Small Craft Advisory 55, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
700 AM HST TUE DEC 30 2014

.UPDATE...
PREFRONTAL CONVERGENCE BANDS ARE BEGINNING TO DEVELOP NEAR MAUI
COUNTY AND NEAR KAUAI. ALL OF THE HIGH RESOLUTION GUIDANCE SHOWS
THESE BANDS CONTINUING TO DEVELOP DURING THE DAY AS THE FRONT
APPROACHES. THUS HAVE UPDATED TO INCREASE POPS AND SKY COVER OVER
THE SMALLER ISLANDS THROUGH THE MORNING. REST OF THE FORECAST IS
UNCHANGED AT THIS TIME.

&&

.SYNOPSIS...
LIGHT WINDS AND DRY AND STABLE CONDITIONS CURRENTLY IN PLACE WILL
CHANGE FROM WEST TO EAST TODAY AND TONIGHT AS A FRONT PASSES OVER
THE ISLANDS. WINDS WILL STEADILY INCREASE AHEAD OF THE FRONT...
BECOMING BREEZY AND GUSTY...ESPECIALLY IN AREAS PRONE TO DOWNSLOPING
SOUTHWESTERLY WINDS. THE FAST MOVING FRONT WILL REACH KAUAI BY MID
DAY...MOVE TO OAHU AND MOLOKAI LATE IN THE AFTERNOON...THEN PASS
DOWN THE REST OF THE ISLAND CHAIN OVERNIGHT. A PERIOD OF RATHER DRY
NORTHERLY FLOW IS EXPECTED WEDNESDAY INTO NEW YEARS DAY...LIKELY
FOLLOWED BY ACTIVE WEATHER THURSDAY NIGHT INTO SATURDAY.

&&

.PREV DISCUSSION.../ISSUED 400 AM HST TUE DEC 30 2014/
DRY AND STABLE CONDITIONS WITH LIGHT WINDS WILL BE CHANGING THIS
MORNING. CURRENTLY...COOL AND DRY PERSIST...AS OVERNIGHT TEMPS
HAVE DROPPED INTO THE LOW TO MID 60/S IN MOST LOCATIONS NEAR SEA
LEVEL. RIDGING ALOFT IS RAPIDLY ERODING AS A STRONG MID TO UPPER
LEVEL TROUGH NEARS. THE INVERSION AT LIHUE HAS LIFTED TO ALMOST
5500 FT...WHILE THE INVERSION AT HILO REMAINS NEAR 4000 FT...AND
PRECIPITABLE WATER VALUES...THOUGH STILL DRY AT ABOUT 0.8 OF AN
INCH...CONTINUE TO CREEP UP. UNDER THESE STABLE AND DRY CONDITIONS
THIN STRATOCUMULUS CLOUDS HAVE FORMED OVER MUCH OF THE REGION.
THESE CLOUDS WILL BURN OFF QUICKLY THIS MORNING...AND MORE
SIGNIFICANT CHANGES WILL DEVELOP THROUGHOUT THE DAY.

