Flash Flooding and Blizzard in Hawaii, December 21 to 26, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
845 PM HST SUN DEC 21 2014

.SYNOPSIS...
A WEAKENING COLD FRONT BOUNDARY WILL MOVE ACROSS KAUAI COUNTY THIS
EVENING AND CONTINUE DOWN INTO THE CENTRAL PORTIONS OF THE ISLAND
CHAIN THROUGH MONDAY AFTERNOON. SHOWERS WILL INCREASE WITH BEST
CHANCES FOR RAIN OVER KAUAI AND OAHU. RAINFALL ACCUMULATIONS SHOULD
REMAIN LIGHT TO MODERATE THROUGH MONDAY AFTERNOON...THEN THE ARRIVAL
OF AN UPPER LEVEL TROUGH WILL BRING POTENTIAL FOR LOCALIZED HEAVY
RAIN AND A FEW THUNDERSTORMS FROM MONDAY NIGHT THROUGH TUESDAY. FOR
THE SECOND HALF OF THE WEEK...SHOWERS WILL DECREASE AND STRONGER
NORTHERLY WINDS ARE EXPECTED TO ESTABLISH ACROSS THE AREA.

&&

.DISCUSSION...
AT 830 PM HST...DATA FROM THE DOPPLER RADARS AROUND HAWAII WERE
SHOWING LINES OF SHOWERS MOVING INTO KAUAI COUNTY FROM THE NW...AND
SEVERAL THIN LINES OF SHOWERS APPROACHING OAHU. THESE SHOWERS ARE
BEING GENERATED BY A WEAKENING COLD FRONT LOCATED JUST TO THE NW OF
KAUAI...WITH AN ASSOCIATED UPPER LEVEL TROUGH ALSO NEARING THE ALOHA
STATE FROM THE NW. THE PRESENCE OF THE COLD FRONT WAS OBSERVED
EARLIER TODAY BY DATA FROM BUOY 51101 LOCATED ABOUT 210 MILES NW OF
KAUAI...WHICH SHOWED A TEMPERATURE DROP OF ABOUT 7 DEGREES. SHOWER
COVERAGE WILL STEADILY INCREASE THROUGH MON AS THE FRONTAL BOUNDARY
PUSHES THROUGH THE W HALF OF THE ISLAND CHAIN.

MODEL SOLUTIONS BRING THE DECAYING BOUNDARY THROUGH OAHU...AND
STALLING IT NEAR MAUI BY NOON MON. A CLOUD BAND MARKS THE LEADING
EDGE OF THE FRONT...WHICH WILL PRODUCE WIDESPREAD SHOWERS OVER KAUAI
AND MAUI...BUT WITH RAINFALL ACCUMULATIONS REMAINING LIGHT TO
MODERATE.

WINDS WILL BE MOSTLY VARIABLE THROUGH MON MORNING...THEN STARTING TO
VEER TO THE N AND NW MON AFTERNOON AND EVENING BEHIND THE FROPA.
MEANWHILE...MODELS REMAIN IN FAIR AGREEMENT IN PUSHING THE AXIS OF
THE AFOREMENTIONED UPPER TROUGH INTO THE ISLAND CHAIN MON NIGHT
THROUGH TUE. THIS TROUGH WILL FURTHER DESTABILIZE THE AIRMASS OVER
THE ISLANDS AND BRING INCREASING POTENTIAL FOR LOCALIZED HEAVY RAIN
AND A SLIGHT CHANCE OF THUNDERSTORMS. HIGHEST POPS/ACCUMULATIONS
RESIDE OVER KAUAI AND OAHU...ESPECIALLY MOUNTAIN AREAS.

