Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 271332
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
332 AM HST FRI FEB 27 2015

.SYNOPSIS...
A SURFACE TROUGH NEAR KAUAI AND OAHU WILL SLOWLY DRIFT EASTWARD
ACROSS THE CENTRAL PART OF THE STATE TODAY THROUGH SATURDAY. THE
TROUGH WILL ACT AS A FOCUS FOR CLOUDS AND SHOWERS...AND LOCALLY
HEAVY RAIN WILL BE POSSIBLE FROM THIS AFTERNOON THROUGH THE
WEEKEND ACROSS MOST OF THE STATE AS THE THE ATMOSPHERE BECOMES
INCREASINGLY MOIST AND UNSTABLE. TRADE WINDS ARE FORECAST TO
REBUILD DURING THE WEEKEND AND CONTINUE INTO NEXT WEEK...ALTHOUGH
THE WET AND UNSETTLED WEATHER PATTERN WILL LIKELY CONTINUE.

&&

.DISCUSSION...
PARTLY CLOUDY BUT MOSTLY DRY CONDITIONS HAVE PREVAILED ACROSS THE
ISLANDS DURING THE NIGHT...ALTHOUGH SCATTERED SHOWERS HAVE
INCREASED RECENTLY TO THE SW OF KAUAI/OAHU AND TO THE SE OF THE
BIG ISLAND. A COMPLEX PATTERN PREVAILS BOTH AT THE SURFACE AND
ALOFT ACROSS THE REGION. A SHARP MID/UPPER LEVEL TROUGH AND
WEAK ASSOCIATED STATIONARY FRONT ARE LOCATED ABOUT 200 MILES NW
OF KAUAI...WITH A WEAK LOW LEVEL TROUGH NEAR KAUAI AND OAHU...
AND ANOTHER UPPER LOW AND ASSOCIATED SURFACE TROUGH ABOUT 500
MILES ESE OF THE BIG ISLAND. ALL OF THESE FEATURES WILL INTERACT
ACROSS THE ISLANDS AT VARIOUS TIMES DURING THE NEXT FEW DAYS...
LEADING TO PERIODS OF UNSETTLED WEATHER. THE TROUGH ALOFT OVER THE
CENTRAL PACIFIC IS SLOWLY ADVANCING EAST TOWARDS THE STATE...AND
THE 12Z SOUNDINGS REFLECT THIS WITH ADDITIONAL SUBSTANTIAL
COOLING OCCURRING THROUGH THE MID AND UPPER LEVELS. 500 MB TEMPS
HAVE DROPPED TO -12C AT LIHUE...OR ABOUT ONE STANDARD DEVIATION
BELOW NORMAL. THIS COOLING ALOFT HAS WIPED OUT THE TYPICAL MID
LEVEL INVERSION...AND ATMOSPHERIC MOISTURE HAS INCREASED SOMEWHAT
AS WELL WITH PWATS AT BOTH SOUNDING LOCATIONS COMING IN AT 1.35
INCHES.

FOR TODAY...THE LOW LEVEL TROUGH WILL DRIFT SLOWLY BACK TO THE
EAST ACROSS OAHU AND MAUI COUNTY. REMNANTS OF THE WEAKENING FRONT
TO OUR NW WILL BE PUSHING EAST TOWARD THE STATE...AND THE TROUGH
ALOFT WILL ALSO MOVE SLOWLY EAST...BRINGING FURTHER MID LEVEL
COOLING AND THE DIFFLUENT REGION OF A JET STREAM OVERHEAD.
CONTINUED LIGHT FLOW ALONG THE TROUGH AXIS WILL ALLOW SEABREEZES
TO DEVELOP OVER OAHU AND MAUI COUNTY...WHICH SHOULD BE ENOUGH OF
A TRIGGER GIVEN THE INSTABILITY ALOFT AND MOISTURE IN PLACE TO
TRIGGER AT LEAST ISOLATED HEAVY DOWNPOURS. MODELS INDICATE THAT
DRIER NORTHERLY FLOW WILL SPREAD ACROSS KAUAI DURING THE DAY...
WHICH SHOULD REDUCE THE POTENTIAL FOR HEAVY SHOWERS THERE.
ALSO DECIDED TO ADD A SLIGHT CHANCE OF THUNDER FOR OAHU THIS
AFTERNOON...WHERE THE BEST COMBINATION OF ENHANCED MOISTURE...
INSTABILITY AND MESOSCALE FORCING ALONG SEABREEZES WILL OCCUR.

