359 FXHW60 PHFO 302000 AFDHFO AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 1000 AM HST MON DEC 30 2013 .SYNOPSIS... MOIST AND UNSTABLE CONDITIONS WILL MAINTAIN THE THREAT FOR HEAVY SHOWERS AND THUNDERSTORMS OVER THE BIG ISLAND TODAY...WHILE A RATHER STABLE NORTHEASTERLY FLOW PREVAILS ACROSS THE REST OF THE STATE. IMPROVING CONDITIONS ARE IN STORE ON THE BIG ISLAND TONIGHT AS A MODERATE TRADE WIND FLOW SPREAD OVER THE ENTIRE STATE. WINDS WILL BECOME SOUTHERLY ON NEW YEARS DAY...FOLLOWED BY THE PASSAGE OF A COLD FRONT ON FRIDAY. && .DISCUSSION... UNSETTLED WEATHER WILL CONTINUE ON THE BIG ISLAND TODAY...WHERE A FLASH FLOOD WATCH IS IN EFFECT. MOISTURE FROM A DISSIPATED FRONT IS POOLED OVER THE BIG ISLAND...AND A SHARP...SLOW-MOVING UPPER LEVEL TROUGH IS LOCATED JUST TO THE WEST. THIS COMBINATION HAS BEEN PRODUCING PERIODS OF HEAVY SHOWERS AND THUNDERSTORMS...SOME STRONG WITH HAIL...OVER WINDWARD BIG ISLAND FOR THE PAST DAY. A SPECIAL SOUNDING TAKEN AT 7000 AM HST AT HILO SHOWS PRECIPITABLE WATER VALUES OF 1.81 INCHES AND COLD AND UNSTABLE CONDITIONS ALOFT. SINCE THE UPPER TROUGH WILL INCH SLOWLY ACROSS THE BIG ISLAND TODAY...THE INSTABILITY WILL HANG ON...AND HEAVY SHOWERS AND THUNDERSTORMS COULD POP UP JUST ABOUT ANYWHERE. THE GROUND IS SATURATED ACROSS MUCH OF WINDWARD BIG ISLAND...SO IT WON/T TAKE MUCH ADDITIONAL HEAVY RAINFALL TO PRODUCE MORE FLOODING. THUS...A FLASH FLOOD WATCH HAS BEEN ISSUED. IN STARK CONTRAST...A RATHER STABLE NORTHEASTERLY LOW LEVEL FLOW IS IN PLACE ACROSS THE REST OF THE STATE. THE OVERNIGHT LIHUE SOUNDING REVEALED A SOLID INVERSION AROUND 6000 FT WITH PRECIPITABLE WATER VALUES NEAR 0.9 OF AN INCH. CLOUDS AND LIGHT SHOWERS ARE PILED UP ON WINDWARD SLOPES FROM MAUI TO KAUAI...WHILE LEEWARD SECTIONS ARE MOSTLY CLEAR. IMPROVING CONDITIONS ARE EXPECTED ON THE BIG ISLAND TONIGHT. THE UPPER LEVEL TROUGH AXIS WILL PUSH EAST OF THE STATE...BRINGING AN INCREASE IN STABILITY THAT SHOULD SHUT DOWN THUNDERSTORM ACTIVITY. REBUILDING TRADE WINDS WILL KEEP WINDWARD SLOPES A BIT WET...BUT HEAVY SHOWERS ARE NOT IN THE FORECAST. BY TUESDAY...A RATHER STABLE...LIGHT TO MODERATE TRADE WIND FLOW WILL BRIEFLY TAKE OVER STATE-WIDE. RIDGING ALOFT WILL BE IN CONTROL...LIMITING SHOWERS TO WINDWARD SLOPES AS WELL AS LEEWARD BIG ISLAND SLOPES IN THE AFTERNOON. TRADE WINDS WILL BE ON A RAPID DECLINE ON NEW YEARS EVE. WEDNESDAY AND THURSDAY WILL FEATURE A STRENGTHENING SOUTHERLY AND SOUTHWESTERLY FLOW AHEAD OF AN APPROACHING FRONT. THE FRONT WILL SWEEP DOWN THE ISLAND CHAIN THURSDAY NIGHT AND FRIDAY. && .AVIATION... +RA/TSRA WILL CONTINUE OVER THE BIG ISLAND NE WINDWARD SLOPES THRU 22Z WITH FREQUENT MVFR/IFR CONDITIONS. ADDITIONAL TSRA/+RA WILL DEVELOP OVER THE LEEWARD SLOPES AFT 22Z. AREAS OF MVFR/IFR CONDITIONS IS LIKELY WITH CB TOPS FL250-400. ELSEWHERE VFR WILL PREVAIL WITH ISOL MVFR CONDITIONS FOCUSED ON WINDWARD SECTIONS. AIRMETS FOR SIERRA TANGO AND ZULU ARE ALL IN EFFECT FOR THE RESPECTIVE HAZARDS...MAINLY OVER THE FAR ERN PORTION OF THE FA. PLEASE SEE THE AIRMETS FOR GREATER DETAIL. SIGMET NOVEMBER REMAINS IN EFFECT FOR CAT ALOFT OVER THE ERN PORTION OF THE STATE AND ADJ WTRS. THE SIGMET AREA EXTENDS 900 NM SW AND WILL LIKELY AFFECT SOUTHBOUND HIGH LVL TRAFFIC. && .MARINE... THE NORTHWEST SWELL IS ON A DECLINE. TRENDS AT BUOY 51101 AND MORNING SURF OBSERVATIONS HAVE LED US TO DOWNGRADE TO A HIGH SURF ADVISORY FOR MOST NORTH AND WEST FACING SHORES OF THE SMALLER ISLANDS. THE ADVISORY SHOULD BE DROPPED BY EVENING. MORE ADVISORY LEVEL SURF IS POSSIBLE THIS WEEKEND. A SMALL CRAFT ADVISORY /SCA/ ALSO REMAINS IN EFFECT FOR EXPOSED COASTAL WATERS DUE TO COMBINED SEAS...MAINLY FROM THE LARGE NW SWELL. THE SCA WILL BE DOWN BY EVENING. && .HFO WATCHES/WARNINGS/ADVISORIES... HIGH SURF ADVISORY UNTIL 6 PM HST TODAY FOR THE NORTH AND WEST FACING SHORES OF NIIHAU KAUAI OAHU AND MOLOKAI...AND NORTH FACING SHORES OF MAUI. SMALL CRAFT ADVISORY UNTIL 6 PM HST TODAY FOR ALL HAWAIIAN WATERS EXCEPT LEEWARD WATERS OF MAUI INCLUDING MAALAEA BAY AND WATERS SOUTH OF THE BIG ISLAND. && $$ PUBLIC AND MARINE...WROE AVIATION...DEJESUS