Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 291331
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST FRI AUG 29 2014

.SYNOPSIS...
THE TRADE WINDS WILL WEAKEN FURTHER...BECOMING LIGHT BY EARLY NEXT
WEEK. A TROUGH MOVING OVER THE SOUTHEAST HALF OF THE STATE MAY
INCREASE CLOUDS AND SHOWERS THROUGH ABOUT NOON TODAY. OVER THE
WEEKEND...SEA BREEZES WILL ENCOURAGE CLOUD BUILDUPS AND A FEW
SHOWERS IN ISLAND INTERIORS BY DAY...WHILE LAND BREEZES BRING
CLEARING AT NIGHT. THE TRADE WINDS MAY START TO RETURN BY THE MIDDLE
OF NEXT WEEK...THOUGH THEY WILL REMAIN ON THE LIGHT SIDE OF AVERAGE
FOR SOME TIME.

&&

.DISCUSSION...
SURFACE OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS REPORTED VERY
LIGHT TRADE WINDS. PRECIPITATION ACROSS THE STATE REMAINED SPARSE...
WITH INDIVIDUAL TOTALS ALSO DIMINISHING THROUGH THE NIGHT. SINCE THE
INVERSION STAYED HIGH...AND PRECIPITABLE WATER ADEQUATE...THESE DRY
CONDITIONS PROBABLY WERE SUPPORTED AT LEAST IN PART BY LAND BREEZES.

ALTHOUGH A MID-LEVEL RIDGE PREVAILED TO THE SOUTHEAST OF THE
ISLANDS...A BROAD TROUGH WAS PRESENT TO THE NORTHWEST THROUGH
NORTHEAST. MOST LIKELY IT WAS THIS FEATURE THAT ENCOURAGED ACTIVE
TOWERING CUMULI TO DEVELOP NEAR 30N.

SATELLITE ESTIMATES SHOWED A PLUME OF MOISTER AIR APPROACHING MAUI
COUNTY FROM THE EAST...AND THE CLOUD FEATURE ASSOCIATED WITH THIS
PLUME DEVELOPED CONSIDERABLY DURING THE PAST FEW HOURS. IN-STATION
ANALYSIS SUGGESTED THAT THIS FEATURE REMAINED A TROUGH RATHER THAN
A CLOSED LOW...AT LEAST NEAR THE SURFACE...BUT IN ANY CASE IT MAY
ENHANCE RAINFALL LATER TODAY AS IT MOVES ASHORE OVER MAUI AND HAWAII
COUNTIES. POPS AND ASSOCIATED FIELDS HAVE BEEN INCREASED ACCORDINGLY.

GUIDANCE PREDICTED ADDITIONAL MOISTURE SURGES TO REACH THE STATE
PERIODICALLY INTO NEXT WEEK...THOUGH WITH TIME THE DIFFERENT
SOLUTIONS ENDED UP FOLLOWING DIFFERENT PERIODS...COMPLICATING A
DETERMINISTIC FORECAST. WITH TRADE WINDS VERY WEAK BY MONDAY...
DIURNAL SHOWERS PRODUCED BY SEA BREEZES MAY DOMINATE WEATHER FROM
DAY TO DAY...WITH THE MOISTURE SURGES ONLY AMPLIFYING THE MAGNITUDE
OF THE DAILY EVENT.

IN ANY CASE...RIDGING ALOFT WILL EXPAND OVER THE ISLANDS FROM THE
SOUTHEAST DURING THE WEEKEND...SO BY NEXT WEEK SUBSIDENCE WILL START
TO CRUSH DOWN THE INVERSION. HOWEVER...A FRONT NORTH OF 30N WILL
KEEP THE SURFACE RIDGE ANCHORED NEAR THE ISLANDS WELL INTO NEXT
WEEK...SO THE TRADE WINDS WILL RECOVER ONLY VERY SLOWLY.

&&

.MARINE...
EASTERLY SWELL IS STILL FORECAST TO BUILD OVER THE HAWAIIAN COASTAL
WATERS TODAY...AND ADVISORY-LEVEL SURF ALSO WILL AFFECT SOUTH-FACING
SHORES. INTERACTION BETWEEN THE LONG-PERIOD EAST AND SOUTH SWELLS
MAY PRODUCE STRONG CURRENTS IN SOME AREAS. THE SURF FROM BOTH SWELLS
WILL DECLINE SLOWLY THROUGH THE WEEKEND.

WITH TRADE WIND SPEEDS MORE LIKELY TO DIMINISH THAN TO INCREASE
THROUGH THE FIRST HALF OF THE FORECAST PERIOD...IT IS DOUBTFUL THAT
THEY WILL APPROACH THE CRITERION FOR A SMALL CRAFT ADVISORY.
HOWEVER...THE LONG-PERIOD EASTERLY AND SOUTHERLY SWELL COULD PRODUCE
LOCALLY LARGE AND CONFUSED SEAS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST SATURDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-OAHU SOUTH SHORE-WAIANAE COAST-OAHU
KOOLAU-OLOMANA-MOLOKAI-LANAI MAKAI-KAHOOLAWE-MAUI WINDWARD WEST-
MAUI LEEWARD WEST-MAUI CENTRAL VALLEY-WINDWARD HALEAKALA-LEEWARD
HALEAKALA-KONA-SOUTH BIG ISLAND-BIG ISLAND NORTH AND EAST.

&&

$$

RYSHKO





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