High Surf in Hawaii, December 4 to 14, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST THU DEC 4 2014

.SYNOPSIS...
LIGHT TRADE WINDS WILL DIMINISH FURTHER INTO THE WEEKEND. HIGH
CLOUDS FROM THE WEST MAY BLOCK THE SKY AT TIMES...AND LIGHT SHOWERS
WILL AFFECT MUCH OF THE STATE AT LEAST INTO FRIDAY. DRIER CONDITIONS
SHOULD PREVAIL BY AROUND SUNDAY. WINDS WILL TURN LIGHT AND SOUTHERLY
AHEAD OF A FRONT THAT WILL APPROACH THE STATE BY THE MIDDLE OF NEXT
WEEK.

&&

.DISCUSSION...
SURFACE OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS REPORTED LIGHT
TO MODERATE NORTHEAST WINDS. SOUNDING DATA DEPICTED AN EVEN MOISTER
AIR MASS...ESPECIALLY OVER HILO...THOUGH THE ORIGIN OF THIS WATER
VAPOR REMAINED UNCLEAR GIVEN THE DRY AIR DETECTED FURTHER UPWIND BY
SATELLITE. SIMILARLY...THE INVERSION REMAINED VERY MUCH ON THE HIGH
SIDE OF USUAL...POSSIBLY UNDER THE INFLUENCE OF WEAK TROUGHS ALOFT
PASSING ALONG THE NORTH EDGE OF THE ERODING MID-LEVEL RIDGE
EXTENDING FROM WEST TO EAST OVER THE STATE.

GIVEN THESE CHANGES IN THE LOCAL ATMOSPHERE...AND THE HISTORY OF THE
PAST FEW DAYS...ANOTHER WET MORNING SEEMED LIKELY FOR THE SMALLER
ISLANDS...AND FOR OAHU IN PARTICULAR. SHOWERS STILL SHOULD BE MORE
WIDESPREAD OVER WINDWARD SLOPES...THOUGH SOME WILL CONTINUE TO DRIFT
LEEWARD AT TIMES.

CONVECTION ALONG THE DATELINE PRODUCED EXTENSIVE CIRRUS LAYERS THAT
FOLLOWED A JET STREAM OVER THE STATE BEFORE DISSIPATING. WHILE THE
CIRRUS LAYERS MAY THIN AT TIMES DURING THE NEXT COUPLE OF DAYS...
PERSISTENT TROUGHING ALONG THE DATELINE LIKELY WILL PRODUCE MORE...
KEEPING CLOUD COVER MORE EXTENSIVE THAN USUAL ACROSS THE ISLANDS.
THIS CIRRUS COVER LIKELY WILL INTERFERE WITH LAND BREEZES...REDUCING
THE ALREADY SEASONALLY WEAK DIURNAL CONVECTION ON THE BIG ISLAND.

GUIDANCE PREDICTED ONLY GRADUAL CHANGES TO THE PREVAILING SYNOPTIC
SCENARIO INTO SATURDAY. STRONG IMPULSES WILL PASS QUICKLY IN THE
MAIN STORM TRACK NORTH OF ABOUT 30N...SLOWLY ERODING THE RIDGE
ALOFT. HOWEVER...THE RIDGE SHOULD SURVIVE...BARELY...BEFORE
STRENGTHENING AGAIN FROM SATURDAY INTO NEXT WEEK. SOLUTIONS ALSO
PREDICTED PRECIPITABLE WATER TO DIMINISH RAPIDLY FROM SATURDAY INTO
SUNDAY...POSSIBLY UNDER THE INFLUENCE OF MORE SIGNIFICANT SUBSIDENCE
UNDER THE REBUILDING MID-LEVEL RIDGE.

AT THE SAME TIME...A FRONT CURRENTLY NORTH OF 30N WILL FORCE ITS WAY
THROUGH THE SUBTROPICAL RIDGE AT THE SURFACE TO THE NORTH. THIS
STRUGGLE WILL WEAKEN BOTH THE FRONT AND THE RIDGE. SOLUTIONS
DIFFERED WITH RESPECT TO WHEN ON SUNDAY THIS FEATURE MAY ARRIVE...
BUT IN ANY CASE IT WILL BE SO BADLY WEAKENED BY THAT POINT THAT IT
MAY CONSIST OF LITTLE MORE THAN A MODEST MOISTURE SOURCE AND A
SLIGHT THERMAL DISCONTINUITY...ESPECIALLY IF THE SOLUTIONS PROVE TO
BE CORRECT ABOUT THE GENERAL DRYING. THUS...THE FRONTAL PASSAGE...IF
IT CAN BE SO CALLED...LIKELY WILL BRING ONLY A SLIGHT INCREASE IN
WINDWARD SHOWERS...AND MILDLY COOLER CONDITIONS AFTER LIMITED
WARMING EARLIER IN THE WEEKEND.

