695
FXHW60 PHFO 020632
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST SUN NOV 1 2009
SYNOPSIS
MODERATE TRADE WINDS WILL BRING A FEW WINDWARD SHOWERS TONIGHT AND
ON MONDAY...BEFORE A COLD FRONT USHERS IN A WEATHER CHANGE MONDAY
NIGHT AND TUESDAY. THE COLD FRONT WILL BRING A PERIOD OF WIDESPREAD
SHOWERS...AND A SLIGHT CHANCE OF THUNDERSTORMS AS IT MOVES DOWN THE
ISLAND CHAIN. STRONG NORTHEAST WINDS AND A COOLER AIR MASS WILL
FOLLOW IMMEDIATELY BEHIND THE FRONT. A RETURN TO TRADE WIND WEATHER
IS EXPECTED FOR THE SECOND HALF OF THE WORK WEEK...AND NEXT WEEKEND.
DISCUSSION
A STRONG HIGH PRESSURE CELL IS CURRENTLY LOCATED WELL NW OF THE
ISLANDS...WITH A WEAKER HIGH WELL TO THE NE. A STALLED FRONTAL
BOUNDARY IS LOCATED ABOUT 250 TO 300 MILES NW OF KAUAI...WITH
STRONG N AND NE WINDS LOCATED NW OF THIS BOUNDARY. MODERATE ENE
TRADE WINDS EXIST OVER THE ISLANDS...SUPPORTED BY THE HIGH TO THE NE
AND IT/S ASSOCIATED RIDGE TO THE NE. OVERNIGHT...AND INTO MONDAY...
NOT EXPECTING BIG CHANGES TO THE CURRENT REGIME...WITH THE TRADES
SUPPLYING CLOUDS AND A FEW SHOWERS TO WINDWARD AREAS.
SIGNIFICANT CHANGES TO ISLAND WEATHER ARE EXPECTED ON MONDAY NIGHT
AND TUESDAY AS THE HIGH WELL TO THE NW EDGES EASTWARD...AND THE
STALLED FRONTAL BOUNDARY IS SHUNTED SE DOWN THE ISLAND CHAIN. AS
THIS SURFACE BOUNDARY MOVES DOWN THE CHAIN...IT WILL INITIALLY
AFFECT KAUAI MONDAY EVENING...OAHU EARLY TUESDAY...MAUI COUNTY
DURING THE DAY TUESDAY...BEFORE REACHING THE BIG ISLAND TUESDAY
NIGHT AS IT WEAKENS. THE SURFACE BOUNDARY WILL BE ACCOMPANIED BY A
MID-LEVEL TROUGH...WHICH COULD PROVIDE SUFFICIENT DYNAMICAL SUPPORT
FOR THUNDERSTORMS...HENCE THEIR MENTION IN THE FORECAST. WHETHER TO
CALL THE BOUNDARY A FRONT OR SHEAR LINE IS ALWAYS A POINT OF
CONTENTION AMONGST FORECASTERS...BUT STRONG NE WINDS FOLLOWING THE
PASSAGE OF THE SURFACE BOUNDARY WILL USHER IN A NOTICEABLY COOLER
AIR MASS THAT WILL LINGER FOR SEVERAL DAYS.
THE SURFACE BOUNDARY WILL WASH OUT NEAR THE BIG ISLAND ON WEDNESDAY
AS THE HIGH TO THE NW GRADUALLY WEAKENS WHILE DRIFTING E. THE LOW
LEVEL WIND FLOW WILL FAVOR A NE DIRECTION ON WEDNESDAY AND THEN VEER
TO THE ENE ON THURSDAY...WITH GLOBAL MODELS INDICATING A WEAK
SHOWER BAND MOVING ACROSS THE ISLAND CHAIN FROM THE NE AS THIS
OCCURS. A RETURN TO MORE TYPICAL TRADE WIND WEATHER IS THEN EXPECTED
AS WE HEAD INTO NEXT WEEKEND...BUT THIS SOLUTION IS NOT SHARED BY
ALL MODELS AND CONFIDENCE IS MODERATE.
NE WINDS WILL SURGE TO NEAR 25 KT AFTER THE PASSAGE OF THE SURFACE
BOUNDARY ON MONDAY NIGHT AND TUESDAY...AND MAY BE STRONG ENOUGH TO
NECESSITATE THE ISSUANCE OF A WIND ADVISORY THAT INCLUDES THE LOWER
ELEVATIONS. PREVIOUS MODEL RUNS BROUGHT ADVISORY LEVEL WINDS TO THE
SUMMITS OF MAUI AND THE BIG ISLAND WITH THE PASSAGE OF THE UPPER
TROUGH...BUT HAVE SINCE BACKED OFF ON THIS SOLUTION.
MARINE
A LARGE...LONG PERIOD NW SWELL CONTINUES TO MOVE THROUGH ISLAND
WATERS THIS EVENING...WITH A HIGH SURF ADVISORY /HSA/ REMAINING IN
EFFECT FOR N AND W FACING SHORES OF MOST ISLANDS. A SMALL CRAFT
ADVISORY /SCA/ IS CURRENTLY IN EFFECT FOR WATERS AROUND KAUAI AND
OAHU...DUE TO COMBINED SEAS NEAR 10 FEET...BUT IS SLATED TO EXPIRE
THIS EVENING AS THE SWELL GRADUALLY DIMINISHES.
THE NW SWELL WILL DIMINISH ON MONDAY AND TUESDAY...WITH SURF HEIGHTS
EXPECTED TO DROP BELOW ADVISORY LEVELS ON MONDAY. WHILE THE SCA FLAG
IS EXPECTED TO BE DROPPED THIS EVENING...IT WILL NEED TO BE RAISED
ONCE AGAIN LATER MONDAY AND TUESDAY AS WINDS AND SEAS BUILD BEHIND
THE FRONT. EVEN WITH WINDS EXPECTED TO EASE SOMEWHAT TOWARD THE
MIDDLE OF THE WEEK...COMBINED SEAS ABOVE 10 FEET WILL LIKELY
NECESSITATE THE SCA THROUGH THE WEEK. ALTHOUGH CONDITIONS WILL BE
MARGINALIZED DUE TO THE CLOSE PROXIMITY OF THE SWELL SOURCE AND THE
NORTHERLY ANGLE OF THE WINDS...SURF WILL BE ELEVATED ALONG NORTH
FACING SHORES FROM TUESDAY INTO FRIDAY...LIKELY REQUIRING A HSA.
HFO WATCHES/WARNINGS/ADVISORIES
HIGH SURF ADVISORY UNTIL 6 PM HST MONDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-OAHU NORTH SHORE-OAHU KOOLAU-MOLOKAI-MAUI
WINDWARD WEST-MAUI CENTRAL VALLEY-WINDWARD HALEAKALA.
HIGH SURF ADVISORY UNTIL 6 AM HST MONDAY FOR WAIANAE COAST.
SMALL CRAFT ADVISORY UNTIL 10 PM HST THIS EVENING FOR KAUAI
NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-
KAUAI CHANNEL-OAHU WINDWARD WATERS.
BIRCHARD
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