High Surf in Hawaii, April 15 to 16, 2016

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
358 AM HST FRI APR 15 2016

.SYNOPSIS...
MODERATE TO LOCALLY FRESH TRADE WINDS WILL WEAKEN SLIGHTLY DURING
THE NEXT DAY. A SLIGHTLY ACTIVE RAINFALL PATTERN WILL FOCUS CLOUDS
AND SHOWERS ALONG WINDWARD SLOPES...WITH A FEW SHOWERS SPREADING
LEEWARD ON THE SMALLER ISLANDS. AN INCREASE IN SHOWERS AND TRADE
WINDS IS DUE ON SUNDAY INTO MONDAY AS A BAND OF MOISTURE PUSHES
SOUTHWARD ACROSS THE ISLANDS. MODERATE TRADE WINDS AND A TYPICAL
SHOWER PATTERN WILL DOMINATE NEXT WEEK.

&&

.DISCUSSION...
TRADE WINDS ARE GRADUALLY BACKING OFF AS A FRONT CURRENTLY LOCATED
675 MILES NORTHWEST OF KAUAI ADVANCES EASTWARD. THIS TREND WILL
CONTINUE THROUGH TONIGHT EVEN AS THE FRONT WEAKENS. LATE SATURDAY...
STRENGTHENING HIGH PRESSURE TO THE NORTHWEST WILL CAUSE
NORTHEASTERLY WINDS TO BUILD BEHIND...AND POSSIBLY BLEED THROUGH...
THE DISSIPATING FRONT. AS A RESULT...WINDS NEAR KAUAI COULD BE
SLIGHTLY STRONGER AND MORE NORTHEASTERLY.

A SLIGHTLY ACTIVE SHOWER PATTERN IS EXPECTED THROUGH SATURDAY AS
THE MID LEVEL RIDGE OVERHEAD WEAKENS. EVEN THOUGH WATER VAPOR
IMAGERY DEPICTS CONTINUED SUBSIDENCE OVER THE ISLANDS...OVERNIGHT
SOUNDINGS SHOWED SOME MID LEVEL COOLING AND A WEAKENING OF THE
INVERSION BASED NEAR 8000 FT. THE UPPER LEVEL TROUGH DRIVING THE
ABOVE MENTIONED FRONT WILL CONTINUE TO SLOWLY ERODE THE MID LEVEL
RIDGE. THIS DESTABILIZING PROCESS...ALONG WITH LOW LEVEL
CONVERGENCE GENERATED BY SHIFTING TRADE WINDS...WILL LIKELY
PRODUCE A SLIGHTLY ACTIVE...WINDWARD-FOCUSED SHOWER REGIME...
MAINLY OVER THE WESTERN HALF OF THE STATE. PRECIPITABLE WATER
VALUES ARE FORECAST TO HOVER NEAR APRIL NORMAL...SO SIGNIFICANT
RAINFALL IS NOT EXPECTED.

AN INCREASE SHOWERS AND TRADE WINDS IS DUE ON SUNDAY. A BAND OF
MOISTURE MARKING THE REMNANTS OF THE FRONT WILL BE PUSHED
SOUTHWARD OVER THE ISLANDS BY STRENGTHENING HIGH PRESSURE TO THE
NORTH. WHILE RAINFALL WILL BE FOCUSED OVER WINDWARD SLOPES...
BREEZY NORTHEASTERLY TRADE WINDS ALONG AND BEHIND THE REMNANT
FRONTAL BAND WILL SPREAD SOME SHOWERS TO LEEWARD SECTIONS OF THE
SMALLER ISLANDS AT TIMES. BY MONDAY...THE CLOUD BAND IS EXPECTED
BE NEAR MAUI AND THE BIG ISLAND...WITH DECREASING WINDWARD SHOWERS
ELSEWHERE.

