FXHW60 PHFO 251957
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST FRI DEC 25 2009
.SYNOPSIS...
A DISSIPATING FRONT STALLED ACROSS OAHU AND MAUI COUNTY WILL BRING
LIGHT TO MODERATE SHOWERS TO THE SMALLER ISLANDS TODAY AND TONIGHT.
LEFTOVER MOISTURE FROM THE FRONT WILL MOVE NORTH OF THE STATE ON
SATURDAY...AS A SOUTHEASTERLY LOW-LEVEL FLOW DEVELOPS AHEAD OF A
SURFACE RIDGE. THE RIDGE WILL SETTLE OVER THE STATE ON SUNDAY AND
MONDAY...LEADING TO LIGHT WINDS AND LOCALLY DRIVEN SEA BREEZES AND
LAND BREEZES. ANOTHER COLD FRONT WILL APPROACH THE STATE LATE
TUESDAY...AND BRING AN INCREASE IN CLOUDS AND SHOWERS FOR THE MIDDLE
OF NEXT WEEK.
&&
.DISCUSSION...
WATER VAPOR IMAGERY SHOWS A NEARLY ZONAL UPPER AIR PATTERN ACROSS
THE CENTRAL PACIFIC. THE CORE OF A +160KT 250MB JET IS LOCATED ABOUT
700 MILES NORTH OF THE STATE. AT THE SURFACE...A STALLED AND
WEAKENING FRONT IS LOCATED OVER OAHU AND MAUI COUNTY. THE 12Z
SOUNDING FROM HILO SHOWS A DRY AND STABLE AIRMASS...WITH AN
INVERSION HEIGHT OF 4 KFT AND PRECIPITABLE WATER JUST UNDER ONE
INCH. THE 12Z SOUNDING FROM LIHUE IS SOMEWHAT MORE UNSTABLE...WITH
AN INVERSION HEIGHT OF 8 KFT AND A PRECIPITABLE WATER OF 1.25
INCHES. THE AMSU/SSMI BLENDED TOTAL PRECIPITABLE WATER PRODUCT SHOWS
SATELLITE-DERIVED PW VALUES ONLY UP TO 1.4 INCHES POOLED ALONG THE
FRONT.
THE FRONT STALLED ACROSS THE STATE WILL DISSIPATE TODAY...BUT CLOUDS
AND MOISTURE WILL LINGER ACROSS THE SMALLER ISLANDS THROUGH TONIGHT.
REGIONAL RADARS AND RAIN GAUGES SHOW SHOWERS HAVE BEEN AFFECTING
MAINLY WINDWARD AREAS...WITH MODERATE SHOWERS BRINGING AROUND AN
INCH OF RAIN OVERNIGHT TO SOME LOCATIONS...MAINLY ON WINDWARD OAHU.
HIGH PRESSURE NORTH OF THE STATE WILL MOVE EAST AS ANOTHER COLD
FRONT APPROACHES FROM THE WEST. THIS FRONT WILL NOT REACH OUR
LATITUDE...BUT WILL SHIFT THE SURFACE RIDGE SOUTHWARD OVER THE
STATE. AS THE RIDGE APPROACHES...WINDS WILL TURN SOUTHEAST AND HELP
TO CLEAR OUT THE LINGERING MOISTURE ON SATURDAY.
WITH THE SURFACE RIDGE OVER THE STATE...THE GRADIENT WILL BE LIGHT
AND WINDS WILL BE DOMINATED BY ONSHORE SEA BREEZES DURING THE
AFTERNOONS AND OFFSHORE LAND BREEZES AT NIGHT. CLOUDS AND SHOWERS
WILL BE FOCUSED ACROSS INTERIOR SECTIONS OF THE ISLANDS DURING THE
AFTERNOONS. FORECAST SOUNDINGS SHOW INVERSION HEIGHTS LOWERING AND
PRECIPITABLE WATERS REMAINING BELOW ONE INCH THROUGH MONDAY NIGHT.
