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Hawaiian Islands Synoptic Discussion and Guidance

807
FXHW60 PHFO 270641
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST TUE MAY 26 2015

.SYNOPSIS...
WINDS ARE EXPECTED TO BE SUFFICIENTLY LIGHT TO ALLOW LOCALIZED LAND
AND SEA BREEZES THROUGH THE REST OF THE WEEK. INCREASING MOISTURE
WILL LEAD TO AN INCREASINGLY CLOUDY AND SHOWERY WEATHER PATTERN...
PARTICULARLY DURING THE AFTERNOONS AND EARLY EVENINGS.

&&

.DISCUSSION...
A WEAK UPPER LEVEL SHORTWAVE OVER THE CENTRAL ISLANDS THIS EVENING
CONTINUES TO ADVANCE SOUTHEAST. COUPLED WITH THE LINGERING MOISTURE
IN THE ISLAND VICINITY...QUITE A BIT OF LOW CLOUDS HAVE DEVELOPED IN
THE AREA...ESPECIALLY OVER THE BIG ISLAND AND MAUI. MOREOVER...THESE
CLOUDS HAVE DEEPENED A BIT OVER THE EASTERN ISLANDS...AS THE LATEST
SATELLITE IMAGERY INDICATED CLOUD TOPS ARE AT LEAST ABOVE THE SUMMIT
LEVELS. THERE ARE SHOWERS ASSOCIATED WITH THESE CLOUDS...THOUGH MUCH
OF THESE SHOWERS ARE MAINLY OVER COASTAL WATERS.
INTERESTINGLY...EVEN WITH THE PRESENT OF AN UPPER LEVEL FEATURE IN
THE AREA...AIR MASS REMAINS STABLE...AS DEPICTED BY AFTERNOON
SOUNDINGS FROM LIHUE AND HILO. THUS RAINFALL AMOUNTS REMAIN LIMITED
WITH THESE CLOUDS.

AS THE SHORTWAVE EXITS EAST OF THE STATE OVERNIGHT...THERE MAY BE A
SLIGHT IMPROVEMENT IN THE CLOUD COVERAGE OVER THE EASTERN ISLANDS.
BUT THEN LOW LEVEL MOISTURE IS EXPECTED TO LINGER IN THE ISLAND
VICINITY...WITH THE RATHER WEAK SYNOPTIC WINDS PRESENT. IN
ADDITIONAL...WITH THE EXTENSIVE CLOUD COVERAGE...LAND BREEZES WILL
BE SLOW TO DEVELOP OVER THE BIG ISLAND AND MAUI. THUS THE CLEARING
FOR THOSE ISLANDS WILL BE SLOW...IF ANY. THERE IS A WEAK SURFACE
RIDGE NORTHWEST OF THE ISLANDS THIS EVENING...WHILE THERE IS ALSO A
WEAK SURFACE TROUGH NEAR THE BIG ISLAND. THE POSITION OF THE RIDGE
AND TROUGH ALLOWS LIGHT NORTHEAST WINDS TO THE AREA. ONCE
AGAIN...THE BACKGROUND WIND FLOW WILL BE LIGHT ENOUGH FOR LAND
BREEZES TO DEVELOP OVER THE REST OF THE ISLANDS OVERNIGHT...AND MAY
BRING SOME CLEARING AS WELL.

