High Surf in Hawaii, March 21 to 22, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST THU MAR 21 2013

.SYNOPSIS...
A FRONT WILL APPROACH THE STATE FROM THE WEST LATER TODAY WITH AN
INCREASE IN SHOWERS EXPECTED AHEAD OF AND ALONG THE FRONT. THE FRONT
IS EXPECTED TO REACH KAUAI ON FRIDAY...THEN IT IS FORECAST TO STALL
AND WEAKEN NEAR OAHU OR MAUI COUNTY SATURDAY. EXPECT WEAK SOUTH TO
SOUTHEAST FLOW EAST OF THE FRONT...WITH NORTH TO NORTHEAST WINDS
DEVELOPING BEHIND THE FRONT. THE SOUTHERLY FLOW WILL CONTINUE TO
BRING VOLCANIC HAZE UP OVER MOST OF THE SMALLER ISLANDS THROUGH
FRIDAY. HIGH PRESSURE WILL GRADUALLY BUILD IN NORTHWEST OF THE AREA
THIS WEEKEND...WITH A TRADE WIND WEATHER PATTERN RETURNING EARLY
NEXT WEEK.

&&

.DISCUSSION...
THE WESTERN END OF A ROUNDED SURFACE RIDGE REMAINS ACROSS THE
NORTHERN HAWAIIAN ISLANDS EARLY THIS MORNING. ELSEWHERE...A
WEAKENING NEARLY STATIONARY SURFACE FRONT IS ABOUT 250 MILES
NORTHWEST OF LIHUE. THE PRESENCE OF THE RIDGE AND THE FRONT IS
CAUSING THE WINDS TO BE RELATIVELY LIGHT WITH SOUTHERLY WINDS NEAR
KAUAI...WHILE A SOUTHEASTERLY SYNOPTIC FLOW IS AFFECTING MOST OF
THE REMAINDER OF THE STATE.

LOOPS OF WATER VAPOR IMAGERY INDICATE THE AXIS OF AN UPPER LEVEL
TROUGH IS LOCATED ABOUT 1000 MILES WEST OF KAUAI. THIS TROUGH HAS
PROPAGATED EASTWARD AT 25 TO 30 MPH DURING THE PAST 6 HOURS. THE
UPPER LEVEL FLOW AHEAD OF THIS TROUGH OVER THE MAIN HAWAIIAN ISLANDS
IS FROM THE WEST SOUTHWEST AT 75 TO 80 MPH.

RADAR REFLECTIVITY DATA AND SATELLITE IMAGERY SHOW OVERCAST LAYERED
CLOUDS WITH EMBEDDED SHOWERS AND ISOLATED THUNDERSTORMS JUST WEST OF
THE KAUAI COASTAL WATERS. THIS AREA OF CLOUDS AND PRECIPITATION
APPEARS TO BE PROPAGATING SLOWLY EASTWARD. ADDITIONAL ISOLATED
SHOWERS ARE IN THE VICINITY OF MAUI AND THE SOUTHEASTERN BIG ISLAND.
THE LIGHT WINDS ALLOWED THE ESTABLISHMENT OF LOCAL LAND BREEZE
CIRCULATIONS OVER MOST OF THE INDIVIDUAL ISLANDS TONIGHT. ALSO...THE
SOUTH TO SOUTHEAST FLOW IS BRINGING UP PLENTY OF VOLCANIC HAZE
ACROSS MOST OF THE SMALLER ISLANDS.

