High Surf in Hawaii, December 13 to 15, 2013

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST FRI DEC 13 2013

.UPDATE...
THE HANALEI BUOY NEAR NORTH KAUAI SHOWED TWO SUCCESSIVE OBSERVATIONS
OF 14 FEET WITH A WAVE PERIOD OF 17 SECONDS. THEREFORE...HAVE
INCREASED SURF HEIGHTS IN THE HIGH SURF WARNING PRODUCT. HAVE ALSO
INCLUDED THE WEST FACING SHORES OF OAHU IN THE WARNING.

&&

.SYNOPSIS...
A FRONT APPROACHING THE STATE FROM THE NORTHWEST WILL KEEP WINDS
LIGHT ENOUGH OVER THE ISLANDS TO ALLOW LOCAL LAND AND SEA BREEZE
CIRCULATIONS TO DEVELOP THROUGH SATURDAY. EXPECT CLOUDS AND ISOLATED
SHOWERS TO DEVELOP OVER THE INTERIOR SECTIONS OF THE ISLANDS DURING
SATURDAY AFTERNOON...WHILE THE SOUTHEASTERLY FLOW WILL BRING SOME
LOW CLOUDS AND SHOWERS TO THE EAST AND SOUTHEAST FACING SLOPES.
WETTER WEATHER WILL AFFECT MOST OF THE STATE FROM SATURDAY NIGHT
THROUGH MONDAY WHEN THE FRONT REACHES THE ISLANDS.

&&

.DISCUSSION...
A 1030 MB SURFACE HIGH IS LOCATED NEAR 38N 133W...OR ABOUT 1900
MILES EAST NORTHEAST OF HONOLULU. THIS HIGH IS MOVING TOWARD THE
NORTHEAST AT ABOUT 10 MPH. A NEARLY STATIONARY RIDGE EXTENDS
SOUTHWEST FROM THIS HIGH TO JUST NORTHWEST OF KAUAI. A WEAK FRONTAL
BOUNDARY IS ALSO EVIDENT ABOUT 400 MILES NORTHWEST OF LIHUE. LAYERED
CLOUDS WITH EMBEDDED SHOWERS AND SCATTERED THUNDERSTORMS ASSOCIATED
WITH THIS NEARLY STATIONARY FRONTAL BOUNDARY ARE EVIDENT IN
SATELLITE IMAGERY. THE CLOSE PROXIMITY OF THE SURFACE RIDGE AND THE
FRONTAL BOUNDARY TO THE ISLANDS HAS DISRUPTED THE PRESSURE GRADIENT
ACROSS THE MAIN HAWAIIAN ISLANDS. AS A RESULT...THE SYNOPTIC FLOW
ACROSS THE ISLANDS IS MAINLY FROM THE EAST SOUTHEAST OR SOUTHEAST.

ALOFT...WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL TROUGH WEST OF THE
ISLANDS. THE AXIS OF THIS TROUGH ALOFT EXTENDS FROM NEAR 30N 165W
THROUGH A POINT ABOUT 300 MILES WEST OF LIHUE TO 16N 167W. THE FLOW
ALOFT EAST OF THIS UPPER LEVEL FEATURE...WHICH HAS PROPAGATED SLOWLY
TOWARD THE EAST NORTHEAST DURING THE PAST SEVERAL HOURS...IS
BRINGING HIGH LEVEL CLOUDS FROM THE SOUTH SOUTHWEST UP OVER THE
ALOHA STATE THIS AFTERNOON. THE EARLY AFTERNOON SOUNDINGS SHOWED
THAT THE LOW-LEVEL INVERSION WAS AROUND 5500 FEET AT LIHUE...AND
NEAR 6400 THOUSAND FEET AT HILO. PRECIPITABLE WATER /PW/ VALUES AT
BOTH OF THESE SITES WERE LESS THAN 1.3 INCHES...WHICH MATCHES
CLOSELY WITH THE SATELLITE DERIVED PW FIELDS. SO...THE ISLANDS
CONTINUE TO REMAIN IN A RELATIVELY DRY AND STABLE ATMOSPHERIC REGIME
THIS AFTERNOON.

