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Hawaiian Islands Synoptic Discussion and Guidance

225
FXHW60 PHFO 290135
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST TUE JUL 28 2015

.SYNOPSIS...
WINDS WILL BECOME LOCALLY BREEZY ON WEDNESDAY AS A RATHER STABLE
RAINFALL PATTERN FOCUSES MODEST SHOWERS OVER WINDWARD SLOPES. TRADE
WINDS WILL PERSIST INTO THE WEEKEND...WHEN AN INCREASE IN TROPICAL
MOISTURE WILL LIKELY BRING ADDITIONAL SHOWERS TO PORTIONS OF THE
ISLAND CHAIN.

&&

.DISCUSSION...
MODERATE EAST TO EAST-SOUTHEAST WINDS GAVE WAY TO SEA BREEZES OVER
SHELTERED LEEWARD AREAS THIS AFTERNOON...BUT UNLIKE THE PAST FEW
DAYS...THERE HAS BEEN MINIMAL SHOWER ACTIVITY ON LEEWARD SLOPES.
THIS IS LIKELY DUE TO A DECREASE IN LOW LEVEL MOISTURE OBSERVED
DURING THE PAST DAY AND SOME STABILIZATION CAUSED BY MID TO UPPER
LEVEL RIDGING BUILDING OVERHEAD FROM THE SOUTHEAST. MOISTURE ON THE
FLANK OF A WEAK TROPICAL DISTURBANCE SKIRTING SOUTH OF THE BIG
ISLAND MAY FUEL A FEW SHOWERS ON LEEWARD BIG ISLAND SLOPES THIS
AFTERNOON AND EVENING...BUT OTHERWISE SHOWERS WILL BE MODEST AND
CONFINED TO WINDWARD SLOPES TONIGHT.

MODERATE TO LOCALLY BREEZY...EASTERLY TRADE WINDS WILL BECOME
ESTABLISHED ON WEDNESDAY AS SURFACE TROUGHS TO THE NORTH AND
NORTHWEST MOVE AWAY FROM THE ISLANDS AND SURFACE HIGH PRESSURE HOLDS
ABOUT 1300 MILES TO THE NORTH. MID TO UPPER LEVEL RIDGING WILL
STRENGTHEN OVERHEAD...LEADING TO A RATHER STABLE TRADE WIND FLOW
THAT WILL CONFINE MOST SHOWERS TO WINDWARD SLOPES.

AN INCREASE IN MAINLY WINDWARD RAINFALL IS POSSIBLE THIS WEEKEND.
THE LATEST OFFICIAL FORECAST FROM NATIONAL HURRICANE CENTER CALLS
FOR DISSIPATION OF TROPICAL DEPRESSION 08E FAR EAST OF THE STATE ON
THURSDAY. THE GFS TRACKS THE REMNANT MOISTURE OVER THE EASTERN END
OF THE STATE AS EARLY AS SATURDAY...WHILE THE ECMWF IS ABOUT TWELVE
HOURS SLOWER WITH THE ARRIVAL OF THE MOISTURE. THE FORECAST IS
PAINTED GENERALLY WETTER OVER THE EASTERN PORTION OF THE STATE INTO
EARLY NEXT WEEK.

&&

.AVIATION...
LIGHT EAST-SOUTHEAST FLOW ACROSS THE ISLANDS IS RESULTING FROM A
TROUGH WEST OF THE STATE. LEEWARD SEA BREEZES WILL CONTINUE INTO THE
EARLY EVENING HOURS RESULTING IN BRIEF MTN OBSC OVER THE NEXT COUPLE
OF HOURS. OTHERWISE...VFR CONDITIONS ARE EXPECTED TO PREVAIL OVER
ACROSS THE STATE. TRADE WINDS ARE EXPECTED TO STRENGTHEN SLIGHTLY ON
WEDNESDAY. NO AIRMETS ARE IN EFFECT AT THIS TIME.

&&

.MARINE...
RECENT BUOY DATA SHOW THE SOUTH-SOUTHWEST SWELL HANGING IN THERE
NEAR 4 FT WITH A DOMINANT PERIOD OF 14 SECONDS. RESULTING SOUTH
SHORE SURF IS AROUND THE 8 FOOT HIGH SURF ADVISORY THRESHOLD...AND
GIVEN THE RECENT BUOY DATA...WE HAVE OPTED TO EXTEND THE HIGH SURF
ADVISORY THROUGH THE NIGHT. CONFIDENCE IS HIGH THAT THE ADVISORY
WILL BE DROPPED BEFORE SUNRISE. THE SWELL WILL CONTINUE A GRADUAL
DECLINE THROUGH THURSDAY.

A SMALL CRAFT ADVISORY /SCA/ WAS ISSUED EARLIER IN THE DAY FOR THE
ALENUIHAHA CHANNEL AND WATERS SOUTH OF THE BIG ISLAND AND WILL BE
EXPANDED TO COVER THE PAILOLO CHANNEL AND MAALAEA BAY TOMORROW. THE
SCA CURRENTLY RUNS THROUGH THURSDAY BUT WILL LIKELY BE EXTENDED INTO
THE WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST WEDNESDAY FOR SOUTH FACING SHORES
OF ALL ISLANDS.

SMALL CRAFT ADVISORY UNTIL 6 PM HST THURSDAY FOR ALENUIHAHA
CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.

SMALL CRAFT ADVISORY FROM 6 AM WEDNESDAY TO 6 PM HST THURSDAY
FOR MAALAEA BAY-PAILOLO CHANNEL.

&&

$$

DISCUSSION/MARINE...WROE
AVIATION...FOSTER







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