Flash Flood Warning 32, NWS Honolulu, HI

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE HONOLULU HI
415 PM HST MON DEC 22 2014

.SYNOPSIS...
AN ACTIVE WEATHER PATTERN WILL DEVELOP OVER THE PORTIONS OF THE
STATE TONIGHT AND WILL CONTINUE THROUGH WEDNESDAY. THUNDERSTORMS
COULD BECOME STRONG TONIGHT...ESPECIALLY OVER THE CENTRAL ISLANDS AS
A POTENT DISTURBANCE ALOFT DROPS OVER THE STATE. WINDWARD AND
NORTHERN PORTIONS OF THE SMALLER ISLANDS WILL REMAIN WET AS MOISTURE
FROM A SLOW MOVING FRONT STALLS NEAR MAUI AND THE THREAT OF
THUNDERSTORMS INCREASES. THE POTENTIAL FOR HEAVY FLOODING RAINFALL
AND THUNDERSTORMS...AS WELL AS DANGEROUS WINTER WEATHER ON THE BIG
ISLAND SUMMITS...WILL PERSIST THROUGH AT LEAST WEDNESDAY. DRIER
CONDITIONS ARE EXPECTED THURSDAY AND FRIDAY.

&&

.DISCUSSION...
AN ACTIVE WEATHER PATTERN FEATURING THREATS OF HEAVY RAINFALL AND
STRONG THUNDERSTORMS WILL DEVELOP ACROSS MAINLY THE SMALLER ISLANDS
TONIGHT...THEN SPREAD STATE-WIDE TUESDAY THROUGH WEDNESDAY.

THE LEADING EDGE OF A SLOW-MOVING FRONT WILL REMAIN ON MOLOKAI
THROUGH THE REST OF THE AFTERNOON...WHILE INCREASING NORTHEAST
WINDS BEHIND THE FRONT PRODUCE WET CONDITIONS OVER NORTHERN AND
WINDWARD SLOPES OF OAHU AND KAUAI. A STRONG MID TO UPPER LEVEL
TROUGH APPROACHING THE STATE FROM THE NORTHWEST WILL LEAD TO RAPID
DESTABILIZATION OF THE ATMOSPHERE...CREATING THE POSSIBILITY OF
THUNDERSTORMS ALONG THE LEADING EDGE OF THE FRONT BEFORE SUN DOWN.

ACTIVE WEATHER WILL DEVELOP OVER THE SMALLER ISLANDS TONIGHT WITH
THUNDERSTORM AND HEAVY RAIN CHANCES INCREASING SIGNIFICANTLY THIS
EVENING. A STRONG MID TO UPPER LEVEL DISTURBANCE CURRENTLY CENTERED
ABOUT 250 MILES NORTHWEST OF KAUAI WILL MOVE OVER THE ISLANDS
TONIGHT. THE INITIAL COLD POOL IN THE CORE OF THE DISTURBANCE WILL
BRING 500 MB TEMPS BELOW -15C...WHICH IS EXTREMELY RARE OVER HAWAII.
WHILE THE GREATEST THUNDERSTORM THREAT WILL BE ALONG FRONT NEAR THE
CENTRAL ISLANDS TONIGHT...THUNDERSTORMS COULD POP UP ANYWHERE
WITHIN THE CORE OF THE LOW OVER THE WESTERN ISLANDS. THESE
THUNDERSTORMS COULD BE STRONG WITH THE POTENTIAL TO PRODUCE
HAZARDOUS LIGHTNING...STRONG AND GUSTY WINDS...HAIL...AND HEAVY
RAINFALL.

THE THREAT FOR HEAVY SHOWERS AND THUNDERSTORMS WILL PERSIST THROUGH
AT LEAST WEDNESDAY AS THE DISTURBANCE ALOFT FORMS A STRONG CUTOFF
LOW. THE FRONTAL BOUNDARY WILL LIKELY WASH OUT ON TUESDAY.
HOWEVER...THE CUTOFF LOW WILL MEANDER NEARBY...AND THE GFS AND
ECMWF 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 IS IN
PLACE FROM THIS EVENING THROUGH WEDNESDAY AFTERNOON. DUE TO
UNCERTAINTY INVOLVED WITH THE POSSIBILITY OF A SURFACE LOW
DEVELOPING...THE SURFACE WIND FORECAST BECOMES UNCERTAIN LATE
TUESDAY AS DOES THE EXACT PLACEMENT OF HEAVY RAINFALL AND
THUNDERSTORMS.

