High Surf in Hawaii, November 29 to 30, 2004

HAWAIIAN ISLANDS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST MON NOV 29 2004

.SYNOPSIS...
SHOWERS WILL CONTINUE TO TAPER OFF TODAY...AS A LOW
ALOFT WEST OF KAUAI MAINTAINS IT TRACK AWAY FROM THE ISLANDS. HIGH
PRESSURE IS BUILDING BOTH AT THE SURFACE AND ALOFT NORTH OF THE MAIN
HAWAIIAN ISLANDS. AS A RESULT...OUR TRADE WINDS WILL STRENGTHEN AND
BECOME QUITE BREEZY BY MID WEEK. THE BREEZY TRADES WILL CONTINUE
THROUGH EARLY NEXT WEEK. DRIER WEATHER WILL ACCOMPANY THE BREEZY
TRADES.

&&

.DISCUSSION...
THE BAND OF SHOWERS CURRENTLY AFFECTING THE ISLANDS THIS MORNING IS
SHOWING SIGNS OF DISSIPATING. OVERNIGHT RAINFALL TOTALS WERE
GREATEST ACROSS THE WINDWARD BIG ISLAND...WITH HILO RECEIVING ABOUT
AN INCH. ACROSS THE SMALLER ISLANDS...A FEW SELECT AND NORMALLY
WETTER LOCATIONS WINDWARD AND MAUKA LOCATIONS MANAGED TO SQUEEZE OUT
A HALF INCH OR MORE. THE SHOWERS SHOULD DIMINISH FURTHER AS THE DAY
PROGRESSES...THEN FLARE UP SLIGHTLY AGAIN TONIGHT. THE UPPER LOW WE
ARE WATCHING WEST OF KAUAI CONTINUES TO MOVE FURTHER AWAY FROM THE
ISLANDS AS FORECAST...AND WILL NOT HAVE MUCH IF ANY OF AN INFLUENCE
ON ISLAND WEATHER AFTER TODAY. ONCE WEDNESDAY ROLLS AROUND...THE
CLOUDS AND SHOWERS FORECAST GETS SOMEWHAT TRICKY. WITH DEEP AND
MODERATE TO STRONG TRADES ALONG WITH STABLE CONDITIONS...EXPECT THE
CLOUDS AND SHOWERS TO MARKEDLY DECREASE...EVEN OVER WINDWARD AND
MAUKA SECTIONS. THE REASONING IS THAT STABLE CONDITIONS WILL PREVENT
ANY SIGNIFICANT CLOUD DEVELOPMENT AND THE BRISK TRADES WILL PREVENT
WHAT CLOUDS DO FORM VIA OROGRAPHIC ENHANCEMENT TO ANCHOR OVER THE
MOUNTAINS. THE EXCEPTION WILL BE WINDWARD BIG ISLANDS...WHERE THE
CLOUDS AND SHOWERS GET TRAPPED UP AGAINST THE SLOPES DUE TO THE
HEIGHT OF THE MOUNTAINS. USING THIS RATIONAL...EXPECT DRIER
CONDITIONS TO PREVAIL...SO HAVE TWEAKED THE LONG TERM FORECAST TO
KNOCK DOWN THE CLOUDS AND SHOWERS A CATEGORY OR TWO. WINDWARD BIG
ISLAND WILL BE THE EXCEPTION...AND REMAIN RATHER CLOUDY AND SHOWERY
THROUGHOUT THE FORECAST. THE SPOILER TO THIS DRIER FORECAST WILL BE
SHOWER BANDS EMBEDDED IN THE TRADE WIND FLOW...BUT THESE WILL BLOW
THROUGH RATHER QUICKLY.

