Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 270639
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
839 PM HST THU FEB 26 2015

.SYNOPSIS...
A SURFACE TROUGH NEAR KAUAI AND OAHU WILL SLOWLY DRIFT EASTWARD
FRIDAY THROUGH SATURDAY. THE TROUGH WILL ACT AS A FOCUS FOR
CLOUDS AND SHOWERS...AND LOCALLY HEAVY RAIN WILL BE POSSIBLE FROM
FRIDAY AFTERNOON THROUGH AT LEAST SATURDAY AS THE ATMOSPHERE
BECOMES INCREASINGLY MOIST AND UNSTABLE. TRADE WINDS MAY REBUILD
ON SUNDAY...ALTHOUGH THE UNSETTLED WEATHER WILL LIKELY CONTINUE
INTO NEXT WEEK.

&&

.DISCUSSION...
PARTLY CLOUDY BUT MOSTLY DRY CONDITIONS PREVAIL ACROSS THE STATE
THIS EVENING...WITH RADAR DETECTING JUST ISOLATED SMALL SHOWERS
AT THE MOMENT. LATE IN THE AFTERNOON INTO THE EARLY EVENING THERE
WAS A LINE OF HEAVY SHOWERS WITH TOPS ABOVE 30K FEET WELL NORTH OF
OAHU...AND A LONE HEAVY SHOWER ALONG THE SW SLOPES OF HALEAKALA...
BUT THAT ACTIVITY HAS SINCE DISSIPATED. A COMPLEX PATTERN
PREVAILS BOTH AT THE SURFACE AND ALOFT ACROSS THE REGION. A SHARP
MID/UPPER LEVEL TROUGH AND ASSOCIATED STATIONARY FRONT ARE LOCATED
ABOUT 300 MILES NW OF KAUAI...WITH A WEAK LOW LEVEL TROUGH STALLED
IN THE KAUAI CHANNEL...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 00Z SOUNDINGS REFLECT THIS WITH
SUBSTANTIAL COOLING OCCURRING THROUGH THE MID AND UPPER LEVELS.
THIS COOLING ALOFT BASICALLY WIPED OUT THE TYPICAL MID LEVEL
INVERSION...BUT ATMOSPHERIC MOISTURE REMAINED QUITE MODEST WITH
PWATS JUST BELOW 1.2 INCHES.

OVERNIGHT...THE HIGHEST RAIN CHANCES SHOULD REMAIN OVER THE
WESTERN END OF THE STATE...WHERE WEAK LOW LEVEL CONVERGENCE IS
PRESENT ALONG THE STALLED TROUGH. ALTHOUGH INSTABILITY ALOFT IS
INCREASING...MOISTURE REMAINS SOMEWHAT LACKING AND THERE IS NO
STRONG FORCING PRESENT. THEREFORE WOULD GENERALLY EXPECT WIDELY
SCATTERED SHOWERS FOR OAHU AND KAUAI. FURTHER EAST...A DRIER
E/SE FLOW PREVAILS AROUND MAUI AND THE BIG ISLAND. THIS PATTERN
IS TYPICALLY RATHER DRY FOR MAUI DUE TO SHADOWING FROM THE BIG
ISLAND...AND SATELLITE IMAGERY ALSO INDICATES MOSTLY CLEAR SKIES
UPSTREAM FROM THE BIG ISLAND. WOULD EXPECT ONLY ISOLATED SHOWERS
FOR THOSE ISLANDS. THE EXISTING FORECAST APPEARS TO BE ON
TRACK...AND NO UPDATES ARE PLANNED FOR THIS EVENING.

ON FRIDAY...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 THE SMALLER ISLANDS...WHICH SHOULD BE ENOUGH OF A
TRIGGER GIVEN THE INSTABILITY ALOFT AND MOISTURE IN PLACE TO
TRIGGER AT LEAST ISOLATED HEAVY DOWNPOURS. AN ISOLATED THUNDERSTORM
WILL BE POSSIBLE AS WELL FRIDAY AFTERNOON...BUT THE CHANCES APPEAR
TOO LOW TO MENTION IN THE FORECAST AT THIS TIME.

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. ISOLATED THUNDER WILL REMAIN A POSSIBILITY AS WELL. 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 DIVERGE EARLY NEXT WEEK...WITH THE GFS AND CANADIAN
DEVELOPING ANOTHER SURFACE TROUGH OVER OR JUST EAST OF THE STATE...
WHILE THE ECMWF MAINTAINS MORE OF A WET TRADE PATTERN. WE HAVE
OPTED FOR THE ECMWF SOLUTION FOR NOW. EITHER WAY...ABOVE NORMAL
RAIN CHANCES WILL LIKELY CONTINUE THROUGH THE EARLY TO MID WEEK
PERIOD.

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

&&

.AVIATION...
WEAK LAND BREEZES AND MOSTLY CLEAR SKIES ARE EXPECTED ACROSS THE
EASTERN HALF OF THE STATE OVERNIGHT. LIGHT SEA BREEZES AND INTERIOR
CLOUDINESS WILL REDEVELOP IN THE AFTERNOON ON FRIDAY.

FOR THE WESTERN HALF OF THE STATE...EXPECT SCATTERED SHOWERS AND
INCREASING HIGH CLOUDS THROUGH FRIDAY. LIGHT AND VARIABLE WINDS
OVERNIGHT WILL SHIFT TO THE NORTH OR NORTHWEST DURING THE DAY ON
FRIDAY IN RESPONSE TO A NEARLY STALLED FRONT TO THE NW OF THE
ISLANDS.

LOCALIZED MVFR CONDS IN PASSING SHOWERS ARE POSSIBLE FRIDAY
AFTERNOON ON KAUAI AND OAHU...OTHERWISE VFR CONDS WILL PREVAIL ALL
AREAS.

&&

.MARINE...
THE THURSDAY MORNING ASCAT PASS SHOWED SOME AREAS OF 20 KT WINDS
SOUTH OF THE BIG ISLAND AND NORTHEAST OF MAUI...BUT NOTHING WORSE
THAN THAT. WINDS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT
ADVISORY LEVELS ACROSS THE COASTAL WATERS THROUGH FRIDAY AS A
TROUGH LINGERS OVER THE AREA. STRONGER N/NE WINDS WILL BUILD BACK
INTO THE FAR WESTERN SECTIONS FRIDAY NIGHT 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 BECOME MORE LIKELY BY THE MIDDLE OF NEXT WEEK AS
TRADE WINDS STRENGTHEN FURTHER.

SHORT PERIOD EASTERLY SWELL REMAINS ELEVATED AT SOME OF THE
WINDWARD BUOYS...PARTICULARLY PAUWELA NORTH OF MAUI WHERE SEAS
HAVE BEEN RUNNING NEAR 10 FT DURING THE DAY. THIS APPEARS TO BE A
LOCALIZED MAXIMUM...WITH SEAS AT MOKAPU POINT EAST OF OAHU ONLY
RUNNING NEAR 6 FT. THIS SWELL SHOULD PEAK OVERNIGHT THEN DROP BACK
A BIT ON FRIDAY. RESULTING SURF ALONG EAST FACING SHORES IS
EXPECTED TO BE ELEVATED BUT REMAIN JUST 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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