Winter Storm and Heavy Rain in Hawaii, March 4 to 6, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST WED MAR 4 2015

.SYNOPSIS...
A TROUGH ALOFT WILL PRODUCE HEAVY RAIN THROUGH TONIGHT ON MAUI AND
THE BIG ISLAND OF HAWAII. SNOW AND STRONG WINDS WILL LIKELY AFFECT
THE HIGH ELEVATIONS ON THE BIG ISLAND. THE TROUGH WILL ALSO BRING
OVERCAST CLOUDS TO ALL THE ISLANDS. A STRONG SURFACE HIGH NORTHWEST
OF THE AREA WILL KEEP TRADE WINDS BLOWING...BRINGING SCATTERED
SHOWERS TO WINDWARD AREAS FROM MOLOKAI TO KAUAI. THE WEATHER WILL
TURN DRIER ON THURSDAY...BUT THAT MAY BE TEMPORARY. THE TROUGH ALOFT
WILL PERSIST THROUGH NEXT WEEK...SO MORE PERIODS OF STORMY WEATHER
ARE POSSIBLE.

&&

.DISCUSSION...
A STRONG SURFACE HIGH ABOUT 1500 MILES NORTHWEST IS PRODUCING
MODERATE TO STRONG TRADE WINDS ACROSS THE ISLANDS. A PERSISTENT
TROUGH ALOFT CONTINUES TO MAKE THE ATMOSPHERE UNSTABLE...BUT SO FAR
IT HAS NOT BEEN UNSTABLE ENOUGH TO PRODUCE ANY THUNDERSTORMS OVER
THE ISLANDS. AS OF 300 AM THE CLOSEST THUNDERSTORMS ARE ABOUT 100
MILES SOUTHEAST OF THE BIG ISLAND. THE CHANCE OF THUNDERSTORMS IS
USUALLY GREATEST OVER WATER AT NIGHT AND OVER LAND DURING THE DAY SO
THE THREAT WILL LIKELY SHIFT AFTER SUNRISE. TRADE-WIND WEATHER WILL
PERSIST OVER THE SMALLER ISLANDS WITH SCATTERED SHOWERS MAINLY OVER
WINDWARD AREAS. THICK LAYERED CLOUDS WILL CONTINUE TO BLANKET THE
SKIES OVER ALL THE ISLANDS.

A BROAD AND DEEP TROUGH ALOFT LIES NORTH OF THE AREA. A SHORT-WAVE
TROUGH WITHIN THE LARGER TROUGH IS APPROACHING THE ISLANDS FROM THE
NORTHWEST. AS THE TROUGH GETS CLOSER TODAY...THE ATMOSPHERE WILL
BECOME MORE UNSTABLE AND MORE MOISTURE WILL SPREAD OVER THE ISLANDS
FROM THE SOUTHEAST. THE GREATEST THREAT FOR HEAVY PRECIPITATION
WILL BE TONIGHT ON THE WINDWARD SIDES OF MAUI AND THE BIG ISLAND.
THE TROUGH ALOFT WILL ALSO LIKELY PRODUCE SNOW OVER THE HIGH
ELEVATIONS ON THE BIG ISLAND. THE RAIN AND SNOW WILL SUBSIDE
TOMORROW AS THE SHORT-WAVE MOVES OFF TO THE NORTHEAST.

THE LARGE-SCALE TROUGH ALOFT WILL PERSIST NORTH OF THE ISLANDS
THROUGH NEXT WEEK. MORE PERIODS OF HEAVY PRECIPITATION ARE POSSIBLE
AS LONG AS THIS TROUGH REMAINS. THE MOST ACTIVE PERIODS WILL COME AS
SHORT WAVE TROUGHS WITHIN THE LARGER TROUGH MOVE OVER THE ISLANDS
FROM THE NORTHWEST. THE GLOBAL MODELS ARE IN GOOD AGREEMENT ON THE
SHORT WAVE AFFECTING THE ISLANDS TODAY BUT THEY DIFFER ON THE TIMING
AND STRENGTH OF SUBSEQUENT SHORT WAVES.

&&

.AVIATION...
AIRMET TANGO IS IN EFFECT FOR HIGH LEVEL TURBULENCE OVER THE AREA
DUE TO THE TROUGH ALOFT. THE TURBULENCE IS LIKELY TO CONTINUE
THROUGH TODAY. AIRMET TANGO ALSO HAS LOW LEVEL TURBULENCE IN THE
LEE OF THE ISLANDS DUE TO THE STRONG TRADE WINDS. AIRMET SIERRA IS
IN EFFECT FOR MTN OBSC OVER WINDWARD AREAS FROM THE BIG ISLAND TO
MOLOKAI. THE POSSIBILITY OF LIGHT ICING WILL BE MENTIONED IN AIRMET
ZULU. VFR CONDITIONS WILL PREVAIL FROM LANAI TO KAUAI BUT THERE MAY
BE ISOLATED MVFR CEILINGS OVER WINDWARD AREAS.

&&

.MARINE...
THERE IS A SLIGHT CHANCE OF THUNDERSTORMS OVER THE COASTAL WATERS
AROUND THE BIG ISLAND AND MAUI THROUGH TONIGHT. A SMALL CRAFT
ADVISORY IS IN EFFECT FOR STRONG TRADE WINDS AND ROUGH SEAS. ROUGH
SURF WILL BUILD ALONG EAST FACING SHORES...AND THIS SURF COULD
REQUIRE A HIGH SURF ADVISORY LATER IN THE WEEK. OTHERWISE...SURF IS
EXPECTED TO REMAIN BELOW THE ADVISORY THRESHOLDS THROUGH THE WEEK. A
NORTH SWELL ARRIVING SUNDAY MAY PRODUCE ADVISORY LEVEL SURF ALONG
THE NORTH FACING SHORES.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY FOR THE KAUAI...KAIWI...MOLOKAI AND ALENUIHAHA
CHANNELS...WATERS WEST OF KAUAI...MAALAEA BAY AND WATERS SOUTH OF
THE BIG ISLAND FOR STRONG NORTHEAST TRADE WINDS AND ROUGH SEAS.

FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR MAUI AND THE BIG ISLAND
OF HAWAII.

WINTER STORM WARNING THROUGH LATE TONIGHT FOR THE SUMMITS OF MAUNA
KEA AND MAUNA LOA.

&&

DONALDSON