FXHW60 PHFO 261413
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST SAT DEC 26 2009
.SYNOPSIS...
EXPECT THE TRADE WINDS TO GRADUALLY WEAKEN AND SHIFT TO A
SOUTHEASTERLY DIRECTION AHEAD OF A SURFACE RIDGE SAGGING DOWN ACROSS
THE STATE SUNDAY AND MONDAY. THIS RIDGE IN THE VICINITY OF THE ALOHA
STATE WILL RESULT IN LIGHT WINDS WITH LOCAL AFTERNOON SEA BREEZES
AND NIGHT TIME LAND BREEZES. SKIES WILL BE MOSTLY CLEAR...EXCEPT FOR
CLOUD BUILD UPS AND A SLIGHT CHANCE OF A SHOWER MAINLY OVER INTERIOR
SECTIONS OF THE ISLANDS EACH AFTERNOON. ANOTHER COLD FRONT
APPROACHING KAUAI LATE TUESDAY WILL BRING AN INCREASE IN CLOUDS AND
SHOWERS TO THE ISLANDS DURING THE MIDDLE OF NEXT WEEK.
&&
.DISCUSSION...
THE DIFFUSE BAND OF CLOUDS AND SHOWERS LEFT OVER FROM AN OLD FRONTAL
BAND HAS CONTINUED TO SHIFT NORTHWARD AWAY FROM THE STATE OVERNIGHT.
THIS BAND SHIFTED BACK OVER THE NORTHERN HAWAIIAN ISLANDS YESTERDAY
AFTERNOON AND EVENING IN RESPONSE TO THE RETURN FLOW AROUND THE BACK
SIDE OF A BUBBLE HIGH THAT MOVED TO A POSITION NORTH NORTHEAST OF
THE BIG ISLAND OVERNIGHT.
THE LARGEST RAINFALL TOTALS ACROSS THE STATE FOR THE 12 HOUR PERIOD
ENDING AT 200 AM HST THIS MORNING BY ISLAND WERE...0.54 INCHES AT
MOUNT WAIALEALE ON KAUAI...AND 0.18 INCHES AT OAHU FOREST NWR ON
OAHU. NO RAINFALL WAS REPORTED DURING THAT TIME PERIOD IN THE MAUI
COUNTY AND BIG ISLAND RAIN GAGES.
LOOPS OF WATER VAPOR IMAGERY INDICATE WEAK UPPER TROPOSPHERIC
RIDGING IS OCCURRING HIGH ABOVE THE STATE. VERY STRONG...NEARLY
ZONAL...UPPER LEVEL WESTERLY WINDS ARE EVIDENT JUST NORTH OF THIS
RIDGE ALOFT OVER THE NORTH CENTRAL PACIFIC OCEAN. THE WATER VAPOR
IMAGERY ALSO SHOWS SIGNIFICANT SUBSIDENCE ALOFT ABOVE MOST OF THE
STATE...WHICH IS CONTRIBUTING TO THE STABLE ATMOSPHERIC CONDITIONS
WE ARE EXPERIENCING.
THE 1020 MB SURFACE HIGH LOCATED NEAR 26N 151W...OR ABOUT 500 MILES
NORTH NORTHEAST OF HILO...WILL CONTINUE TO MOVE EASTWARD TODAY AS
ANOTHER COLD FRONT IS FORECAST TO APPROACH THE STATE FROM THE
NORTHWEST. THIS FRONT IS NOT EXPECTED TO REACH KAUAI...BUT WILL
CAUSE A SURFACE RIDGE EXTENDING WEST OF THE HIGH TO SHIFT SOUTHWARD
OVER THE STATE ONCE AGAIN BY TONIGHT OR SUNDAY MORNING. THE LACK OF
A SIGNIFICANT PRESSURE GRADIENT OVER THE ISLANDS WILL PRODUCE LIGHT
AND VARIABLE WINDS WITH LOCAL AFTERNOON SEA BREEZES AND NIGHT TIME
LAND BREEZES FROM SUNDAY THROUGH MONDAY NIGHT. THE SEA BREEZES WILL
LIKELY PRODUCE SOME CLOUD BUILD UPS AND A CHANCE FOR SHOWERS MAINLY
ACROSS INTERIOR SECTIONS OF THE ISLANDS EACH AFTERNOON. HOWEVER...
THE RATHER DRY AND STABLE ATMOSPHERIC CONDITIONS WILL RESULT IN
LIMITED SHOWER COVERAGE AND INTENSITY. IN ADDITION...THE WEAK
SOUTHEASTERLY FLOW UNDER THE SURFACE RIDGE WILL LIKELY TRANSPORT VOG
ACROSS SOME OF THE SMALLER ISLANDS...AS WELL AS OVER PORTIONS OF THE
BIG ISLAND NOT NORMALLY PRONE TO VOG.
