Flash Flood and Heavy Rain in Hawaii, May 5 to 9, 2016

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
858 PM HST THU MAY 5 2016

.SYNOPSIS...
A BIT OF UNSETTLE WEATHER IS EXPECTED FOR PARTS OF THE STATE FOR
NEXT COUPLE OF DAYS AS A LATE SEASON COLD FRONT MAKES IT WAY DOWN
THE ISLAND CHAIN. THE FRONT IS EXPECTED TO REACH KAUAI LATE FRIDAY
AFTERNOON AND CONTINUE SLOWLY EASTWARD...REACHING MAUI COUNTY
SATURDAY MORNING. THE FRONT IS EXPECTED TO STALL OVER THE EASTERN
END OF THE ISLAND CHAIN OVER THE WEEKEND. THE WESTERN ISLANDS WILL
BE UNDER THE INFLUENECE OF A TYPICAL TRADE WIND REGIME.

&&

.DISCUSSION...
A WEAKENING COLD FRONT LOCATED ABOUT 470 MILES NORTHWEST OF KAUAI
AT 8 PM HST...CONTINUES TO PRESS EAST AND SOUTHEASTWARD TOWARD THE
MAIN HAWAIIAN ISLANDS. IT IS EXPECTED TO REACH KAUAI LATE FRIDAY
AFTERNOON. THE FRONT WEAKENS TO A POINT WHERE IT BECOMES DIFFICULT
TO IDENTIFY AS IT APPROACHES OAHU AT AROUND MIDNIGHT. BUT IT
LOOKS LIKE THE ECMWF AND GFS ARE IN GOOD AGREEMENT WITH A SLOW
DRAG EASTWARD ONCE IT REACHES OAHU. THE FRONT IS TABBED TO REACH
MOLOKAI SHORTLY AFTERNOON DAY BREAK SATURDAY...THEN TO THE REST OF
MAUI COUNTY LATER IN THE MORNING. THE FRONT CONTINUES SLOWLY ON TO
THE BIG ISLAND THE REST OF THE DAY AND EVENING...FINALLY STALLING
OVER THE BIG ISLAND SUNDAY. THE MODELS ARE ALSO SHOWING A TROUGH
THAT FORMS AHEAD OF THE FRONT ON FRIDAY..AND MOVES EASTWARD
STAYING AHEAD OF THE FRONT. BEHIND THE FRONT IS A MORE TYPICAL
TRADE WIND REGIME WITH SHOWERS FAVORING THE WINDWARD AND MOUNTAIN
AREAS. IT WILL BE A DRIER AND SLIGHTLY COOLER AIR MASS AS WELL.

CURRENTLY...SOME HEAT DRIVEN SHOWERS HAVE FORMED OVER OAHU. THE
SHOWERS...A FEW BRIEFLY HEAVY...ARE MOST CONCENTRATED ALONG THE
WINDWARD COAST BETWEEN OLOMANA AND KAHUKU. ANOTHER HEAVY SHOWER
IS OCCURRING IN THE WAIPAHU KUNIA AREAS. THEY ARE NEARLY
STATIONARY...AND SHOULD BE DISSIPATING IN THE NEXT COUPLE OF
HOURS. OTHER ISOLATED SHOWERS ARE PRESENT OVER OR NEAR MOLOKAI
AND LANAI. THE SOUTHEAST WIND FLOW IS ALSO BRINGING IN A FEW
SHOWERS TO THE EASTERN END OF MAUI.

THE CURRENT WINDFLOW IS SOUTHERLY ACROSS KAUAI COUNTY AND THE
SURROUNDING WATERS...MAINLY SOUTH OVER LEEWARD OAHU AND SLIGHTLY
SOUTH OF EAST ON THE WINDWARD SIDE. WINDWARD MAUI IS SOUTHEAST
BUT IT IS LIGHT AND VARIABLE SOUTH OF LANAI. THE BIG ISLAND IS
EASTERLY. THERE ARE PLENTY OF CLOUDS OVER THE LEEWARD WATERS SOUTH
OF OAHU...MOLOKAI...LANAI...AND NIIHAU/KAUAI. THESE CLOUDS WITH
EMBEDDED SHOWERS WILL THREATEN THESE ISLANDS OVERNIGHT. ISOLATED
SHOWERS ARE IN THE FORECAST AFTER MIDNIGHT FOR ALL THESE ISLANDS
SHOULD THE DEVELOPING LAND BREEZE FAILS TO HOLD THEM OFF.

A SEPARATE CLOUD MASS IS THREATENING MAUI FROM THE EAST. THE
SOUTHEAST WINDS THERE MAY JUST BE ABLE TO KEEP IT AWAY FROM THE
ISLAND. PART OF THIS SAME CLOUD MASS HAS MOVED INTO THE HILO AND
PUNA DISTRICTS OF THE BIG ISLAND. NOT MUCH IN TERMS IN SHOWERS AS
PER RAIN GAGES REPORTS BUT PLENTY OF CLOUDS AND MAINLY HIGH BASE
CLOUDS ABOVE 4K FEET. THE KONA SIDE IS CLOUDY AS WELL BUT LITTLE
IF ANY IN TERMS OF SHOWERS. THE FORECAST WAS UPDATED TO INCLUDE
THE SLIGHT CHANCE OF A LATE NIGHT SHOWER ALONG THE COAST.

&&

.AVIATION...
AN APPROACHING FRONT FROM THE NORTHWEST WILL MAKE THE ATMOSPHERE
INCREASINGLY UNSTABLE THROUGH FRIDAY. OVERNIGHT...HOWEVER...
CLOUDINESS SHOULD DECREASE OVER MOST OF THE STATE AS LAND BREEZES
DEVELOP.  FOR KAUAI...MOISTURE TO ITS SOUTH MAY MOVE NORTH AND BRING
INCREASING CHANCES OF TEMPO MVFR WEATHER IN LOWER CEILINGS AND
SHOWERS AFTER MIDNIGHT. ON THE BIG ISLAND...SHOWERY LOW CLOUDS
TREKKING WESTWARD WILL LIKELY BRING TEMPO MVFR CONDITIONS TO
WINDWARD AREAS THROUGH TONIGHT AND FRIDAY.

&&

.MARINE...
A SMALL WEST NORTHWEST SWELL WILL PERSIST THROUGH FRIDAY. A
REINFORCING SMALL TO MODERATE SIZE NORTH NORTHWEST SWELL WILL
ARRIVE FRIDAY NIGHT AND SATURDAY...LASTING THROUGH THE WEEKEND.
FORERUNNERS FROM A LONG PERIOD SOUTH SWELL IS HERE. THIS SWELL
WILL BUILD TO 3 FEET FRIDAY AND PEAK SATURDAY. A GRADUAL DROP WILL
FOLLOW SUNDAY THROUGH MONDAY. SURF HEIGHTS ARE EXPECTED TO STAY
JUST BELOW THE HIGH SURF ADVISORY CRITERIA ALONG SOUTH FACING
SHORES...BUT WE WILL BE MONITORING CLOSELY THE BUOY READINGS
LOCATED SOUTH OF THE ISLANDS.

TRADE WIND SPEEDS ARE MARGINAL AT BEST AT THIS POINT AS PER GFS
AND ECMWF MODELS. THEY WILL BE MONITORED CLOSELY HOWEVER SHOULD
THE WINDS REACH SMALL CRAFT ADVISORY CRITERIA OF 23 KTS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

DISCUSSION/MARINE...LAU
AVIATION...KINEL

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