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000
FXHW60 PHFO 182021
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST SAT MAY 18 2013

.SYNOPSIS...
A LOW ALOFT WILL DEVELOP NORTHEAST OF THE ISLANDS AND LINGER THROUGH
MID-WEEK...BEFORE WEAKENING AND MOVING OFF TO THE NORTH. THE LOW
WILL WEAKEN THE WINDS AND BRING A CHANCE OF LOCALLY HEAVY SHOWERS.
AS THE LOW ALOFT DEPARTS...TRADE WINDS...AND MORE SETTLED WEATHER...
WILL SPREAD BACK OVER THE AREA BY NEXT WEEKEND. HIGH SURF WILL
CONTINUE ALONG THE SOUTH SHORES THROUGH SUNDAY...AND POSSIBLY INTO
MONDAY.

&&

.DISCUSSION...
THE GLOBAL MODELS AGREE PRETTY WELL ON THE WEATHER PATTERN OVER THE
NEXT WEEK...BUT THE PATTERN WILL BE COMPLICATED...AND IT MAY BE
DIFFICULT TO PIN DOWN THE DETAILS.

THE SURFACE HIGH THAT HAS BEEN BRINGING TRADE WINDS TO THE ISLANDS
HAS MOVED FAR NORTHEAST OF THE ISLANDS AND THE TRADES HAVE WEAKENED
TO GENTLE SPEEDS. THE LOW ALOFT THAT HAS BEEN OVER THE AREA HAS
KICKED OUT TO THE NORTHEAST AHEAD OF A SHARP TROUGH ALOFT DIGGING
SOUTH TOWARD THE ISLANDS. THERE WERE LOCALLY HEAVY SHOWERS OVERNIGHT
FROM THE BIG ISLAND TO OAHU AND ONE THUNDERSTORM BRIEFLY FORMED OFF
KONA. THIS ACTIVITY MAY HAVE BEEN ASSOCIATED WITH THE LOW ALOFT AS
IT MOVED BY OVERNIGHT. IN ANY CASE...SHOWERS HAVE BECOME LESS ACTIVE
SINCE SUNRISE.

AS THE UPPER TROUGH CONTINUES DIGGING TOWARD THE ISLANDS TODAY WE
EXPECT A NORTH TO SOUTH SURFACE TROUGH OVER MAUI COUNTY TO RAPIDLY
SHARPEN... WITH WINDS VEERING OUT OF THE SOUTHEAST NEAR THE BIG
ISLAND... BACKING TO NORTH NORTHEAST NEAR KAUAI...AND BECOMING LIGHT
AND VARIABLE AROUND OAHU AND MAUI COUNTY. TRADE-WIND-LIKE WEATHER
WILL PERSIST OVER KAUAI COUNTY FOR THE NEXT DAY OR TWO. WITH LIGHTER
WINDS AND MORE INSTABILITY FROM OAHU TO MAUI...THERE WILL BE A
CONVECTIVE PATTERN WITH CLOUDS AND LOCALLY HEAVY SHOWERS IN THE
AFTERNOONS AND EVENINGS AND PARTIAL CLEARING OVERNIGHT. THE
ATMOSPHERE WILL BE MOST UNSTABLE NEAR THE BIG ISLAND SO WE ARE
FORECASTING A SLIGHT CHANCE OF THUNDERSTORMS THERE THROUGH THIS
EVENING.

THE SURFACE TROUGH WILL LINGER NEAR MAUI THROUGH MONDAY...THEN
SLOWLY WEAKEN AND MOVE OFF TO THE WEST. ALOFT...A LOW WILL DEVELOP
IN THE TROUGH NORTH OF THE ISLANDS AND PERSIST NORTHEAST OF THE AREA
THROUGH MID-WEEK. LIGHT WINDS ASSOCIATED WITH THE SURFACE TROUGH AND
INSTABILITY FROM THE LOW ALOFT WILL KEEP A CONVECTIVE PATTERN OVER
THE ISLANDS THROUGH WEDNESDAY OR THURSDAY. LATER IN THE WEEK...AND
THE TIMING IS STILL UNCERTAIN...HIGH PRESSURE WILL BUILD IN FROM THE
NORTHEAST AND TRADE WINDS WILL RETURN.

THE MODELS ARE IN GOOD AGREEMENT SHOWING THE TRADE WINDS
WELL-ESTABLISHED BY FRIDAY...AND LOCALLY BREEZY NEXT WEEKEND. THE
CONVECTIVE PATTERN WILL END AND THE TRADES WILL BRING SHOWERS TO
WINDWARD AREAS. ANOTHER TROUGH ALOFT MAY DIG DOWN OVER THE AREA NEXT
WEEKEND AND MAY ENHANCE THE WINDWARD SHOWERS.

&&

.AVIATION...
A DEVELOPING CONVECTIVE PATTERN OVER THE ISLANDS WILL BRING LOCALLY
HEAVY SHOWERS FROM THE BIG ISLAND TO OAHU OVER THE NEXT FEW DAYS
WITH THUNDERSTORMS POSSIBLE OVER THE BIG ISLAND THROUGH THIS
EVENING. THE GREATEST CHANCE FOR MVFR CONDITIONS AND MOUNTAIN
OBSCURATION FOR THE NEXT FEW DAYS WILL BE DURING THE AFTERNOONS AND
EVENINGS.

&&

.MARINE...
WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY
LEVELS STATEWIDE THROUGH NEXT WEEK. A SERIES OF SWELLS WILL KEEP
ELEVATED SURF ALONG SOUTH SHORES THROUGH MOST OF THE UPCOMING
WEEK WITH SURF EXPECTED TO REMAIN ABOVE THE ADVISORY THRESHOLD
THROUGH AT LEAST SUNDAY EVENING AND PROBABLY LONGER. A MARINE
WEATHER STATEMENT ALSO CONTINUES FOR WAVES BREAKING NEAR CHANNEL
ENTRANCES AND POSSIBLE HARBOR SURGES. SEE THE SURF ZONE FORECAST AND
COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST FOR OAHU.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST SUNDAY FOR SOUTH SHORES OF ALL
ISLANDS.

&&

$$
DONALDSON