Heavy Rain in Hawaii, November 3 to 4, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
845 PM HST MON NOV 3 2014

.SYNOPSIS...
A FRONT APPROACHING FROM THE NORTH WILL LEAD TO LIGHTER WINDS
TONIGHT AND TUESDAY...WITH OVERNIGHT LAND BREEZES GIVING WAY TO
AFTERNOON SEA BREEZES ON TUESDAY. THE FRONT WILL STALL NORTH OF
KAUAI...AND MODERATE TRADE WINDS WILL DELIVER BRIEF WINDWARD SHOWERS
FROM TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. WINDS WILL WEAKEN AGAIN
ON THURSDAY AS A SECOND FRONT APPROACHES. THE SECOND FRONT IS
EXPECTED TO MOVE DOWN THE ISLAND CHAIN FRIDAY NIGHT AND SATURDAY
WITH AN INCREASE IN SHOWERS ASSOCIATED WITH ITS PASSAGE. BREEZY AND
COOL NORTHEAST WINDS WILL FILL IN BEHIND THE FRONT...AND PERSIST
THROUGH THE WEEKEND.

&&

.DISCUSSION...
CURRENTLY...THE ISLAND AIR MASS REMAINS MOIST AND RELATIVELY
UNSTABLE...ALTHOUGH THE CENTER OF A PERSISTENT LOW ALOFT S OF KAUAI
IS NO LONGER DISCERNIBLE. THE LOW HAS DEVOLVED INTO A WEAKENING
TROUGH ALOFT THAT IS IN THE PROCESS OF MOVING E OVER THE ISLAND
CHAIN...BUT CONTINUES TO PRODUCE SIGNIFICANT LAYERED CLOUDINESS OVER
THE ISLANDS FROM OAHU TO THE BIG ISLAND. INSTABILITY ASSOCIATED WITH
THE TROUGH IS HELPING TO TRIGGER ISOLATED HEAVY DOWNPOURS...WITH
RADAR CURRENTLY DETECTING A FEW HEAVY SHOWERS OVER INTERIOR KAUAI.
RADAR IS ALSO DETECTING LIGHT STRATIFORM RAIN FALLING FROM A
MID-LEVEL CLOUD DECK OVER THE BIG ISLAND AND ADJACENT WATERS. THE
OVERNIGHT FORECAST WILL BE UPDATED SHORTLY TO INCREASE CLOUDINESS
FOR THE FIRST PART OF THE NIGHT...WITH THE EXPECTATION BEING THAT
THE LAYERED CLOUDS WILL DIMINISH BY MORNING AS THE TROUGH ALOFT
CONTINUES TO WEAKEN AND MOVE E OF THE ISLANDS. WITH LOW-LEVEL
WINDS ON THE DECREASE AND LAND BREEZES DEVELOPING OVER THE
ISLANDS...THE LATE NIGHT RAIN CHANCES WILL BE LOWERED AS WELL.

A SURFACE HIGH FAR NE OF THE ISLANDS HAS AN ASSOCIATED RIDGE THAT IS
CURRENTLY ABOUT 350 MILES N OF KAUAI...WHILE AN APPROACHING FRONT IS
ABOUT 550 MILES NW OF KAUAI. THE APPROACH OF THIS FRONT WILL WEAKEN
THE W END OF THE RIDGE...AND LOOSEN /AT LEAST TEMPORARILY/ THE
PRESSURE GRADIENT OVER THE AREA...WITH WINDS BECOMING LIGHT
OVERNIGHT AND TUESDAY. WITH WIND SPEEDS DIMINISHING SIGNIFICANTLY
AND VEERING TO THE SE TONIGHT...ISLAND SCALE LAND AND SEA BREEZES
WILL PREVAIL FOR THE NEXT 24 HOURS OR SO. LATEST MODEL GUIDANCE
CONTINUE TO INDICATE THE APPROACHING FRONT WILL STALL N OF KAUAI
TUESDAY AND WEDNESDAY. A HIGH BUILDING TO THE NW OF THE AREA WILL
RE-BUILD THE RIDGE AND TIGHTEN THE LOW LEVEL PRESSURE GRADIENT...
WITH MODERATE TRADE WINDS AND A TYPICAL TRADE WIND WEATHER REGIME
PREVAILING FROM TUESDAY NIGHT THROUGH WEDNESDAY NIGHT.

ON THURSDAY A NEW FRONT APPROACHING FROM THE NW WILL WEAKEN THE
RIDGE AND WINDS WILL DIMINISH AGAIN...BECOMING LIGHT AND VARIABLE
AGAIN THURSDAY NIGHT AND EARLY FRIDAY. INCREASING N TO NE WINDS ON
FRIDAY WILL USHER THE SECOND FRONT DOWN THE CHAIN THROUGH SUNDAY...
AND BRING LOWER DEW POINTS AND SLIGHTLY COOLER TEMPERATURES. THE
FRONT IS EXPECTED TO REACH KAUAI LATE FRIDAY AND GRADUALLY MOVE DOWN
THE ISLAND CHAIN ON SATURDAY BEFORE STALLING AND WEAKENING NEAR MAUI
OR THE BIG ISLAND ON SUNDAY. THE FRONT WILL BE ACCOMPANIED BY AN
INCREASE IN SHOWERS ESPECIALLY ALONG NORTH AND NORTHEAST FACING
SLOPES. LIGHT TO MODERATE TRADES AND RELATIVELY QUIET TRADE
WIND WEATHER IS EXPECTED EARLY NEXT WEEK. THE OFFICIAL FORECAST
CONTINUES TO DISCOUNT THE LONGER RANGE GFS SOLUTIONS...WITH THE NEW
00Z RUN CONTINUING TO DEVELOP A TROPICAL LOW S OF THE BIG ISLAND...
AND MOVING IT NORTHWARD.

