High Surf in Hawaii, September 26 to 27, 2014

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HONOLULU HI
615 AM HST FRI SEP 26 2014

.UPDATE...
THE FORECAST WAS UPDATED TO INCREASE POPS THIS MORNING OVER KAUAI
AND VARIOUS PARTS OF THE COASTAL WATERS BASED ON CURRENT RADAR DATA..

&&

.SYNOPSIS...
THE MODERATE TRADE WIND FLOW WILL TURN LIGHTER LATE IN THE WEEKEND
AS THE HIGH PRESSURE SYSTEM NORTH NORTHEAST OF THE ISLANDS CONTINUES
TO MOVE EASTWARD. THE TRADE WINDS WILL BE CARRYING REMNANTS OF A
SHEAR LINE ONTO THE ISLANDS THROUGH THE WEEKEND. THESE SHOWERS WILL
BE FAVORING MAINLY THE WINDWARD AND MOUNTAIN AREAS BUT THE LEE SIDE
OF THE SMALLER ISLANDS WILL GET THEIR SHARE OF PASSING SHOWERS. A
CONVECTIVE PATTERN IS ON TAP FOR EARLY NEXT WEEK DUE TO THE LIGHT
WINDS.

&&

.DISCUSSION...
HIGH PRESSURE FAR NORTH NORTHEAST OF THE ISLANDS THIS MORNING WILL
CONTINUE TO MOVE EAST THROUGH THE WEEKEND. THE RESULT OF THIS IS THE
MODERATE TRADES TRENDING LIGHTER THROUGH THE WEEKEND AND INTO
EARLY NEXT WEEK. THE TRADES WILL BE CARRYING THE REMNANTS OF AN OLD
SHEAR LINE...FIRST OVER THE SMALLER ISLANDS...THEN SPREADING TO THE
BIG ISLAND TONIGHT. THIS SHOWERY TRADE WIND REGIME IS LIKELY TO LAST
THROUGH SUNDAY. ALTHOUGH THE SHOWERS WILL AFFECT PRIMARILY THE
WINDWARD AND MOUNTAIN AREAS...THE LEEWARD AREAS OF THE SMALLER
ISLANDS WILL ENDURE SOME PASSING SHOWERS.

THE LATEST MODELS HAVE A SLIGHT CHANGE WHERE THE MODERATE TRADES
WILL NOT START TRENDING LIGHTER UNTIL SATURDAY NIGHT. WE HAVE
BEEN FORECASTING THE TRADES TO START BECOMING LIGHTER TONIGHT.

WE ARE LOOKING AT LIGHT TRADES FROM MONDAY ON. THIS WILL FAVOR AN
ONSHORE FLOW OVER INTERIOR AND LEEWARD AREAS OF THE SMALLER ISLANDS
DURING THE MORNINGS. THE END RESULT WILL BE AFTERNOON CLOUDS AND
SHOWERS.

A SIDE NOTE...THE ECMWF AND GFS ARE STILL MAINTAINING THEIR
DIFFERENCES AFTER MONDAY. THE GFS STILL HAS SOUTHEAST WINDS FOR
ESPECIALLY THE SMALLER ISLANDS ON TUESDAY...WHILE THE EC IS STILL
HANGING ON TO EASTERLY WINDS. THE GFS GOES ON IN BREAKING DOWN THE
TRADES TUESDAY NIGHT WITH A SURFACE TROUGH JUST WEST OF KAUAI. THERE
ARE SOME AGREEMENTS AT THE MID LEVELS BETWEEN THESE TWO MODELS WITH
A WEAK LOW OR TROUGH AND A POOL OF COOLER AIR OF AROUND MINUS 8 C
OVER THE CENTRAL ISLANDS. THE GFS TRIMMED BACK ON THE PRECIP WATER
BUT THE AIR MASS WILL STILL BE MOIST WITH ENOUGH INSTABILITY FOR
SCATTERED AFTERNOON CONVECTIVE SHOWERS. FOR NOW...WE WILL STAY WITH
THE EC SOLUTION OF LIGHT TRADES THROUGH THE MIDDLE OF NEXT WEEK.

