Waterspout in Hawaiian Waters, March 25, 2016

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1001 AM HST FRI MAR 25 2016

.SYNOPSIS...
A DEEP LAYERED TROUGH OF LOW PRESSURE WILL TRACK EASTWARD ACROSS
THE ISLAND CHAIN TODAY THROUGH SATURDAY. AN UNSTABLE AIRMASS WILL
ACCOMPANY THE TROUGH...BRINGING UNSETTLED WEATHER ALONG WITH THE
POTENTIAL FOR HEAVY RAINFALL AND THUNDERSTORMS. A DRIER AIRMASS
WILL MOVE BACK OVER THE ISLANDS SATURDAY NIGHT THROUGH SUNDAY
NIGHT. A WEAKENING COLD FRONT WILL APPROACH FROM THE NORTHWEST ON
MONDAY AND SLOWLY PUSH SOUTHEASTWARD THROUGH THE STATE MONDAY
NIGHT THROUGH TUESDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD OVER
THE ISLANDS DURING THE MIDDLE OF NEXT WEEK...WITH A STRONGER AREA
OF HIGH PRESSURE EXPECTED TO BUILD NORTH OF THE STATE LATE NEXT
WEEK...FINALLY ALLOWING THE TRADE WINDS TO RETURN.

&&

.DISCUSSION...
CURRENTLY AT THE SURFACE...A TROUGH OF LOW PRESSURE STRETCHES FROM
SOUTHWEST TO NORTHEAST FROM 20N162W TO 30N154W...PLACING THE
FEATURE AROUND 100 MILES WEST OF KAUAI. MEANWHILE...A 1029 MB HIGH
PRESSURE AREA IS CENTERED NEAR 35N136W...WITH RIDGING EXTENDING
SOUTHWESTWARD INTO THE BIG ISLAND. ALOFT...A STRONG UPPER LEVEL
TROUGH IS EVIDENT IN WATER VAPOR IMAGERY ROUGHLY 150 MILES TO THE
WEST OF KAUAI. SATELLITE IMAGERY SHOWS AN ABUNDANCE OF DEEP LAYER
MOISTURE ACROSS THE CENTRAL AND WESTERN ISLANDS...WITH MOSTLY
CLOUDY OR CLOUDY SKIES IN PLACE HERE. ACROSS THE BIG
ISLAND...CLEAR TO PARTLY CLOUDY SKIES ARE SEEN IN LEEWARD
AREAS...WITH PARTLY TO MOSTLY CLOUDY SKIES IN WINDWARD LOCALES.
RADAR IMAGERY SHOWS WIDESPREAD SHOWERS AND THUNDERSTORMS AFFECTING
KAUAI...WITH THE ACTIVITY ENCROACHING ON OAHU. MAIN SHORT TERM
CONCERNS FOR TODAY REVOLVE AROUND THE POTENTIAL FOR FLOODING AND
SEVERE WEATHER.

