Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 311330
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST THU JUL 31 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 MAINLY TO WINDWARD SLOPES. HOWEVER...A VERY
MOIST AIR MASS WILL BRING MORE WIDESPREAD RAIN TO THE BIG ISLAND AND
MAUI COUNTY FROM LATER TODAY INTO SATURDAY...AND POSSIBLY INCREASED
SHOWERS TO OAHU OR KAUAI AROUND FRIDAY NIGHT.

&&

.DISCUSSION...
SURFACE OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS STILL REPORTED
LIGHT TO MODERATE TRADE WINDS...AND SPEEDS REMAINED HIGHER WHERE THE
FLOW ACCELERATED AROUND HEADLANDS AND BETWEEN ISLANDS. PRECIPITATION
WAS QUITE SPARSE OVERNIGHT...BUT THE AIR MASS MOISTENED SLIGHTLY...
AND THE INVERSION ABOVE IT ROSE CONSIDERABLY OVER THE SOUTHEAST END
OF THE STATE. SHREDS OF CIRRUS FOLLOWED A JET STREAM OUT OF THE
ITCZ...PASSING OVER THE STATE AT TIMES. 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.

GUIDANCE MORE SOLIDLY AGREED IN PREDICTING THE ACTIVE ITCZ TO SPOUT
A DEEP PLUME OF ENHANCED MOISTURE OVER SEVERAL ISLANDS FROM LATE
TODAY INTO SATURDAY. THE MASS OF STRATUS LAYERS VISIBLE ON SATELLITE
IMAGES TO THE SOUTHEAST OF THE BIG ISLAND POSSIBLY REPRESENTED THE
LEADING EDGE OF THIS PLUME. AS THIS FEATURE MOVES NORTHWEST...SHOWER
ACTIVITY WILL INCREASE OVER THE BIG ISLAND...AND THEN MAUI COUNTY.
WHILE IT MAY NOT REACH OAHU OR KAUAI AT ALL...MORE LIKELY THESE
ISLANDS WILL RECEIVE SOME OF THE CLOUDS AND SHOWERS BY SATURDAY...
THOUGH TO A MUCH LESSER DEGREE THAN MAUI OR HAWAII COUNTIES.
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.

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 ACROSS THE STATE THROUGH THIS AFTERNOON.
PASSING SHOWERS AND BRIEF MVFR CONDITIONS WILL AFFECT MAINLY
WINDWARD SLOPES. INCREASING TROPICAL MOISTURE IS FORECAST TO MOVE
INTO THE BIG ISLAND LATER THIS AFTERNOON AND TONIGHT...BRINGING THE
POTENTIAL FOR MORE WIDESPREAD SHOWERS AND MVFR CONDITIONS ALONG WITH
AREAS OF MOUNTAIN OBSCURATION. AIRMET SIERRA MAY BE NEEDED FOR
PARTS OF THE BIG ISLAND AT THAT TIME. TYPICAL TRADE WIND CONDITIONS
SHOULD PREVAIL ACROSS THE SMALLER ISLANDS THROUGH TONIGHT...WITH
ISOLATED MVFR CONDITIONS REMAINING CONFINED PRIMARILY TO WINDWARD
SLOPES.

DUE TO CONTINUED MODERATE TO LOCALLY BREEZY TRADE WINDS...AIRMET
TANGO FOR LOW LEVEL TURBULENCE REMAINS 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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