Areal Flood Advisory 252, NWS Honolulu, HI

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HONOLULU HI
840 AM HST TUE DEC 23 2014

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0530 AM     FLASH FLOOD      6 ESE HAWI              20.22N 155.75W
12/23/2014                   HAWAII             HI   EMERGENCY MNGR

            HIGHWAY 270 CLOSED AT MILE MARKER 27

&&

RBALLARD