AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HONOLULU HI 1000 AM HST TUE DEC 23 2014 .SYNOPSIS... AN ACTIVE WEATHER PATTERN WILL FOCUS HEAVY SHOWERS AND THUNDERSTORMS MAINLY OVER THE EASTERN END OF THE STATE TODAY...THOUGH FLOODING IS POSSIBLE ON ALL ISLANDS. THE POTENTIAL FOR HEAVY FLOODING RAINFALL AND THUNDERSTORMS...AS WELL AS DANGEROUS WINTER WEATHER ON THE BIG ISLAND SUMMITS...WILL PERSIST TONIGHT AND WEDNESDAY AS A POTENT DISTURBANCE ALOFT SETTLES OVER THE ISLANDS. A DRIER NORTHERLY FLOW IS EXPECTED THURSDAY AND FRIDAY. && .DISCUSSION... THE ACTIVE WEATHER PATTERN WILL PERSIST INTO WEDNESDAY...WITH THE FOCUS FOR HEAVY FLOODING SHOWERS AND THUNDERSTORMS OVER THE EASTERN END OF THE ISLAND CHAIN TODAY. HEAVY SHOWERS AND THUNDERSTORMS PERSIST THIS MORNING ALONG A DISSIPATING FRONTAL BOUNDARY STALLED NEAR MAUI AND NORTHERN BIG ISLAND...WHILE A STRONG MID TO UPPER LEVEL TROUGH IS DIGGING OVER THE ISLANDS FROM THE NORTHWEST. TEMPERATURES AT 500 MB WITHIN THE UPPER TROUGH WERE DOWN TO -18C ON THE OVERNIGHT LIHUE...EXTREMELY COLD BY HAWAII STANDARDS. THIS FEATURE WILL CONTINUE TO TRIGGER THE ACTIVE WEATHER ALONG THE FRONT TODAY NEAR MAUI AND THE BIG ISLAND...MAINTAINING THE FLASH FLOOD THREAT. TO THE WEST OF THE FRONT...A BREEZY AND DRIER NORTHERLY IS OCCURRING. EVEN WITH THE IMPRESSIVE MID TO UPPER LEVEL INSTABILITY...IT WILL BE DIFFICULT... THOUGH NOT IMPOSSIBLE...TO TRIGGER THUNDERSTORMS OVER KAUAI AND OAHU TODAY DUE TO MEAGER LOW LEVEL MOISTURE. THAT SAID...GROUNDS ARE SATURATED AND STREAMS ARE RUNNING HIGH...SO A FLOOD THREAT IS STILL PRESENT FOR THE WESTERN ISLANDS TODAY. THE THREAT FOR HEAVY SHOWERS AND THUNDERSTORMS WILL PERSIST THROUGH AT LEAST WEDNESDAY AS THE MID TO UPPER LEVEL TROUGH FORMS A STRONG CUTOFF LOW. THE FRONTAL BOUNDARY WILL LIKELY WASH OUT LATER TODAY AND TONIGHT. HOWEVER...THE CUTOFF LOW WILL MEANDER NEARBY...AND MODELS DEPICT DEEP MOISTURE BEING DRAWN OVER THE ISLANDS FROM THE SOUTHEAST WITH A SURFACE LOW POSSIBLY DEVELOPING OVER THE ISLANDS. THE THREAT FOR HEAVY FLOODING RAINFALL WITH THUNDERSTORMS WILL CONTINUE THROUGH AT LEAST WEDNESDAY...AND A FLASH FLOOD WATCH REMAINS IN PLACE THROUGH WEDNESDAY AFTERNOON. HAZARDOUS WEATHER IS ALSO EXPECTED OVER THE BIG ISLAND SUMMITS. AS THE UPPER LEVEL TROUGH MOVES EASTWARD AND FORMS A CUTOFF LOW...VERY WINDY CONDITIONS WILL DEVELOP ON THE HIGH BIG ISLAND SUMMITS. WINDS ON THE SUMMITS ROSE TO WARNING LEVELS OVERNIGHT AS LAYERED CLOUDS ALOFT DROPPED DOWN TO SUMMIT LEVEL...BUT THE SUMMITS ARE CURRENTLY UNDER A LULL. EXPECT A SHARP INCREASE IN WINDS TODAY AS THE UPPER TROUGH NEARS. DEEP MOISTURE IS ALSO FORECAST TO DRAWN UP FROM THE SOUTHEAST TODAY...PRODUCING PERIODS OF HEAVY SNOW AND REDUCED VISIBILITY. WITH THIS IN MIND...THE BLIZZARD WATCH HAS BEEN UPGRADED TO A WARNING...AND THE HIGH WIND WARNING HAS BEEN MERGED WITH THIS PRODUCT. THE HIGHEST PROBABILITY FOR BLIZZARD CONDITIONS WILL BE THIS AFTERNOON AND TONIGHT. SNOW CHANCES DECREASE ON WEDNESDAY...BUT STRONG WINDS WILL CONTINUE. MOST FORECAST MODELS DEPICT THE CUTOFF LOW AND ANY ASSOCIATED