High Surf in Hawaii, February 28, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
345 AM HST THU FEB 28 2013

.SYNOPSIS...
MODERATE TRADE WINDS TODAY WILL STRENGTHEN TONIGHT...REMAIN STRONG
THROUGH SATURDAY...AND CONTINUE ON THE BREEZY SIDE INTO NEXT WEEK.
SOMEWHAT DRY TRADE WIND WEATHER WILL CONTINUE THROUGH FRIDAY...WITH
A TYPICAL PATTERN OF WINDWARD AND MAUKA SHOWERS IN STORE FOR THE
WEEKEND. A MORE SIGNIFICANT INCREASE IN TRADE SHOWERS IS POSSIBLE
EARLY NEXT WEEK.

&&

.DISCUSSION...
IN A NUT SHELL...TRADE WINDS WILL PERSIST THROUGH THE FORECAST
PERIOD. WHILE INITIALLY DRIER THAN NORMAL...TRADE WIND SHOWER
COVERAGE WILL RETURN TO MORE NORMAL LEVELS OVER THE WEEKEND...WHILE
A GREATER INCREASE IN WINDWARD RAINFALL IS POSSIBLE TUESDAY/
WEDNESDAY AS A RIDGE ALOFT IS REPLACED BY A TROUGH.

CURRENTLY...A 1031 MB HIGH CENTERED ABOUT 1700 MILES NE OF THE
ISLANDS IS SUPPORTING MODERATE TO LOCALLY STRONG TRADE WINDS...
WHILE A STRONG MID AND UPPER LEVEL RIDGE NEAR THE ISLANDS IS
PROVIDING LARGE SCALE SINKING MOTION...RESULTING IN A STABLE AIR
MASS. MEANWHILE...PRECIPITABLE WATER IS QUITE LOW...AND THE TRADE
WIND FLOW IS RATHER DRY...WITH SATELLITE AND RADAR INDICATING LITTLE
IN THE WAY OF PRECIPITATION FALLING FROM THE STABLE BROKEN LOW
CLOUDS MOVING OVER THE ISLANDS FROM THE E. THE COMBINATION OF A
RIDGE ALOFT N OF THE ISLANDS AND A LOW TO THE E CONTINUES TO SUPPORT
STRONG...BUT GRADUALLY WEAKENING...WINDS ALOFT...AND A WIND ADVISORY
FOR THE BIG ISLAND SUMMITS HAS BEEN EXTENDED THROUGH NOON TODAY.

A FRONT ABOUT 600 MILES NW OF KAUAI HAS WEAKENED THE RIDGE
ASSOCIATED WITH THE HIGH TO THE NE OVER THE PAST 24 HOURS...WHILE
ALSO SUBTLY LOOSENING THE LOW LEVEL PRESSURE GRADIENT OVER THE
ISLANDS...AND TRADE WINDS HAVE RESPONDED BY EASING SLIGHTLY. THIS
WEAKENING TREND IS NOT EXPECTED TO LAST LONG...HOWEVER...AS A 1032
MB HIGH CENTERED ABOUT 1750 MILES NW OF THE ISLANDS WILL MOVE INTO A
POSITION N OF THE ISLANDS TONIGHT AND FRIDAY...RESULTING IN
INCREASING TRADE WINDS ONCE AGAIN. WINDS WILL APPROACH ADVISORY
LEVEL SPEEDS ON FRIDAY AND SATURDAY...MAINLY OVER PORTIONS OF THE
BIG ISLAND AND MAUI COUNTY...WHERE TERRAIN HELPS TO ACCELERATE THE
FLOW. BY SUNDAY THE HIGH WILL BE FAR NE OF THE ISLANDS...AND THE
TRADES WILL EASE SLIGHTLY. A NEW HIGH PASSING N OF THE ISLANDS ON
MONDAY WILL ENSURE LOCALLY BREEZY TRADE WINDS INTO THE MIDDLE OF
NEXT WEEK. LATEST FORECAST GUIDANCE INDICATES A WEAKENING AND
VEERING FLOW BY THE END OF NEXT WEEK AS A FRONT APPROACHES FROM THE
NW.

