High Surf in Hawaii, December 24 to 28, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
357 AM HST THU DEC 24 2015

.SYNOPSIS...
MODERATE TRADE WINDS WILL CONTINUE TODAY...THEN BECOME WINDY AGAIN
FROM LATE TONIGHT THROUGH THIS WEEKEND AS A NEW SURFACE HIGH PASSES
FAR NORTH OF THE ALOHA STATE. LOW CLOUDS AND SHOWERS WILL BE FOCUSED
MAINLY ACROSS WINDWARD AND MAUKA AREAS TODAY...THEN RAINFALL WILL
INCREASE AS WE HEAD INTO THE HOLIDAY WEEKEND. TRADE SHOWERS WILL
CONTINUE TO FAVOR WINDWARD AND MAUKA AREAS...BUT THE STRONG TRADES
WILL CARRY SOME SHOWERS OVER LEEWARD SECTIONS OF THE SMALLER ISLANDS.

&&

.DISCUSSION...
A 1030 MB SURFACE HIGH CENTERED NEAR 35N 144W...OR ABOUT 1250 MILES
NORTHEAST OF HONOLULU...IS MOVING TOWARD THE EAST-NORTHEAST AT ABOUT
10 MPH. A SURFACE RIDGE EXTENDS FROM THIS HIGH WEST-SOUTHWEST TO A
POINT ABOUT 580 MILES NORTH OF HONOLULU. THE PRESSURE GRADIENT SOUTH
AND SOUTHWEST OF THESE FEATURES IS MAINTAINING MODERATE TRADE WINDS
ACROSS THE MAIN HAWAIIAN ISLANDS EARLY THIS MORNING. ELSEWHERE...THE
LEADING EDGE OF A BAND OF LAYERED CLOUDS AND SHOWERS ASSOCIATED WITH
A SURFACE COLD FRONT IS MORE THAN 900 MILES WEST-NORTHWEST OF LIHUE.
THIS LEADING EDGE IS ADVANCING EASTWARD AT ABOUT 30 MPH.

LOOPS OF WATER VAPOR IMAGERY DEPICT A MID TO UPPER TROPOSPHERIC
LOW ABOUT 575 MILES EAST OF HILO. THIS FEATURE ALOFT CONTINUES TO
PROPAGATE EASTWARD AWAY FROM THE REGION. THE EARLY MORNING
SOUNDINGS FROM LIHUE AND HILO SHOWED WEAK LOW LEVEL TRADE WIND
INVERSIONS NEAR 6 THOUSAND FEET. PRECIPITABLE WATER VALUES
WERE 1.1 TO 1.2 INCHES AT BOTH SITES.

THE FORECAST MODELS SHOW THE COLD FRONT FAR WEST-NORTHWEST OF THE
MAIN HAWAIIAN ISLANDS WILL CONTINUE TO MOVE RAPIDLY EASTWARD DURING
THE NEXT COUPLE OF DAYS. THIS WILL CAUSE THE SURFACE RIDGE NORTH OF
THE ISLANDS TO WEAKEN AS THE HIGH TO OUR NORTHEAST CONTINUES TO MOVE
AWAY FROM THE AREA. THE PRESSURE GRADIENT SOUTH OF THE RIDGE WILL
MAINTAIN MODERATE TRADE WINDS ACROSS THE REGION. NOTE THAT THE FRONT
IS NOT EXPECTED TO REACH THE ISLANDS...SO WE CAN EXPECT A MORE
TYPICAL TRADE WIND WEATHER PATTERN THROUGH TONIGHT. LOW CLOUDS
AND SHOWERS WILL BE FOCUSED MAINLY ACROSS WINDWARD AND MAUKA AREAS.
CONDITIONS ARE EXPECTED TO BE DRIER AND INVERSION HEIGHTS SOMEWHAT
LOWER ACROSS THE WESTERN HALF OF THE STATE. NOTE THAT SCATTERED TO
LOCALLY BROKEN CUMULUS CLOUDS AND ISOLATED SHOWERS EAST AND NORTHEAST
OF MAUI AND THE BIG ISLAND MAY ENHANCE TRADE SHOWERS OVER SOME AREAS
LATER TODAY...BUT RAINFALL AMOUNTS WILL LIKELY BE LOWER COMPARED WITH
EARLIER THIS WEEK.

DURING THE CHRISTMAS HOLIDAY WEEKEND...A NEW SURFACE HIGH WILL PASS FAR
NORTH OF THE STATE BEHIND THE FRONT. THIS WILL CAUSE THE PRESSURE
GRADIENT TO REBOUND ACROSS THE STATE...WHICH WILL PRODUCE STRONG AND
GUSTY TRADES STARTING LATE TONIGHT AND FRIDAY. THE FORECAST MODELS ALSO
APPEAR TO SHOW A WEAK MID-TROPOSPHERIC TROUGH SHIFTING WESTWARD TOWARD
THE STATE THIS WEEKEND. THE ARRIVAL OF THIS FEATURE ALOFT WOULD LIKELY
DESTABILIZE THE ATMOSPHERE. THE UNSTABLE ATMOSPHERE COMBINED WITH AN
INCREASE IN LOW-LEVEL MOISTURE TRANSPORTED INTO THE STATE BY THE
STRENGTHENING TRADES IS FORECAST TO CAUSE AN INCREASE IN LOW CLOUDS
AND TRADE SHOWERS FROM FRIDAY THROUGH THE WEEKEND. WHILE MOST RAINFALL
WILL BE FOCUSED ACROSS WINDWARD AND MAUKA AREAS...THE STRONGER TRADES
WILL ONCE AGAIN SPREAD SOME OF THE SHOWERS OVER LEEWARD SECTIONS OF THE
SMALLER ISLANDS. THIS MID-LEVEL TROUGH IS ALSO EXPECTED TO LOWER THE
FREEZING LEVEL. THE INCREASING MOISTURE DEPTH COMBINED WITH ELEVATED
INVERSIONS WILL RESULT IN AN INCREASING CHANCE OF WINTER WEATHER
CONDITIONS DEVELOPING ACROSS THE BIG ISLAND SUMMITS THIS WEEKEND.