TODAY...
THE SURFACE TROUGH OF LOW PRESSURE WILL REMAIN NEARLY STATIONARY
JUST TO THE WEST OF KAUAI...WHILE THE UPPER LEVEL TROUGH PIVOTS
EASTWARD AND CLOSE TO OAHU BY THIS EVENING. MIMIC TOTAL
PRECIPITABLE WATER /PW/ SATELLITE IMAGERY SHOWS A LARGE AREA OF
1.5 TO 2.0 INCH VALUES OVER KAUAI AND TO THE SOUTH OF OAHU AND THE
MAUI COUNTY ISLANDS. WITH THE DEEP LAYER MOISTURE IN
PLACE...STRONG FORCING FOR ASCENT AND COLD MID-LEVEL TEMPERATURES
ASSOCIATED WITH THE DEEP UPPER LEVEL TROUGH...WIDESPREAD SHOWERS
AND THUNDERSTORMS ARE EXPECTED ACROSS KAUAI AND OAHU THROUGH THE
REMAINDER OF THE DAY. AS A RESULT...A FLASH FLOOD WATCH HAS BEEN
ISSUED FOR NIIHAU...KAUAI AND OAHU THROUGH TONIGHT. THE WATCH MAY
NEED TO BE EXPANDED TO INCLUDE MAUI COUNTY LATER TODAY. AT THIS
POINT THE BIG ISLAND APPEARS TO BE DISPLACED FAR ENOUGH EAST FROM
THE DEEPEST MOISTURE AND BEST FORCING SUCH THAT ANY FLOODING WHICH
MAY OCCUR SHOULD BE LOCALIZED. AS FOR SEVERE WEATHER
POTENTIAL...THE BIG QUESTION MARK REMAINS THE DEGREE OF
DESTABILIZATION THAT WILL OCCUR THIS AFTERNOON GIVEN THE CLOUD
COVER CURRENTLY IN PLACE. GIVEN THE COLD MID-LEVEL TEMPERATURES OF
BETWEEN -12 AND -14C AT 500 MILLIBARS AND DEEP LAYER 0-6 KM BULK
SHEAR VALUES OF 25 TO 30 KNOTS...WE CERTAINLY CAN/T RULE OUT A FEW
STRONG TO SEVERE STORMS...WITH THE MAIN HAZARDS FROM THE STRONGEST
STORMS IF THEY MANAGE TO DEVELOP BEING LARGE HAIL AND/OR DAMAGING
WINDS. BASED ON CURRENT SATELLITE AND RADAR TRENDS...IT APPEARS
THAT THE AREA HAVING THE HIGHEST POTENTIAL...ALBEIT LOW...TO SEE
SEVERE WEATHER THIS AFTERNOON WOULD BE ACROSS MAUI COUNTY.

TONIGHT AND SATURDAY...
THE SURFACE TROUGH TO THE WEST OF KAUAI WILL SLOWLY WEAKEN AS THE
UPPER LEVEL TROUGH SHIFTS EASTWARD THROUGH THE CENTRAL ISLANDS
TONIGHT AND THROUGH THE BIG ISLAND ON SATURDAY. WITH THE DEEP
MOISTURE AND STRONG FORCING FOR ASCENT REMAINING IN PLACE
TONIGHT...WE EXPECT THE COVERAGE OF SHOWERS AND THUNDERSTORMS TO
REMAIN HIGH. THERE SHOULD BE SOME DECREASE IN DEEP LAYER MOISTURE
ON SATURDAY AS THE UPPER LEVEL TROUGH SHIFTS FURTHER EAST...BUT
THE LINGERING INSTABILITY SHOULD STILL RESULT IN GOOD COVERAGE OF
SHOWERS IN MOST AREAS...PARTICULARLY ACROSS MAUI AND THE BIG
ISLAND WHERE THUNDERSTORMS WILL REMAIN POSSIBLE. THERE ALSO COULD
BE SOME SNOW SHOWERS ON THE BIG ISLAND SUMMITS ABOVE 12 KFT AS
THE UPPER LEVEL TROUGH MOVES THROUGH. THE DEEPEST MOISTURE APPEARS
TO PASS BY TO THE NORTH OF THE BIG ISLAND...SO WE ARE NOT
ANTICIPATING A NEED FOR A WINTER WEATHER ADVISORY AT THIS TIME.

SATURDAY NIGHT THROUGH SUNDAY NIGHT...
WEAK SURFACE TROUGHING WILL REMAIN OVER THE ISLAND CHAIN THROUGH
THE PERIOD...WITH OVERNIGHT LAND BREEZES AND DAYTIME SEA BREEZES
EXPECTED. AN INCREASE IN SOUTHWESTERLY WINDS IS EXPECTED LATE
SUNDAY NIGHT AS A COLD FRONT BEGINS TO APPROACH FROM THE WEST. THE
DEEPEST MOISTURE WILL HAVE SHIFTED NORTHEAST AND AWAY FROM THE
STATE BY SATURDAY EVENING...WITH THE MID-LEVEL TEMPERATURES
REBOUNDING OR WARMING CLOSER TO SEASONAL LEVELS. AS A
RESULT...WE/RE EXPECTING DRIER CONDITIONS TO RETURN TO THE ISLAND
CHAIN...WITH SHOWERS FAVORING THE COASTAL WATERS DURING THE NIGHT
AND THE INTERIOR OF THE ISLANDS DURING THE AFTERNOON/EVENING
HOURS.

