Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 271358
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST WED MAY 27 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...
EXTENSIVE LOW CLOUDS CONTINUE TO AFFECT THE BIG ISLAND AS WELL AS
EASTERN MAUI EARLY THIS MORNING...EVEN AS A WEAK UPPER LEVEL
SHORTWAVE EXITS THE STATE TO THE EAST. ONCE AGAIN...NOT MUCH
RAINFALL WAS REPORTED BY THE RAIN GAGES ON THOSE ISLANDS. ELSEWHERE
ONLY OAHU DID CLEAR OUT A BIT. ANOTHER BATCH OF LOW CLOUDS HAS
REACHED KAUAI EARLIER THIS MORNING...KEEPING SKIES A LITTLE MORE
CLOUDY OVER THAT ISLAND. THERE ARE SHOWERS EMBEDDED IN THESE CLOUDS
AND THE LATEST RADAR DATA INDICATE SOME OF THESE SHOWERS ARE MORE
MODERATE. BUT THEN EARLY MORNING LIHUE SOUNDING CONTINUES TO
SHOW A RATHER DRY AND STABLE AIRMASS...WHILE HILO SOUNDING AT LEAST
HAS MOISTENED UP QUITE A BIT BUT STILL STABLE. MUCH OF THE LOW LEVEL
MOISTURE IS EXPECTED TO LINGER IN THE ISLAND VICINITY TODAY...UNDER
THE RATHER WEAK SYNOPTIC WINDS. A WEAK SURFACE RIDGE CONTINUES JUST
NORTHWEST OF THE ISLANDS EARLY THIS MORNING...WHILE A WEAK SURFACE
TROUGH PERSISTS NEAR THE BIG ISLAND. THE POSITION OF THE RIDGE AND
TROUGH ALLOWS LIGHT NORTHEAST WINDS TO THE AREA. THE BACKGROUND WIND
FLOW WILL BE LIGHT ENOUGH FOR SEA BREEZES AS THE DAY
PROGRESSES...WITH INCREASING CLOUDS AND SHOWERS OVER THE ISLANDS
AGAIN...ESPECIALLY BY THE AFTERNOON AND EARLY EVENING.

THE WEAK SURFACE RIDGE WILL EXTEND SOMEWHAT FURTHER EAST IN THE
NEXT COUPLE OF DAYS...WHILE THE WEAK SURFACE TROUGH WILL PERSIST
NEAR THE BIG ISLAND AS WELL. AS SUCH...THE SLIGHTLY STRONGER TRADE
WINDS WILL BE LIMITED MAINLY TO KAUAI...WITH SYNOPTIC WINDS
PROGRESSIVELY WEAKER FURTHER DOWN THE ISLAND CHAIN. THUS...LAND AND
SEA BREEZES WILL REMAIN THE PROMINENT LOCAL WIND FEATURES ACROSS THE
ISLANDS THROUGH THURSDAY...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 STILL HINT THERE WILL BE AN INCREASE
IN THE LOW LEVEL MOISTURE IN THE ISLAND VICINITY...WHILE WEAK UPPER
LEVEL SHORTWAVES PASSING NORTHEAST OF THE STATE MAY HELP TO WEAKEN
THE INVERSION...ALLOWING LOW LEVEL MOISTURE TO DEEPEN A BIT.
THEREFORE...LINGERING CLOUDS MAY PERSIST IN THE ISLAND
VICINITY...WITH INCREASING CLOUDS AND SHOWERS OVER THE ISLANDS IN
THE AFTERNOONS AND EARLY EVENINGS. SOME OF THE SHOWERS MAY BECOME
MORE MODERATE.

BY THE WEEKEND...A STRONGER SURFACE HIGH FROM THE FAR NORTHWEST WILL
EDGE EAST...CLOSER TO THE ISLANDS. THIS WILL RESULT IN A SLIGHT
STRENGTHENING OF PRESSURE GRADIENT OVER THE ISLANDS...LEADING TO
SLIGHTLY STRONGER TRADE WINDS RETURNING TO THE STATE.
NEVERTHELESS...WINDS MAY STILL BE LIGHT ENOUGH FOR LOCALIZED SEA
BREEZES TO DEVELOP ACROSS SHELTERED LEEWARD AREAS IN THE AFTERNOON.
A HYBRID RAINFALL PATTERN MAY DEVELOP ACROSS THE ISLANDS...WITH
CLOUDS AND SHOWERS FOCUSED ACROSS WINDWARD AREAS AT NIGHT AND
MORNING BUT ACROSS LEEWARD AREAS DURING THE AFTERNOON AND EARLY
EVENING.

THE RETURN OF STRONGER TRADE WINDS WILL PROBABLY BE SHORT-LIVED...AS
THE LATEST MODELS INDICATE THE TRADE WIND GENERATING SURFACE HIGH
WILL WEAKEN AND BE REPLACED BY A DEEPENING LOW FROM THE FAR
NORTHWEST EARLY NEXT WEEK. MODEL SOLUTIONS SUGGEST THE BULK OF THIS
SYSTEM WILL STAY NORTH OF THE STATE...THOUGH THIS SYSTEM WILL
POSSIBLE BE CLOSE ENOUGH FOR WINDS OVER THE ISLANDS TO TURN
SOUTHEASTERLY. THERE ARE QUITE A BIT DIFFERENCES ON THE SOLUTIONS
BETWEEN MODEL RUNS. THEREFORE UNCERTAINTY FOR THE EXTENDED FORECAST
REMAINS HIGH.

&&

.AVIATION...
A WEAK PRESSURE GRADIENT ACROSS HAWAII WILL ALLOW LAND AND SEA
BREEZES TO DOMINATE THE WEATHER PATTERN THROUGH TODAY. VFR
CONDITIONS SHOULD PREVAIL ACROSS MOST AREAS. DAYTIME SEA BREEZES
WILL LIKELY DEVELOP ONCE AGAIN BY MIDDAY...AND AIRMET SIERRA FOR MTN
OBSC MAY BE NEEDED DURING THE AFTERNOON DUE TO AREAS OF MVFR CIGS
AND SCATTERED SHOWERS...ESPECIALLY ACROSS LEEWARD AND INTERIOR
SECTIONS.

&&

.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. LATEST WAVEWATCH GUIDANCE CONTINUES TO
SHOW A SIGNIFICANT SOUTH SWELL REACHING US SATURDAY NIGHT AND
PEAKING LATE SUNDAY ONTO MONDAY...WITH SURF LIKELY REACHING ADVISORY
LEVELS FOR SOUTH FACING SHORES. THIS SWELL WAS PRODUCED BY A STRONG
GALE LOW EAST OF NEW ZEALAND WITH A LONG FETCH POINTED TOWARD THE
STATE A COUPLE OF DAYS AGO.

&&

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

&&

$$

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





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