AS MENTIONED ABOVE...THE LOW ALOFT IS FORECAST TO LIFT OUT TO THE NE
AND GRADUALLY FILL THROUGH TUESDAY. THE DEPARTING LOW WILL TAKE THE
BULK OF THE ATMOSPHERIC INSTABILITY WITH IT...AND WILL ALLOW A WEAK
MID LEVEL RIDGE TO NOSE INTO THE AREA FROM THE E. THIS RIDGE WILL
MORE OR LESS REMAIN IN PLACE MOST OF THE WEEK...KEEPING AT LEAST A
WEAK CAP ON THE ISLAND ATMOSPHERE. THE FRONT SLATED FOR NEXT WEEKEND
MAY HAVE SOME SUPPORT FROM ALOFT AS A MID-LEVEL TROUGH ACCOMPANIES
IT.

&&

.AVIATION...
A SURFACE FRONT APPROACHING FROM THE NORTHWEST RESULTS IN WINDS
EASING ACROSS THE ISLANDS THIS EVENING. WITH THE WEAKER WINDS...
AIRMET TANGO FOR LOW LEVEL TURBULENCE HAS BEEN CANCELLED.
THERE ARE QUITE A BIT OF MID AND HIGH CLOUDS COVERING THE AREA AND
WILL CONTINUE THROUGH EARLY TUESDAY MORNING AS AN UPPER LEVEL LOW
REMAINS JUST S OF THE STATE. THIS LOW ALSO ACTS TO KEEP AIR MASS
UNSTABLE OVER THE ISLANDS...LEADING TO SHOWERS BECOMING ENHANCED.
LOCALLY HEAVY DOWNPOURS MAY RESULT IN ISOL IFR CEILING AND MVFR VIS
CONDITIONS. REGARDLESS...EXPECT MAINLY VFR CONDITIONS TO PREVAIL FOR
MOST SITES...EXCEPT FOR MVFR CONDITIONS MAY PERSIST OVERNIGHT FOR
THE WINDWARD BIG ISLAND. AN AIRMET FOR MT OBSC CONTINUES FOR
WINDWARD BIG ISLAND AT THIS TIME...AND MAY PERSIST THROUGH REST OF
THE EVENING INTO EARLY TUESDAY MORNING.

&&

.MARINE...
NO MARINE ADVISORIES ARE CURRENTLY POSTED...AS WINDS ARE ON THE
DOWNTREND...AND WILL REMAIN LIGHT TO LOCALLY MODERATE ON TUESDAY.
WHILE SMALL SWELLS FROM THE NW AND SW ARE EXPECTED TO BUILD
OVERNIGHT AND TUESDAY...COMBINED SEAS WILL REMAIN BELOW SMALL CRAFT
ADVISORY /SCA/ CRITERIA. WINDS MAY ONCE AGAIN INCREASE BRIEFLY TO
SCA LEVELS IN THE WINDIER MARINE ZONES AROUND MAUI AND THE BIG
ISLAND ON WEDNESDAY...BEFORE LOWERING AGAIN THURSDAY AND FRIDAY.
FRIDAY NIGHT AND SATURDAY...NE WINDS FILLING IN BEHIND A FRONT WILL
COMBINE WITH A BUILDING NNW SWELL TO BRING SCA CONDITIONS TO NEARLY
ALL MARINE ZONES.

THE SMALL NW SWELL BUILDING TONIGHT AND TUESDAY WILL GRADUALLY SWING
AROUND TO A MORE NORTHERLY DIRECTION WEDNESDAY AND THURSDAY AS THE
SWELL PERIOD DIMINISHES. A MUCH LARGER NNW SWELL IS EXPECTED TO
ARRIVE FRIDAY NIGHT...BUILD ON SATURDAY...PEAK SATURDAY NIGHT AND
REMAIN LARGE INTO SUNDAY. RESULTANT SURF WILL BE LARGE ENOUGH TO
REQUIRE A HIGH SURF ADVISORY FOR N AND W FACING SHORES OF MOST
ISLANDS...AND PEAK SURF HEIGHTS MAY APPROACH WARNING LEVELS OF 25
FEET ALONG N FACING SHORES...ALTHOUGH IT IS TOO EARLY TO BE CERTAIN
ABOUT THE DETAILS. THERE WILL BE A SERIES OF SMALL S/SW SWELLS
THROUGH THE WEEK...WITH THE LARGEST SURF EXPECTED TUESDAY AND
WEDNESDAY. THE OAHU SURF DISCUSSION /SRDHFO/ WAS UPDATED TODAY AND
CONTAINS DETAILS THAT CAN BE LOOSELY APPLIED STATEWIDE.

&&

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

&&

SYNOPSIS/DISCUSSION/MARINE...BIRCHARD
AVIATION...HUI