High Surf in Hawaii, March 21, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
950 AM HST SAT MAR 21 2015

.SYNOPSIS...
BREEZY TRADE WINDS WILL DELIVER LOW CLOUDS AND SHOWERS TO WINDWARD
AND MAUKA SECTIONS THROUGH MUCH OF THE WEEKEND. THE GUSTY TRADE
WINDS WILL ALSO CARRY A FEW SHOWERS OVER TO LEEWARD SECTIONS OF SOME
OF THE SMALLER ISLANDS THROUGH TONIGHT. WINDS WILL BECOME LIGHT WITH
DRIER CONDITIONS EXPECTED EARLY NEXT WEEK...FOLLOWED BY
STRENGTHENING TRADE WINDS AND INCREASING TRADE SHOWERS RETURNING
AGAIN STARTING NEXT WEDNESDAY.

&&

.DISCUSSION...
A 1025 MB SURFACE CENTERED NEAR 28N157W...OR ABOUT 500 MILES NORTH
HONOLULU...IS MOVING TOWARD THE EAST NORTHEAST AT ABOUT 20 MPH.
THE HIGH IS RESULTING IN BREEZY TRADE WINDS ACROSS THE ISLAND CHAIN
THIS MORNING.

THE TAIL END OF A DECAYING FRONT IS EVIDENT ABOUT 400 MILES EAST
NORTHEAST OF HILO. SATELLITE IMAGERY AND RADAR SHOWS LOW CLOUDS
AND SHOWERS ASSOCIATED WITH THIS FEATURE BEING TRANSPORTED BY THE
TRADE WIND FLOW TOWARDS HAWAII. ALOFT...THE MID AND UPPER LEVEL
FLOW DIRECTLY ABOVE THE STATE IS FROM THE NORTHWEST AS RIDGING
DEVELOPS TO THE SOUTHWEST OF THE AREA. INVERSION HEIGHTS FROM THE
EARLY MORNING SOUNDINGS AT LIHUE AND HILO SHOWED THE TRADE WIND
INVERSION WAS AROUND 9 THOUSAND FEET. AS A RESULT...EVEN THOUGH
THE ATMOSPHERE REMAINS RELATIVELY STABLE ACROSS THE ISLANDS...THE
LOW CLOUDS AND SHOWERS RIDING IN ON THE TRADES ARE BEING ENHANCED
LOCALLY BY OROGRAPHIC LIFT AS THEY REACH THE ISLANDS. SO MOST
WINDWARD AND MAUKA AREAS REMAIN WET EARLY THIS MORNING. ALSO...THE
BREEZY LOW-LEVEL TRADE WIND FLOW IS CARRYING A FEW OF THESE
SHOWERS OVER TO LEEWARD SECTIONS OF SOME OF THE SMALLER ISLANDS.

THE FORECAST MODELS INDICATE THE PRESSURE GRADIENT WILL REMAIN TIGHT
ACROSS THE AREA THROUGH SUNDAY MORNING AS THE SURFACE HIGH TO THE
NORTH OF THE STATE DRIFTS FURTHER AWAY TO THE EAST-NORTHEAST. THIS
WILL RESULT IN THE BREEZY TRADE WINDS MAINTAINING THROUGH THEN. THE
MOISTURE FROM UPSTREAM WILL CONTINUE CARRY IN AND PRODUCE WET
WEATHER OVER MOST WINDWARD AND MAUKA SECTIONS OF THE STATE THROUGH
SUNDAY MORNING. BY LATE SUNDAY...THE MOISTURE ASSOCIATED WITH THE
DISSIPATED FRONT IS EXPECTED TO LIFT NORTH AND LIKELY LEAD
TO FEWER TRADE SHOWERS.

TRADE WINDS WILL ALSO BEGIN TO WEAKEN LATE SUNDAY AND MONDAY AS A NEW
FRONT BEGINS TO APPROACH FROM THE NORTHWEST. THE SURFACE WINDS
WILL INITIALLY SHIFT TO AN EAST SOUTHEAST DIRECTION NEAR KAUAI TO
MODERATE EAST WINDS NEAR THE BIG ISLAND AS THE APPROACHING FRONT
MOVES FORCES THE RIDGE JUST NORTH OF THE ISLANDS. MONDAY NIGHT AND
TUESDAY WILL SEE A DIURNAL PATTERN OF LOCAL NIGHTTIME LAND BREEZES
AND AFTERNOON SEA BREEZE CIRCULATIONS WILL LIKELY DEVELOP OVER
EACH OF THE INDIVIDUAL ISLANDS. THE AFTERNOON SEA BREEZES WILL
RESULT IN AFTERNOON CLOUDS AND ISOLATED SHOWERS...MAINLY OVER
INTERIOR AND LEEWARD SECTIONS OF THE ISLANDS...WITH CLEARING SKIES
OVER MOST AREAS AT NIGHT. IN ADDITION...VOLCANIC HAZE FROM SOURCES
ON THE BIG ISLAND MAY SPREAD TO THE SMALLER ISLANDS FROM MONDAY
NIGHT THROUGH TUESDAY. HOWEVER...CONFIDENCE IN THIS FORECAST IS
LOW...SINCE THE LATEST MODEL GUIDANCE INDICATES THAT LOW-LEVEL
WIND TRAJECTORIES MAY NOT BE CONDUCIVE FOR THE VOLCANIC HAZE TO BE
TRANSPORTED TO THE SMALLER ISLANDS.

