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Hawaiian Islands Synoptic Discussion and Guidance

007
FXHW60 PHFO 262005
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST THU FEB 26 2015

.SYNOPSIS...
WINDS WILL BECOME LIGHT AND VARIABLE OVER THE SMALLER ISLANDS
TODAY AND SOUTHEAST AROUND THE BIG ISLAND TONIGHT...AS A SURFACE
TROUGH SETTLES OVER THE STATE. THE TROUGH WILL REMAIN NEAR KAUAI
AND OAHU TONIGHT THEN DRIFT EASTWARD FRIDAY AND SATURDAY. THE
TROUGH WILL ACT AS A FOCUS FOR CLOUDS AND SHOWERS...AND LOCALLY
HEAVY RAIN WILL BE POSSIBLE FROM FRIDAY NIGHT INTO THE WEEKEND AS
THE ATMOSPHERE BECOMES INCREASINGLY MOIST AND UNSTABLE. AN UNSETTLED
TRADE WIND PATTERN WILL LIKELY CONTINUE THROUGH THE WEEKEND AND MAY
PERSIST INTO NEXT WEEK.

&&

.DISCUSSION...
A COMPLEX UNSETTLED WEATHER PATTERN IS SLOWLY EVOLVING OVER THE
STATE. AN ERODING RIDGE ALOFT LIES OVER THE ISLANDS...WHILE A WEAK
SURFACE TROUGH NEAR OAHU THIS MORNING IS DRIFTING TO THE WEST. A
DEEP...NEARLY STATIONARY TROUGH IS OBSERVED TO THE NORTHWEST WITH AN
ASSOCIATED FRONT SITTING ABOUT 150 MILES NORTHWEST OF KAUAI. A
COMPACT UPPER LEVEL LOW AND AN ASSOCIATED SURFACE TROUGH CENTERED
ABOUT 600 MILES EAST-SOUTHEAST OF HILO ARE DRIFTING TOWARD THE
STATE. THESE FEATURES WILL COME TOGETHER OVER THE ISLANDS AT VARIOUS
TIMES DURING THE NEXT FEW DAYS...LEADING TO AN UNSETTLED WEATHER
PATTERN.

FOR TODAY...THE HIGHEST CHANCES FOR SHOWERS WILL BE OVER THE SMALLER
ISLANDS...ESPECIALLY OAHU...DURING THE AFTERNOON. THE ABOVE
MENTIONED SURFACE TROUGH WILL BE WEAKENING...BUT IT WILL REMAIN
STRONG ENOUGH TO ALTER THE BACKGROUND WIND FLOW OUT OF THE EAST-
SOUTHEAST. THIS WILL LEAD TO WIDESPREAD AFTERNOON SEA BREEZES ON THE
SMALLER ISLANDS THAT WILL TRIGGER INTERIOR CLOUDS AND SHOWERS...
AND WITH LOW LEVEL MOISTURE REMAINING CONCENTRATED NEAR THE
TROUGH...OAHU WILL HAVE THE HIGHEST CHANCES FOR SHOWERS TODAY.
ALTHOUGH WEAKENING...THE RIDGE ALOFT SHOULD REMAIN STRONG ENOUGH TO
INHIBIT HEAVY SHOWER DEVELOPMENT. EXPECT A DRIER EASTERLY TRADE WIND
FLOW ACROSS THE BIG ISLAND.

THE HIGHEST CHANCES FOR ENHANCED SHOWER ACTIVITY WILL BE OVER THE
WESTERN END OF THE STATE TONIGHT AND FRIDAY. THE SURFACE TROUGH WILL
WASH OUT...BUT SOME ENHANCED MOISTURE SHOULD LINGER WEST OF MAUI.
THE TROUGH AND FRONT TO THE NORTHWEST OF KAUAI WILL BE WEAKENING
AND PUSHING EASTWARD TO KAUAI AND OAHU AT THE SAME TIME...AND THE
DIFLUENT PORTION OF THE JET STREAM ALOFT WILL BE MOVING OVER THE
STATE. THIS WILL SET UP MOIST UNSTABLE CONDITIONS OVER THE WESTERN
HALF OF THE STATE. HEAVY SHOWERS ARE CURRENTLY NOT INCLUDED IN THE
FORECAST...BUT WE WILL HAVE TO TAKE A CLOSE LOOK AT THAT DURING THE
DAY SHIFT.