IN ADDITION...HAZARDOUS WEATHER IS POSSIBLE OVER THE BIG ISLAND
SUMMITS. AS THE UPPER LEVEL TROUGH DIGS NEAR THE STATE TONIGHT AND
FORMS A CUTOFF ON TUESDAY...VERY WINDY CONDITIONS WILL OCCUR ON THE
HIGH BIG ISLAND SUMMITS...AND A HIGH WIND WARNING HAS BEEN ISSUED.
AS DEEP MOISTURE IS DRAWN TOWARD THE STATE ON TUESDAY...PERIODS OF
HEAVY SNOW ARE POSSIBLE. IN COMBINATION WITH THE STRONG WINDS
ALREADY IN PLACE...BLIZZARD CONDITIONS ARE POSSIBLE BUT ARE BY NO
MEANS CERTAIN AT THIS TIME. A BLIZZARD WATCH HAS BEEN ISSUED FOR
TUESDAY THROUGH WEDNESDAY AFTERNOON.

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...
SHOWERS AND CLOUDS CONTINUE TO STREAM OVER THE SMALLER
ISLANDS...WITH THE FRONT NOW NEAR MOLOKAI. MAJOR SHOWER ACTIVITY
HAS SHIFTED AND IS NOW OVER MOLOKAI AND BEGINNING TO FLARE UP ALONG
WINDWARD MAUI SLOPES. CLOUD TOPS NORTH OF MOLOKAI ARE REACHING
ABOVE 25 KFT WITH ISOLATED TOPS ABOVE 35 KFT. AIRMET SIERRA FOR
MOUNTAIN OBSCURATION IS NOW POSTED FOR KAUAI...OAHU...MOLOKAI...AND
MAUI. WIDESPREAD CLOUDS AND SHOWERS ARE EXPECTED TO CONTINUE THROUGH
THE NIGHT...WITH TEMPO MVFR AND ISOL IFR CIGS/VIS IN SHOWERS.
AIRMET TANGO FOR LOW LEVEL TURB IS STILL POSTED OVER KAUAI. THE PHKI
VAD WIND PROFILE IS SHOWING 20 TO 25 KTS BELOW 8 KFT. THIS IS LIKELY
TO BE EXPANDED TO INCLUDE THE REMAINING SMALLER ISLANDS AT 04Z AS
STRONGER WINDS FILL IN BEHIND THE FRONT.

THE BIG ISLAND HAS REMAINED FAIRLY QUIET TODAY AND WILL LIKELY
REMAIN THAT WAY UNTIL EARLY TUESDAY MORNING. A DEVELOPING LOW IS
EXPECTED TO START MOVING OVER THE STATE THIS EVENING. THERE IS A
CHANCE OF THUNDERSTORMS OVER THE SMALLER ISLANDS STARTING THIS
AFTERNOON AND EXPANDING OVER THE BIG ISLANDS BY EARLY TUESDAY
MORNING AND CONTINUING INTO WEDNESDAY. THIS WILL BRING AVIATION
HAZARDS INCLUDING ICING...TURBULENCE...WIND SHEAR AND IFR
CONDITIONS.

&&

.MARINE...
HAZARDOUS CONDITIONS WILL REMAIN IN PLACE OVER MOST WATERS THROUGH
TOMORROW WITH STRONG THUNDERSTORMS ALSO POSSIBLE.

STRONG NORTH-NORTHEAST WINDS ARE BLOWING ACROSS THE WESTERN HALF OF
THE ISLAND CHAIN BEHIND A SLOW-MOVING FRONT OVER MOLOKAI. 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 LARGE NORTHWEST SWELL HAS PEAKED BUT WILL MAINTAIN WARNING LEVEL
SURF ACROSS MOST NORTH AND WEST FACING SHORES THROUGH TONIGHT.
EXPECT THE WARNING TO BE DOWNGRADED TO AN ADVISORY FOR TUESDAY...
WHILE ADVISORY LEVEL SURF WILL ALSO OCCUR ALONG SOME EAST FACING
SHORES EXPOSED TO NORTHERLY SWELL. SEE THE NEWLY ISSUED
COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST...SRDHFO...FOR MORE
DETAILS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM THIS EVENING THROUGH WEDNESDAY AFTERNOON
FOR ALL HAWAII ISLANDS.

HIGH SURF WARNING UNTIL 6 AM HST TUESDAY 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.

HIGH WIND WARNING FROM THROUGH 6 AM HST THURSDAY FOR BIG ISLAND
SUMMITS.

BLIZZARD WATCH FROM FROM 6 AM HST TUESDAY THROUGH WEDNESDAY
AFTERNOON FOR BIG ISLAND SUMMITS.

SMALL CRAFT ADVISORY UNTIL 6 AM HST WEDNESDAY FOR ALL HAWAIIAN
WATERS.

&&

DISCUSSION/MARINE...WROE
AVIATION...EATON