FROM SUNDAY ONWARD...STRONGER RIDGING ALOFT WILL EXPAND RAPIDLY FROM
WEST TO EAST OVER THE STATE AGAIN. ORDINARILY...SUCH A DEVELOPMENT
WOULD STRENGTHEN THE SUBTROPICAL RIDGE...LEADING TO RESURGING TRADE
WINDS. HOWEVER...IN THIS CASE WINDS WILL WEAKEN AND BECOME
SOUTHEASTERLY...AND THEN SOUTHWESTERLY...AS THE SUBTROPICAL RIDGE
RECEDES TO THE EAST AHEAD OF ANOTHER FRONT APPROACHING FROM THE
NORTHWEST.

GUIDANCE GENERALLY AGREED IN MOVING THIS FEATURE OVER THE ISLANDS
FROM WEDNESDAY NIGHT INTO THURSDAY. CONVERGENCE IN THE FLOW SOUTH OF
THE FRONT...TOGETHER WITH MOISTURE ADVECTION FROM THE DEEP
TROPICS...MAY INCREASE THE CHANCE OF RAIN OVER PARTS OF THE STATE
EVEN BEFORE THE FRONT ARRIVES. RECENT SOLUTIONS HAVE TRENDED TOWARD
A WEAKER FRONTAL BAND...FOLLOWED BY A RAPID RETURN OF TRADE WINDS.

&&

.AVIATION...
SCATTERED SHOWERS AND AREAS OF MVFR CEILINGS CONTINUE TO AFFECT
WINDWARD SECTIONS OF OAHU...MOLOKAI...MAUI AND THE BIG ISLAND...
AND AIRMET SIERRA FOR MOUNTAIN OBSCURATION REMAINS IN EFFECT.
CONDITION IN THESE AREAS MAY IMPROVE BY LATE MORNING...BUT THIS
IS A RATHER LOW CONFIDENCE FORECAST. VFR WILL PREVAIL ELSEWHERE
THROUGH TODAY...WITH JUST ISOLATED/BRIEF MVFR CONDITIONS POSSIBLE
DUE TO PASSING SHOWERS.

&&

.MARINE...
LOW PRESSURE OFF THE NW US COAST SET UP A LONG FETCH AIMED AT
HAWAII OVER THE PAST FEW DAYS. SURF FROM THIS SWELL PEAKED TUESDAY
NIGHT...AND HAS DIMINISHED SINCE. A HIGH SURF ADVISORY REMAINED IN
EFFECT THROUGH THIS AFTERNOON.

A MODERATE NNW SWELL WILL DECLINE TODAY. ANOTHER NNW SWELL IS
EXPECTED FRIDAY...POSSIBLY PRODUCING SURF NEAR THE ADVISORY LEVEL
ALONG NORTH-FACING SHORES THROUGH SATURDAY. ANOTHER SWELL WILL
ARRIVE SATURDAY NIGHT...BRINGING SOLID HIGH-END ADVISORY-LEVEL SURF
SUNDAY. A THIRD NNW SWELL WILL ENTER HAWAIIAN WATERS MONDAY...
KEEPING ABOVE-AVERAGE SURF ALONG NORTH- AND WEST-FACING SHORES.

OTHERWISE...A SMALL CRAFT ADVISORY /SCA/ REMAINED IN EFFECT FOR ALL
COASTAL WATERS EXCEPT MAALAEA BAY. LIGHT TO MODERATE TRADE WINDS
WILL WEAKEN THROUGH THE WEEKEND. COMBINED SEAS OF THE NNE AND WNW
SWELLS...PLUS WIND WAVES...WILL REQUIRE AN SCA FOR MOST COASTAL
WATERS THROUGH THURSDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST THIS EVENING FOR KAUAI
WINDWARD-OAHU KOOLAU-OLOMANA-MOLOKAI WINDWARD-MAUI WINDWARD WEST-
MAUI CENTRAL VALLEY-WINDWARD HALEAKALA-BIG ISLAND NORTH AND EAST.

SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING FOR ALL
HAWAIIAN WATERS EXCEPT MAALAEA BAY.

&&

JACOBSON...AVIATION
REST...RYSHKO