BESIDES THE HIGH CLOUDS...VISIBLE SATELLITE IMAGERY SHOWS SCATTERED
TO LOCALLY BROKEN LOW CLOUDS OVER THE ISLANDS FROM MOLOKAI WESTWARD.
THERE WERE SCATTERED BROKEN LOW CLOUDS ALONG EAST AND SOUTHEAST
FACING SLOPES AND BEACHES ON MAUI AND THE BIG ISLAND. BROKEN TO
LOCALLY OVERCAST LOW CLOUDS WERE ACROSS PARTS OF THE LEEWARD BIG
ISLAND. RADAR REFLECTIVITY DATA SHOWS ISOLATED TO LOCALLY SCATTERED
LOW SHOWERS OVER THE EASTERN AND SOUTHEASTERN COASTAL SECTIONS OF
MAUI AND THE BIG ISLAND.

THE LATEST GUIDANCE FROM THE FORECAST MODELS INDICATE THE FRONTAL
BOUNDARY WILL MOVE LITTLE THROUGH EARLY SATURDAY. THEREFORE...WITH
THE CLOSE PROXIMITY OF THE FRONTAL BOUNDARY AND THE SURFACE RIDGE TO
THE STATE...WE EXPECT A SOUTHEASTERLY SYNOPTIC FLOW WILL PREVAIL
ACROSS THE AREA THROUGH EARLY SATURDAY. THE BACKGROUND FLOW WILL
ALSO REMAIN RELATIVELY LIGHT OVER THE WESTERN ISLANDS. THESE LIGHT
WINDS WILL ALLOW THE DEVELOPMENT OF LOCAL AFTERNOON SEA BREEZES...
WHICH WILL LIKELY LEAD TO THE DEVELOPMENT OF CLOUDS AND ISOLATED
SHOWERS OVER THE INTERIOR SECTIONS OF THE ISLANDS DUE TO DAYTIME
HEATING. THE SOUTHEASTERLY FLOW WILL ALSO CONTINUE TO BRING A FEW
LOW CLOUDS AND SHOWERS TO EAST AND SOUTHEAST FACING SECTIONS OF THE
STATE...PARTICULARLY OVER PARTS OF MAUI AND THE BIG ISLAND. ALSO...
NIGHT TIME COOLING WILL ALLOW LOCAL NIGHT TIME LAND BREEZES TO
DEVELOP...WHICH WILL LIKELY LIMIT LOW CLOUD COVER AND SHOWERS OVER
INTERIOR AND LEEWARD AREAS OF MOST ISLANDS BY LATE THIS EVENING.

THE FORECAST MODELS INDICATE THE FRONT WILL BEGIN TO START MOVING
TOWARD KAUAI SOME TIME DURING THE DAY ON SATURDAY...AS A NEW UPPER
LEVEL TROUGH MOVES DOWN FROM THE NORTHWEST SATURDAY. THE ADVANCEMENT
OF THIS FRONT TOWARD THAT ISLANDS WILL CAUSE THE CHANCE FOR RAIN TO
INCREASE OVER KAUAI FROM LATE SATURDAY INTO SUNDAY...WHILE OAHU AND
MAUI COUNTY WILL HAVE INCREASING SHOWERS STARTING EARLY SUNDAY AS
THE FRONT MOVES CLOSER TO THE STATE. THE ATMOSPHERE WILL ALSO BEGIN
TO DESTABILIZE AS DYNAMIC LIFT AND COLD AIR ALOFT ASSOCIATED WITH
THE SYSTEM PASSES ACROSS THE ISLAND CHAIN. THE CURRENT FORECAST
CONTINUES TO INDICATE A SLIGHT CHANCE OF THUNDERSTORMS...AS WELL AS
THE POTENTIAL FOR LOCALLY HEAVY RAIN ACROSS THE SMALLER ISLANDS ON
SUNDAY. WE CURRENTLY DO NOT SEE MUCH EVIDENCE FOR WIDESPREAD
FLOODING RAINS OR SEVERE THUNDERSTORMS WITH THIS FRONT BASED ON THE
LATEST GUIDANCE. HOWEVER...THERE IS A SLIGHT CHANCE OF HEAVIER
RAINFALL OVER KAUAI COUNTY...SO LOOK FOR FUTURE UPDATES AS THIS
WEATHER PATTERN CONTINUES TO DEVELOP THIS WEEKEND. ALSO NOTE THAT
VOLCANIC HAZE FROM SOURCES ON THE BIG ISLAND IS FORECAST TO SPREAD
UP OVER THE WESTERN ISLANDS LATER THIS WEEKEND DUE TO THE
SOUTHEASTERLY FLOW.

