High Surf in Hawaii, February 24 to 26, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1010 AM HST TUE FEB 24 2015

.SYNOPSIS...
LOCALLY BREEZY TRADE WINDS WILL DEVELOP TODAY...AND CONTINUE
THROUGH WEDNESDAY...BEFORE DIMINISHING THURSDAY AND FRIDAY. THE
TRADE WINDS WILL DELIVER CLOUDS AND SHOWERS TO WINDWARD AREAS...WITH
MOST LEEWARD AREAS REMAINING DRY. LIGHTER WINDS AND INCREASED
CLOUDS AND SHOWERS ARE EXPECTED FROM THURSDAY INTO THE WEEKEND AS A
SURFACE TROUGH DEVELOPS OVER THE ISLANDS.

&&

.DISCUSSION...
CURRENTLY...A DRY WEATHER PATTERN PREVAILS OVER MANY ISLAND
AREAS...WITH LIGHT TO LOCALLY FRESH EASTERLY TRADE WINDS DELIVERING
A VARYING AMOUNT OF LOW CLOUDS TO WINDWARD COASTS AND SLOPES.
GENERALLY SPEAKING...SHOWERY AND STABLE LOW CLOUDS INCREASE FROM W
TO E ACROSS THE ISLAND CHAIN...WITH FEW CLOUDS OVER AND NEAR KAUAI
AND BROKEN TO OVERCAST CLOUDS OVER AND NEAR WINDWARD MAUI AND THE
BIG ISLAND. THE EASTERLY TRADE WIND FLOW IS BEING SUPPORTED BY A
1034 MB SURFACE HIGH CENTERED ABOUT 2000 MILES TO THE NE...WITH IT/S
ATTENDANT SURFACE RIDGE LOCATED ABOUT 150 MILES N OF KAUAI. WITH THE
RIDGE IN THIS LOCATION...WINDS ARE WEAKEST NEAR KAUAI...AND
STRONGEST NEAR AND S OF THE BIG ISLAND. AN AMPLIFIED FLOW ALOFT HAS
DEVELOPED OVER THE CENTRAL NORTH PACIFIC OVER THE PAST COUPLE OF
DAYS...WITH A SHARP NNE-SSW ORIENTED RIDGE ALIGNED OVER THE
ISLANDS...AND WELL-DEVELOPED TROUGHS LOCATED BOTH NW AND SE OF
HAWAII. THE TROUGH TO THE SE CONTAINS A LONG-LIVED WELL-DEVELOPED
WESTWARD-MOVING CLOSED LOW...WITH THIS FEATURE CENTERED ABOUT 1000
MILES SE OF THE BIG ISLAND...NEAR 14N 140W. MEANWHILE THE TROUGH TO
THE NE IS SLOWLY PUSHING E...WITH THE TROUGH AXIS ABOUT 1000 MILES
NW OF KAUAI. DEEP LAYERED CLOUDS ARE STREAMING NORTHEASTWARD TO THE
E OF THE TROUGH AXIS.

WHILE A FAIRLY TYPICAL TRADE WIND FLOW HAS RETURNED TO THE ISLANDS
FOR THE TIME BEING...THIS PATTERN IS EXPECTED TO CHANGE...BEGINNING
AS EARLY AS THURSDAY. UNTIL THEN...EXPECT TRADE WINDS TO STRENGTHEN
SLIGHTLY TONIGHT AND REMAIN BREEZY ON WEDNESDAY BEFORE DIMINISHING
ON THURSDAY. THE TRADE WINDS WILL DELIVER CLOUDS AND SHOWERS TO
WINDWARD AREAS...BUT THE GRADUALLY ERODING RIDGE ALOFT WILL CONTINUE
TO EFFECTIVELY CAP THE ISLAND ATMOSPHERE AT ABOUT 6-8 KFT.

WHILE FORECAST MODELS HAVE NOT BEEN ENTIRELY CONSISTENT IN THE
EVOLUTION OF THE FLOW ALOFT LATER THIS WEEK THROUGH EARLY NEXT
WEEK...AND HAVE TRENDED A LITTLE DRIER FOR THE WEEKEND...THEY HAVE
BEEN CONSISTENT IN DEPICTING A FAIRLY SHARP LOW-LEVEL TROUGH
DEVELOPING OVER THE ISLAND CHAIN THURSDAY INTO FRIDAY. THE SPECIFICS
ON WHERE THE TROUGH DEVELOPS AND MOVES WILL HAVE SIGNIFICANT EFFECTS
ON THE SENSIBLE WEATHER...WITH BREEZY NE WINDS W OF THE TROUGH AXIS
AND LIGHTER SE WINDS IMMEDIATELY E OF THE TROUGH AXIS. LATEST GFS
GUIDANCE HAS THE TROUGH AXIS OVER THE CENTER OF THE ISLAND CHAIN ON
THURSDAY INTO FRIDAY WITH MODEST SUPPORT FROM ALOFT...WITH THE
TROUGH DRIFTING E AND WEAKENING SATURDAY AND SUNDAY. A WEAKER
SURFACE TROUGH IS THEN DEPICTED AS DRIFTING W BACK OVER THE ISLAND
CHAIN EARLY NEXT WEEK...AND PHASING IN WITH A NEW SHORT WAVE
ALOFT...LEADING TO A WET TRADE WIND PATTERN. OVERALL...THE ECMWF
SOLUTION IS WETTER THAN THE GFS...WITH THE TROUGH AXIS NOT MOVING E
LIKE THE GFS...INSTEAD REMAINING OVER THE ISLAND CHAIN UNTIL THE
MIDDLE OF NEXT WEEK...WITH SEVERAL RIPPLES ALOFT SUPPORTING ENHANCED
CLOUDS AND PRECIPITATION THROUGH MOST OF THE PERIOD. OUR FORECAST
GRIDS DO NOT NECESSARILY FAVOR ONE SOLUTION OVER THE OTHER...AND
INSTEAD BROAD-BRUSH A RELATIVELY WET PATTERN FROM THE END OF THIS
WEEK THROUGH THE WEEKEND. IF LATEST MODEL TRENDS CONTINUE...THEN THE
SLIGHT DRYING TREND CONTAINED IN OUR FORECAST FOR NEXT WEEK WILL
NEED TO BE REEVALUATED.

