High Surf in Hawaii, December 25 to 31, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST TUE DEC 25 2007

.SYNOPSIS...HIGH PRESSURE BUILDING NORTH OF THE STATE WILL CONTINUE
TO BRING GUSTY TRADE WINDS THROUGH SATURDAY. IN GENERAL...THE
ISLANDS WILL SEE A RATHER WET TRADE WIND WEATHER PATTERN THIS WEEK.
THE BIG ISLAND WILL SEE THE MOST SHOWER ACTIVITY TODAY.

&&

.DISCUSSION...WATER VAPOR IMAGERY SHOWS A COMPLEX UPPER LEVEL
PATTERN OVER THE CENTRAL PACIFIC. A BROAD UPPER LEVEL TROUGH IS
APPROACHING THE STATE FROM THE WEST...WHILE THE MID-LEVEL TROUGH
CONTINUES TO LINGER SOUTHEAST OF THE BIG ISLAND. 12Z SOUNDINGS ARE
NOT TOO MUCH DIFFERENT FROM THE 00Z SOUNDINGS...WITH PHTO STILL
UNSTABLE AND PHLI ONLY SHOWING A WEAK INVERSION. 13Z POES AMSU PASS
SHOWED THE FIRST BAND OF HIGHER TOTAL PRECIPITABLE WATER SPREADING
ACROSS THE SMALLER ISLANDS...WITH ANOTHER AREA OF MOISTURE JUST
UPSTREAM FROM THE BIG ISLAND. TPW VALUES ARE NEAR 1.5 INCHES...WHICH
IS ACTUALLY A TOUCH UNDER THE 1.67 INCHES FROM THE 12Z PHTO RAOB.
CONVECTION CONTINUES TO FLARE ACROSS THE BIG ISLAND EARLY THIS
MORNING...ALTHOUGH CLOUD TOPS ARE BEGINNING TO WARM. DESPITE THE
DEEP CONVECTION...RAINFALL RATES HAVE BEEN RATHER BENIGN. MOST
HYDRONET GAGES REPORTED RAINFALL RATES OF A FEW TENTHS OF AN INCH
PER HOUR...WITH THE WAIAKEA UKA GAGE THE ONLY ONE TO BRIEFLY HIT ONE
INCH PER HOUR. HOWEVER...SHOWERS WERE PERSISTENT AND TOTAL RAINFALL
BEGAN TO ADD UP. THE HONOLII STREAM AND WAILUKU RIVER BOTH SHOWED
SIGNIFICANT RISES OVERNIGHT...BUT BOTH ARE ON THEIR WAY DOWN AS THE
FIRST WAVE OF SHOWERS DIMINISHES.

ANOTHER BAND OF CLOUDS IS MOVING INTO THE COASTAL WATERS UPSTREAM
FROM MAUI AND THE BIG ISLAND. THESE CLOUDS AND SHOWERS WILL AFFECT
MAUI AND THE BIG ISLAND THIS MORNING...AND SPREAD DOWN ACROSS THE
REST OF THE STATE BY THIS AFTERNOON. WHILE THE BULK OF THE RAIN
WILL FALL OVER WINDWARD LOCATIONS...THE STRONG WINDS WILL BLOW SOME
SHOWERS TO LEEWARD AREAS AS WELL. LOW-LIGHT WEB CAMS ON MAUNA KEA
SHOW THE SUMMIT HAS BEEN CLOUDED OVER FOR A FEW HOURS. THE BIG
ISLAND IS EXPECTED TO REMAIN UNSTABLE AHEAD OF THE APPROACHING UPPER
TROUGH...AND THE NEXT ROUND OF SHOWERS SHOULD BE ABLE TO REACH THE
SUMMIT AS WELL. THE FREEZING LEVEL ON THE PHTO SOUNDING IS 12.8KFT.
ANY SHOWERS THAT REACH THE SUMMIT COULD BRING ADDITIONAL SNOW
ACCUMULATION. THEREFORE WE EXTENDED THE WINTER WEATHER ADVISORY
THROUGH THE DAY. GFS CROSS SECTIONS SHOW MOISTURE DEPTH DIMINISHING
TONIGHT.

