVECTS IN FROM THE NORTHEAST.

&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL OVERNIGHT AND THURSDAY MORNING
THROUGHOUT THE HAWAIIAN ISLANDS. PASSING SHOWERS AND BRIEF MVFR
CONDITIONS WILL BE POSSIBLE...MAINLY ON WINDWARD SLOPES. INCREASING
TROPICAL MOISTURE IS FORECAST TO MOVE INTO THE BIG ISLAND THURSDAY
AFTERNOON...BRINGING THE POTENTIAL FOR MORE WIDESPREAD SHOWERS AND
MVFR CONDITIONS ALONG WITH AREAS OF MOUNTAIN OBSCURATION. TYPICAL
VFR TRADE WIND CONDITIONS SHOULD PREVAIL ACROSS THE SMALLER ISLANDS
THROUGH THURSDAY AFTERNOON.

DUE TO CONTINUED MODERATE TO LOCALLY BREEZY TRADE WINDS...AIRMET
TANGO FOR LOW LEVEL TURBULENCE IS IN EFFECT...COVERING THE AREAS
OVER AND IMMEDIATELY SOUTH THROUGH WEST OF THE HIGHER TERRAIN.

&&

.MARINE...
A SMALL CRAFT ADVISORY /SCA/ REMAINED IN EFFECT FOR TYPICALLY WINDY
WATERS AROUND MAUI COUNTY AND THE BIG ISLAND THROUGH FRIDAY. THE
ADVISORY LIKELY WILL BE EXTENDED SEVERAL TIMES INTO NEXT WEEK.

A SMALL TO MODERATELY LARGE SWELL FROM THE SOUTH-SOUTHWEST SHOULD
ARRIVE OVER THE WEEKEND. OTHERWISE...A SERIES OF SMALL SOUTH SWELLS
WILL KEEP ARRIVING THROUGH NEXT WEEK. PREVAILING TRADE WINDS WILL
CONTINUE TO PRODUCE SHORT-PERIOD...CHOPPY SURF ALONG EAST-FACING
SHORES.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST FRIDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.

&&

$$

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



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