High Surf in Hawaii, April 2 to 4, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST WED APR 2 2014

.SYNOPSIS...
BREEZY TRADE WINDS WILL PREVAIL THROUGH THE WEEK...AND MOST SHOWERS
WILL BECOME LIMITED TO WINDWARD SLOPES. LIGHTER SOUTHERLY WINDS WITH
INCREASED AFTERNOON SHOWERS INLAND WILL ARRIVE BY SATURDAY. A FRONT
ARRIVING OVER THE WEEKEND WILL BRING MORE WIDESPREAD RAIN...BUT
MAINLY INCREASED NORTHERLY WINDS AND A COOLER AIR MASS FROM SUNDAY
INTO MONDAY.

&&

.DISCUSSION...
ACROSS THE MAIN HAWAIIAN ISLANDS...SURFACE OBSERVATIONS REPORTED
MODERATE TRADE WINDS BLOWING. THE LIHUE SOUNDING SHOWED PLENTY OF
MOMENTUM THROUGH THE LOWER ATMOSPHERE...HINTING AT THE POSSIBILITY
OF SOME FURTHER INCREASE IN WIND SPEED THROUGH THE SHORT RUN.

THE AIR MASS WAS ON THE MOIST SIDE OF USUAL...BOTH OVER THE ISLANDS
THEMSELVES...AND FOR A DISTANCE UPWIND TO THE NORTHEAST...THOUGH A
DRIER AIR MASS PREVAILED FURTHER OUT. ALOFT...A TROUGH OVER THE
SOUTHEAST HALF OF THE STATE FILLED AND RECEDED TOWARD THE EAST
NORTHEAST AS A RIDGE EXPANDED FROM THE NORTHWEST.

ALTHOUGH THE DEEPER CONVECTION OVER THE EAST COAST AND SLOPES OF THE
BIG ISLAND LARGELY DISSIPATED DURING THE PAST SIX HOURS...THE
WEAKENING MID-LEVEL TROUGH CONTINUED TO ENCOURAGE THE GROWTH OF
TOWERING CUMULI...AND AT LEAST ONE THUNDERSTORM...OVER WATERS EAST
OF MAUI AND THE BIG ISLAND. RESULTING SHOWERS THEN MOVED ASHORE
ALONG EAST SLOPES OF THE SMALLER ISLANDS...PRODUCING LOCALLY
IMPRESSIVE RAIN ACCUMULATION...THOUGH ON THE WHOLE ALSO MOVING TOO
FAST TO CAUSE SERIOUS PROBLEMS. LAND BREEZES PROBABLY HELPED TO KEEP
MOST OF THESE SHOWERS OFF OF THE BIG ISLAND. IN ANY CASE...WINTER
WEATHER HAD ENDED OVER THE BIG ISLAND SUMMITS. THE GRIDS HAVE BEEN
ADJUSTED FOR ALL THESE CHANGES...AND FOR GOOD MEASURE A SLIGHT
CHANCE OF THUNDERSTORMS HAS BEEN ADDED TO UPSLOPE PARTS OF THE BIG
ISLAND THIS AFTERNOON. PRECIPITATION FROM THESE HYPOTHETICAL
THUNDERSTORMS...IF THEY DO OCCUR...SHOULD NOT BE WIDESPREAD ENOUGH
TO REQUIRE A WINTER WEATHER ADVISORY.

DURING THE MIDDLE TERM...THE GROWING RIDGE ALOFT FROM THE NORTHWEST
WILL DOMINATE LOCAL WEATHER...PROVIDING SUBSTANTIAL SUPPORT FOR THE
SUBTROPICAL RIDGE NEAR THE SURFACE. BY THAT POINT...THE DRIER AIR
MASS SHOULD ARRIVE AS WELL...SO GENERAL CONDITIONS WILL TREND TOWARD
CLIMATOLOGY...WITH MODERATE TO STRONG TRADE WINDS...AND MOSTLY
WINDWARD SHOWERS. HOWEVER...THIS WEATHER REGIME WILL NOT LAST LONG.

BY FRIDAY NIGHT...GUIDANCE PREDICTED A BROAD MID-LEVEL TROUGH TO
START DIGGING SOUTHEAST TOWARD THE STATE. UNDER THIS INFLUENCE...THE
SUBTROPICAL RIDGE WILL BREAK DOWN...AND SURFACE WINDS WILL WEAKEN
AND BECOME MORE SOUTHERLY. SOME CONVERGENCE WILL BE LIKELY IN THE
LOW-LEVEL FLOW...BUT THE DRIER AIR MASS SHOULD LIMIT MOST SHOWER
DEVELOPMENT TO AFTERNOON BUILDUPS.

THE MAIN FRONTAL BAND WILL SWEEP DOWN THE STATE FROM SUNDAY INTO
MONDAY...THOUGH THIS TIMING DID DIFFER AMONG SOLUTIONS FROM SUNDAY
MORNING TO SUNDAY NIGHT. THE NORTHERLY WINDS AND COOLER AIR MASS
BEHIND THE FRONT LIKELY WILL BE MORE SIGNIFICANT THAN THE WEAK
FEATURE ITSELF. THE WIND DIRECTION WILL RETURN TO A MORE FAMILIAR
NORTHEASTERLY DIRECTION BY AROUND NEXT TUESDAY...WHILE MOISTURE
LINGERING FROM THE FRONT WILL BLOW AWAY...OR ONTO WINDWARD SLOPES.

&&

.MARINE...
A SMALL CRAFT ADVISORY REMAINED IN EFFECT FOR ALL WINDWARD WATERS...
CHANNELS...AND TYPICALLY WINDY AREAS AROUND THE ISLANDS FOR WIND
SPEEDS AND EASTERLY WIND SWELL.

A MODERATE NORTHWEST SWELL WILL BUILD STARTING TONIGHT...AND THEN
PEAK BELOW ADVISORY LEVELS ON THURSDAY. A WEST-NORTHWEST SWELL
EXPECTED TO ARRIVE BY THE END OF THE WEEK MAY PRODUCE PEAK SURF
HEIGHTS AT OR ABOVE ADVISORY LEVELS ALONG SHORES FACING NORTH OR
WEST ON SATURDAY. A SWELL FROM THE SOUTH ALSO SHOULD ARRIVE FROM
WEDNESDAY THROUGH FRIDAY. STRENGTHENING TRADE WINDS WILL INCREASE
WAVE ACTION ALONG EAST SHORES THROUGH FRIDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST THURSDAY FOR KAUAI WINDWARD-
OAHU KOOLAU-OLOMANA-MOLOKAI WINDWARD-MAUI WINDWARD WEST-WINDWARD
HALEAKALA-SOUTH BIG ISLAND-BIG ISLAND NORTH AND EAST.

SMALL CRAFT ADVISORY UNTIL 6 PM HST THURSDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI CHANNEL-OAHU WINDWARD WATERS-
KAIWI CHANNEL-MAUI COUNTY WINDWARD WATERS-MAALAEA BAY-PAILOLO
CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND WINDWARD WATERS-BIG ISLAND
LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.

&&

RYSHKO