UNSETTLED WEATHER WILL PERSIST ACROSS PORTIONS OF THE STATE THROUGH
AT LEAST THE WEEKEND. THE UPPER LEVEL TROUGH WITH COLD TEMPS ALOFT
WILL REMAIN OVERHEAD...WHILE A LOW LEVEL TROUGH WILL LIKELY CONTINUE
TO BE THE FOCUS FOR CLOUDS AND HEAVY SHOWERS. UNCERTAINTY REMAINS
SOMEWHAT HIGH AS TO THE EXACT LOCATION OF THE TROUGH...BUT IT WILL
LIKELY DRIFT FROM OAHU TO AS FAR EAST AS MAUI OR THE BIG ISLAND ON
SATURDAY BEFORE WEAKENING. TO FURTHER COMPLICATE ISSUES...THE GFS IS
SHOWING THE AREA OF LOW LEVEL MOISTURE...CURRENTLY 800 MILES TO THE
SOUTHEAST OF THE STATE...PROVIDING A BOOST TO RAINFALL CHANCES ON
SUNDAY AND MONDAY.

&&

.AVIATION...
A SURFACE TROUGH OVER OAHU THIS MORNING IS CONTINUING TO ENHANCE
SHOWERS...MAINLY BETWEEN MOLOKAI AND KAUAI. AIRMET SIERRA FOR
MOUNTAIN OBSCURATIONS ARE IN PLACE OVER LANAI AND N THRU E SECTIONS
OF MOLOKAI...OAHU...AND KAUAI.

TERMINALS...OVERALL...SHOULD REMAIN PREDOMINATELY VFR WITH ONLY
POSSIBLE PERIODS OF MVFR IN SHOWERS. LOWER CLOUDS ARE LIKELY TO HANG
AROUND OVER LANAI...CREATING MVFR WITH ISOL IFR CIGS THROUGHOUT THE
DAY. A STALLED COLD FRONT TO THE WEST OF KAUAI AND THE SURFACE
TROUGH ARE HELPING TO CREATE LIGHT EAST TO SOUTH EAST FLOW OVER THE
ISLANDS...PROMOTING SEA BREEZE AND INTERIOR CLOUDS THIS AFTERNOON.

&&

.MARINE...
NO MARINE WARNINGS OR ADVISORIES ARE IN EFFECT. THE WEST-NORTHWEST
SWELL CONTINUES TO DROP AT BUOY 51101...DOWN TO JUST OVER 5 FT AT 11
SECONDS AT THE LAST OBSERVATION. THIS STEADY TREND ALONG WITH A
LOOK AT SURF CAMERAS NEAR KAILUA-KONA HAS LED TO THE HIGH SURF
ADVISORY BEING DROPPED FOR WEST FACING SHORES OF THE BIG ISLAND. THE
NEXT SWELL WITH BORDER LINE HIGH SURF ADVISORY POTENTIAL WILL BE
FROM THE NORTH-NORTHWEST ON SUNDAY NIGHT AND MONDAY. A SMALL
INCREASE IN FRESH...SHORT-PERIOD EASTERLY IS ALSO DUE TONIGHT AND
THURSDAY WITH EAST SHORE SURF EXPECTED TO REMAIN BELOW ADVISORY
LEVELS.


LIGHTER WINDS WILL PREVAIL TODAY THROUGH FRIDAY AS A SURFACE TROUGH
LINGERS OVER THE ISLANDS. TRADE WINDS SHOULD BUILD BACK IN ACROSS
THE STATE DURING THE WEEKEND INTO EARLY NEXT WEEK...WITH SOME CHANCE
THAT WINDS MAY APPROACH ADVISORY LEVELS ACROSS THE WINDIER ZONES.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...

&&

$$

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






Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office