MONDAY THROUGH NEXT FRIDAY...
MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT SHOWING A WEAKENING
COLD FRONT APPROACHING FROM THE NORTHWEST ON MONDAY...THEN PUSHING
SLOWLY THROUGH THE ISLAND CHAIN MONDAY NIGHT THROUGH TUESDAY
NIGHT. THE MOISTURE IS EXPECTED TO BE RATHER SHALLOW WITH LITTLE
TO NO UPPER LEVEL FORCING FOR ASCENT...SO NOT MUCH MORE THAN A
BROKEN LINE OF SHOWERS IS EXPECTED TO MOVE THROUGH THE ISLANDS IN
ASSOCIATION WITH THE FRONT. WEAK HIGH PRESSURE IS THEN EXPECTED TO
BUILD OVER OR JUST NORTH OF THE ISLANDS DURING THE MIDDLE OF NEXT
WEEK...WITH AN AFTERNOON SEA BREEZES AND OVERNIGHT LAND BREEZES
EXPECTED. BOTH THE 12Z GFS AND 12Z ECMWF SHOW A STRONGER RIDGE OF
HIGH PRESSURE BUILDING NORTH OF THE STATE LATE NEXT WEEK...AND
THIS SHOULD ALLOW THE TRADE WINDS TO RETURN TO THE ISLAND CHAIN BY
NEXT FRIDAY.

&&

.AVIATION...
THE AIRMASS OVER THE STATE REMAINS MOIST AND UNSTABLE. A WEAK TROUGH
PASSING WEST TO EAST ACROSS THE AREA WILL TRIGGER LOCALLY HEAVY
SHOWERS AND THUNDERSTORMS. DAYTIME HEATING WILL FURTHER ENCOURAGE
CONVECTIVE DEVELOPMENT AND FOCUS IT OVER INLAND AREAS.

AIRMETS HAVE BEEN ISSUED FOR MOUNTAIN OBSCURATION OVER KAUAI AND
OAHU...AND CONDITIONS MAY SPREAD EASTWARD TO MAUI COUNTY IN THE
AFTERNOON...AND POSSIBLY TO WINDWARD BIG ISLAND OVERNIGHT.

LIGHTNING ACTIVITY ACROSS KAUAI AND OAHU THIS MORNING IS EXPECTED TO
SPREAD ACROSS THE REMAINDER OF THE ISLANDS BY AFTERNOON AND PERSIST
OVERNIGHT. EXPECT GUSTY VARIABLE WINDS IN AND NEAR ANY THUNDERSTORMS.
SHOWERS AND THUNDERSTORMS WILL ALSO BRING REDUCED VISIBILITIES AND
CEILINGS. SIGMET NOVEMBER IS IN EFFECT FOR EMBEDDED THUNDERSTORMS
NEAR KAUAI AND OAHU.

&&

.MARINE...
AN ACTIVE WEATHER PATTERN OVER THE ISLANDS WILL LEAD TO
THUNDERSTORMS OVER THE COASTAL WATERS TODAY INTO TONIGHT.
THUNDERSTORMS WILL BRING THE CHANCE OF HEAVY RAIN...REDUCED
VISIBILITIES...STRONG GUSTY WINDS...LIGHTNING...AND HAIL. IF
CONDITIONS WARRANT...SHORT-FUSED SPECIAL MARINE WARNINGS MAY NEED
TO BE ISSUED.

OTHERWISE...WINDS AND SEAS AROUND HAWAII ARE EXPECTED TO REMAIN
QUIET THROUGH MONDAY. THE CURRENT SMALL NORTH-NORTHWEST SWELL WILL
SUBSIDE THROUGH TODAY. ANOTHER SMALL NORTHWEST SWELL WILL PEAK
SUNDAY AND SUBSIDE THROUGH MONDAY. SURF WILL REMAIN BELOW ADVISORY
LEVELS WITH THESE EPISODES.

A VERY LARGE NORTHWEST SWELL IS FORECAST TO ARRIVE BEGINNING TUESDAY
AND PEAK LATE TUESDAY BEFORE SUBSIDING THROUGH THE WEEK...WITH WARNING
LEVEL SURF EXPECTED ACROSS NORTH AND WEST FACING SHORES.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR NIIHAU-KAUAI-OAHU.

&&

DISCUSSION...JELSEMA
AVIATION...A BEDAL
MARINE...EATON