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Hawaiian Islands Synoptic Discussion and Guidance

401
FXHW60 PHFO 271951
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST FRI FEB 27 2015

.SYNOPSIS...
A SURFACE TROUGH NEAR OAHU WILL SLOWLY DRIFT EASTWARD ACROSS THE
CENTRAL PART OF THE STATE THROUGH TOMORROW...DISRUPTING THE TRADE
WIND FLOW AND ACTING AS A FOCUS FOR CLOUDS AND SHOWERS. AN UPPER
LEVEL TROUGH LINGERING OVER THE STATE WILL MAINTAIN A CHANCE OF
LOCALLY HEAVY SHOWERS NEAR THE TROUGH...MAINLY DURING THE AFTERNOON
HOURS AS SEA BREEZES DRIVE CONVECTION. TRADE WINDS WILL ON SUNDAY
AND CONTINUE INTO NEXT WEEK...ALTHOUGH THE WET AND UNSETTLED WEATHER
PATTERN WILL LIKELY CONTINUE.

&&

.DISCUSSION...
THE CENTRAL ISLANDS ARE EXPECTED TO BE THE FOCUS FOR AFTERNOON
SHOWERS TODAY...SOME HEAVY WITH A SLIGHT CHANCE OF THUNDERSTORMS. A
NORTH-SOUTH ORIENTED SURFACE TROUGH...ARGUABLY THE TAIL END OF A
FRONT...CURRENTLY CROSSES OAHU...AND ALTHOUGH OVERNIGHT LAND BREEZES
HAVE KEPT OAHU RATHER QUIET...SCATTERED SHOWERS...SOME HEAVY...ARE
OBSERVED OFFSHORE. THE SURFACE TROUGH WILL DRIFT EASTWARD TO MAUI
COUNTY LATER TODAY...KEEPING WINDS LIGHT AND VARIABLE ACROSS THE
CENTRAL ISLANDS AND POOLING LOW LEVEL MOISTURE NEAR OAHU AND MAUI
COUNTY. DAYTIME SEA BREEZES WILL TAP THIS MOISTURE...PRODUCING
CLOUDS AND SHOWERS. ALOFT...THE ISLANDS LIE UNDER THE EXIT REGION OF
A JET STREAM AND THE SOUTHEAST PORTION OF A MID LEVEL TROUGH.
INSTABILITY CREATED BY THESE FEATURES WILL BE ENOUGH TO SUPPORT
LOCALIZED HEAVY SHOWERS...ALONG WITH A SLIGHT CHANCE OF
THUNDERSTORMS FOR OAHU.

ELSEWHERE ACROSS THE STATE TODAY...AVAILABLE MOISTURE WILL BE
SOMEWHAT LIMITED. A DRIER NORTHERLY FLOW WITH DEW POINTS DOWN
SEVERAL DEGREES HAS DEVELOPED NEAR KAUAI TO THE WEST OF THE SURFACE
TROUGH. SOME AFTERNOON CONVECTION IS EXPECTED...BUT IT SHOULD BE
WEAKER WITH FEWER SHOWERS. ON THE BIG ISLAND...A SOUTHEASTERLY FLOW
IS PRODUCING LITTLE IN THE WAY OF SHOWERS THIS MORNING...BUT THERE
IS ENOUGH MOISTURE TO PRODUCE WIDESPREAD AFTERNOON CLOUDS WITH SOME
SHOWERS ON THE SLOPES.

UNSETTLED WEATHER WILL LIKELY CONTINUE ACROSS THE STATE THROUGH
THE WEEKEND. THE MID/UPPER LEVEL TROUGH WILL REMAIN 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 BY 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...
A SURFACE TROUGH SITS OVER OAHU THIS MORNING AND WILL SLOWLY MOVE
EAST TO MAUI COUNTY TODAY. AS OF 19Z...SCATTERED SHOWERS ARE MAINLY
FOCUSED ALONG THE TROUGH...IN THE COASTAL WATERS NORTH AND SOUTH OF
OAHU. THESE SHOWERS LIKELY CARRY MVFR CIGS/VIS WITH POTENTIAL ISOL
IFR. CLOUD TOPS ARE GENERALLY BETWEEN 100 AND 150 WITH SOME TOPS
REACHING ABOVE FL220. LIGHTNING ACTIVITY THIS MORNING REMAINS APPROX
175 NM NORTH OF PHNL. CONDITIONS MAY BE CONDUCIVE FOR INTERIOR
CONVECTION...AND THERE IS A SLIGHT CHANCE OF THUNDERSTORMS OVER
OAHU THIS AFTERNOON. AS THE TROUGH SHIFTS EAST...EXPECT SHOWER
ACTIVITY TO INCREASE OVER MAUI COUNTY.

OVER THE BIG ISLAND...EXPECT THE CLEAR MORNING SKIES TO CLOUD UP
ALONG THE SLOPES THIS AFTERNOON. HOWEVER...VFR IS FORECAST TO
REMAIN. SHOWER ACTIVITY WILL BEGIN TO INCREASE LATER THIS EVENING
AND TONIGHT ALONG THE NORTH AND EAST SECTIONS ON THE BIG ISLAND.
FOR KAUAI...EXPECT PREVAILING VFR TODAY...WITH PASSING ISOLATED
SHOWERS.

&&

.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 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.

EASTERLY SWELL AROUND 5 FT 11 SECONDS WILL REMAIN THE DOMINANT
SOURCE OF SEAS ACROSS MOST AREAS TODAY...THOUGH FRESH NORTHERLY
WINDS DEVELOPING AROUND KAUAI WILL LEAD TO LARGER SEAS AROUND THE
GARDEN ISLE. SURF ALONG EAST FACING SHORES WILL STAY BELOW HIGH SURF
ADVISORY LEVELS AS THE EAST SWELL WILL GRADUALLY DECLINE THROUGH
SATURDAY. SURF ALONG NORTH FACING SHORES WILL REMAIN LOW THROUGH
SUNDAY. A NORTH-NORTHWEST SWELL WILL PUSH NORTH SHORE SURF TO AROUND
THE ADVISORY LEVEL SUNDAY NIGHT AND MONDAY. SEE THE COLLABORATIVE
NEARSHORE SWELL AND WIND FORECAST /SRDHFO/ FOR MORE DETAILS.

&&

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

&&

$$

DISCUSSION/MARINE...WROE/JACOBSON
AVIATION...EATON






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