High Surf in Hawaii, February 1 to 5, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST FRI FEB 1 2008

.SYNOPSIS...
STRENGTHENING HIGH PRESSURE NORTH OF THE STATE WILL LEAD TO STRONG
AND GUSTY TRADE WINDS OVER THE ISLANDS THROUGH THE WEEKEND. AN UPPER
LEVEL TROUGH WILL LINGER OVER THE STATE...KEEPING THE ATMOSPHERE
UNSTABLE. SHOWERS WILL FAVOR WINDWARD AND MAUKA AREAS...BUT RAINFALL
COVERAGE AND INTENSITY WILL BE GREATER THAN NORMAL DUE TO THE
UNSTABLE AIRMASS. THE STRONG WINDS WILL BLOW SHOWERS ACROSS LEEWARD
AREAS OF THE SMALLER ISLANDS AS WELL.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS THE CORE OF THE UPPER LOW MOVING AWAY TO
THE NORTHEAST OF THE BIG ISLAND...WITH A TROUGH LINGERING BACK
ACROSS THE STATE. 12Z PHLI/PHTO SOUNDINGS HAVE WARMED A COUPLE
DEGREES MORE ABOVE 600MB OVER THE PAST 24 HOURS...WITH A WEAK
INVERSION AT PHLI BUT PHTO STILL INVERSION FREE. THE PRECIPITABLE
WATER AT PHTO HAS RISEN TO 1.5 INCHES...WITH AN INCREASINGLY
SATURATED COLUMN. 13Z POES AMSU TOTAL PRECIPITABLE WATER PASS SHOWS
A NARROW RIBBON OF HIGHER PRECIPITABLE WATER NEAR WINDWARD MAUI/BIG
ISLAND.

THE COMBINATION OF GREATER MOISTURE AND LINGERING INSTABILITY
CONTINUE TO SUPPORT GREATER THAN NORMAL SHOWER COVERAGE AND
INTENSITY. HOWEVER...DEEP CONVECTION HAS DIMINISHED OVER THE COASTAL
AND OFFSHORE WATERS...WITH ANY LINGERING THUNDERSTORMS ARE FAR TO
THE NORTHEAST UNDER THE CORE OF THE UPPER LOW. ON THE BIG ISLAND...
TRADE SHOWERS HAVE MOSTLY STAYED CONFINED TO THE WINDWARD SLOPES
OVERNIGHT...BUT DEEPER CLOUDS HAVE PERSISTED ACROSS THE SUMMITS.
MESONET OBSERVATIONS ATOP MAUNA KEA SHOW THE AIRMASS IS SATURATED...
WITH TEMPERATURES SLOWLY RISING INTO THE MID 20S. RAOBS/FORECAST
SOUNDINGS SHOW THE MOISTURE DEPTH ONLY EXTENDS UP TO ABOUT -9C...
WHICH IS TOO WARM TO ACTIVATE MOST ICE NUCLEI. THEREFORE THE CLOUDS
ARE MOST LIKELY COMPRISED OF SUPERCOOLED WATER...AND EITHER FREEZING
DRIZZLE OR RIMING COULD CREATE ICY CONDITIONS. THEREFORE HAVE
EXTENDED THE WINTER WEATHER ADVISORY FOR THE BIG ISLAND SUMMITS
THROUGH TODAY FOR A MIX OF HAZARDOUS WINTRY WEATHER.

00Z NAM/GFS SHOW THE SURFACE HIGH BUILDING NORTH OF THE STATE
THROUGH SATURDAY. TRADES DROPPED OFF A BIT TODAY...BUT WILL PICK UP
AGAIN AS THE GRADIENT TIGHTENS AND REMAIN BREEZY AND GUSTY INTO THE
WEEKEND. THE UPPER TROUGH WILL LINGER OVER THE STATE. FORECAST
SOUNDINGS SHOW THE TEMPERATURE PROFILE STABILIZING SOME...BUT
SATURATING AND REMAINING INVERSION FREE THROUGH THE FORECAST PERIOD.
THE GREATER MOISTURE DEPTH WITH THE LACK OF AN INVERSION WILL HELP
TO MAINTAIN THE CURRENT WET TRADE PATTERN. SHOWERS WILL FAVOR
WINDWARD AND MAUKA AREAS...BUT WILL BE MORE WIDESPREAD AND HEAVIER
THAN TYPICAL TRADE WIND SHOWERS. THE STRONG WINDS WILL ALSO BLOW
SHOWERS ACROSS WINDWARD SECTIONS OF THE SMALLER ISLANDS MORE
FREQUENTLY.