CURRENTLY...A POCKET OF ENHANCE SHOWERS IS MOVING THROUGH KAUAI.
APPARENTLY...AN UPPER LEVEL LOW PASSING SOUTH OF THE BIG ISLAND HAS
BROUGHT SOME INSTABILITY TO THE ISLANDS THIS MORNING WITH ENHANCED
TOPS TO 25000 FEET...AND EVEN FLASHES OF COLDER TOPS. WITH THIS
SAID...A SLIGHT CHANCE OF THUNDERSTORMS IS IN THE FORECAST FOR THE
WINDWARD WATERS WEST OF THE BIG ISLAND FOR TODAY.

SOME PESKY DIE HARD SHOWERS ALONG THE KONA COAST SHOULD BE
DISSIPATING SOON.

&&

.AVIATION...
A FRAGMENTED E TO W ORIENTED BAND OF MOISTURE WILL REMAIN STALLED
OVER THE NORTHERN HALF OF THE ISLAND CHAIN TODAY. MVFR CONDITIONS
WILL BE COMMON OVER WINDWARD PORTIONS OF KAUAI...WITH PERIODS OF
MVFR LIKELY ON WINDWARD SECTIONS OF OAHU...MAUI AND MOLOKAI TODAY.
EXPECT ISOL IFR CONDITIONS IN +SHRA OVER AND NORTH OF KAUAI AND
OAHU. AIRMET SIERRA FOR MOUNTAIN OBSC REMAINS IN EFFECT FOR KAUAI
AND OAHU BUT MAY BE ABLE TO BE LOWERED ON OAHU BY SUNRISE. THE BAND
OF MOISTURE IS EXPECTED TO EASE SOUTHWARD ONTO THE BIG ISLAND
TONIGHT.

AIRMET TANGO FOR LOW LEVEL TURB IS IN EFFECT FOR AREAS TO THE LEE OF
TERRAIN ON ALL ISLANDS. CONDITIONS ARE BORDER LINE AND WILL REMAIN
THAT WAY THROUGH TODAY.

&&

.MARINE...
A RECENT SCATTEROMETER PASS FROM THE ASCAT SYSTEM CONFIRMED THERE
WERE STRONG SURFACE WINDS JUST NORTH OF THE SHEAR LINE...WHICH
CONTINUES TO SAG SLOWLY SOUTHWARD. AS A RESULT...A SMALL CRAFT
ADVISORY /SCA/ HAS BEEN ISSUED FOR THE WINDWARD COASTAL WATERS
ADJACENT TO KAUAI AND OAHU THROUGH THIS AFTERNOON. WINDS ARE
FORECAST TO REMAIN BELOW THE SCA CRITERIA ELSEWHERE OVER THE
HAWAIIAN WATERS TODAY. HOWEVER...IT IS POSSIBLE THESE STRONGER TRADE
WINDS MAY SPREAD OVER SOME ADDITIONAL SECTIONS OF THE COASTAL WATERS
AS THE SHEAR LINE CONTINUES TO PUSH SLOWLY SOUTHWARD.

A SMALL NORTH NORTHEAST SWELL PRODUCED BY A STRONG SURFACE LOW THAT
WAS OVER THE NORTHEASTERN PACIFIC OCEAN EARLIER THIS WEEK HAS
ARRIVED AT THE BUOYS THIS MORNING. THIS SWELL WILL CONTINUE TO
GRADUALLY FILL IN TODAY...SO EXPECT A SLIGHT BUMP IN SURF HEIGHTS
ALONG MOST NORTH AND EAST FACING SHORES OF THE STATE. THIS NORTH
NORTHEAST SWELL WILL CONTINUE THROUGH THIS WEEKEND. A NEW SMALL...
BUT LONG-PERIOD NORTHWEST SWELL ARRIVING TUESDAY WILL BOOST SURF
HEIGHTS ALONG MOST NORTH AND WEST FACING SHORES OF THE STATE THROUGH
MID-WEEK.

A NEW SOUTH SWELL ARRIVING SATURDAY WILL CAUSE A SLIGHT BUMP IN SURF
HEIGHTS ALONG SOUTH FACING SHORES THIS WEEKEND. A REINFORCING
LONG-PERIOD SOUTH SWELL ARRIVING MONDAY WILL GRADUALLY BUILD...WITH
SURF HEIGHTS APPROACHING THE HIGH SURF CRITERIA ALONG MOST SOUTH
FACING SHORES OF THE ISLAND CHAIN STARTING TUESDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY FOR WINDWARD WATERS OF OAHU AND KAUAI UNTIL 6
PM HST THIS EVENING.

&&

UPDATE...M BALLARD
DISCUSSION...LAU
AVIATION...WROE
MARINE...HOUSTON