A TYPICAL TRADE WIND WEATHER REGIME IS EXPECTED NEXT WEEK. THERE
IS SOME DISAGREEMENT AS TO THE STRENGTH OF THE WINDS...WITH THE
GFS STILL PREDICTING A DEEPER HIGH NORTH OF THE STATE AND STRONGER
TRADES. THE EXTENDED FORECAST REMAINS A BLEND OF THE GFS AND
ECMWF...CALLING FOR MODERATE WINDS. THE ABOVE DESCRIBED BAND OF
MOISTURE MAY LINGER OVER THE SOUTHERN END OF THE STATE THROUGH THE
MIDDLE OF NEXT WEEK...BUT OVERALL...A TYPICAL SHOWER PATTERN IS
EXPECTED...WITH MID LEVEL RIDGING NOSING IN FROM THE WEST AND
CREATING STABLE CONDITIONS.

&&

.AVIATION...
MODERATE TRADE WINDS WILL CONTINUE TO EASE TODAY. SHOWERS AND CLOUDS
HAVE INCREASED ACROSS WINDWARD SECTIONS DURING THE NIGHT...AND
AIRMET SIERRA FOR MOUNTAIN OBSCURATION HAS BEEN POSTED OVER WINDWARD
OAHU. CONDITIONS SHOULD IMPROVE WITH SHOWERS DECREASING BY MIDDAY.
SHOWERS AND CLOUDS COULD INCREASE OVER WINDWARD AREAS ONCE AGAIN
TONIGHT INTO SATURDAY MORNING...AND AIRMET SIERRA MAY BE NEEDED OVER
SOME WINDWARD AREAS AGAIN AT THAT TIME.

AIRMET TANGO HAS BEEN POSTED FOR THE LAST FEW DAYS FOR LOW LEVEL
TURB TO THE S AND W OF THE HIGHER ISLAND TERRAIN...BUT EXPECT THIS
TO BE DROPPED EARLY THIS MORNING DUE TO DECREASING TRADE WINDS.

&&

.MARINE...
A LONG PERIOD NORTHWEST SWELL WILL SPREAD DOWN THE ISLAND CHAIN
TODAY. THE SWELL HAS BEEN BUILDING AT BUOY 51101 FAIRLY CLOSE TO
WAVEWATCH PREDICTIONS...WITH THE LATEST READING SHOWING A SWELL
OF 8 TO 9 FT AT 19 SECONDS. A HIGH SURF ADVISORY HAS BEEN POSTED
FOR MOST NORTH AND WEST FACING SHORES FROM KAUAI TO MAUI. THE
SWELL WILL PEAK TONIGHT...AND ALTHOUGH THE ADVISORY CURRENTLY RUNS
THROUGH 6 AM SATURDAY...IT MAY NEED TO BE EXTENDED THROUGH THE DAY
ON SATURDAY.

WITH THE TRADE WINDS COMING DOWN A NOTCH...THE SMALL CRAFT
ADVISORY /SCA/ HAS BEEN CANCELED. THAT SAID...WINDS WILL BE AT
BORDER LINE SCA STRENGTH OVER THE TYPICALLY WINDY WATERS AROUND
THE BIG ISLAND AND MAUI...AND SEAS WILL BE CLOSE TO THE 10 FT SCA
THRESHOLD DUE TO A COMBINATION OF OF LOCAL WIND WAVES AND THE
INCOMING NORTHWEST SWELL. SCA CONDITIONS ARE DUE OVER MOST WATERS
ON SUNDAY AND MONDAY...AND AS EARLY AS SATURDAY NIGHT NEAR
KAUAI...AS NORTHEASTERLY TRADE WINDS INCREASE.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY FROM 6 AM THIS MORNING TO 6 AM HST SATURDAY
FOR NORTH AND WEST FACING SHORES OF NIIHAU KAUAI OAHU AND MOLOKAI
AND FOR NORTH FACING SHORES OF MAUI.

&&

DISCUSSION AND MARINE...WROE
AVIATION...JACOBSON