THE FORECAST MODELS INDICATE THE UPPER LEVEL TROUGH WILL CONTINUE TO
PROPAGATE EASTWARD THROUGH FRIDAY. AS A RESULT...THE STALLED FRONT
THAT IS NOW NORTHWEST OF KAUAI WILL BECOME REINVIGORATED AND BEGIN
TO MOVE TOWARD KAUAI STARTING LATER TODAY OR TONIGHT. THE FRONT WILL
LIKELY REACH KAUAI ON FRIDAY...THEN WILL REACH OAHU LATE FRIDAY OR
EARLY SATURDAY MORNING. THE FRONT WILL LIKELY MOVE TO MAUI COUNTY
WHERE IT IS EXPECTED TO STALL AND WEAKEN ON SATURDAY. BANDS AND/OR
CLUSTERS OF SHOWERS ARE EXPECTED TO DEVELOP AND INCREASE IN AREAL
COVERAGE AHEAD OF AND ALONG THE FRONT. THE GREATEST INSTABILITY WILL
LIKELY REMAIN FAR NORTH OF THE STATE. HOWEVER...WE HAVE ADDED A
SLIGHT CHANCE OF THUNDERSTORMS OVER THE COASTAL WATERS NORTHWEST AND
NORTH OF KAUAI THROUGH THIS EVENING. THERE IS ALSO A POSSIBILITY OF
THUNDER ON KAUAI THIS AFTERNOON... WITH THE THREAT OF LOCALLY HEAVY
RAINFALL POSSIBLE ON THAT ISLANDS FROM THIS AFTERNOON THROUGH
TONIGHT. WE ALSO EXPECT AN INCREASE IN HIGH CLOUDS ACROSS THE STATE
AHEAD OF THE UPPER LEVEL TROUGH AS IT APPROACHES THE AREA.

THE STALLED FRONT WILL LIKELY WEAKEN INTO A TROUGH THIS WEEKEND
SOMEWHERE NEAR WESTERN MAUI COUNTY. WINDS WEST OF THE FRONT/TROUGH
WILL SWING AROUND TO THE NORTH OR NORTHEAST...AND WILL BE LIGHT
SOUTHEASTERLY TO THE EAST OF THIS FEATURE. THE NORTH TO NORTHEAST
FLOW SHOULD PUSH THE VOLCANIC HAZE AWAY FROM MOST OF THE WESTERN
ISLANDS...BUT THESE CONDITIONS MAY LINGER INTO THIS WEEKEND FOR
PARTS OF MAUI COUNTY IF THE FRONT/TROUGH REMAINS WEST OF THERE.

CURRENTLY...WE ARE NOT MENTIONING HEAVY RAINFALL AHEAD OF OR ALONG
THE FRONT ON FRIDAY OR SATURDAY. WE WILL NEED TO MONITOR
QUANTITATIVE PRECIPITATION FORECASTS...OR QPF...IN CASE WE NEED TO
MENTION LOCALLY HEAVY RAINFALL FROM FRIDAY INTO THIS WEEKEND. WITH
MOST OF THE INSTABILITY EXPECTED TO BE NORTH OF THE STATE AFTER
TONIGHT...WE DO NOT HAVE ANY MENTION OF HEAVY SHOWERS IN THE
CURRENT FORECAST...EXCEPT FOR KAUAI THROUGH TONIGHT.

AS THE NORTHEASTERLY FLOW BECOMES ESTABLISHED OVER THE WESTERN
ISLANDS...EXPECT CLOUDS AND PASSING SHOWERS TO BECOME A MORE TYPICAL
WINDWARD AND MAUKA PATTERN...WITH THE GREATEST CONCENTRATION OF
SHOWERS BEING WHERE THE REMNANT MOISTURE FROM THE FRONT LINGERS.
HIGH PRESSURE WILL BUILD IN TO THE NORTHWEST AND NORTH OF THE AREA
FROM THIS WEEKEND INTO EARLY NEXT WEEK. THIS IS EXPECTED TO ALLOW A
RETURN TO A MORE TYPICAL TRADE WIND WEATHER PATTERN.

&&

.AVIATION...
VFR WEATHER WILL PREVAIL OVER MOST AREAS. BRIEF MVFR CONDITIONS ARE
NOT OUT OF THE QUESTION...HOWEVER...IN LOWER CLOUDS AND SHOWERS THAT
MAY DEVELOP SOUTH OF THE ISLANDS AND MOVE NORTH WITH THE KONA WIND
REGIME.

