High Surf Advisory 46, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST THU DEC 15 2011

.SYNOPSIS...
A COLD FRONT NORTHWEST OF THE AREA WILL STALL AND WEAKEN NORTH OF
THE ISLANDS ON FRIDAY. TRADE WINDS WILL INCREASE ON FRIDAY AND
CONTINUE THROUGH THE WEEKEND AS HIGH PRESSURE BUILDS IN BEHIND THE
FRONT. AN UPPER LEVEL TROUGH WILL MOVE ACROSS THE STATE THIS
WEEKEND...BRINGING A SLIGHT INCREASE IN SHOWERS FOR MAINLY WINDWARD
AND MAUKA SECTIONS. WITH THE STRONGER WINDS...SOME SHOWERS WILL ALSO
SPREAD ACROSS LEEWARD SECTIONS AS WELL. THE UPPER LEVEL TROUGH WILL
DEVELOP INTO A LOW SOUTH OF THE STATE EARLY NEXT WEEK...AND MAY
BRING ADDITIONAL MOISTURE AND SHOWERS TO THE BIG ISLAND.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL LOW FAR NORTHEAST OF THE
STATE...WITH A TROUGH EXTENDING SOUTHWESTWARD FROM IT...LOCATED JUST
SOUTHEAST OF THE BIG ISLAND. THE 12Z SOUNDING FROM HILO SHOWS THE
ATMOSPHERE FURTHER STABILIZING AS HEIGHTS REBUILD BEHIND THE
TROUGH...WITH UP TO 5C OF WARMING AT MID-LEVELS OVER THE PAST 24
HOURS AND SIGNIFICANT DRYING ABOVE 700MB. THE 12Z SOUNDING FROM
LIHUE IS SLIGHTLY MORE STABLE...WITH A WEAK INVERSION NEAR 5KFT /AS
OPPOSED TO NEAR 9KFT ON THE HILO SOUNDING/. AT THE SURFACE...A WEAK
RIDGE IS LOCATED OVER THE NORTHERN OFFSHORE WATERS...WITH A COLD
FRONT ABOUT 500 MILES NORTHWEST OF KAUAI.

THE 12Z GFS AND NAM ARE SIMILAR AND CONSISTENT WITH PREVIOUS RUNS...
SHOWING THE FRONT NORTHWEST OF THE STATE STALLING NORTH OF KAUAI ON
FRIDAY BEFORE DISSIPATING. HIGH PRESSURE BUILDS IN NORTH AND
NORTHEAST OF THE STATE BEHIND THE FRONT...STRENGTHENING THE PRESSURE
GRADIENT OVER THE ISLANDS. WINDS BACK TO A MORE TYPICAL TRADE WIND
DIRECTION ON FRIDAY UNDER INFLUENCE OF THE NEW HIGH. THE MORE
NORTHEASTERLY WINDS MAY BRING LINGERING MOISTURE FROM THE DISSIPATED
BOUNDARY TOWARD KAUAI SATURDAY/SATURDAY NIGHT...HELPING TO ENHANCE
TRADE WIND SHOWERS. FORECAST SOUNDINGS SHOW THE ATMOSPHERE REMAINING
STABLE...SO HEAVY RAINS ARE NOT EXPECTED.

FOR THE SECOND HALF OF THE WEEKEND...THE GFS AND 00Z ECMWF ARE ALSO
SIMILAR SHOWING AN UPPER LEVEL TROUGH DEVELOPING OVER THE STATE.
WITH ADDITIONAL ENERGY...THIS TROUGH DEVELOPS INTO A CUTOFF LOW
SOUTH OF THE STATE BY EARLY NEXT WEEK. BY THIS POINT DIFFERENCES
DEVELOP WITH RESPECT TO THE AMOUNT OF SURFACE DEVELOPMENT ASSOCIATED
WITH THE SYSTEM. THE 12Z GFS IS STRONGER THAN THE 06Z RUN...AND
DEVELOPS A COMPACT SURFACE LOW THAT PASSES JUST SOUTH OF THE BIG
ISLAND. A NUMBER OF GFS ENSEMBLES ALSO SHOW A SURFACE WAVE...BUT
NONE ARE AS STRONG AS THE OPERATIONAL RUN. IT WILL BE INTERESTING TO
SEE HOW THE 12Z ECMWF LOOKS. AS IT STANDS...THE 00Z ECMWF ALREADY
SHOWED A STRONGER GRADIENT OVER THE ISLANDS THAN THE 06Z GFS RUN...
AND THE NEW 12Z GFS WOULD INDICATE EVEN STRONGER WINDS ACROSS THE
STATE. AS FOR RAINFALL...GIVEN THE LOCATION OF THE UPPER LOW...THE
BIG ISLAND WOULD LIKELY BEAR THE BRUNT OF ANY ACTIVITY. THE AMOUNT
OF RAINFALL WILL DEPEND ON THE DEGREE OF SURFACE DEVELOPMENT TO
FOCUS ACTIVITY...AND THAT REMAINS UNCERTAIN GIVEN THE MODEL
VARIABILITY.

&&

.AVIATION...
EXPECT BRIEF HEAVY SHOWERS FOR HILO...LOWERING VISIBILITIES AND
CEILINGS. OTHERWISE...VFR CONDITIONS WILL PREVAIL FOR ALL TERMINALS
WITH BRIEF MVFR CONDITIONS FROM SHOWERS EMBEDDED IN THE TRADE WIND
FLOW. THESE SHOWERS WILL FAVOR THE WINDWARD AND MOUNTAIN AREAS.

&&

.MARINE...
THE 12Z WAVEWATCH III GUIDANCE SHOWS THE NEXT MAJOR NORTHWEST SWELL
BUILDING LATE THURSDAY NIGHT. THIS SWELL IS EXPECTED TO EXCEED 10 FT
AND LEAD TO SMALL CRAFT ADVISORY CONDITIONS FOR MOST EXPOSED COASTAL
WATERS. SURF WILL ALSO EXCEED ADVISORY LEVELS FOR NORTH AND WEST
FACING SHORES OF 15FT/12FT RESPECTIVELY BY FRIDAY...AND MAY APPROACH
WARNING LEVELS OF 25FT/20FT AS WELL. THIS SWELL WILL PERSIST INTO
SATURDAY BEFORE DIMINISHING. IN ADDITION TO THE SEAS...WINDS THROUGH
THE TYPICALLY WINDIER LOCATIONS ARE ALSO EXPECTED TO REACH 25 KNOT
SMALL CRAFT ADVISORY LEVELS BEGINNING FRIDAY.

&&

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

&&

PUBLIC/MARINE...BRAVENDER
AVIATION...LUTU-MCMOORE