UNSETTLED WEATHER WILL LIKELY CONTINUE ACROSS THE STATE THROUGH
THE WEEKEND. THE MID/UPPER LEVEL TROUGH WILL LINGER NEARBY...
MAINTAINING COLD TEMPERATURES ALOFT...WHILE THE LOW LEVEL TROUGH
WILL ALSO LINGER OVER THE STATE THROUGH AT LEAST SATURDAY NIGHT...
PROVIDING A FOCUS FOR SHOWERS...SOME OF WHICH WILL LIKELY BE
HEAVY AT TIMES FROM OAHU THROUGH THE BIG ISLAND. ISOLATED THUNDER
WILL REMAIN A POSSIBILITY AS WELL. GUIDANCE HAS TRENDED DRIER FOR
KAUAI THROUGH THE WEEKEND...WITH THE LATEST GFS AND ECMWF SHOWING
PWATS BELOW ONE INCH. THEREFORE HAVE SCALED BACK POPS THERE AND
REMOVED MENTION OF HEAVY RAIN. MODEL CONSENSUS SUGGESTS THAT THE
LOW LEVEL TROUGH WILL FINALLY WASH OUT ON SUNDAY...WITH WET TRADES
DEVELOPING ACROSS THE STATE...AS THE AREA OF ENHANCED MOISTURE
CURRENTLY SEVERAL HUNDRED MILES ESE OF THE BIG ISLAND SHIFTS
WESTWARD OVER THE AREA.

MODELS HAVE COME INTO BETTER AGREEMENT FOR EARLY NEXT WEEK...
WITH THE GFS FALLING INTO LINE WITH THE EC IN SHOWING JUST A VERY
SUBTLE TROUGH DRIFTING WEST OVER THE STATE...AND A WET TRADE WIND
PATTERN CONTINUING.

THE GFS AND ECMWF FINALLY BRING A DRIER AND BREEZY TRADE WIND
PATTERN ACROSS THE STATE TOWARD THE END OF NEXT WEEK.

&&

.AVIATION...
WEAK LAND BREEZES AND MOSTLY CLEAR SKIES WILL LINGER THROUGH THE
MORNING HOURS ACROSS MAUI COUNTY AND THE BIG ISLAND. LIGHT SEA
BREEZES AND INTERIOR CUMULUS BUILD UPS WILL DEVELOP IN THE AFTERNOON
ON FRIDAY.

FOR THE REMAINDER OF THE STATE...EXPECT INCREASING CLOUDS AND
SCATTERED SHOWERS THROUGH FRIDAY EVENING. LIGHT AND VARIABLE WINDS
THIS MORNING WILL SHIFT TO THE NORTH OR NORTHWEST BY AFTERNOON IN
RESPONSE TO A NEARLY STALLED FRONT TO THE NW OF THE ISLANDS.

LOCALIZED MVFR CONDS IN HEAVY SHOWERS ARE POSSIBLE TOWARDS EVENING
MOLOKAI WESTWARD...OTHERWISE VFR CONDS WILL PREVAIL ALL AREAS.

&&

.MARINE...
WINDS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS
ACROSS THE COASTAL WATERS TODAY AS A TROUGH LINGERS OVER THE AREA.
STRONGER N/NE WINDS WILL BUILD BACK INTO THE WESTERN SECTIONS
AROUND KAUAI TONIGHT TONIGHT AND SATURDAY...THEN INCREASED TRADES
WILL SPREAD ACROSS THE ENTIRE STATE SUNDAY INTO EARLY NEXT WEEK.
THERE IS SOME CHANCE THAT ADVISORY WINDS MAY OCCUR AROUND KAUAI AS
EARLY AS SATURDAY NIGHT OR SUNDAY. SCA CONDITIONS WILL BE POSSIBLE
IN THE TYPICALLY WINDY AREAS AROUND MAUI COUNTY AND THE BIG ISLAND
AS WELL SUNDAY INTO MONDAY.

SHORT PERIOD EASTERLY SWELL REMAINS ELEVATED AT THE PAUWELA BUOY
NORTH OF MAUI...ALTHOUGH SEAS HAVE DROPPED FROM NEAR 10 FT LAST
EVENING TO AROUND 8 FT NOW. THIS APPEARS TO BE A LOCALIZED
MAXIMUM...WITH SEAS AT MOKAPU POINT EAST OF OAHU ONLY RUNNING NEAR
5 FT. THIS SWELL SHOULD DECREASE SOMEWHAT LATER TODAY. RESULTING
SURF ALONG EAST FACING SHORES IS EXPECTED TO BE ELEVATED BUT
REMAIN SLIGHTLY BELOW ADVISORY LEVELS. OTHERWISE...SURF ALONG
NORTH FACING SHORES WILL REMAIN LOW THROUGH SUNDAY...THEN A NEW
NORTH- NORTHWEST SWELL MAY PUSH NORTH SHORE SURF TO ADVISORY
LEVELS SUNDAY NIGHT AND MONDAY. SEE THE COLLABORATIVE NEARSHORE
SWELL AND WIND FORECAST /SRDHFO/ FOR MORE DETAILS.

&&

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

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...BEDAL






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