THE STRONG HIGH PRESSURE CELL NORTH OF THE STATE IS MOVING EAST
RATHER FAST AHEAD OF ANOTHER NORTHERN STREAM LOW. IT IS NOT UNTIL
WEDNESDAY/THURSDAY THAT THE HIGH BEGINS TO EDGE BACK TOWARD THE
STATE. EVEN THOUGH THE HIGH WILL BE WEAKENING AT THAT POINT...THIS
LOOKS TO BE THE MOST FAVORABLE TIME FOR STRONG WINDS ACROSS THE
STATE. THE LOCAL HIGH RESOLUTION WRF-NMM FROM 00Z/24 SHOWS WIND
SPEEDS STRENGTHENING ON TUESDAY. HOWEVER...THE 00Z/25 NAM AND GFS
BOTH SHOW THE STRONGEST WINDS PICKING UP AT THE END OF THE WEEK.

EXTENDED MODELS CONTINUE TO SHOW A PATTERN CHANGE BY THE END OF THE
FORECAST PERIOD...ALTHOUGH THERE IS A WIDE SPREAD IN THE DETAILS.
THE 00Z ECMWF IS SHARPER AND FARTHER SOUTH THAN THE 00Z GFS WITH
THE UPPER TROUGH DIGGING ACROSS THE CENTRAL PACIFIC. HOWEVER...THE
18Z GFS WAS FARTHER SOUTH THAN THE ECMWF. THE GFS RUNS HAVE BEEN
BOUNCING BACK AND FORTH BETWEEN DRY AND STABLE AND WET AND SHOWERY
CONDITIONS ACROSS THE STATE OVER THE PAST FEW RUNS. FOR NOW IT LOOKS
SAFE TO SAY THAT THE RIDGE WILL WEAKEN AND BE DISPLACED SOUTHWARD
TOWARDS US...WEAKENING THE TRADES BY SUNDAY. HOWEVER ADDITIONAL
DETAILS ARE HARD TO PIN DOWN GIVEN THE LARGE UNCERTAINTY ASSOCIATED
WITH THE PATTERN CHANGE.

&&

.MARINE...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR ALL COASTAL
WATERS...AND WILL CONTINUE FOR MUCH OF THE WEEK. THE EVENING
QUIKSCAT PASS MISSED HAWAII...BUT DID SHOW THE STRONGEST WINDS
ASSOCIATED WITH THE TIGHTEST PRESSURE GRADIENT BETWEEN 140W AND
150W. CONSIDERING THAT THE HIGH WILL CONTINUE MOVING EASTWARD
THROUGH WEDNESDAY...THE STRONGEST WINDS WILL REMAIN EAST OF THE
STATE. BY LATE WEDNESDAY/THURSDAY THE HIGH WILL BEGIN TO EDGE
SOUTHWESTWARD TOWARD THE STATE. THE 00Z/06Z NAM/GFS SHOW THIS TIME
FRAME AT THE END OF THE WEEK AS BEING OUR BEST CHANCE FOR STRONG
WINDS. THEREFORE WE DROPPED THE GALE WATCH FOR NOW.

WAVES AT THE KAILUA BAY BUOY HAVE RISEN TO 9FT...ALTHOUGH THE PERIOD
IS DOWN TO 10 SECONDS. 00Z/06Z WAVEWATCH III GUIDANCE BACKED OFF A
FEW FEET FROM EARLIER RUNS...BUT CONTINUES TO SHOW THE EASTERLY
TRADE WIND SWELL SLOWLY BUILDING OVER THE NEXT SEVERAL DAYS. HIGH
SURF ALONG EAST FACING SHORES MAY LAST INTO THE WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST THURSDAY FOR KAUAI WINDWARD-
OAHU KOOLAU-OLOMANA-MOLOKAI WINDWARD-MAUI WINDWARD WEST-WINDWARD
HALEAKALA-SOUTH BIG ISLAND-BIG ISLAND NORTH AND EAST.

WINTER WEATHER ADVISORY UNTIL 6 PM HST THIS AFTERNOON FOR BIG
ISLAND SUMMITS.

SMALL CRAFT ADVISORY UNTIL 6 AM HST THURSDAY FOR ALL HAWAIIAN
WATERS-

&&

BRAVENDER