Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 250150
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST FRI APR 24 2015

.SYNOPSIS...
A FRONT IS APPROACHING FROM THE NORTHWEST. LOCALLY BREEZY SOUTHEAST
WINDS AHEAD OF THE FRONT WILL FOCUS SHOWERS OVER SOUTHEAST AREAS OF
THE ISLANDS AND CARRY VOLCANIC HAZE OVER THE SMALLER ISLANDS. THERE
WILL ALSO BE AFTERNOON CLOUDS AND SHOWERS OVER INTERIOR AREAS
SATURDAY AFTERNOON. A BAND OF SHOWERS ALONG THE FRONT IS EXPECTED TO
REACH KAUAI SATURDAY EVENING...THEN STALL AND WEAKEN OVER THE
CENTRAL ISLANDS BY SUNDAY NIGHT. A STRONG HIGH MOVING EAST BEHIND
THE FRONT WILL BRING BREEZY TRADE WINDS AND SHOWERY WEATHER TO
WINDWARD AREAS THROUGH MUCH OF NEXT WEEK.

&&

.DISCUSSION...
SURFACE ANALYSES SHOW A 1028 MB HIGH CENTERED ABOUT 1200 MILES
NORTHEAST OF HILO NEAR 31N141W WITH A BROAD RIDGE EXTENDING FROM THE
HIGH TO NEAR MAUI. A STRONG 1036 MB HIGH LIES 2150 MILES NORTHWEST
OF KAUAI. A 1011 MB LOW IS ABOUT 650 MILES NORTHWEST OF KAUAI NEAR
28N167W. A SLOW-MOVING FRONT ASSOCIATED WITH THE LOW IS ABOUT 250
MILES NORTHWEST OF KAUAI. THE PRESSURE GRADIENT BETWEEN THE HIGH AND
THE LOW IS PRODUCING SOUTHEAST WINDS NEAR THE BIG ISLAND...WITH THE
WINDS VEERING OUT OF THE SOUTH NEAR KAUAI. THESE WINDS REMAIN STRONG
OFF THE WINDWARD COASTS FROM THE BIG ISLAND TO MOLOKAI BUT THE BIG
ISLAND IS PARTLY BLOCKING THE SOUTHEAST FLOW SO WINDS ARE WEAKER
AND QUITE VARIABLE ACROSS MAUI COUNTY AND OAHU. THE WINDS WILL
CARRY SHOWERS OVER SOUTHEAST SECTIONS OF THE ISLANDS.

THE COMPUTER MODELS ARE IN PRETTY GOOD AGREEMENT SHOWING THE FRONT
MOVING SOUTHEAST AND WEAKENING OVER THE NEXT 36 HOURS. AS THE FRONT
APPROACHES...THE STRONG SOUTHEAST WINDS WILL GRADUALLY SHIFT OUT OF
THE SOUTH AND WEAKEN. THE FRONT IS EXPECTED TO REACH KAUAI SATURDAY
EVENING...OAHU ON SUNDAY AND THEN GRADUALLY DISSIPATE NEAR MAUI
SUNDAY NIGHT.  A BAND OF SHOWERS ALONG THE FRONT WILL PRODUCE
WIDESPREAD SHOWERS DOWN TO OAHU. THE MODELS DISAGREE ON HOW FAR
THE DISSIPATING SYSTEM WILL GET BEYOND OAHU. THE FRONTAL BAND MAY
PRODUCE LOCALLY HEAVY SHOWERS BUT IT DOES NOT LOOK AS IF THE
ATMOSPHERE WILL BE UNSTABLE ENOUGH TO PRODUCE THUNDERSTORMS OR
WIDESPREAD FLOODING RAINS.

THE HIGH FAR NORTHWEST OF THE AREA WILL MOVE EAST BEHIND THE FRONT
AND BECOME QUITE STRONG. BOTH THE GFS AND ECMWF MODELS SHOW THE HIGH
BUILDING TO NEAR 1040 MB SATURDAY NIGHT. THE HIGH WILL WEAKEN A BIT
AFTER THAT...BUT WILL REMAIN STRONG ENOUGH TO PRODUCE BREEZY TRADE
WINDS BEHIND THE FRONT. TRADE-WIND WEATHER IS EXPECTED TO PERSIST
THROUGH AT LEAST THE MIDDLE OF NEXT WEEK. THE TRADES WILL CARRY
REMNANTS OF THE FRONT BACK OVER THE ISLANDS AND A WEAK TROUGH ALOFT
WILL LINGER NEAR THE ISLANDS SO WINDWARD AREAS WILL LIKELY BE RATHER
SHOWERY NEXT WEEK.

&&

.AVIATION...
VFR CONDITIONS PREVAIL OVER THE AREA BUT THERE MAY BE MVFR
CONDITIONS OVER SOUTHEAST SLOPES OVERNIGHT. CLOUDS AND SHOWERS COULD
PRODUCE ENOUGH MTN OBSC TO REQUIRE ISSUANCE OF AIRMET SIERRA.

&&

.MARINE...
A LONG FETCH OF FRESH TO STRONG EASTERLY TRADE WINDS WILL MAINTAIN
ROUGH SURF ALONG EAST FACING SHORES BUT THIS SURF IS BELOW THE
ADVISORY THRESHOLD AND WILL CONTINUE TO SUBSIDE THROUGH THE
WEEKEND. THE CURRENT SOUTH SOUTHWEST SWELL WILL ALSO CONTINUE TO
SUBSIDE. A SMALL WEST NORTHWEST SWELL ARRIVING TONIGHT WILL PRODUCE
SURF WELL BELOW ADVISORY LEVELS THROUGH THE WEEKEND. A NORTH
NORTHWEST SWELL IS EXPECTED TO ARRIVE SUNDAY...THEN BUILD AND SHIFT
OUT OF THE NORTH BY MONDAY NIGHT. THIS SWELL WILL LIKELY PRODUCE
SURF ABOVE THE ADVISORY THRESHOLD ALONG NORTH FACING SHORES BY
MONDAY MORNING AND COULD PRODUCE ADVISORY-LEVEL SURF ALONG EAST
FACING SHORES ON TUESDAY AS THE SWELL DIRECTION SHIFTS OUT OF THE
NORTH NORTHEAST. SOME NORTH NORTHWEST THROUGH NORTHEAST SWELL WILL
PERSIST THROUGH THE MIDDLE OF NEXT WEEK.

A SMALL CRAFT ADVISORY REMAINS UP FOR BIG ISLAND WINDWARD WATERS FOR
STRONG SOUTHEAST WINDS THROUGH SATURDAY EVENING. STRONG NORTHEAST
WINDS ARE EXPECTED BEHIND THE FRONT AS EARLY AS SUNDAY NIGHT NEAR
KAUAI AND SPREADING DOWN NEAR THE BIG ISLAND AS EARLY AS MONDAY
NIGHT. THE MODELS ARE NOT YET IN GOOD AGREEMENT ON THE STRENGTH OF
THE WINDS BEHIND THE FRONT...SO WE MAY NEED TO ADJUST THE WIND
FORECASTS OVER THE NEXT FEW DAYS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 600 PM SATURDAY FOR BIG ISLAND WINDWARD
WATERS.

&&

$$
DONALDSON







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