High Surf in Hawaii, December 16 to 18, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST FRI DEC 16 2011

.SYNOPSIS...
A SLOW MOVING COLD FRONT NORTHWEST OF THE MAIN HAWAIIAN ISLANDS WILL
STALL AND WEAKEN TO OUR NORTH TODAY. TRADE WINDS WILL THEN INCREASE
AND REMAIN STRONG THROUGH THE WEEKEND AS HIGH PRESSURE BUILDS 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. HOWEVER...WITH THE STRONGER WINDS...SOME SHOWERS
WILL 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...
THERE IS LITTLE OR NO CHANGE IN FORECAST PHILOSOPHY FROM LAST
EVENING. A 1030 MB HIGH NEAR 40N131W...JUST OFF THE NORTHERN
CALIFORNIA COAST...HAS AN ASSOCIATED RIDGE WHICH EXTENDS
SOUTHWESTWARD THROUGH 28N145W AND 27N153W. A FRONTAL BOUNDARY ABOUT
250 MILES NORTHWEST OF KAUAI HAS PUSHED THIS RIDGE RATHER CLOSE TO
THE ISLANDS THIS MORNING...YET THE PRESSURE GRADIENT ACROSS THE
ISLANDS IS SUFFICIENTLY STEEP TO SUPPORT 15 TO 20 MPH TRADE WINDS
ACROSS LOCAL WATERS. SATELLITE LOOP SHOWS GENERALLY SCATTERED LOW
CLOUDS UPWIND FROM THE ISLANDS...WITH PATCHY BROKEN LOW CLOUDS
FORMING ALONG LEEWARD CONVERGENCE LINES TO THE WEST OF THE ISLANDS.
WATER VAPOR LOOP SHOWS UPPER TROUGHING JUST EAST OF THE
ISLANDS...WITH ANOTHER UPPER TROUGH APPROACHING US FROM THE
NORTHWEST. OVERNIGHT SOUNDINGS SHOW THE PRESENCE OF LINGERING UPPER
TROUGH-INDUCED INSTABILITY...WITH WEAK INVERSIONS AND NEGATIVE
LIFTED INDEX VALUES.

MODELS SHOW THE FRONT TO OUR NORTHWEST WILL STALL LATER TODAY...
BEFORE REACHING THE MAIN ISLAND CHAIN. AS IT SLOWS...THIS FRONT WILL
BEGIN TO WEAKEN...AT THE SAME TIME THE FOLLOWING HIGH BEGINS TO
STRENGTHEN. THE PRESSURE GRADIENT ACROSS THE ISLANDS WILL STEEPEN AS
THE HIGH STRENGTHENS...CAUSING TRADE WINDS TO INCREASE ACROSS LOCAL
WATERS. WITH NO MAJOR SYSTEMS EXPECTED THROUGH THE NEXT WEEK...THE
RIDGE WILL DOMINATE LOW LEVEL FLOW AND TRADE WINDS WILL CONTINUE
BLOWING THROUGH THE FORECAST PERIOD. CLOUDS AND SHOWERS WILL FAVOR
WINDWARD AND MAUKA AREAS...BLOWING LEEWARD AT TIMES DURING WINDIER
PERIODS.

THE UPPER TROUGH NORTHWEST OF THE ISLANDS WILL CONTINUE DIGGING TO
THE SOUTHEAST TOWARD US...SETTLING ACROSS THE ISLANDS OVER THE
WEEKEND. THE UPPER TROUGH WILL ENHANCE TRADE SHOWERS A BIT SATURDAY
AND SUNDAY...WITH MOST ENHANCEMENT SHIFTING EASTWARD TOWARD THE BIG
ISLAND AFTER THE WEEKEND AS THE UPPER TROUGH DRIFTS EASTWARD. THE
06Z GFS WANTS TO DEVELOP A SURFACE LOW JUST SOUTHEAST OF THE ISLANDS
NEXT THURSDAY AND FRIDAY...BENEATH THE UPPER TROUGH. HOWEVER...THIS
IS TOO FAR OUT IN TIME TO CONFIDENTLY ADD TO THE GRIDDED DATABASE.

&&

.MARINE...
A NORTHWEST SWELL WILL BUILD ACROSS THE SMALLER ISLANDS THROUGH THE
DAY TODAY AND...AS A RESULT...A HIGH SURF ADVISORY IS NOW IN EFFECT
FOR NORTH AND WEST FACING SHORES OF MOST OF THE SMALLER ISLANDS. THE
SWELL WILL PEAK TODAY...BUT WILL ONLY GRADUALLY DIMINISH THROUGH THE
WEEKEND. THE ADVISORY RUNS THROUGH SUNDAY. IF THE SWELL IS SLIGHTLY
LARGER THAN EXPECTED...SURF COULD APPROACH WARNING LEVELS.

IN ADDITION TO THE SURF HAZARD...THIS SWELL IS EXPECTED TO EXCEED
THE 10 FOOT SMALL CRAFT ADVISORY THRESHOLD. WINDS WILL ALSO INCREASE
TO NEAR 25 KNOTS THROUGH THE WINDIER CHANNELS LATER TODAY. THE
COMBINATION OF WINDS AND COMBINED SEAS WILL LEAD TO SMALL CRAFT
ADVISORY CONDITIONS. A SMALL CRAFT ADVISORY WILL GO INTO EFFECT
BEGINNING THIS MORNING FOR MOST WATERS...EXPANDING TO ADDITIONAL
WATERS TONIGHT.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY THROUGH 6 PM HST SUNDAY FOR NORTH AND WEST FACING
SHORES OF NIIHAU KAUAI AND OAHU...AND FOR NORTH FACING SHORES OF
MOLOKAI AND MAUI.

SMALL CRAFT ADVISORY THROUGH 6 AM HST SATURDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-KAUAI CHANNEL-OAHU
WINDWARD WATERS-KAIWI CHANNEL-MAUI COUNTY WINDWARD WATERS-MAALAEA
BAY-PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.

SMALL CRAFT ADVISORY FROM 6 PM TODAY TO 6 AM HST SATURDAY FOR OAHU
LEEWARD WATERS-BIG ISLAND WINDWARD WATERS.

&&

POWELL