HEAVIER SHOWERS AND ISOLATED THUNDERSTORMS ARE POSSIBLE BY THE
AFTERNOON HOURS...ESPECIALLY IN THE VICINITY OF KAUAI...AS A FRONT
SLOWLY ADVANCES TOWARD THE STATE FROM THE WEST.

&&

.MARINE...
THE NEW NORTHWEST SWELL CONTINUES TO BUILD AT BUOY 51101. THE LATEST
READINGS INDICATE THE SWELL HEIGHT IS NEAR 14 FEET WITH A WAVE
PERIOD OF AROUND 16 SECONDS. THE WAIMEA BAY BUOY ALSO SHOWS A
SIGNIFICANT INCREASE IN WAVE HEIGHTS DUE TO THIS NEW SWELL. THESE
READINGS ARE ABOUT 2 FEET ABOVE THE GUIDANCE FROM THE WAVE WATCH III
MODEL. THEREFORE...A HIGH SURF WARNING HAS BEEN ISSUED FOR MOST
NORTH AND WEST FACING SHORES OF THE SMALLER ISLANDS. A HIGH SURF
ADVISORY HAS ALSO BEEN ISSUED STARTING JUST BEFORE DAWN THIS MORNING
FOR THE WEST FACING SHORES OF THE BIG ISLAND. THIS SWELL IS EXPECTED
TO PEAK LATER TODAY OR TONIGHT...AND THEN GRADUALLY LOWER FROM
FRIDAY INTO THE WEEKEND. ANOTHER MODERATE NORTHWEST SWELL IS
EXPECTED TO ARRIVE SUNDAY NIGHT...AND CONTINUE ON MONDAY. THIS SWELL
WILL SLOWLY DIMINISH NEXT TUESDAY.

THE NEW NORTHWEST SWELL COMBINED WITH LOCALLY GENERATED WIND WAVES
IS CAUSING SEAS TO REACH THE SMALL CRAFT ADVISORY /SCA/ THRESHOLD OF
10 FEET ACROSS WATERS EXPOSED TO THIS SWELL. THEREFORE...A SCA HAS
BEEN ISSUED FOR ALL OF THE HAWAIIAN COASTAL WATERS EXCEPT MAALAEA
BAY. THE SEAS WILL GRADUALLY LOWER OVER THE WEEKEND. NO OTHER SCA
CONDITIONS ARE EVIDENT IN THE LATEST FORECAST FROM SATURDAY INTO
EARLY NEXT WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING UNTIL 600 AM HST FRIDAY FOR NORTH AND WEST FACING
SHORES OF NIIHAU...KAUAI...OAHU...AND MOLOKAI...AND FOR NORTH FACING
SHORES OF MAUI.

HIGH SURF ADVISORY FROM 600 AM THIS MORNING UNTIL 600 PM HST FRIDAY
FOR WEST FACING SHORES OF THE BIG ISLAND.

SMALL CRAFT ADVISORY UNTIL 600 AM HST FRIDAY FOR THE OAHU LEEWARD
WATERS...MAUI COUNTY LEEWARD WATERS...THE WATERS SOUTH OF THE BIG
ISLAND...AND THE KAIWI...PAILOLO AND ALENUIHAHA CHANNELS.

SMALL CRAFT ADVISORY UNTIL 600 PM HST FRIDAY FOR THE KAUAI NORTHWEST
WATERS...KAUAI WINDWARD WATERS...KAUAI LEEWARD WATERS...KAUAI
CHANNEL...OAHU WINDWARD WATERS...MAUI COUNTY WINDWARD WATERS AND THE
BIG ISLAND WINDWARD WATERS.

&&

DISCUSSION/MARINE...HOUSTON
AVIATION...KINEL