THIS WEAK SURFACE RIDGE WILL TRY TO EXTEND TO NORTH OF THE STATE IN
THE NEXT FEW DAYS...THOUGH THE WEAK SURFACE TROUGH WILL PERSIST NEAR
THE BIG ISLAND AS WELL. AS SUCH...THE SLIGHTLY STRONGER TRADE WINDS
WILL BE CONFINED MAINLY TO KAUAI...WITH SYNOPTIC WINDS PROGRESSIVELY
BECOMING WEAKER FURTHER DOWN THE ISLAND CHAIN. THUS...LAND AND SEA
BREEZES WILL REMAIN THE PROMINENT LOCAL WIND FEATURES ACROSS THE
ISLANDS...ESPECIALLY OVER THE EASTERN HALF OF THE STATE. CONVERGING
SEA BREEZES WILL LEAD TO CLOUD BUILDUPS WITH POSSIBLE SHOWERS ACROSS
INTERIOR/LEEWARD SECTIONS DURING THE AFTERNOON. FORECAST SOLUTIONS
HINT THERE WILL BE AN INCREASE IN THE LOW LEVEL MOISTURE IN THE
ISLAND VICINITY...WHILE UPPER LEVEL SHORTWAVES PASSING NORTHEAST OF
THE STATE WILL HELP TO WEAKEN AND LIFT THE INVERSION...ALLOWING FOR
GREATER MOISTURE DEPTH. THE CURRENT FORECAST HAVE THE SCENARIO
COVERED WITH INCREASING RAINFALL CHANCES THROUGH THE REST OF THE
WEEK.

OVER THE WEEKEND...THE WEAK SURFACE HIGH IS EXPECTED TO EDGE FURTHER
EAST...STAYING JUST NORTH OF THE STATE. THIS WILL SIGNIFY A SLIGHT
STRENGTHENING OF THE GRADIENT OVER THE ISLANDS...WITH POSSIBLE
SLIGHTLY STRONGER TRADE WINDS RETURNING. BUT THEN...WINDS
MAY STAY LIGHT ENOUGH FOR LOCALIZED SEA BREEZES TO DEVELOP ACROSS
SHELTERED LEEWARD AREAS. THE ISLANDS MAY SEE A HYBRID RAINFALL
PATTERN...WITH CLOUDS AND SHOWERS FOCUSED ACROSS WINDWARD AREAS AT
NIGHT AND MORNING BUT ACROSS LEEWARD AREAS DURING THE AFTERNOON AND
EVENING.

&&

.AVIATION...
A WEAK PRESSURE GRADIENT ACROSS HAWAII WILL ALLOW LAND AND SEA
BREEZES TO DOMINATE THE WEATHER PATTERN TONIGHT AND WEDNESDAY.
EARLIER MVFR CIGS ACROSS PARTS OF OAHU AND KAUAI APPEAR TO HAVE
DIMINISHED WITH THE LOSS OF DAYTIME HEATING...AND AIRMET SIERRA
FOR MOUNTAIN OBSCURATION HAS BEEN CANCELLED. VFR CONDITIONS SHOULD
PREVAIL ACROSS MOST AREAS OVERNIGHT DUE TO DEVELOPING LAND BREEZES...
ALTHOUGH PERIODS OF MVFR CIGS WILL BE POSSIBLE ACROSS THE WINDWARD
BIG ISLAND...AND AIRMET SIERRA FOR MTN OBSC MAY BECOME NECESSARY
THERE.

DAYTIME SEA BREEZES WILL LIKELY DEVELOP ONCE AGAIN ON WEDNESDAY...
AND ANOTHER AIRMET FOR MTN OBSC MAY BE NEEDED DURING THE AFTERNOON
DUE TO AREAS OF MVFR CIGS AND SCATTERED SHOWERS.

&&

.MARINE...
THE CURRENT SOUTH SWELL WILL CONTINUE TO SUBSIDE...THOUGH A SERIES
OF SOUTH SWELLS WILL KEEP SURF ALONG SOUTH FACING SHORES ELEVATED
THROUGH THE REST OF THE WEEK. THE LATEST SURFACE ANALYSIS CONTINUES
TO SHOW A STRONG GALE LOW EAST OF NEW ZEALAND WITH A LONG FETCH
POINTED TOWARD THE STATE. LATEST WAVEWATCH GUIDANCE SHOWS THIS SWELL
REACHING US SATURDAY NIGHT AND PEAKING ON MONDAY...WITH SURF LIKELY
REACHING ADVISORY LEVELS FOR SOUTH FACING SHORES.

&&

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

&&

$$

DISCUSSION/MARINE...HUI
AVIATION...JACOBSON



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