High Surf in Hawaii, February 2 to 3, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST THU FEB 2 2012

.SYNOPSIS...
TRADE WINDS WILL DIMINISH RAPIDLY THROUGH FRIDAY...LEAVING LIGHT
WINDS AND DRY CONDITIONS. A FRONT APPROACHING THE STATE BY LATE IN
THE WEEKEND WILL PUSH ON DOWN THE ISLAND CHAIN FROM MONDAY THROUGH
THE MIDDLE OF NEXT WEEK...BRINGING CLOUDS...MODERATELY STRONG
WINDS...AND SOME RAIN.

&&

.DISCUSSION...
OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS REPORTED LIGHT TO
MODERATE TRADE WINDS...BUT PRESSURE TRENDS SUGGESTED A SIGNIFICANT
DECLINE IN WIND SPEEDS THROUGH THE SHORT RUN. LARGE AREAS OF STRATUS
AND STRATOCUMULI AROUND AND ESPECIALLY TO THE EAST OF THE STATE
CONFIRMED THE STABILITY IMPLIED BY THE LOW INVERSION AND
PRECIPITABLE WATER VALUES EVIDENT IN LOCAL SOUNDINGS. THE GRAVITY
WAVE BOOSTING THE STABLE LOW CLOUDS OVER THE PAST ONE TO TWO HOURS
SHOULD MOVE ON BY MIDNIGHT...AND LAND BREEZES WILL LEAD TO SOME
CLEARING OVERNIGHT...BUT A LITTLE DRIZZLE MAY FALL. IN ANY CASE...
ACCUMULATION WILL BE MINIMAL. ALOFT...BROAD...FLAT RIDGING PERSISTED
OVER THE ISLANDS...WHILE A SHALLOW TROUGH LANGUISHED TO THE EAST.

GUIDANCE AGREES THAT THE SUBTROPICAL RIDGE WILL SHIFT SOUTH OVER THE
NEXT 24 HOURS OR SO...STOPPING MORE OR LESS DIRECTLY OVER THE
ISLANDS. FOR LACK OF A SYNOPTIC-SCALE PRESSURE GRADIENT...THE TRADE
WINDS WILL CEASE. ALTHOUGH LOCAL CIRCULATIONS WILL BECOME DOMINANT
IN PLACES...RELATIVELY WEAK WINTER INSOLATION MAY NOT PRODUCE MUCH
OF A SEA BREEZE. WITH SUBSIDENCE PREVAILING THROUGH A LARGE PART OF
THE ATMOSPHERE...CLOUD FORMATION WILL BE SIGNIFICANTLY SUPPRESSED.
EVEN SO...SOME AFTERNOON CLOUDS AND A SPRINKLE OR TWO MIGHT OCCUR
INLAND EACH AFTERNOON...IF ONLY GUIDANCE DID NOT PREDICT SUCH AN
EXTREMELY DRY AIR MASS. IT IS TRICKY TO FORECAST CONDITIONS SO FAR
FROM CLIMATOLOGY...BUT IN THIS CASE THE PICTURE REALLY DOES LOOK
VERY DRY INTO SUNDAY AFTERNOON.

BY LATE IN THE WEEKEND...POWERFUL MID-LEVEL TROUGHS MOVING THROUGH
THE NORTH PACIFIC WILL START TO ERODE THE SHELF-LIKE RIDGING OVER
THE STATE...AND A MODERATELY STRONG FRONT WILL APPROACH AT THE
SURFACE FROM THE NORTHWEST. THE FRONT WILL WEAKEN AS IT PUSHES
THROUGH THE SURFACE RIDGE TOWARD THE STATE...BUT BY LATE SUNDAY
AFTERNOON WINDS WILL START TO BECOME SOUTHWESTERLY AND CLOUD COVER
WILL START TO INCREASE ACROSS KAUAI COUNTY. GUIDANCE ALSO STARTS TO
DISAGREE SLIGHTLY WITH RESPECT TO HOW SOON THE FRONT MAY REACH
OAHU...BUT A STRONG MID-LEVEL TROUGH DIGGING SOUTH FROM SUNDAY NIGHT
INTO MONDAY...ALONG WITH A STRONG SOUTHERLY PUSH OF COLD AIR AT THE
SURFACE...IS EXPECTED TO REINVIGORATE THE FRONT ENOUGH SO THAT IT
WILL PRESS ON THROUGH THE REST OF THE ARCHIPELAGO...REACHING THE BIG
ISLAND BY AROUND WEDNESDAY. THIS SECOND SURGE OF THE FRONT MAY BRING
MODERATELY STRONG...AND NOTICEABLY COOL...NORTHERLY WINDS TO THE
STATE.

ASIDE FROM TIMING...THE MAIN FORECAST QUESTION ABOUT THE FRONT
CONCERNS THE AMOUNT OF RAINFALL TO BE EXPECTED FROM IT. SOME IS
LIKELY FOR MOST OF THE STATE...BUT THE EXTREMELY DRY AIR MASS AHEAD
OF THE FRONT SHOULD LIMIT PREFRONTAL ACCUMULATION SIGNIFICANTLY.
RAINFALL WITH THE FRONT ITSELF WILL DEPEND LARGELY ON HOW MUCH
MOISTURE THE FRONT HAS CONVERGED BY THAT POINT.

&&

.MARINE...
A HIGH SURF ADVISORY REMAINS IS IN EFFECT FOR EXPOSED NORTH- AND
WEST-FACING SHORES. SURF WILL JUST REACH THE ADVISORY THRESHOLD...
WITH HEIGHTS TOPPING OUT AT A BIT OVER 15 FEET THROUGH FRIDAY
AFTERNOON.

A RUN OF VERY LARGE SURF MAY ARRIVE NEXT WEEK. THE NEXT LARGE SWELL
WILL HIT LATE IN THE WEEKEND...FOLLOWED BY A RATHER DISORGANIZED RAW
NORTHWEST SWELL AROUND MID-WEEK THAT COULD BE EXTREMELY LARGE.
CONDITIONS LIKELY WILL INCLUDE NORTHERLY WINDS AND MIXED PERIODS. A
SMALL CRAFT ADVISORY LIKELY WILL ACCOMPANY THE LARGE SWELLS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST FRIDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-WAIANAE COAST-OAHU NORTH SHORE-OAHU
KOOLAU-MOLOKAI-WINDWARD HALEAKALA.

&&

RYSHKO