THE MODEL OUTPUT SHOWS THE FRONT WILL WEAKEN AND EVENTUALLY
DISSIPATE BY MONDAY. A WEAK SURFACE HIGH NORTH OF THE ISLANDS WILL
LIKELY CAUSE THE PRESSURE GRADIENT TO INCREASE OVER THE AREA...WHICH
WOULD ALLOW THE TRADE WINDS TO BEGIN TO RETURN TO PARTS OF THE STATE
BY TUESDAY. THE TRADES MAY CARRY SOME OF THE LINGERING MOISTURE FROM
THE DISSIPATED FRONT BACK ACROSS WINDWARD AND MAUKA AREAS OF THE
ISLAND CHAIN.

IN THE LONGER RANGE BEYOND EARLY NEXT WEEK...THERE CONTINUES TO BE
VARIATIONS IN THE OUTPUT FROM THE VARIOUS MODELS. THE ECMWF MODEL
APPEARS TO INDICATE A WEAK SURFACE TROUGH MAY MOVE WESTWARD ACROSS
THE ISLANDS DURING THE MIDDLE OF NEXT WEEK. HOWEVER...THE GFS SHOWS
THE SUBTROPICAL HIGH NORTH OF THE STATE WILL DOMINATE THE WEATHER
OVER THE REGION DURING THE SECOND HALF OF NEXT WEEK. THIS WOULD
KEEP THE ALOHA STATE IN A RATHER TYPICAL TRADE WIND WEATHER REGIME.
THE CURRENT FORECAST CONTINUES TO KEEP TRADE WINDS FOR THE EXTENDED
PERIOD...BUT THIS IS SUBJECT TO CHANGE.

&&

.AVIATION...
VFR CONDITIONS PREVAIL AT ALL TAF SITES AND THESE CONDITIONS SHOULD
PREVAIL THROUGH THE NIGHT. THERE WILL LIKELY BE SOME LOCAL MVFR
CONDITIONS OVER E AND SE FACING SLOPES ON THE BIG ISLAND AS WELL AS
OVER E MAUI. THERE MAY ALSO BE SOME LOCAL MVFR OVER INTERIOR AND
MOUNTAIN SECTIONS OF THE SMALLER ISLANDS.

&&

.MARINE...
A LARGE NORTHWEST SWELL IS PRODUCING A SWELL HEIGHT OF 13 FEET WITH
A PERIOD OF 15 SECONDS AT BUOY 1....WHICH IS SLIGHTLY HIGHER THAN
GUIDANCE FROM THE WAVE WATCH 111 MODEL. THE MOST RECENT READINGS
FROM THE HANALEI BUOY NEAR NORTH KAUAI SHOWS A SIGNIFICANT WAVE
HEIGHT OF ABOUT 12 FEET WITH A PERIOD OF 17 SECONDS. AS A RESULT
OF THE SWELL BEING SLIGHTLY LARGER THAN EXPECTED...A HIGH SURF
WARNING HAS BEEN ISSUED FOR MOST NORTH FACING SHORES OF THE SMALLER
ISLANDS...AS WELL AS WEST FACING SHORES OF KAUAI COUNTY. A HIGH SURF
ADVISORY REMAINS IN EFFECT THROUGH THIS WEEKEND FOR WEST FACING
SHORES. THIS SWELL IS EXPECTED TO GRADUALLY DIMINISH...BUT SURF
PRODUCED BY THIS SWELL WILL REMAIN ELEVATED THROUGH SATURDAY NIGHT.

EVEN THOUGH WINDS ARE RATHER LIGHT ACROSS MOST OF THE COASTAL
WATERS...THE LARGE NORTHWEST SWELL WILL INCREASE SEAS ENOUGH TO
BRING SMALL CRAFT ADVISORY /SCA/ CONDITIONS TO THE EXPOSED COASTAL
WATERS FROM LATER THIS AFTERNOON THROUGH MID-DAY SATURDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING UNTIL 6 AM HST SATURDAY FOR NORTH AND WEST FACING
SHORES OF KAUAI NIIHAU OAHU AND MOLOKAI AND NORTH FACING SHORES OF
MAUI.

SMALL CRAFT ADVISORY UNTIL NOON HST SATURDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-OAHU WINDWARD
WATERS-KAIWI CHANNEL-MAUI COUNTY WINDWARD WATERS-BIG ISLAND
WINDWARD WATERS.

&&

DISCUSSION/MARINE...HOUSTON
AVIATION...BURKE