LOOKING AHEAD TO NEXT WEEK...THE FORECAST MODELS DEPICT A STRONG
SURFACE LOW TRACKING ACROSS THE NORTH PACIFIC. THIS FEATURE IS EXPECTED
TO WEAKEN THE SURFACE HIGH AND CAUSE THE SURFACE RIDGE TO SHIFT SOUTH
TOWARD THE STATE. THIS WILL LIKELY REDUCE THE PRESSURE GRADIENT ACROSS
THE REGION...WHICH WILL CAUSE THE TRADE WINDS TO DIMINISH NEXT WEEK.
ALSO A MID-LEVEL RIDGE IS EXPECTED TO BUILD EASTWARD ACROSS THE STATE...
LEADING TO SUBSIDENCE AND A STRENGTHENING/LOWERING INVERSION. COMBINED
WITH DECREASING LOW-LEVEL MOISTURE NEAR THE APPROACHING SURFACE RIDGE...
THIS SHOULD LEAD TO DRIER THAN NORMAL CONDITIONS AT LEAST THROUGH THE
MIDDLE OF NEXT WEEK.

&&

.AVIATION...
CLOUDS AND SHOWERS WILL CONTINUE TO FAVOR WINDWARD AND MAUKA AREAS
AS MODERATE TRADE WINDS PERSIST STATEWIDE. THE AIRMASS OVER THE
ISLANDS IS PRESENTLY MOSTLY DRY BUT AN AREA OF ENHANCED MOISTURE
EXISTS UPSTREAM OF THE ISLANDS AND IS EXPECTED TO MOVE INTO
NORTHEASTERN EXPOSURES OF THE BIG ISLAND THIS MORNING. AIRMET SIERRA
FOR MTN OBSC MAY BECOME NECESSARY FOR EASTERN EXPOSURES OF THE BIG
ISLAND AFTER 1600Z.

&&

.MARINE...
AVAILABLE DATA SUGGEST THAT WINDS AND SEAS REMAIN BELOW SMALL CRAFT
ADVISORY /SCA/ CRITERIA ACROSS ALL OF THE HAWAIIAN COASTAL WATERS AT
THIS TIME. WINDS ARE FORECAST TO BEGIN INCREASING AGAIN TONIGHT...
AND SCA CONDITIONS APPEAR LIKELY TO RETURN TO THE TYPICALLY WINDIER
AREAS AROUND MAUI COUNTY AND THE BIG ISLAND. THE PRESSURE GRADIENT
WILL CONTINUE TO INCREASE FRIDAY INTO THE WEEKEND AS A NEW HIGH
MOVES NORTH OF THE STATE. SCA WILL LIKELY BE NEEDED ACROSS ALL
WATERS DURING THE WEEKEND...WITH THE POTENTIAL FOR GALES IN THE
ALENUIHAHA CHANNEL.

SURF OBSERVATIONS FROM WEDNESDAY SHOWED ADVISORY LEVEL SURF AT A FEW
EAST FACING LOCATIONS...BUT WITH SEAS AT THE BUOYS CONTINUING TO
DROP SINCE THEN...WE EXPECT SURF ON EAST FACING SHORES TO REMAIN
BELOW ADVISORY LEVELS ALTHOUGH STILL ELEVATED TODAY THROUGH FRIDAY.
SURF ON EAST FACING SHORES WILL LIKELY RISE ABOVE ADVISORY LEVELS
ONCE AGAIN THIS WEEKEND AS THE NEW HIGH PASSES NORTH OF THE STATE
AND STRENGTHENS THE TRADES. A COUPLE OF SMALL TO MODERATE NORTHWEST
SWELL EVENTS WILL ARRIVE TODAY AND SATURDAY...WITH RESULTING SURF
REMAINING WELL BELOW ADVISORY LEVELS. A LARGER NORTHWEST SWELL IS
FORECAST TO ARRIVE SUNDAY THEN PEAK SUNDAY NIGHT...AND MAY BRING
ADVISORY LEVEL SURF TO NORTH AND WEST FACING SHORES TO THE SMALLER
ISLANDS. THIS SWELL WILL THEN DECLINE MONDAY. A WINTERTIME SOUTHERLY
SWELL WILL MOVE THROUGH DURING THE WEEKEND...PRODUCING A BUMP IN SURF
FOR SOUTH FACING SHORES.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

DISCUSSION...HOUSTON
MARINE...JACOBSON
AVIATION...BEDAL