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Hawaiian Islands Synoptic Discussion and Guidance

188
FXHW60 PHFO 230130
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 PM HST SAT NOV 22 2014

.SYNOPSIS...
DIMINISHING TRADE WINDS WILL ALLOW LAND BREEZES TO DEVELOP LATE
TONIGHT...WITH SEA BREEZES EXPECTED SUNDAY AFTERNOON. THE LAND
BREEZES WILL BRING MOSTLY CLEAR SKIES...WHILE CLOUDS AND A FEW
SHOWERS ARE EXPECTED TO DEVELOP WITH THE SEA BREEZES. A RELATIVELY
WEAK FRONT WILL MOVE DOWN THE ISLAND CHAIN ON MONDAY...BRINGING A
BRIEF BOUT OF SHOWERS. COOL AND DRY NORTHERLY WINDS WILL SURGE
BEHIND THE FRONT...WITH WINDS BECOMING NORTHEASTERLY BY TUESDAY.
BREEZY TRADE WINDS WILL THEN PERSIST INTO NEXT WEEKEND...DELIVERING
A FEW BRIEF WINDWARD SHOWERS.

&&

.DISCUSSION...
CURRENTLY...LIGHT TO LOCALLY FRESH EAST-SOUTHEAST TRADE WINDS
CONTINUE TO BE SUPPORTED BY A SURFACE HIGH CENTERED ABOUT 1400
MILES NE OF THE ISLANDS...AND ITS ASSOCIATED SURFACE RIDGE ABOUT 325
MILES N OF OAHU. AFTERNOON SOUNDINGS SHOW A STRONG LOW-LEVEL
INVERSION IN PLACE NEAR 6 KFT...KEEPING A STRONG CAP ON CLOUD AND
SHOWER DEVELOPMENT. SATELLITE IMAGES SHOW FEW TO SCATTERED LOW
CLOUDS OVER NEAR SHORE WINDWARD WATERS...WITH LOCALIZED SEA BREEZES
FORCING CLOUD DEVELOPMENT OVER LEEWARD PORTIONS OF KAUAI...OAHU AND
THE BIG ISLAND. IN THE SHORT TERM...THESE CLOUDS WILL CLEAR AFTER
SUNSET...AND A MOSTLY DRY NIGHT IS EXPECTED...EXCEPT FOR A SLIGHT
CHANCE OF WINDWARD SHOWERS. LAND BREEZES DEVELOPING BY MORNING
SHOULD LEAD TO CLEAR SKIES IN MOST AREAS.

THE LEADING EDGE OF A COLD FRONT LIES ABOUT 600 MILES NW OF
KAUAI...WITH THE FRONT EXPECTED TO BEGIN A STEADY MARCH TOWARD THE
ISLANDS TONIGHT. THIS WILL OCCUR AS HIGH PRESSURE NW OF THE FRONT
MOVES E...AND A WAVE OF LOW PRESSURE DEVELOPS ALONG THE FRONT N OF
THE ISLANDS...WITH THE TWO COMBINING TO PUSH THE FRONT TOWARD...AND
EVENTUALLY OVER...THE ISLANDS. IN RESPONSE...THE SURFACE RIDGE WILL
WEAKEN AND MOVE S THROUGH SUNDAY...WITH WINDS OVER THE AREA
DIMINISHING TO THE POINT THAT THEY BECOME LIGHT AND VARIABLE. WINDS
WERE ALREADY LIGHT ENOUGH THIS AFTERNOON TO ALLOW LEEWARD SEA
BREEZES TO BECOME A LITTLE MORE WIDESPREAD THAN USUAL...ADDING
CONFIDENCE THAT LAND BREEZES WILL DEVELOP LATE TONIGHT...WITH SEA
BREEZES BECOMING EVEN MORE WIDESPREAD SUNDAY AFTERNOON. WITH THE
ISLAND ATMOSPHERE REMAINING STABLE AND THE FLOW AT CLOUD LEVEL
EXPECTED TO BE FROM THE WSW...THE SEA BREEZES ARE NOT EXPECTED TO
BRING MORE THAN JUST A FEW SHOWERS...WHICH ARE EXPECTED TO
PRIMARILY AFFECT THE NE AND E SIDES OF THE ISLANDS.

