High Surf in Hawaii, December 19 to 22, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST THU DEC 19 2013

.SYNOPSIS...
A COLD LOW ALOFT WILL KEEP THE ATMOSPHERE UNSTABLE ENOUGH THROUGH
TOMORROW MORNING TO PRODUCE THUNDERSTORMS ON THE BIG ISLAND WITH
SNOW OVER THE SUMMITS. HEAVY RAIN IS POSSIBLE FOR MAUI COUNTY. THE
ATMOSPHERE WILL STABILIZE TOMORROW BRINGING MORE SETTLED WEATHER AS
THE LOW MOVES AWAY TO THE NORTHEAST. A RIDGE NORTH OF THE ISLANDS
WILL PRODUCE LOCALLY BREEZY TRADE WINDS THROUGH TOMORROW MORNING.
THE TRADES WILL WEAKEN STARTING TOMORROW AS THE RIDGE SHIFTS CLOSER
TO THE ISLANDS.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS A COLD LOW ALOFT NEAR THE BIG ISLAND WHILE
A SURFACE RIDGE CONTINUES TO PRODUCE MODERATE TO LOCALLY STRONG
TRADE WINDS OVER THE ISLANDS. RADARS SHOW HEAVY SHOWERS MOVING
WESTWARD OVER THE BIG ISLAND IN THE TRADE-WIND FLOW WITH ISOLATED
HEAVY SHOWERS OVER MAUI COUNTY AND OAHU.

THE GLOBAL MODELS ARE IN GOOD AGREEMENT SHOWING THE LOW LINGERING
NEAR THE BIG ISLAND THROUGH THIS EVENING THEN MOVING OFF TO THE
NORTHEAST LATE TONIGHT. THE LOW ALOFT WILL KEEP THE ATMOSPHERE OVER
THE ISLANDS QUITE UNSTABLE SO SHOWERS NEAR THE ISLANDS MAY BE HEAVY
AND THUNDERSTORMS ARE POSSIBLE. THE THREAT OF HEAVY RAIN AND
THUNDERSTORMS WILL BE GREATEST OVER THE BIG ISLAND AND MAUI COUNTY
SINCE THEY ARE CLOSEST TO THE LOW. SHOWER ACTIVITY OVER WATER NEAR
THE ISLANDS HAS WEAKENED SINCE SUNRISE. SHOWERS ARE EXPECTED TO
INCREASE OVER LAND AREAS AS THE ISLANDS HEAT UP. SINCE TEMPERATURES
ARE COLD ALOFT...PRECIPITATION OVER THE HIGHER ELEVATIONS OF THE BIG
ISLAND IS LIKELY TO BE IN THE FORM OF SNOW.

AS THE LOW ALOFT MOVES AWAY LATE TONIGHT THE ATMOSPHERE WILL
STABILIZE AND THE THREAT OF HEAVY RAIN AND THUNDERSTORMS WILL
SUBSIDE. WE STILL EXPECT TO BE ABLE TO LET THE FLASH FLOOD WATCH
AMD THE WINTER WEATHER WARNING END EARLY FRIDAY MORNING.

A STRONG SURFACE HIGH FAR NORTHEAST OF THE AREA WITH A RIDGE
EXTENDING NORTH OF THE ISLANDS WILL KEEP TRADE WINDS BLOWING OVER
THE ISLANDS. THE TRADES WILL BE LOCALLY STRONG OVER WATER AROUND
MAUI AND THE BIG ISLAND THROUGH LATE TONIGHT. THE RIDGE WILL WEAKEN
AS A FRONT APPROACHES FROM THE NORTHWEST AND THAT WILL PRODUCE
LIGHTER WINDS. THE PREVAILING TRADE-WIND FLOW MAY GET LIGHT ENOUGH
TO ALLOW LAND AND SEA BREEZES TO BECOME MORE WIDESPREAD THROUGH
SUNDAY.

