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Hawaiian Islands Synoptic Discussion and Guidance

081
FXHW60 PHFO 011330
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST MON SEP 1 2014

.SYNOPSIS...
A LIGHT EAST-SOUTHEAST FLOW IS EXPECTED TO CONTINUE TODAY WITH HIGH
PRESSURE REMAINS FAR NORTHEAST ...AND A SURFACE TROUGH NEAR THE
ISLANDS. HEADING TOWARDS MIDWEEK...LIGHT TO MODERATE TRADES ARE
EXPECTED TO BUILD IN. THE LIGHT WINDS WILL ALLOW AFTERNOON SEA
BREEZES TO BRING LOCALIZED CLOUD BUILDUPS AND A FEW SHOWERS OVER
LEEWARD AND INTERIOR AREAS. AS THE WEEK PROGRESSES AND THE TRADES
STRENGTHEN...EXPECT THE LIMITED CLOUDS AND SHOWERS TO BE FOCUSED
OVER THE WINDWARD SLOPES. TRADE WIND SHOWERS MAY INCREASE BY FRIDAY
AS LOW LEVEL MOISTURE RIDES IN ON THE TRADES.

&&

.DISCUSSION...
THE OVERNIGHT SOUNDING AT HILO SHOWED A LOW LEVEL INVERSION WITHIN
400 FT OF THE SURFACE. THIS IS SIMILAR TO AN INVERSION OBSERVED
YESTERDAY MORNING...BUT THIS MORNING/S IS NOT QUITE AS STRONG AS
YESTERDAY/S. THE STRONG LOW LEVEL INVERSION YESTERDAY MORNING
ALLOWED SMOKE AND ODORS ASSOCIATED WITH THE RELATIVELY NEW LAVA FLOW
IN THE PUNA DISTRICT TO BECOME TRAPPED NEAR THE SURFACE UNTIL MID
MORNING WHEN THE HEAT OF THE DAY HELPED TO DISSIPATE THE INVERSION.
WITH THE MORNING SOUNDING SHOWING THE INVERSION AGAIN...EVEN THOUGH
NOT QUITE AS STRONG...IT/S VERY LIKELY SIMILAR EVENTS WILL BE
OBSERVED THIS MORNING...THUS THE MENTION OF SMOKE IN THE GRIDS. THE
WEAKER INVERSION TODAY MAY MEAN IT WILL BREAK UP A LITTLE SOONER
THAN YESTERDAY.

NO MAJOR CHANGES TO THE FORECAST FOR THIS MORNING. THE CLOUDS OVER
THE BIG ISLAND LAST EVENING BEGAN TO BREAK UP OVER THE NORTHWEST
HALF OF THE ISLAND SHORTLY AFTER MIDNIGHT...LEAVING CLOUDS AND SOME
SHOWERS OVER THE SLOPES FROM HILO TO CAPE KUMUKAHI TO SOUTH POINT.
THIS BATCH OF CLOUDS IS ASSOCIATED WITH A WEAK SURFACE TROUGH DRAPED
ACROSS THE ISLANDS OF MAUI COUNTY AND THE BIG ISLAND. THESE CLOUDS
ARE MOVING TO THE WEST NORTHWEST...WITH THE BULK OF THE CLOUDS
EXPECTED TO PASS SOUTH OF THE SMALLER ISLANDS TODAY. THE PRESENCE OF
THIS TROUGH IS DISRUPTING THE TRADE WIND FLOW GENERATED BY THE HIGH
PRESSURE SYSTEM FAR NORTHEAST OF THE ISLANDS.

THE MODELS ARE IN GOOD AGREEMENT WITH THE HIGH LINGERING TO THE FAR
NORTHEAST OF THE ISLANDS THROUGH MUCH OF THE WEEK. THE SURFACE
TROUGH NEAR THE ISLANDS SHOULD START TO DISSIPATE AND MOVE AWAY FROM
THE ISLANDS HEADING INTO MID WEEK...WHICH WILL ALLOW THE TRADES TO
MAKE A RETURN APPEARANCE. HOWEVER...A LOW NORTHEAST OF THE
ISLANDS...AND A FRONT PASSING NORTHWEST OF THE ISLANDS WILL HELP
PREVENT MORE THAN LIGHT TO MODERATE TRADES TO BUILD BACK IN. AS THE
WINDS INCREASE...LOOK FOR CLOUDS AND SHOWERS TO BECOME FOCUSED MORE
OVER THE WINDWARD SLOPES. THE GFS AND ECMWF BOTH SHOW LIMITED LOW
LEVEL MOISTURE DURING THE MIDDLE OF THE WEEK...SO EXPECT SHOWER
ACTIVITY TO BE ON THE LIGHT SIDE.

BOTH MODELS DO SHOW ADDITIONAL LOW LEVEL MOISTURE BEING CARRIED IN
ON THE TRADES AT THE END OF THE WEEK. THIS INCREASED MOISTURE
APPEARS TO BE LOOSELY ASSOCIATED WITH THE REMNANT OF MARIE THAT IS
PASSING FAR NORTHEAST OF THE ISLANDS. AS SUCH...LOOK FOR MORE
SHOWERS AT THE END OF THE WEEK THAN AT MIDWEEK.

&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL ACROSS THE STATE TODAY AND TONIGHT.
CLOUDS AND WIDELY SCATTERED SHOWERS SHOULD DEVELOP ONCE AGAIN THIS
AFTERNOON ALONG SEABREEZES ACROSS INTERIOR AND LEEWARD AREAS...WITH
ISOLATED MVFR CONDITIONS POSSIBLE. ISOLATED MVFR WILL ALSO BE
POSSIBLE ACROSS WINDWARD SECTIONS TONIGHT AS WEAK TRADE WIND FLOW
RESUMES.

&&

.MARINE...
THE NEAR SHORE BUOYS CONTINUED TO SHOW STEADY READINGS OVERNIGHT.
THE REINFORCEMENT TO THE CURRENT SOUTH SWELL STARTED TO MAKE AN
APPEARANCE ON THE 51003 BUOY OVERNIGHT WITH PERIODIC 15 SECOND
ENERGY BEING PICKED UP. SURF ALONG THE SOUTH FACING SHORES IS
EXPECTED TO REMAIN ELEVATED...BUT BELOW ADVISORY LEVELS INTO
TUESDAY.

A VERY LONG PERIOD SOUTH SWELL...20-25 SECONDS...IS DUE TO
ARRIVE TUESDAY...AND BUILD THROUGH WEDNESDAY. THIS SWELL WILL LIKELY
PRODUCE ADVISORY LEVEL SURF INTO THURSDAY.

THE LONG PERIOD SWELL FROM THE EAST SHOULD CONTINUE TO TREND DOWN
TODAY. WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY
THRESHOLDS FOR AT LEAST THE NEXT SEVERAL DAYS.

&&

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

&&

$$

DISCUSSION/MARINE...M BALLARD
AVIATION...JACOBSON




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