A COLD FRONT WILL SWEEP DOWN THE ISLAND CHAIN LATER TODAY AND
TONIGHT...BRINGING BREEZY AND GUSTY WINDS. GENERALLY MODEST RAINFALL
WILL ACCOMPANY THE FRONT...THOUGH WE COULD SEE A LINE OF FAST-MOVING
AND BRIEFLY HEAVY SHOWERS EMBEDDED WITHIN THIS FEATURE. THE
STRONGEST PORTION OF THE MID TO UPPER LEVEL TROUGH DRIVING THE FRONT
WILL PASS JUST NORTH OF THE STATE...LIMITING THE THUNDERSTORM THREAT
TO KAUAI AND WATERS NORTH OF THE SMALLER ISLANDS...BUT DYNAMICS OF
THIS SYSTEM SHOULD SUPPORT GUSTY WINDS AHEAD OF AND BEHIND THE
FRONT...MAKING WINDS THE MAIN AREA OF CONCERN. PORTIONS OF THE
ISLANDS PRONE TO DOWNSLOPING SOUTHWESTERLY WINDS WILL EXPERIENCE
SOME STRONG GUSTS AHEAD OF AND ALONG THE FRONT. SOME POCKETS OF 40
MPH GUSTS ARE POSSIBLE OVER AND DOWNWIND OF TERRAIN...BUT WIND
ADVISORY CONDITIONS ARE UNLIKELY AS THE GFS IS PREDICTING 850 MB
WINDS TO TOP OUT AT AROUND 30 KT. THE TIMING FOR FRONTAL PASSAGE IS
ROUGHLY KAUAI MID DAY...OAHU AND MOLOKAI LATE AFTERNOON...MAUI IN
THE EVENING...THEN DOWN TO THE BIG ISLAND TONIGHT.

A PERIOD OF RATHER DRY...POST-FRONTAL NORTHERLY WINDS IS DUE
WEDNESDAY INTO NEW YEARS DAY. THE FRONT WILL WASH OUT EAST OF THE
BIG ISLAND ON WEDNESDAY AS A SURFACE LOW FORMS SEVERAL HUNDRED MILES
NORTH OF THE STATE. BIG ISLAND COULD SEE SOME LINGERING MOISTURE ON
WEDNESDAY WHILE THE REST OF THE STATE SEE LIMITED WINDWARD RAINFALL
DUE TO A DRY POST-FRONTAL AIRMASS WITH PRECIPITABLE WATER VALUES
WELL UNDER AN INCH. NORTHERLY WINDS WILL GRADUALLY DECLINE NEW YEARS
EVE AND DAY AS SURFACE RIDGING JUST NORTH OF THE STATE BREAKS DOWN
AHEAD OF THE NEXT WEATHER SYSTEM. RATHER DRY CONDITIONS SHOULD
HOLD...AND TEMPERATURES WILL BE COOL AS DEW POINTS SHOULD BE IN THE
50/S.

ACTIVE WEATHER IS EXPECTED LATE THURSDAY NIGHT INTO SATURDAY. THE
UPPER TROUGH THAT MOVES IN WITH THE FRONT WILL FLATTEN OUT AND
WEAKEN ON WEDNESDAY BUT WILL LINGER OVERHEAD. A STRONG WESTERN
PACIFIC JET STREAM WILL DROP A STRONG SHORTWAVE ALOFT INTO THIS
TROUGH...LIKELY TRIGGERING A ROUND OF ACTIVE WEATHER OVER THE STATE.
THE DETAILS REMAIN UNCLEAR...BUT IF THE GFS AND ECMWF VERIFY...
STRONG THUNDERSTORMS ARE POSSIBLE...MAINLY ON FRIDAY AND FRIDAY
NIGHT.

AN EXTENDED PERIOD OF ELEVATED WINDS IS DUE FOR THE HIGH SUMMITS OF
THE BIG ISLAND AND TO A LESSER DEGREE ON MAUI. THE MID-LEVEL TROUGH
DRIVING TODAY/S FRONT WILL LEAD TO A SHARP INCREASE IN SUMMIT WINDS
THROUGH THE DAY...LIKELY REACHING HIGH WIND WARNING LEVELS BY
MID DAY. THE VERY WINDY CONDITIONS WILL BACK OFF ON WEDNESDAY BUT
ARE EXPECTED TO REMAIN ABOVE WIND ADVISORY LEVELS ON MAUNA KEA AND
MAUNA LOA. ANOTHER ROUND OF VERY STRONG WINDS IS DUE AGAIN BY NEW
YEARS DAY THROUGH FRIDAY AS THE NEXT SHORTWAVE ALOFT AFFECTS THE
ISLANDS. A HIGH WIND WARNING HAS BEEN ISSUED FOR THE HIGH BIG ISLAND
SUMMITS THROUGH EARLY WEDNESDAY MORNING...AND A WIND ADVISORY HAS
BEEN ISSUED FOR HALEAKALA SUMMIT ON MAUI FOR THE SAME TIME PERIOD.