MOSTLY DRY TRADE WIND WEATHER IS IN STORE THROUGH AT LEAST FRIDAY.
SATELLITE DERIVED PRECIPITABLE WATER /PW/ VALUES ARE NEAR 0.75 OF AN
INCH...AND EARLY MORNING SOUNDINGS VALIDATE THE SATELLITE
MEASUREMENTS...AS WELL AS SHOWING THE BASE OF A STRONG SUBSIDENCE
INVERSION BETWEEN 5 AND 6 KFT. A SLIGHT INCREASE IN MAINLY WINDWARD
SHOWERS IS POSSIBLE HEADING INTO THE WEEKEND AS AN UPPER LEVEL
TROUGH PASSES OVERHEAD THEN LINGERS NEARBY. MORE SIGNIFICANT
TROUGHING ALOFT COULD LEAD TO A GREATER INCREASE IN WINDWARD
RAINFALL TUESDAY OR WEDNESDAY.

&&

.AVIATION...
ALTHOUGH TRADE WINDS HAVE EASED...AIRMET TANGO FOR MODERATE LOW
LEVEL TURB TO THE W AND SW OF TERRAIN WILL REMAIN IN EFFECT TODAY.
WINDS WILL INCREASE AGAIN TONIGHT...AND AIRMET TANGO WILL LIKELY
REMAIN IN PLACE THROUGH THE WEEKEND. OTHERWISE CONDITIONS WILL BE
DRY AND STABLE WITH VFR PREVAILING. SHOWERS WILL BE FOCUSED OVER
WINDWARD SLOPES...WHERE BRIEF MVFR CIG WILL BE POSSIBLE.

&&

.MARINE...
ALTHOUGH TRADE WINDS AND COMBINED SEAS WILL BE BELOW SMALL CRAFT
ADVISORY LEVELS IN MOST AREAS TODAY...INCREASING WINDS TONIGHT WILL
COMBINE WITH A BUILDING NW SWELL TO DRIVE SEAS OVER THE 10 FOOT
CRITERION FOR SCA...THUS A /SCA/ REMAINS IN PLACE FOR ALL WATERS
THROUGH SATURDAY. THE SCA COULD BE TRIMMED BACK TO THE TYPICALLY
WINDY WATERS ON SUNDAY. OUTSIDE CHANCE WINDS REACH GALE FORCE IN THE
WINDY CHANNELS ON FRIDAY AND SATURDAY...BUT CONFIDENCE IS TOO LOW TO
WARRANT A GALE WATCH AT THIS TIME.

LONG PERIOD NW SWELL HAS BEEN BUILDING STEADILY AT BUOY 51101 NW OF
KAUAI SINCE LAST NIGHT...THE PACIOOS BUOY AT WAIMEA OAHU IS
DETECTING 20 SECOND FORERUNNERS...AND A HIGH SURF ADVISORY REMAINS
IN PLACE FOR N AND W SHORES EXPOSED TO THE SWELL. EXPECT SURF TO
BUILD TODAY...REMAIN STEADY AT HIGH LEVELS THROUGH FRIDAY...BEFORE
DIMINISHING BELOW ADVISORY LEVELS SATURDAY. A MODERATE NW SWELL IS
DUE EARLY NEXT WEEK.

INCREASING TRADE WINDS FRIDAY/SATURDAY WILL LIKELY DRIVE SURF ALONG
E FACING SHORES TO ADVISORY LEVELS BY THIS WEEKEND BEFORE LOWERING
EARLY NEXT WEEK.

&&

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

SMALL CRAFT ADVISORY UNTIL 6 PM HST SATURDAY FOR ALL WATERS.

WIND ADVISORY FOR MAUNA KEA AND MAUNA LOA THROUGH NOON TODAY.

&&

BIRCHARD