FROM TUESDAY NIGHT THROUGH THURSDAY...THE NUMERICAL FORECAST OUTPUT
INDICATES A NEW SURFACE HIGH BUILDING NORTHWEST OF THE MAIN HAWAIIAN
ISLAND CHAIN WILL PUSH THE AFOREMENTIONED WEAKENING FRONT CLOSER TO
KAUAI. IF SO...EXPECT INCREASING NORTHEAST WINDS ON WEDNESDAY...
FOLLOWED BY THE LOW-LEVEL FLOW VEERING TO THE EAST BY THURSDAY.
SIMILAR THE CURRENT WEATHER REGIME...MOISTURE ASSOCIATED WITH THE
FRONT...WHICH IS EXPECTED TO GRADUALLY WEAKEN AS IT ARRIVES IN THE
AREA...WILL ALLOW THE DEVELOPMENT OF ENHANCED TRADE WIND SHOWERS...
ESPECIALLY OVER WINDWARD AND MAUKA SECTIONS OF KAUAI AND OAHU.

THE LONG-RANGE FORECAST MODELS ALSO SHOW A MID-LEVEL RIDGE JUST
SOUTH OF THE ISLANDS WILL KEEP RELATIVELY STABLE ATMOSPHERIC
CONDITIONS ACROSS THE AREA AROUND MID-WEEK. THIS RIDGING ALOFT IS
EXPECTED TO STRENGTHEN AS IT SHIFTS NORTHWARD DIRECTLY ABOVE THE
ISLAND CHAIN DURING THE SECOND HALF OF NEXT WEEK. AS A RESULT...
THESE INCREASINGLY STABLE CONDITIONS WILL LIKELY NOT ALLOW DEEP
CONVECTION OR HEAVY RAIN TO DEVELOP. HOWEVER...ABUNDANT SHOWERS
ASSOCIATED WITH THE FRONT NEXT WEEK MAY ONCE AGAIN SOAK NORTH FACING
SLOPES AND THE HIGHER TERRAIN ON KAUAI.

&&

.AVIATION...
MODERATE NORTHEAST TO EAST WINDS WILL CONTINUE TODAY...AND REMAIN STRONG
ENOUGH TO CONTINUE AIRMET TANGO FOR LOW LEVEL TURB. EXPECT AIRMET
TANGO TO REMAIN POSTED THROUGH THE DAY BEFORE WINDS BEGIN TO EASE ON
SUNDAY. REMNANT FRONTAL MOISTURE WILL BE CARRIED TOWARD THE ISLANDS
WITH THE WINDS...CAUSING PERIODS OF TEMPO MVFR WITH POSSIBLE ISOL
IFR IN SHOWERS AND MAINLY ALONG WINDWARD AREAS. AIRMET SIERRA FOR
MOUNTAIN OBSCURATION IS POSTED OVER N THRU E SECTIONS. LEEWARD AREAS
MAY EXPERIENCE SOME SPILLOVER SHOWERS.

&&

.MARINE...
A HIGH SURF ADVISORY HAS BEEN PUSHED BACK TO 6 PM TODAY FOR NORTH AND
WEST FACING SHORES OF NIIHAU AND KAUAI...AND FOR NORTH FACING
SHORES OF OAHU MOLOKAI AND MAUI. CURRENT NEAR SHORE BUOY OBSERVATIONS
SHOWING BELOW ADVISORY CONDITIONS THIS MORNING. SWELL HEIGHTS UPSTREAM
AT BUOY 51101 WHICH HAS NOT SHOWN MUCH OF THE EXPECTED JUMP...BUT
WILL CONTINUE TO MONITOR FOR IT/S PEAK. WAVEWATCH III MODEL GUIDANCE
SHOWS THIS ANTICIPATED PEAK OF THIS SWELL THIS EVENING....THEN
GRADUALLY SUBSIDING ON SUNDAY. ANOTHER NORTHWEST SWELL OF SIMILAR
SIZE IS EXPECTED TO ARRIVE LATE WEDNESDAY NIGHT.

A SMALL TO MODERATE LONG PERIOD SOUTH SOUTHWEST SWELL IS FORECAST
TO ARRIVE MONDAY...AND THEN PERSIST FOR MUCH OF THE WEEK...WITH
THE PEAK ON MONDAY NIGHT AND TUESDAY.

A SMALL CRAFT ADVISORY /SCA/ IS POSTED FOR THE TYPICALLY WINDY
WATERS ADJACENT TO THE BIG ISLAND AND THE ISLANDS OF MAUI COUNTY. IN
ADDITION...THE BUILDING NORTH NORTHWEST SWELL COMBINED WITH LOCALLY
GENERATED WIND WAVES IS FORECAST TO INCREASE THE SEAS TO SCA HEIGHTS
OVER PARTS OF THE COASTAL WATERS AROUND KAUAI AND OAHU. THE SCA HAS
BEEN POSTED FOR THE AFFECTED COASTAL WATERS THROUGH EARLY SUNDAY
MORNING...SEE LIST OF AFFECTED ZONES BELOW. THE WINDS ARE EXPECTED
TO WEAKEN ON LATE SUNDAY...ENDING SCA CONDITIONS.

THE LATEST FORECAST SUGGESTS THAT NORTHEASTERLY TRADE WINDS MAY INCREASE
AGAIN NEXT WEDNESDAY...SO A SCA MAY BE REQUIRED FOR SOME MARINE ZONES
AGAIN AROUND THE MIDDLE OF NEXT WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY FROM 6 PM HST TODAY TO 10 AM HST SUNDAY
FOR NORTH AND WEST FACING SHORES OF KAUAI AND NIIHAU...AND FOR
NORTH FACING SHORES OF OAHU...MOLOKAI AND MAUI.

SMALL CRAFT ADVISORY UNTIL 6 AM HST SUNDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-KAUAI CHANNEL-
OAHU WINDWARD WATERS-MAALAEA BAY-PAILOLO CHANNEL-ALENUIHAHA
CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.

&&

DISCUSSION/MARINE...FOSTER
AVIATION...EATON