&&

.AVIATION...
EXPECT AIRMET TANGO FOR STRENGTHEN SLY WINDS AND AIRMET SIERRA FOR
MTN OBSC ABV 025 AFT 19Z TO GO INTO EFFECT WITH THE 16Z PACKAGE...
AFFECTING KAUAI. THESE CONDS SHOULD BE SPREADING TO OAHU AND MOLOKAI
AFT 22Z. THIS WEATHER IS RELATED TO A FRONT MOVING DOWN THE ISLAND
CHAIN. REFER TO DISCUSSION ABOVE FOR MORE DETAILS.

&&

.MARINE...
ALTHOUGH WINDS ARE CURRENTLY LIGHT...SOUTHWESTERLY WINDS WILL
STEADILY INCREASE THIS MORNING AS A FRONT NEARS THE ISLANDS. A SMALL
CRAFT ADVISORY...SCA...HAS BEEN ISSUED FOR MOST WATERS AS FRESH TO
STRONG SOUTHWESTERLY WINDS DEVELOP AHEAD OF THE FRONT. FRESH TO
STRONG WINDS WILL SHIFT OUT OF THE NORTHWEST BEHIND THE FRONT ACROSS
KAUAI WATERS THIS AFTERNOON AND OVER MOST OTHER WATERS OVERNIGHT. IN
ADDITION...LOCALLY GENERATED WIND WAVES COMBINED WITH BUILDING
NORTHWEST SWELL WILL CREATE HAZARDOUS SEAS OF 10 FT OR MORE. SCA
CONDITIONS WILL LINGER INTO WEDNESDAY WITH WINDS DECLINING ON NEW
YEARS EVE.

A NORTHWEST SWELL WILL BUILD LATER TODAY AND TONIGHT. THIS SWELL
COMBINED WITH FRESH TO STRONG NORTHWEST WINDS BEHIND THE FRONT WILL
PRODUCE VERY ROUGH SURF AROUND THE ADVISORY LEVEL ACROSS NORTH
FACING SHORES...THOUGH WE HAVE ELECTED TO MONITOR BUOY 51101 TRENDS
TO DETERMINE IF SURF WILL REACH THE 15 FOOT ADVISORY LEVEL. NORTH
SHORE SURF WILL REMAIN ELEVATED ON WEDNESDAY AND WILL BE REINFORCED
ON NEW YEARS EVE AND DAY BY A SHORT-PERIOD NORTH SWELL GENERATED BY
A LOW DEVELOPING SEVERAL HUNDRED MILES NORTH OF THE STATE. A MIX OF
MODERATE...LONG PERIOD NORTHWEST SWELL AND SHORT PERIOD NORTH SWELL
WILL CONTINUE INTO THE WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 6 AM HST WEDNESDAY FOR BIG ISLAND
SUMMITS.

WIND ADVISORY UNTIL 6 AM HST WEDNESDAY FOR HALEAKALA SUMMIT.

SMALL CRAFT ADVISORY UNTIL 6 PM HST WEDNESDAY FOR KAUAI
NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-
KAUAI CHANNEL-OAHU WINDWARD WATERS-OAHU LEEWARD WATERS-MAUI
COUNTY WINDWARD WATERS-BIG ISLAND WINDWARD WATERS.

SMALL CRAFT ADVISORY UNTIL 6 AM HST WEDNESDAY FOR KAIWI CHANNEL-
MAUI COUNTY LEEWARD WATERS-PAILOLO CHANNEL-ALENUIHAHA CHANNEL.

&&

UPDATE...R BALLARD
PREV DISCUSSION/MARINE/AVIATION...WROE/LAU