THIS DRY AND STABLE AIRMASS WILL REALLY LIMIT SHOWER COVERAGE AND
INTENSITY. IN ADDITION...THE WEAK SOUTHEASTERLY GRADIENT UNDER THE
SURFACE RIDGE MAY TRANSPORT VOG ACROSS THE SMALLER ISLANDS...AS WELL
AS ACROSS AREAS OF THE BIG ISLAND NOT NORMALLY PRONE TO VOG.
THE 12Z GFS AND ECMWF HAVE TRENDED SLOWER WITH THE NEXT COLD FRONT
THAT IS EXPECTED TO IMPACT THE STATE. THEY ARE SIMILAR SHOWING THE
FIRST APPROACHING FRONT STALLING NORTH OF THE STATE...THE ONE THAT
DISPLACES THE RIDGE SOUTHWARD OVER US. THE SECOND FRONT IS EXPECTED
TO APPROACH KAUAI LATE TUESDAY/TUESDAY NIGHT. THERE REMAINS SOME
UNCERTAINTY AT THIS POINT AS TO HOW FAR THE FRONT WILL MAKE IT DOWN
THE ISLAND CHAIN BEFORE STALLING. THE ECMWF TAKES IT FARTHER THAN
THE GFS...STALLING IT EAST OF MAUI AS OPPOSED TO NEAR OAHU...BEFORE
BEING PULLED NORTHWARD AHEAD OF THE NEXT SYSTEM. THE GFS APPEARS TO
BE TRENDING TOWARD THIS SOLUTION...AND WILL NUDGE THE FORECAST IN
THIS DIRECTION.
&&
.MARINE...
THE CURRENT NORTHWEST SWELL IS RUNNING AT 17-18 FEET/18-20 SECONDS
AT THE WAIMEA BAY BUOY. COMBINED SEAS ARE IN LINE WITH THE 12Z
WAVEWATCH III GUIDANCE...ALTHOUGH THE PERIOD REMAINS LONGER THAN THE
MODEL INDICATES. THE BACKUP BUOY 51101 NORTHWEST OF THE STATE SHOWS
THE SWELL PEAKED OVERNIGHT AND HAS FALLEN THROUGH THE MORNING. GIVEN
THE SWELL TRAVEL TIME FROM BUOY 101...THIS WOULD INDICATE THAT THE
CURRENT NORTHWEST SWELL WILL PEAK SHORTLY AROUND OAHU...AND LATE
THIS AFTERNOON NEAR THE BIG ISLAND. THE LOW PRESSURE SYSTEM THAT
PRODUCED THIS SWELL WAS LARGE AND CREATED A PROLONGED FETCH OF WINDS
POINTED AT THE STATE. SURF IS EXPECTED TO REMAIN ABOVE WARNING
LEVELS FOR NORTH AND WEST FACING SHORES THROUGH THE NIGHT...BEFORE
LOWERING BELOW WARNING LEVEL ON SATURDAY.
IN ADDITION TO HIGH SURF WARNINGS...A SMALL CRAFT ADVISORY IS ALSO
IN EFFECT FOR COASTAL WATERS EXPOSED TO THE NORTHWEST SWELL /ALL
WATERS EXPECT FOR THE PAILOLO CHANNEL AND MAALAEA BAY/ DUE TO THE
HAZARDOUS SEAS.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING UNTIL 6 PM HST SATURDAY FOR KONA-KOHALA
NIIHAU-KAUAI WINDWARD-KAUAI LEEWARD-WAIANAE COAST-OAHU NORTH
SHORE-OAHU KOOLAU-MOLOKAI-MAUI WINDWARD WEST-MAUI CENTRAL VALLEY-
WINDWARD HALEAKALA.
SMALL CRAFT ADVISORY UNTIL 6 PM HST SATURDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-KAUAI CHANNEL-
OAHU WINDWARD WATERS-OAHU LEEWARD WATERS-KAIWI CHANNEL-MAUI
COUNTY WINDWARD WATERS-MAUI COUNTY LEEWARD WATERS-ALENUIHAHA
CHANNEL-BIG ISLAND WINDWARD WATERS-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.
&&
$$
BRAVENDER
