Flash Flood Warning 27, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
644 PM HST SUN JAN 27 2013

.UPDATE...
INCREASED CHANCES FOR RAIN ALONG THE FRONT FOR TONIGHT AND MONDAY MORNING.
THIS MOSTLY AFFECTED THE ISLANDS OF OAHU AND MOLOKAI AND
SURROUNDING COASTAL WATERS.

&&

.SYNOPSIS...
A COLD FRONT HAS REACHED KAUAI AND WILL MOVE SLOWLY SOUTHEAST ACROSS
THE ISLAND CHAIN TONIGHT AND MONDAY. RAINFALL MAY BE HEAVY ALONG AND
AHEAD OF THE FRONT...WITH SHARPLY DECREASED RAINFALL EXPECTED AFTER
FRONTAL PASSAGE. TRADE WINDS ARE EXPECTED TO RETURN BEGINNING ON
TUESDAY...ALONG WITH DRIER CONDITIONS AND MAINLY WINDWARD AND MAUKA
SHOWERS.

&&

.PREV DISCUSSION.../ISSUED 330 PM HST SUN JAN 27 2013/

SATELLITE LOOP...RADAR AND A TIMELY ASCAT PASS SHOW THAT A WIND
SHIFT LINE...LIKELY THE FRONT...HAS REACHED KAUAI AND IS ABOUT TO
EMERGE INTO THE KAUAI CHANNEL LATE THIS AFTERNOON. A LINE OF HEAVY
SHOWERS WRAPPING AROUND THE SOUTH AND EAST FACING SHORES OF KAUAI
WHICH HAD APPEARED TO BE DRIFTING NORTH NOW APPEARS TO BE MOVING
EASTWARD. IN CONTRAST...ANOTHER LINE OF HEAVY SHOWERS WITHIN THE
KAUAI CHANNEL HALFWAY BETWEEN KAUAI AND OAHU IS STILL MOVING TOWARD
THE NORTHEAST. EVEN MORE HEAVY SHOWERS ARE FORMING SOUTH THROUGH
WEST OF OAHU...HEADED NORTHEASTWARD. GIVEN THIS EVIDENCE WE EXPECT
HEAVY RAINFALL REMAINS POSSIBLE FOR KAUAI AND NIIHAU...BUT WE HAVE
REMOVED THE THREAT OF THUNDERSTORMS FOR THOSE ISLANDS. BOUTS OF
HEAVY SHOWERS...ALONG WITH A SLIGHT CHANCE OF THUNDERSTORMS...WILL
SHIFT EAST TO THE KAUAI CHANNEL...OAHU AND POSSIBLY WESTERN MOLOKAI
THIS EVENING AND OVERNIGHT. A FLASH FLOOD WATCH REMAINS IN EFFECT
FOR NIIHAU...KAUAI AND OAHU THROUGH MONDAY AFTERNOON. ENHANCED
SHOWERS...SOME HEAVY...MAY ALSO OCCUR FARTHER SOUTHEAST DOWN THE
ISLAND CHAIN...BUT THE LIKELIHOOD IS LOWER SINCE WE EXPECT THE FRONT
TO GRADUALLY WEAKEN AS IT MOVES SOUTHEASTWARD. MODELS SHOW RESIDUAL
SHOWERS MAY LINGER ACROSS MAUI COUNTY AND POSSIBLY THE BIG ISLAND
THROUGH TUESDAY.

MOST OF THE ENERGY ASSOCIATED WITH THE SUPPORTING UPPER TROUGH IS
NORTH OF THE MAIN ISLANDS...BUT TEMPERATURES ALOFT ARE COLD ENOUGH
AND INSTABILITY IS HIGH ENOUGH TO SUPPORT A SLIGHT CHANCE OF
THUNDERSTORMS IN THE FORECAST THROUGH TONIGHT. IF THUNDERSTORMS
OCCUR...THE MAIN THREAT WILL BE ACROSS OAHU...WESTERN MOLOKAI AND
ADJACENT WATERS. AFTER TONIGHT...HEAVY RAINFALL IS STILL POSSIBLE
FOR THE CENTRAL ISLANDS...BUT THE THREAT OF THUNDERSTORMS HAS BEEN
REMOVED FROM THE FORECAST.