SURFACE WINDS AHEAD OF THE FRONT WILL BECOME WESTERLY MOST AREAS
SUNDAY NIGHT...WITH THE FRONT BRINGING A SHIFT TO STRONGER
NORTHERLY WINDS AS IT PASSES KAUAI LATE SUNDAY NIGHT...OAHU BY
MID-MORNING MONDAY...MAUI COUNTY IN THE AFTERNOON...AND THE BIG
ISLAND BY MONDAY NIGHT. THIS TIMING CONTINUES TO BE SUPPORTED BY THE
MOST RECENT RUNS OF BOTH THE GFS AND ECMWF. LIMITED MOISTURE AND
INSTABILITY MEANS THAT THIS FRONT WILL BE FAIRLY SHALLOW...WITH A
RELATIVELY BRIEF PERIOD OF SHOWERS AS IT PASSES...MAINLY OVER THE
SMALLER ISLANDS. THE FRONT WILL BE DISSIPATING AS IT NEARS THE BIG
ISLAND...BUT WE STILL EXPECT A GENERAL INCREASE IN SHOWERS...MAINLY
ALONG NE FACING SLOPES MONDAY NIGHT AND TUESDAY.

POST-FRONTAL NORTHERLY WINDS WILL USHER IN A COOL AND DRY AIR MASS
WITH LIMITED SHOWERS EXPECTED THEREAFTER...MAINLY LIGHT AND ALONG N
FACING SLOPES. DEW POINTS ARE EXPECTED TO DIP INTO THE UPPER 50/S BY
MONDAY NIGHT...REMAINING THERE INTO TUESDAY. THE HIGH SUPPORTING THE
COOL NORTHERLIES WILL EVENTUALLY MOVE INTO A POSITION N OF THE
ISLANDS TO SUPPORT A MORE TYPICAL ENE TRADE WIND BY WEDNESDAY...
WITH DEW POINTS GRADUALLY REBOUNDING INTO THE MID TO UPPER 60/S
THROUGH THE END OF THE WEEK. BREEZY TRADE WINDS ARE THEN EXPECTED TO
CONTINUE THROUGH NEXT WEEKEND. WITH A MID LEVEL RIDGE NEARBY...THE
ISLAND ATMOSPHERE WILL BE STABLE...WITH JUST A FEW BRIEF WINDWARD
SHOWERS EXPECTED.

&&

.AVIATION...
WIND SHEAR OVER THE STATE HAS DIMINISHED...AS THE SHARP UPPER LEVEL
TROUGH OVER US BEGINS TO WEAKEN WITH THE APPROACH OF A LARGER TROUGH
FROM THE NORTHWEST. TURBULENCE GUIDANCE FIELDS SHOW A STRONG
WEAKENING TREND BETWEEN THIS MORNING AND THIS AFTERNOON...AND RECENT
PILOT REPORTS INDICATE NIL OR LIGHT TURBULENCE ALONG THE TROUGH
AXIS. WITH THIS IN MIND...WILL DROP THE AIRMET FOR MODERATE
TURBULENCE THAT WAS ALREADY SCHEDULED TO END BY 04Z THIS EVENING.

OTHERWISE PRIMARILY VFR CONDITIONS ARE EXPECTED. BRIEF MVFR CEILINGS
ARE POSSIBLE IN SHOWERS ACROSS EASTERN SECTIONS OF THE ISLANDS.
WEAKENING WINDS TONIGHT WILL ALLOW LAND BREEZES TO FORM ACROSS
LEEWARD SECTIONS...WHICH WILL HELP TO CLEAR OUT ANY LINGERING
LOW-LEVEL CLOUDS THAT DEVELOPED OVER THESE AREAS DURING THE DAY.

&&

.MARINE...
THE SMALL CRAFT ADVISORY /SCA/ THAT WAS POSTED FOR WINDIER MARINE
ZONES AROUND THE BIG ISLAND HAS BEEN DROPPED...WITH WINDS CONTINUING
TO TREND DOWN. HOWEVER...INCREASING WINDS...SEAS AND LONG-PERIOD
SWELL ON MONDAY WILL REQUIRE THE SCA FLAG TO BE HOISTED ONCE
AGAIN...THIS TIME FOR MOST MARINE ZONES...WITH SEAS REMAINING
ELEVATED THROUGH TUESDAY. BREEZY TRADE WINDS WILL REQUIRE THE SCA
FOR THE WINDIER MAUI AND BIG ISLAND ZONES FOR MUCH OF THE WEEK
HOWEVER.

A NEW LONG-PERIOD NNW SWELL WILL BUILD TONIGHT INTO SUNDAY...WITH
PEAK SURF HEIGHTS APPROACHING...BUT EXPECTED TO REMAIN BELOW...
ADVISORY LEVELS ALONG EXPOSED N AND W SHORES. THE SWELL WILL BE
REINFORCED ON MONDAY...WITH PEAK SURF HEIGHTS LIKELY REQUIRING AN
ADVISORY FOR EXPOSED N AND W SHORES THROUGH TUESDAY. BREEZY TRADE
WINDS LATER IN THE WEEK WILL PRODUCE CHOPPY SURF ALONG E FACING
SHORES THAT IS EXPECTED TO REMAIN BELOW ADVISORY LEVELS.

&&

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

&&

$$

SYNOPSIS/DISCUSSION/MARINE...BIRCHARD
AVIATION...BRAVENDER



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