THE LATEST GFS AND ECMWF MODEL RUNS INDICATE THE A COLD FRONT WILL
REACH KAUAI BY LATE TUESDAY. THERE CONTINUES TO BE SOME UNCERTAINTY
IN HOW FAR THE FRONT WILL MAKE IT DOWN THE ISLAND CHAIN BEFORE
STALLING. THE ECMWF NOW TAKES THE FRONT DOWN TO NEAR OAHU...WHILE
THE GFS MODEL STALLS THE FRONT NEAR KAUAI...BEFORE IT WEAKENS AND
SHIFTS NORTHWARD AHEAD OF THE NEXT FRONTAL SYSTEM. IT STILL APPEARS
THE ECMWF SOLUTION IS BEST...SO HAVE CONTINUED TO NUDGE THE FORECAST
TOWARD THIS MODEL FOR NOW.
&&
.MARINE...
THE LARGE NORTHWEST SWELL CONTINUES TO AFFECT THE ISLANDS EARLY THIS
MORNING. THE STRONG LOW PRESSURE SYSTEM THAT PRODUCED THIS SWELL WAS
VERY LARGE WITH HURRICANE FORCE WINDS AIMED AT THE ISLANDS FOR AN
EXTENDED PERIOD OF TIME. THIS WILL RESULT IN SURF NEAR WARNING
LEVELS FOR MOST NORTH AND WEST FACING SHORES OF THE STATE AGAIN
TODAY. THE SIGNIFICANT WAVE HEIGHT IS 11 TO 12 FEET WITH A DOMINANT
WAVE PERIOD OF 17 SECONDS FROM 315 DEGREES AZIMUTH AT THE WAIMEA BAY
BUOY. READINGS FROM THE BACK UP BUOY 51101 LOCATED NORTHWEST OF
KAUAI INDICATE THE SWELL HEIGHT HAS DROPPED TO 10 FEET WITH A PERIOD
OF 14 SECONDS. THE SWELL PEAKED YESTERDAY ALONG THE SMALLER
ISLANDS...AND LIKELY PEAKED EARLIER TONIGHT ALONG THE LEEWARD SHORES
OF THE BIG ISLAND. WILL CONTINUE TO MONITOR SURF OBSERVATIONS AND
BUOY READINGS LATER TODAY TO DETERMINE IF WE NEED TO FINE TUNE THE
HIGH SURF WARNING FOR LATER THIS MORNING.
ONCE THE HIGH SURF WARNING CRITERIA IS NO LONGER MET...MOST OF THE
SAME SHORELINES WILL STILL REQUIRE A HIGH SURF ADVISORY THROUGH
EARLY SUNDAY MORNING. THIS HIGH SURF ADVISORY WILL LIKELY BE
DISCONTINUED BY SUNDAY AFTERNOON. THE NEXT NORTHWEST SWELL
ARRIVING LATE SUNDAY NIGHT WILL LIKELY RESULT IN A NEW HIGH SURF
ADVISORY FROM MONDAY INTO TUESDAY.
A SMALL CRAFT ADVISORY /SCA/ ALSO REMAINS IN EFFECT FOR COASTAL
WATERS EXPOSED TO THE LARGE NORTHWEST SWELL...WHICH INCLUDES ALL
HAWAIIAN WATERS EXPECT FOR THE PAILOLO CHANNEL AND MAALAEA BAY...DUE
TO HAZARDOUS SEAS WITH SIGNIFICANT WAVE HEIGHTS OF 10 FEET OR
GREATER. THE SCA IS CURRENTLY IN EFFECT THROUGH THIS AFTERNOON.
HOWEVER...BASED ON THE LATEST GUIDANCE...THE SEAS WILL CONTINUE TO
DECLINE BY THIS EVENING. IF SO...THERE DOES NOT APPEAR TO BE A NEED
TO EXTEND THE SCA FOR ANY OF THE HAWAIIAN WATERS TONIGHT. A SCA MAY
BE REQUIRED FOR PORTIONS OF THE HAWAIIAN COASTAL WATERS WHEN THE
NEXT REINFORCING NORTHWEST SWELL BUILDS LATE SUNDAY AND MONDAY.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING UNTIL 600 PM HST THIS AFTERNOON FOR NORTH AND WEST
FACING SHORES OF NIIHAU...KAUAI...OAHU AND MOLOKAI...FOR NORTH
FACING SHORES OF MAUI...AND FOR WEST FACING SHORES OF THE BIG ISLAND.
SMALL CRAFT ADVISORY UNTIL 600 PM HST THIS AFTERNOON FOR ALL
HAWAIIAN WATERS...EXCEPT MAALAEA BAY AND THE PAILOLO CHANNEL.
&&
$$
HOUSTON
