FXHW60 PHFO 262002
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST SAT DEC 26 2009
.SYNOPSIS...
TRADE WINDS WILL WEAKEN AND TURN SOUTHEASTERLY TONIGHT...AS A
SURFACE RIDGE TO OUR NORTH MOVES DOWN ACROSS THE STATE. THE RIDGE
NEARBY WILL LEAD TO LIGHT WINDS AND LOCAL DAYTIME SEA BREEZES AND
NIGHTTIME 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 BROAD UPPER LEVEL RIDGE JUST SOUTH OF
THE STATE...WITH A FAST NEARLY ZONAL FLOW ACROSS THE NORTH CENTRAL
PACIFIC. A SHORTWAVE EMBEDDED IN THE FAST FLOW IS LOCATED NORTHWEST
OF THE STATE. AT THE SURFACE...HIGH PRESSURE IS LOCATED NORTHEAST OF
THE STATE...WITH A RIDGE EXTENDING WEST...PASSING ABOUT 300 MILES
NORTH OF US. 12Z SOUNDINGS FROM HILO AND LIHUE SHOW A STABLE AIRMASS
ACROSS THE STATE. INVERSION HEIGHTS RANGE FROM JUST OVER 4000 FT AT
HILO TO JUST OVER 7000 FT AT LIHUE. PRECIPITABLE WATERS ALSO RANGE
FROM 1 INCH TO 1.2 INCHES. THE AMSU/SSMI BLENDED TOTAL PRECIPITABLE
WATER IMAGERY SHOWS THE AREA OF MOISTURE LEFT BEHIND BY THE
DISSIPATED FRONT FROM LATE LAST WEEK HAS MOVED NORTH OF KAUAI.
SATELLITE AND RADAR IMAGERY SHOW THE AREA OF CLOUDS AND SHOWERS
NORTH OF THE SMALLER ISLANDS CONTINUES TO EDGE TO THE WEST NORTHWEST
AWAY FROM THE STATE. THE MAIN AREA OF CLOUDS WILL BRUSH BY JUST
NORTH OF KAUAI. WINDS FROM THE MOLOKAI RADAR VWP SHOW A SLIGHT
EAST-SOUTHEAST COMPONENT TO THE WINDS BELOW 4000 FT...WHICH ACCOUNTS
FOR THE CLOUD MOVEMENT. SKIES ARE CLEAR TO START THE DAY ACROSS MUCH
OF THE REST OF THE STATE...WITH CLOUDS ONLY ACROSS SOUTHEAST
SECTIONS EAST MAUI AND THE BIG ISLAND. THE AIRMASS IS RELATIVELY DRY
AND STABLE SOUTHEAST OF KAUAI...AND ONLY LIMITED DIURNAL BUILDUPS
ARE EXPECTED THIS AFTERNOON.
A COLD FRONT NORTHWEST OF THE STATE WILL PASS BY TO OUR NORTH...
SUPPRESSING THE RIDGE SOUTHWARD OVER US BY SUNDAY. 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
TUESDAY. 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.
A SECOND FRONT WILL APPROACH THE STATE TUESDAY/WEDNESDAY. THE
CURRENT 12Z RUNS OF GFS AND ECMWF HAVE BOTH BACKED OFF ON THE
APPROACH OF THIS FRONT...AND NOW STALL IT JUST WEST OF KAUAI.
EARLIER RUNS HAD BROUGHT IT TO OAHU OR AS FAR AS MAUI. THE SIMILAR
TRENDS AND BETTER AGREEMENT LENDS WEIGHT TO THE CURRENT SOLUTION.
GFS ENSEMBLES ALSO DO NOT SHOW ANY SIGNIFICANT OUTLIERS WITH THE
PARENT LOW OR UPPER LEVEL FEATURES. EVEN WITH THE CURRENT SOLUTION
THERE REMAINS SOME MOISTURE ADVECTION/CONVERGENCE AHEAD OF THE FRONT
THAT WILL INCREASE PRECIPITABLE WATERS AND LEAD TO HIGHER POPS
ACROSS THE WESTERN HALF OF THE STATE. THIS IS REFLECTED IN THE
CURRENT FORECAST...BUT MAY NEED TO BE TRIMMED BACK GIVEN THE
DIFFERENT FRONTAL POSITION.
&&
.MARINE...
THE SWELL AT THE WAIMEA BAY BUOY HAS DROPPED TO AROUND 10 FEET/14
SECONDS...WHICH WOULD INDICATE ADVISORY LEVEL SURF. SURF
OBSERVATIONS THIS MORNING ALSO INDICATE THAT SURF HAS DROPPED BELOW
WARNING LEVELS. THEREFORE WE HAVE DOWNGRADED THE WARNING TO AN
ADVISORY...AND EXTENDED IT THROUGH TONIGHT. 12Z WAVEWATCH III
GUIDANCE HAS BEEN PRETTY CONSISTENT SHOWING SURF DROPPING STEADILY
THIS WEEKEND. SURF SHOULD DROP BELOW ADVISORY LEVELS BY SUNDAY.
THE SMALL CRAFT ADVISORY ALSO CONTINUES THROUGH TODAY FOR COASTAL
WATERS EXPOSED TO THE NORTHWEST SWELL /ALL WATERS EXPECT FOR THE
PAILOLO CHANNEL AND MAALAEA BAY/ DUE TO HAZARDOUS SEAS
A SERIES OF ADDITIONAL NORTHWEST SWELLS WILL ARRIVE THIS WEEK. THE
FIRST ONE WILL ARRIVE SUNDAY NIGHT...AND PEAK MONDAY AND TUESDAY
ABOVE ADVISORY LEVELS. AFTER A BRIEF DECLINE...A NEW SWELL WILL
ARRIVE WEDNESDAY NIGHT/THURSDAY...AGAIN BRINGING SURF ABOVE ADVISORY
LEVELS.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST SUNDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-WAIANAE COAST-OAHU NORTH SHORE-OAHU
KOOLAU-MOLOKAI-MAUI WINDWARD WEST-MAUI CENTRAL VALLEY-WINDWARD
HALEAKALA-KONA-KOHALA.
SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING 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