MODELS DISAGREE ON THE SPEED OF THE FRONT ACROSS THE ISLANDS AND
WHETHER OR NOT THE FRONT DISSIPATES NEAR MAUI OR PASSES BEYOND THE
BIG ISLAND...SO OUR FORECAST MAY BE ADJUSTED FURTHER AS THIS EVENT
UNFOLDS. WE CONTINUE TO FAVOR THE GFS SOLUTION GIVEN ITS SLIGHTLY
BETTER INITIALIZATION AND RUN-TO-RUN CONSISTENCY. THE FRONT WILL
WEAKEN AND EVENTUALLY DISSIPATE AS ITS PARENT LOW MOVES WELL AWAY
FROM THE AREA BY LATE MONDAY AND INTO EARLY TUESDAY. HOWEVER...AS
TRADE WINDS RETURN LATER IN THE WEEK...ENOUGH REMNANT MOISTURE WILL
LINGER ACROSS THE MAIN HAWAIIAN ISLANDS TO FUEL WINDWARD AND MAUKA
SHOWERS. SOME SNOW SHOWERS ARE POSSIBLE AT THE BIG ISLAND SUMMITS
WITH COLD TEMPERATURES ALOFT MONDAY LATE AFTERNOON AND EVENING.

&&

.AVIATION...
MOST TAF SITES ARE PRESENTLY EXPERIENCING VFR CONDITIONS EXCEPT FOR
PHLI WHERE THERE HAS BEEN OCNL MVFR AND IFR CONDITIONS ASSOCIATED
WITH PASSING SHOWERS.

AIRMET TANGO IS IN EFFECT FOR THE ENTIRE AREA FOR TEMPO MODERATE
TURB BETWEEN FL300 AND FL400...AND BLW 090 FOR KAUAI AND OAHU.
AIRMET SIERRA IS IN EFFECT FOR MOUNTAIN OBSC FOR KAUAI AND MAY NEED
TO BE EXTENDED TO OAHU SHORTLY. AIRMET ZULU IS IN EFFECT FOR KAUAI
AND ADJ WATERS FOR MOD RIME ICE INC IN PRECIPITATION LYR 125-180.

&&

.MARINE...
A FRONTAL PASSAGE WILL BRING CHOPPY CONDITIONS ACROSS THE LEEWARD
WATERS AROUND THE SMALLER ISLANDS THROUGH LATE MONDAY. HEAVY RAINS
AND THUNDERSTORMS ARE POSSIBLE ACROSS PORTIONS OF COASTAL WATERS
OVERNIGHT TONIGHT.

THERE IS ENOUGH ENERGY EXPECTED WITH THE NEXT NORTHWEST SWELL TO
PROMPT ISSUANCE OF HIGH SURF WARNINGS FOR EXPOSED NORTH AND/OR WEST
SHORES OF THE SMALLER ISLANDS...BEGINNING AT 6 PM HST TODAY AND
LASTING THROUGH MONDAY AFTERNOON. HIGH SURF ADVISORIES ARE IN EFFECT
SPECIFICALLY FOR WEST FACING SHORES OF OAHU AND THE BIG ISLAND FOR
THE SAME TIME PERIOD.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH MONDAY AFTERNOON FOR NIIHAU-KAUAI-OAHU.

HIGH SURF WARNING FROM 6 PM HST TODAY THROUGH 6 PM HST MONDAY FOR
NORTH AND WEST FACING SHORES OF NIIHAU AND KAUAI...AND NORTH FACING
SHORES OF OAHU MOLOKAI AND MAUI.

HIGH SURF ADVISORY FROM 6 PM HST TODAY THROUGH 6 PM HST MONDAY FOR
WEST FACING SHORES OF OAHU AND THE BIG ISLAND.

&&

UPDATE...FOSTER
DISCUSSION/MARINE...POWELL
AVIATION...BURKE