WHILE WINDS WILL LIKELY HAVE SOME SORT OF AN EASTERLY COMPONENT...
THE BULK OF THE EXPECTED CLOUDS AND SHOWERS WILL FAVOR WINDWARD
AREAS...BUT WHERE WINDS ARE LIGHTEST NEAR THE TROUGH AXIS...
ISLAND-SCALE SEA BREEZE CIRCULATIONS COULD DRIVE CLOUD AND SHOWER
DEVELOPMENT OVER LEEWARD AREAS.

WINDS OVER THE BIG ISLAND SUMMITS STEADILY INCREASED THROUGH
MID-MORNING...AND HAVE SINCE STABILIZED NEAR 50 MPH...AND A WIND
ADVISORY IS IN EFFECT. THESE WINDS MAY CONTINUE INTO WEDNESDAY
BEFORE DIMINISHING.

&&

.AVIATION...
VFR WILL PREVAIL OVER THE ALOHA STATE TODAY. HOWEVER...TEMPO MVFR
CONDITIONS ARE POSSIBLE OVER WINDWARD AND MAUKA SECTIONS AS BROKEN
LOW CLOUDS AND SHOWERS ARE SWEPT ALONG ON A REESTABLISHED TRADE
FLOW. THIS IS ESPECIALLY SO FOR THE ISLAND OF HAWAII.

AIRMET SIERRA FOR MOUNTAIN OBSCURATION IN WINDWARD BIG ISLAND
REMAINS IN EFFECT...AND WILL BE REEVALUATED LATER FOR CONTINUED
RELEVANCE.

&&

.MARINE...
A HIGH SURF ADVISORY IS IN EFFECT FOR W FACING SHORES OF KAUAI
COUNTY AND THE BIG ISLAND WITH THE ARRIVAL OF A BUILDING WNW SWELL.
WITH THIS PARTICULAR SWELL DIRECTION...SHADOWING OF THE SWELL IS
EXPECTED ON OAHU AND MAUI COUNTY...AND RESULTANT SURF HEIGHTS ARE
EXPECTED TO REMAIN BELOW ADVISORY LEVELS. LATEST OBSERVATIONS AT
BUOY 51101 NW OF KAUAI SHOW SWELL HEIGHTS ON THE INCREASE...BUT
HEIGHTS THUS FAR ARE ABOUT 2 FEET LOWER THAN WAVE WATCH GUIDANCE.
THE SWELL IS STILL EXPECTED TO PEAK TONIGHT AND WEDNESDAY BEFORE
DIMINISHING. MEANWHILE...SHORT-PERIOD WIND WAVES WILL GRADUALLY
INCREASE IN SIZE ALONG E FACING SHORES THROUGH WEDNESDAY BEFORE
DIMINISHING THEREAFTER. NOT MUCH SWELL EXPECTED THROUGH THE
WEEKEND...WITH A MODERATE NNW SWELL EXPECTED TO ARRIVE SUNDAY AND
PEAK MONDAY OF NEXT WEEK.

A SMALL CRAFT ADVISORY /SCA/ IS SLATED TO BEGIN TONIGHT FOR WATERS
AROUND MAUI AND THE BIG ISLAND...AS BOTH TRADE WINDS AND SEAS
INCREASE. THE SCA IS EXPECTED TO BE RELATIVELY SHORT-LIVED...AS
WINDS AND SEAS DIMINISH ON THURSDAY. A SURFACE TROUGH IS EXPECTED TO
DEVELOP OVER THE ISLANDS THIS WEEKEND...AND THEN DRIFT E. AS THIS
OCCURS...NNE WINDS ARE EXPECTED TO INCREASE NEAR KAUAI AND OAHU...
AND MAY GET STRONG ENOUGH TO NECESSITATE A SCA.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL 6 PM HST THIS EVENING FOR THE BIG ISLAND SUMMITS.

HIGH SURF ADVISORY UNTIL 6 PM HST WEDNESDAY FOR WEST FACING SHORES
OF NIIHAU AND KAUAI...AND UNTIL 6 AM HST THURSDAY FOR WEST FACING
SHORES OF THE BIG ISLAND.

SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 PM HST WEDNESDAY
FOR PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.

&&

DISCUSSION/MARINE...BIRCHARD
AVIATION...KINEL