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Hawaiian Islands Synoptic Discussion and Guidance

177
FXHW60 PHFO 301950
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST SAT AUG 30 2014

.SYNOPSIS...
GENTLE TRADE WINDS WILL PREVAIL THROUGH THE HOLIDAY WEEKEND...
DELIVERING A FEW CLOUDS AND SHOWERS TO WINDWARD AREAS...MAINLY
DURING NIGHTS AND MORNINGS. THE LIGHT WINDS WILL ALSO ALLOW
AFTERNOON SEA BREEZES TO PRODUCE LOCALIZED CLOUD BUILDUPS AND A FEW
SHOWERS OVER LEEWARD AND INTERIOR AREAS. A MORE TYPICAL TRADE WIND
WEATHER PATTERN IS EXPECTED BY THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...
CURRENTLY...LIGHT TRADE WINDS FAVOR AN ENE DIRECTION...SUPPORTED BY
A RELATIVELY WEAK 1025 MB SURFACE HIGH CENTERED ABOUT 1300 MILES N
OF THE ISLANDS. A WEAK LOW 700 MILES N OF THE ISLANDS...NEAR 30N
153W...LIES BETWEEN THE HIGH AND THE ISLANDS...MARKING THE REMNANT
OF WHAT ONCE WAS TROPICAL CYCLONE LOWELL. CLOSER TO THE ISLANDS...A
N-S TROUGH LIES OFF THE WINDWARD SHORES OF MAUI AND THE BIG ISLAND...
AND THE PRESENCE OF THESE FEATURES HAS LED TO A RELATIVELY LOOSE
PRESSURE GRADIENT NEAR THE ISLANDS. SHOWERY LOW CLOUDS ASSOCIATED
WITH THE NEARBY TROUGH ARE OVER NEAR SHORE WINDWARD WATERS OF MAUI
AND THE BIG ISLAND...AND ABOUT 100 TO 200 MILES EAST OF MAUI. WHILE
A FEW CLOUDS AND SHOWERS ARE OVER WINDWARD AREAS OF KAUAI OAHU
MOLOKAI AND MAUI...SKIES OVER MOST OTHER AREAS ARE SUNNY THIS
MORNING. A MID-LEVEL RIDGE IN THE AREA IS MAINTAINING A STRONG YET
SOMEWHAT ELEVATED CAP ON THE ISLAND ATMOSPHERE...WITH MORNING
SOUNDINGS INDICATING THE INVERSION BASE IS NEAR 10 KFT.

THE FORECAST CALLS FOR THE NEARBY TROUGH AND LOWELL REMNANT TO MOVE
GENERALLY WNW WHILE WEAKENING OVER THE NEXT DAY OR TWO...WITH LOW
LEVEL WINDS NEAR THE ISLANDS REMAINING LIGHT...BUT VEERING TO AN
ESE DIRECTION TONIGHT AND SUNDAY. WHILE VOLCANIC EMISSIONS FROM THE
BIG ISLAND ARE NOT EXPECTED TO SPREAD OVER THE SMALLER ISLANDS WITH
THIS FLOW...SURFACE DEW POINTS ARE EXPECTED TO INCREASE SLIGHTLY...
AND WILL BE IN THE LOW 70/S STATEWIDE SUNDAY AND MONDAY. COMBINED
WITH THE LIGHT WINDS...CONDITIONS WILL BE WARM AND MUGGY. ALTHOUGH
THE REMNANT OF FORMER TROPICAL CYCLONE MARIE WILL BE PASSING FAR NE
OF THE ISLANDS DURING THE UPCOMING WEEK...FORECAST MODELS DEPICT
SUFFICIENT SURFACE RIDGING BUILDING N OF THE ISLANDS TO SUPPORT A
MODERATE TRADE WIND FLOW...INITIALLY STRENGTHENING AND BACKING TO
THE E ON MONDAY...BECOMING ENE TUESDAY...AND REMAINING THAT WAY
THROUGH THE END OF THE WEEK.

WITH THE LIGHT TRADE WINDS...A FEW SHOWERS CAN BE EXPECTED OVER
WINDWARD AREAS...MAINLY NIGHTS AND MORNINGS. WEATHER OVER LEEWARD
AREAS WILL BE DRIVEN BY THE DIURNAL CYCLE OF LAND AND SEA BREEZES...
WITH MOSTLY CLEAR NIGHTS AND MORNINGS...WITH INCREASING LATE MORNING
CLOUDS LEADING TO A FEW AFTERNOON SHOWERS THAT GRADUALLY CLEAR IN
THE EVENING. AS TRADE WINDS STRENGTHEN LATER IN THE WEEK...LEEWARD
AREAS OTHER THAN LEEWARD BIG ISLAND WILL REMAIN MOSTLY DRY...WITH
BRIEF SHOWERS OVER WINDWARD AREAS. MID-LEVEL RIDGING PERSISTING IN
THE AREA WILL KEEP THE ISLAND ATMOSPHERE STABLE...AND NO SIGNIFICANT
MOISTURE SOURCES ARE EXPECTED...THUS RAINFALL TOTALS WILL BE ON THE
LOW END.

&&

.AVIATION...
VFR CONDITIONS PREVAIL AT ALL TAF SITES AND THESE CONDITIONS ARE
EXPECTED TO CONTINUE THROUGHOUT THE DAY. THERE MAY BE SOME BRIEF
MVFR CONDITIONS OVER INTERIOR AND MOUNTAIN AREAS AS DAYTIME HEATING
CAUSES CLOUDS BUILDUPS AND SOME WIDELY SCATTERED SHRA.

WINDS WILL BE RATHER LIGHT OVER MOST LAND AREAS TODAY WITH SEA
BREEZES BECOMING DOMINANT OVER MANY AREAS...WITH LIGHT TRADES OVER
THE ADJACENT COASTAL WATERS.

&&

.MARINE...
A HIGH SURF ADVISORY REMAINS POSTED FOR S FACING SHORES OF MOST
ISLANDS...AND MORE ADVISORY-LEVEL SURF IS POSSIBLE THIS WEEK...AS
SWELLS ARRIVE FROM THE SOUTHERN HEMISPHERE. SOME QUESTION AS TO
WHETHER SURF DROPS BELOW ADVISORY LEVELS SUNDAY/MONDAY AS A
REINFORCING SWELL ARRIVES. A VERY LONG-PERIOD /20-25 SECOND/ S SWELL
ARRIVING TUESDAY AND BUILDING THROUGH WEDNESDAY WILL LIKELY PRODUCE
ADVISORY LEVEL SURF. LONG PERIOD SWELL FROM THE E IS STILL BEING
OBSERVED AT NEAR SHORE BUOYS THIS MORNING...BUT THE MAGNITUDE OF THE
SWELL IS LOW ENOUGH THAT SURF IS EXPECTED TO REMAIN JUST BELOW
ADVISORY LEVELS TODAY...WITH THE SWELL HEIGHT AND PERIOD DIMINISHING
FURTHER SUNDAY/MONDAY.

WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY
THRESHOLDS FOR AT LEAST THE NEXT SEVERAL DAYS...WITH AN OUTSIDE
CHANCE THAT WINDY MARINE ZONES AROUND THE MAUI AND THE BIG ISLAND
REACH CRITERIA AS TRADES INCREASE AROUND MID-WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST SUNDAY FOR SOUTH FACING SHORES OF
NIIHAU KAUAI OAHU MOLOKAI LANAI KAHOOLAWE MAUI AND THE BIG ISLAND.

&&

$$

DISCUSSION/MARINE...BIRCHARD
AVIATION...BURKE



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