THE FORECAST FOR MID WEEK HAS BEEN ADVERTISING A STEADY TRANSITION
TO DECREASING SHOWERS AND STRENGTHENING N AND NE WINDS AS STRONG
HIGH PRESSURE ESTABLISHES N OF THE ISLANDS IN THE WAKE OF THE
FROPA. HOWEVER...THE SOLUTION FROM 00Z FOR THE GFS MODEL IS STARTING
TO SUBSTANTIALLY DEVIATE FROM THE LATEST ECMWF AND THE OFFICIAL
FORECAST PHILOSOPHY. THE LATEST SCENARIO IN GFS FOR WED THROUGH FRI
LOOKS SIGNIFICANTLY WET WITH A MID LEVEL LOW AND A SFC TROUGH
QUICKLY DEVELOPING RIGHT OVER THE ISLANDS. IN CONTRAST...ECMWF KEEPS
THE DEVELOPING LOW AND ITS POTENTIAL IMPACTS FURTHER TO THE NE OF
THE ALOHA STATE. AT THIS TIME...IT IS BETTER TO KEEP FOLLOWING THE
CURRENT FORECAST PHILOSOPHY OF BRINGING INCREASING N FLOW AND A
DRYING TREND FOR THE SECOND HALF OF THE WEEK...AND WAIT FOR MORE
CONSISTENCY/PERSISTENCE FROM UPCOMING GFS RUNS BEFORE INCORPORATING
SIGNIFICANT CHANGES TO THE MID AND LONG RANGE FORECAST. STAY
TUNED.

&&

.AVIATION...
CLOUDS AND SHOWERS ASSOCIATED WITH A COLD FRONT ARE MOVING INTO
KAUAI...AND AIRMETS ARE POSTED THERE FOR BOTH MOUNTAIN OBSCURATION
AND LOW LEVEL TURB...AS N WINDS WILL BE INCREASING THROUGH THE
NIGHT OVER AND NEAR KAUAI. WIDESPREAD MVFR VIS/CIG IN SHRA CAN BE
EXPECTED IN ASSOCIATION WITH THE 150 MILE WIDE FRONTAL CLOUD
BAND...WITH THE POSSIBILITY OF IFR VIS/CIG IN AREAS OF HEAVIER
SHOWERS. VFR WILL PREVAIL OVER OTHER AREAS OF THE STATE TONIGHT AND
EVEN INTO TOMORROW FOR MAUI COUNTY AND THE BIG ISLAND...WITH THE
FRONTAL CLOUD BAND EXPECTED TO BE RELATIVELY SLOW IN ITS
SOUTHEASTWARD PROGRESSION ACROSS THE ISLAND CHAIN. INCREASED
CLOUDS...SHOWERS AND WINDS ASSOCIATED WITH THE FRONT ARE EXPECTED TO
BEGIN AFFECTING OAHU ON MONDAY HOWEVER.

&&

.MARINE...
A LARGE NORTHWEST SWELL WILL REACH WARNING LEVELS TONIGHT. A HIGH
SURF WARNING IS IN EFFECT FOR NORTH AND WEST FACING SHORES OF THE
SMALLER ISLANDS AND FOR WEST FACING SHORES OF THE BIG ISLAND. THIS
SWELL WILL ALSO GENERATE SMALL CRAFT ADVISORY CONDITIONS OVER MOST
COASTAL WATERS DUE TO HAZARDOUS SEAS.

STRONG NORTH TO NORTHEAST WINDS ARE EXPECTED TO MOVE OVER THE AREA
STARTING LATER THIS EVENING. THERE WILL BE WIDESPREAD SMALL CRAFT
ADVISORY STRENGTH WINDS IN THE TYPICALLY WINDIER CHANNELS AROUND
MAUI COUNTY AND THE BIG ISLAND THROUGH AT LEAST WED NIGHT...AND
POSSIBLY EXTENDING INTO THURSDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING UNTIL 600 AM TUESDAY FOR NORTH AND WEST FACING
SHORES OF NIIHAU KAUAI OAHU AND MOLOKAI...FOR NORTH FACING SHORES
OF MAUI AND FOR WEST FACING SHORES OF THE BIG ISLAND.

SMALL CRAFT ADVISORY UNTIL 600 AM TUESDAY FOR ALL HAWAIIAN WATERS
EXCEPT MAALAEA BAY.

&&

DISCUSSION/MARINE...REYNES
AVIATION...BIRCHARD