THE LATEST SURFACE ANALYSIS PEGS THE HIGH NORTHEAST OF THE STATE
NEAR 43N 145W AT A STRENGTH OF 1038 MB. MODELS REMAIN IN DECENT
AGREEMENT AND CONTINUE TO HAVE A GOOD HANDLE ON THIS FEATURE. THE
HIGH IS EXPECTED TO PEAK IN STRENGTH TODAY...THEN WEAKEN A FEW
MILLIBARS OVER THE SECOND HALF OF THIS WEEK. AS THE HIGH WEAKENS
HOWEVER...IT ALSO MIGRATES SOUTHWARD AND MUCH CLOSER TO THE ISLANDS.
THE NET EFFECT WILL BE A STRENGTHENING SURFACE PRESSURE GRADIENT
OVER THE STATE.

IN THE UPPER LEVELS OF THE ATMOSPHERE...THE UPPER LOW WEST OF THE
STATE IS MAINTAINING SOUTHWEST FLOW ABOVE 15 THOUSAND FEET OR
SO...BUT AN UPPER LEVEL RIDGE BUILDING NORTHWEST OF THE STATE WILL
NUDGE THE TROUGH SOUTH OF THE ISLANDS BY MIDWEEK. THIS WILL ALLOW
THE UPPER LEVEL WINDS TO SWING CLOCKWISE TO THE NORTHEAST. THE
OUTCOME WILL BE VERTICALLY STACKED HIGH PRESSURE OVER AND WEST OF
THE ISLANDS...RESULTING IN STABLE CONDITIONS AND A VERY DEEP LAYER
OF MODERATE TO STRONG EAST TO NORTHEAST WINDS.

SO WIND WISE...THE TRADES WILL BECOME BREEZY TODAY AND REMAIN RATHER
STRONG THROUGH EARLY NEXT WEEK. WITH STRONG TRADE WINDS AND STABLE
CONDITIONS...THE TRADES MAY ACCELERATE DOWNSLOPE AND BECOME QUITE
STRONG OVER LEE AREAS. THESE WINDS MAY REQUIRE WIND ADVISORIES LATER
IN THE WEEK. STRONG MID LEVEL FLOW MAY ALSO REQUIRE WIND ADVISORIES
FOR HIGHER ELEVATIONS AS WELL. THE TRADE WINDS WILL PROBABLY PEAK
OVER THE WEEKEND...THEN GRADUALLY DECREASE NEXT WEEK AS A NEW TROUGH
DIGS SOUTHEASTWARD AND WEAKENS THE SUBTROPICAL RIDGE.

&&

.MARINE...
WILL WAIT FOR THE FIRST SURF OBSERVATIONS TO COME IN LATER THIS
MORNING TO DECIDE WHETHER OR NOT TO DROP THE HIGH SURF ADVISORY. AS
INDICATED BY THE BUOYS...THE PEAK OF THIS SWELL HAS PASSED AND SURF
SHOULD FALL BELOW ADVISORY LEVELS TODAY. THE NEXT NORTHWEST SWELL...
ARRIVING THURSDAY...WILL PRODUCE SURF JUST BELOW ADVISORY LEVELS OF
15 FEET.

IT STILL LOOKS LIKE TRADE WINDS WILL BECOME STRONG ENOUGH BY MID
WEEK TO REQUIRE SMALL CRAFT ADVISORIES. ALSO...THE LONG FETCH OF
STRONG TRADE WINDS IS LIKELY TO PRODUCE SURF ABOVE ADVISORY LEVELS
ALONG EAST FACING SHORES AS EARLY AS WEDNESDAY.

&&

.AVIATION...
MODERATE TO STRONG TRADE WINDS UNDER STABLE ATMOSPHERIC CONDITIONS
ARE VERY CONDUCIVE TO MOUNTAIN WAVES AND THUS TURBULENCE IN THE LEE
OF MOUNTAINS. AIRMETS FOR TURBULENCE ARE EXPECTED TO REMAIN POSTED
FOR THE REMAINDER OF THIS WEEK AND THROUGH THE WEEKEND. THE WINDS
ARE EXPECTED TO PEAK OVER THE WEEKEND...AND SEVERE TURBULENCE IS
POSSIBLE FOR SMALLER AIRCRAFT.

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY FOR NORTH AND WEST FACING SHORES.

TANABE