THE 00Z ECMWF CONTINUED THE TREND OF ITS 12Z/31 RUN IN BACKING AWAY
FROM THE SHEAR LINE THAT IT TRIED TO BRING DOWN TOWARD THE STATE AT
THE END OF THE FORECAST PERIOD. THE ECMWF AND GFS BOTH CONTINUE TO
INDICATE AN INVERTED TROUGH WILL DEVELOP JUST WEST OF THE STATE
EARLY NEXT WEEK...WITH A DEEP SOUTHEASTERLY FLOW PULLING ADDITIONAL
MOISTURE UP FROM THE TROPICS. OVERALL THE EXTENDED MODELS ARE COMING
INTO BETTER AGREEMENT. THE OPERATIONAL GFS RUN IS CLOSER TO ITS
ENSEMBLE CONSENSUS...AND THE GFS ENSEMBLE MEAN IS PRETTY SIMILAR TO
THE ECMWF...AT LEAST NEAR HAWAII. WINDS WILL WEAKEN TO MORE MODERATE
LEVELS AND VEER TO THE EAST/SOUTHEAST NEXT WEEK AS THE INVERTED
TROUGH DEVELOPS WEST OF THE STATE. DEEP TROPICAL MOISTURE AND AN
UNCAPPED ATMOSPHERE WILL LEAD TO ABOVE NORMAL RAINFALL THROUGH THE
EXTENDED PERIOD. HOWEVER INSTABILITY LOOKS BORDERLINE FOR MUCH OF
THE TIME...AND IT IS DIFFICULT TO PICK OUT THE PERIOD THAT WILL BE
MOST FAVORABLE FOR HEAVY RAINFALL.

&&

.MARINE...
COMBINED SEAS AT THE KAILUA BAY BUOY HAVE RISEN TO 10FT/9SEC EARLY
THIS MORNING. WAVEWATCH III GUIDANCE HAS TRENDED DOWN WITH THE SHORT
PERIOD EASTERLY SWELL OVER THE PAST FEW RUNS...AND THE 06Z RUN IS
RIGHT IN LINE WITH THE BUOY OBSERVATIONS. THE SURFACE HIGH NORTH OF
THE STATE IS CONTINUING TO BUILD/CONSOLIDATE...AND WINDS AND WAVES
WILL CONTINUE TO INCREASE. WW3 SHOWS THE SHORT PERIOD EASTERLY SWELL
PEAKING AT 12FT/10SEC OVER THE WEEKEND. HAVE ISSUED A HIGH SURF
ADVISORY FOR EAST FACING SHORES...WITH INITIAL SURF HEIGHTS TODAY OF
6 TO 9 FT.

THE LATE EVENING QUIKSCAT PASS SHOWED A SOLID AREA STRONG TRADES
JUST REACHING THE SMALLER ISLANDS. THERE IS A LARGE AREA OF 25-30KT
WINDS UPSTREAM OF THE ISLANDS...LET ALONE THROUGH THE CHANNELS. THE
PHKI/KAUAI RADAR VAD WIND PROFILE ALSO INDICATES 30-35KT AT 3KFT.
THE 00Z/06Z NAM AND 00Z ECMWF SHOW WINDS PEAKING TONIGHT/SATURDAY.
GIVEN THE STRONG SURGE IN TRADE WINDS...HAVE ISSUED A GALE WARNING
FOR PAILOLO AND ALENUIHAHA CHANNELS FOR TODAY THROUGH SATURDAY. THE
STRONGEST WINDS ARE EXPECTED TO FILL IN DURING THE
AFTERNOON/EVENING. SMALL CRAFT ADVISORIES WILL CONTINUE FOR THE
REMAINING WATERS...WITH 30KT THROUGH THE REMAINING CHANNELS AND 25KT
FOR ALL COASTAL WATERS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST SUNDAY 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.

GALE WARNING UNTIL 6 PM HST SATURDAY FOR PAILOLO CHANNEL-
ALENUIHAHA CHANNEL.

SMALL CRAFT ADVISORY UNTIL 6 PM HST SATURDAY FOR THE REMAINING
HAWAIIAN WATERS.

&&

BRAVENDER