A TROUGH ALOFT WILL PERSIST EAST OF THE BIG ISLAND AFTER THE LOW
MOVES OFF TO THE NORTHEAST. A SHORT WAVE DROPPING SOUTH INTO THE
TROUGH MAY DESTABILIZE THE ATMOSPHERE AGAIN SATURDAY NIGHT BUT WE
EXPECT THAT NEXT SYSTEM TO BE WEAKER AND BRING LESS OF A THREAT OF
HEAVY RAIN AND THUNDERSTORMS.

THE RIDGE...AND THE TRADE WINDS WILL STRENGTHEN AGAIN EARLY NEXT
WEEK. RIDGING ALOFT WILL BUILD OVER THE AREA FROM THE WEST KEEPING
THE ATMOSPHERE RATHER STABLE THROUGH NEXT THURSDAY.

&&

.AVIATION...
A DEEP LOW ALOFT NEAR THE BIG ISLAND WILL CONTINUE TO PRODUCE
SIGNIFICANT AVIATION WEATHER IMPACTS TODAY WITH THE GREATEST
IMPACTS EXPECTED ON THE BIG ISLAND ...WHERE TEMPO MVFR AND ISOL IFR
CONDITIONS CAN BE EXPECTED IN +SHRA/+TSRA. ENHANCED SHRA ROTATING
AROUND THE UPPER LOW MAY IMPACT THE SMALLER ISLANDS WITH ISOL MVFR
CIG/VIS IN BRIEF PERIODS OF +SHRA.

AIRMET SIERRA FOR TEMPO MT OBSC CONTINUES FOR THE BIG ISLAND. AIRMET
TANGO CONTINUES FOR MOD TURB ASSOCIATED ALONG THE WEST SIDE OF THE
LOW ALOFT.

&&

.MARINE...
THE LOW ALOFT WILL ENCOURAGE HEAVY SHOWERS AND THUNDERSTORMS TO
DEVELOP OVER WINDWARD BIG ISLAND WATERS THROUGH FRIDAY MORNING. THIS
CONVECTION MAY PRODUCE LIGHTNING...REDUCED VISIBILITY...AND LOCALLY
STRONG...GUSTY WINDS. A SURFACE RIDGE WILL MAINTAIN SMALL CRAFT
ADVISORY STRENGTH WINDS OVER THE WINDY AREAS AROUND THE BIG ISLAND
AND MAUI THROUGH LATE TONIGHT.

THE WEST NORTHWEST SWELL REMAINS MUCH SMALLER THAN EXPECTED AT
BUOY 51101 NEAR NIHOA ISLAND. THIS SWELL IS STILL EXPECTED TO
PRODUCE LARGE SURF ALONG EXPOSED NORTH AND WEST FACING SHORES
THROUGH FRIDAY BUT THE SURF IS NOW EXPECTED TO ARRIVE UNTIL WELL
AFTER DARK. SURF IS EXPECTED TO RISE RAPIDLY ON KAUAI COUNTY SHORES
STARTING AROUND MIDNIGHT...THEN SPREAD DOWN TO THE BIG ISLAND FRIDAY
MORNING. PLEASE SEE THE SURF FORECAST AND HIGH SURF ADVISORY AND
WARNING FOR GREATER DETAILS ON SURF HEIGHTS AND TIMING.

THE LARGE SWELL ALSO WILL PRODUCE COMBINED SEAS ABOVE THE THRESHOLD
FOR A SMALL CRAFT ADVISORY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING TONIGHT THROUGH FRIDAY EVENING FOR NORTH AND
WEST FACING SHORES OF NIIHAU AND KAUAI AND NORTH FACING SHORES OF
OAHU MOLOKAI AND MAUI.

HIGH SURF WARNING FROM EARLY FRIDAY MORNING THROUGH SATURDAY EVENING
FOR WEST SHORES OF THE BIG ISLAND.

HIGH SURF ADVISORY TONIGHT THROUGH FRIDAY EVENING FOR WEST SHORES OF
OAHU LANAI AND KAHOOLAWE.

FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR THE BIG ISLAND AND MAUI
COUNTY.

WINTER STORM WARNING THROUGH EARLY FRIDAY MORNING FOR THE BIG ISLAND
SUMMITS.

SMALL CRAFT ADVISORY THROUGH FRIDAY EVENING FOR MOST AREAS.

&&

DONALDSON