LOW LEVEL FEATURE LIFTING OFF TO THE NORTHEAST ON THURSDAY. NORTHERLY LOW LEVEL WINDS ARE EXPECTED ALONG WITH A DECREASE IN RAINFALL. HOWEVER...THE GFS AND ECMWF ARE SHOWING ANOTHER SHORTWAVE ALOFT DROPPING NEARBY ON FRIDAY INTO SATURDAY...POSSIBLY TRIGGERING SOME INSTABILITY. && .AVIATION... MOUNTAIN OBSCURATIONS CONTINUE FOR ALL ISLANDS EXCEPT OAHU. IT IS LIKELY TO BE EXPANDED TO INCLUDE OAHU BY THIS AFTERNOON. MAIN SHOWER ACTIVITY IS FOCUSED OVER MAUI AND KAUAI. TERMINALS ON THESE ISLANDS...INCLUDING PHLI...PHJH...AND PHOG...WILL LIKELY CONTINUE TO EXPERIENCE PREVAILING MVFR CONDITIONS WITH PERIODS OF IFR. OTHER SMALLER ISLANDS WILL EXPERIENCE PASSING SHOWERS WITH PERIODS OF MVFR TO IFR CONDITIONS. STRONG AND GUSTY WINDS THAT FILLED IN BEHIND THE FRONT...REMAIN OVER THE SMALLER ISLANDS. AIRMET TANGO IS POSTED FOR LOW LEVEL TURB OVER THESE ISLANDS...AND WILL REMAIN THROUGH AT LEAST TONIGHT. MOISTURE FROM THE SOUTH HAS STARTED TO MAKE ITS WAY UP TOWARDS THE EASTERN END OF THE STATE. THICK LAYERED CLOUDS BETWEEN 100 AND FL300 HAVE MADE THEIR WAY OVER THE ISLANDS FROM OAHU THROUGH THE BIG ISLAND. AIRMET ZULU FOR TEMPO LIGHT TO MOD RIME ICE IS POSTED. A COLD UPPER LEVEL TROUGH IS MAKING ITS WAY OVER KAUAI. AN AIRCRAFT THIS MORNING REPORTED SEVERE TURBULENCE BETWEEN FL350 AND FL370 ON THE BACK SIDE OF THE TROUGH. SIGMET NOVEMBER SERIES IS ISSUED...COVERING PARTS OF OAHU AND KAUAI. POTENTIAL FOR TEMPO MOD TURB BETWEEN FL230 AND FL430 TO SPREAD OVER THE OTHER ISLANDS REMAINS AS THE UPPER LEVEL TROUGH MOVES EAST. THE COLD UPPER LEVEL TROUGH WILL ALSO SERVE TO FURTHER DESTABILIZE THE AIR MASS OVER THE STATE. POTENTIAL FOR THUNDERSTORMS REMAINS OVER THE STATE...WITH MOST ACTIVE AREAS OVER THE EASTERN END OF THE STATE. AVIATION HAZARDS ASSOCIATED WITH ACTIVE THUNDERSTORMS INCLUDE ICING...TURBULENCE...WIND SHEAR AND IFR CONDITIONS. && .MARINE... STRONG NORTH-NORTHEAST WINDS ARE BLOWING ACROSS THE WESTERN HALF OF THE ISLAND CHAIN BEHIND A SLOW-MOVING FRONT NEAR THE BIG ISLAND. LARGE SEAS GENERATED BY THESE WINDS WILL COMBINE WITH A LARGE NORTHWEST SWELL TO PRODUCE HAZARDOUS CONDITIONS...AND A SMALL CRAFT ADVISORY IS IN EFFECT FOR ALL WATERS DUE TO THESE THREATS. THE NORTHWEST SWELL HAS DIMINISHED OVERNIGHT AND THE HIGH SURF WARNING HAS BEEN DOWNGRADED TO AN ADVISORY. WE EXPECT ADVISORY LEVEL SURF WILL ALSO OCCUR ALONG SOME EAST FACING SHORES EXPOSED TO NORTHERLY SWELL. NORTH AND EAST PORTIONS OF THE BIG ISLAND MAY BE ADDED TO THIS ADVISORY LATER TODAY IF EASTERLY WINDS PRODUCE SUFFICIENTLY HIGH CHOPPY SURF CONDITIONS. && .HFO WATCHES/WARNINGS/ADVISORIES... FLASH FLOOD WATCH THROUGH WEDNESDAY AFTERNOON FOR ALL HAWAIIAN ISLANDS. HIGH SURF ADVISORY UNTIL 6 AM HST WEDNESDAY FOR NIIHAU-KAUAI WINDWARD-KAUAI LEEWARD-WAIANAE COAST-OAHU NORTH SHORE-OAHU KOOLAU-OLOMANA-MOLOKAI-MAUI WINDWARD WEST-MAUI CENTRAL VALLEY- WINDWARD HALEAKALA-KONA-KOHALA. BLIZZARD WARNING THROUGH WEDNESDAY AFTERNOON FOR BIG ISLAND SUMMITS. SMALL CRAFT ADVISORY UNTIL 6 AM HST WEDNESDAY FOR ALL HAWAIIAN WATERS. && $$ DISCUSSION/MARINE...WROE AVIATION...EATON