Flash Flooding and Hail in Hawaii, December 29 to 31, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST SUN DEC 29 2013

.SYNOPSIS...
UNSETTLED WEATHER IS EXPECTED FOR THE BIG ISLAND TODAY AS AN UPPER
LEVEL TROUGH PASSES OVER THE ISLANDS. THE REST OF THE ISLAND CHAIN
WILL HAVE SCATTERED SHOWERS FAVORING MAINLY THE WINDWARD AND
MOUNTAIN AREAS. THE MODERATE NORTHERLY TRADE WINDS OVER THE SMALLER
ISLANDS WILL REACH THE BIG ISLAND THIS AFTERNOON. THE TRADES WILL
BECOME LIGHT BY THE MIDDLE OF THE WEEK...THEN TURN SOUTHERLY BY
THURSDAY AS ANOTHER FRONT APPROACHES THE ISLANDS FROM THE WEST. THE
FRONT IS EXPECTED TO REACH KAUAI FRIDAY BRINGING POSSIBLE UNSETTLED
WEATHER TO THE ISLANDS THROUGH NEXT WEEKEND.

&&

.DISCUSSION...
AIR MASS HAS BECOME UNSTABLE ENOUGH FOR THUNDERSTORMS TO DEVELOP IN
THE BIG ISLAND VICINITY THIS MORNING...AS AN UPPER LEVEL TROUGH
MOVES ACROSS THE ISLAND CHAIN. DO EXPECT THE UNSETTLED WEATHER TO
AFFECT THE BIG ISLAND THROUGH REST OF TODAY...BRINGING POSSIBLE
LOCALLY HEAVY RAIN AS WELL AS A SLIGHT CHANCE OF THUNDERSTORMS. THE
SURFACE FRONT ASSOCIATED WITH THIS UPPER LEVEL FEATURE HAS PRETTY
MUCH DISSIPATED...THOUGH REMNANT MOISTURE FROM THIS DISSIPATED FRONT
WILL LINGER ACROSS THE ISLAND CHAIN AT LEAST THROUGH MONDAY. THE
NORTHERLY WINDS OVER MUCH OF THE ISLANDS WILL KEEP SHOWERS MAINLY
OVER THE WINDWARD AREAS OF THE SMALLER ISLANDS.

THE PASSING UPPER LEVEL TROUGH WILL DEPART THE STATE BY
MONDAY...WITH MORE STABLE ATMOSPHERIC CONDITIONS RETURNING TO THE
BIG ISLAND AS WELL. FORECAST CHARTS STILL INDICATE SOME LINGERING
MOISTURE MAY AFFECT THE STATE IN THE NEXT COUPLE OF DAYS. AS A
SURFACE HIGH PRESSURE MOVES TO NORTH OF THE ISLANDS...TRADE WINDS
ARE EXPECTED TO PERSIST ACROSS THE ISLANDS. THE STRONGER NORTHERLY
TRADE WINDS CURRENTLY OVER THE ISLANDS WILL BE BRIEF THOUGH...AS
THIS SURFACE HIGH IS EXPECTED TO WEAKEN IN TIME. EXPECT TRADE WIND
WEATHER FOR THE ISLANDS FOR THE NEXT COUPLE OF DAYS...WITH
DECREASING WINDS AS THE WEEK PROGRESSES.

FORECAST CHARTS INDICATE THE SURFACE HIGH TO THE NORTH BECOMES
ALMOST NON EXISTENT BY THE MIDDLE OF THE WEEK. THIS WILL RESULT
LIGHT WINDS OVER THE ISLANDS...ALLOWING LAND AND SEA BREEZES TO
BECOME MORE PROMINENT. EXPECT THE WEATHER OVER THE STATE TO BECOME
MORE CONVECTIVE BY THE MIDDLE OF THE WEEK...WITH AFTERNOON
CLOUDINESS AND CLEARING IN THE MORNING AND LATE NIGHT. MOREOVER...
FORECAST CHARTS INDICATE THE AIR MASS WILL REMAIN STABLE OVER THE
ISLANDS...AND SHOULD LIMIT THE SHOWER ACTIVITIES.

THE NEXT FRONT FROM THE NORTHWEST WILL APPROACH THE ISLANDS TOWARDS
THE SECOND PART OF THE WEEK...WITH INCREASING SOUTHERLY WINDS OVER
THE STATE. THIS PENDING FRONT IS STILL EXPECTED TO REACH KAUAI BY
THE WEEKEND AND WILL SPREAD UNSETTLED WEATHER TO THE ISLANDS
THROUGH THE NEXT WEEKEND.

&&

.AVIATION...
A STALLED SURFACE TROUGH AND MOIST/UNSTABLE AIRMASS OVER THE BIG
ISLAND WILL CONTINUE TO PRODUCE SHOWERS AND ISOLATED THUNDERSTORMS
THROUGH TODAY. AIRMET SIERRA FOR PERIODS OF MOUNTAIN OBSCURATION
WILL LIKELY BE NEEDED AT TIMES THERE...AND PERIODS OF MVFR/IFR
CONDITIONS WILL BE POSSIBLE AS WELL.

FURTHER TO THE WEST...NORTHERLY FLOW ACROSS THE SMALLER ISLANDS TO
THE WEST OF THE FRONT WILL RESULT IN AREAS OF MODERATE LOW LEVEL
TURB OVER AND DOWNWIND OF THE MOUNTAINS...AND AIRMET TANGO IS
POSTED. AIRMET SIERRA IS ALSO IN EFFECT FOR THE NORTHERN SLOPES OF
THE SMALLER ISLANDS DUE TO MOUNTAIN OBSCURATION DUE TO CLOUDS
PRODUCED BY THE NORTHERLY FLOW.

EXPECT VFR CONDITIONS TO PREVAIL ELSEWHERE AROUND THE STATE THROUGH
THE REST OF TODAY AND TONIGHT.

SIGMET NOVEMBER AND AIRMET TANGO ARE IN EFFECT FOR MODERATE TO
OCCASIONALLY SEVERE HIGH LEVEL TURBULENCE OVER PARTS OF THE STATE
DUE TO A NEARBY JET STREAM.

&&

.MARINE...
LOOKS LIKE THE PEAK OF THE CURRENT LARGE NORTHWEST SWELL HAS REACHED
OAHU NORTH SHORES THIS MORNING...AS REVEALED BY THE READINGS OF THE
NEAR SHORE WAIMEA BUOY. THIS SWELL IS CERTAINLY BIG ENOUGH TO
WARRANT THE HIGH SURF WARNING FOR NORTH AND WEST FACING SHORES OF
KAUAI TO MOLOKAI...AND FOR NORTH FACING SHORES OF MAUI.

A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR EXPOSED COASTAL WATERS
DUE TO ELEVATED NW SWELL

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING UNTIL 6 PM HST MONDAY FOR THE NORTH AND WEST
FACING SHORES OF NIIHAU KAUAI OAHU AND MOLOKAI...AND NORTH FACING
SHORES OF MAUI.

SMALL CRAFT ADVISORY UNTIL 6 PM HST MONDAY FOR ALL HAWAIIAN WATERS
EXCEPT LEEWARD WATERS OF MAUI INCLUDING MAALAEA BAY AND WATERS SOUTH
OF THE BIG ISLAND.

&&

AVIATION...JACOBSON
REST...HUI