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Hawaiian Islands Synoptic Discussion and Guidance

045
FXHW60 PHFO 301945
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
945 AM HST SAT APR 30 2016

.SYNOPSIS...
TRADE WINDS WILL PERSIST THROUGH THE FORECAST PERIOD...AND CLOUDS
AND SHOWERS ARE EXPECTED TO FAVOR WINDWARD AND MAUKA AREAS.
HOWEVER...WIND SPEEDS MAY DECREASE SLIGHTLY TODAY AS A FRONT FAR
TO OUR NORTH WEAKENS THE GOVERNING RIDGE. WIND SPEEDS WILL THEN
REBOUND SUNDAY AND AFTERWARDS AS A NEW HIGH BUILDS TO OUR NORTH.
ANOTHER FRONT MAY APPROACH THE ISLANDS FROM THE NORTHWEST LATE
NEXT WEEK INTO THE FOLLOWING WEEKEND.

&&

.DISCUSSION...
A FRONT 400 TO 500 MILES NORTHWEST OF THE MAIN HAWAIIAN ISLANDS
IS ACTING TO WEAKEN THE SUBTROPICAL RIDGE EXTENDING EAST TO WEST
ROUGHLY ALONG 30N. THIS RIDGE...GOVERNING THE STRENGTH OF TRADE
FLOW ACROSS LOCAL HAWAIIAN WATERS...IS ANCHORED BY HIGH PRESSURE
CENTERS OFF THE NORTHERN CALIFORNIA COAST AND FAR NORTHWEST OF THE
MAIN HAWAIIAN ISLANDS. PATCHY BROKEN LOW CLOUDS EMBEDDED WITHIN
TRADE FLOW ARE MOVING ACROSS THE ISLANDS THIS MORNING...FAVORING
WINDWARD AND MAUKA AREAS. PW VALUES ARE NEAR 1.2 INCHES...BUT A
CAPPING INVERSION NEAR 8000 FEET AND THE LACK OF A CONVECTIVE
TRIGGER...BESIDES LOCAL TERRAIN...KEEP TOTAL RAINFALL AMOUNTS
LIGHT. WE EXPECT THIS GENERAL TRADE WIND SHOWER PATTERN TO
CONTINUE INTO NEXT WEEK.

MODELS SHOW THE FRONT FAR NORTHWEST OF THE MAIN HAWAIIAN ISLANDS
WILL MOVE EASTWARD AND WEAKEN THROUGH SUNDAY AS HIGH PRESSURE
BEHIND IT BUILDS IN STRENGTH. BY THE MIDDLE OF NEXT WEEK...TRADE
WINDS ALONG THE SOUTHERN FLANK OF THIS NEW HIGH MAY PUSH REMNANT
FRONTAL MOISTURE ACROSS THE ISLANDS...INCREASING TRADE SHOWER
COVERAGE. BEFORE THIS HOWEVER...WE EXPECT THE NEW HIGH WILL CAUSE
TRADE WIND SPEEDS TO REBOUND TO SMALL CRAFT ADVISORY THRESHOLD
ACROSS MORE OF THE WINDIER LOCAL WATERS BEGINNING SUNDAY. ANOTHER
FRONT MAY APPROACH THE ISLANDS TOWARD NEXT WEEKEND.

&&

.AVIATION...
A STABLE TRADE WIND FLOW WILL CONTINUE TODAY WITH AN INVERSION
CAPPING LOW CLOUDS BETWEEN 6000 TO 8000 FT. EXTENSIVE MVFR CIGS
THAT WERE IN PLACE OVER WINDWARD BIG ISLAND AND MAUI HAVE
DECREASED IN COVERAGE...AND AIRMET SIERRA FOR MOUNTAIN OBSC HAS
BEEN CANCELED. EXPECT AREAS OF MVFR CIGS OVER WINDWARD AREAS OF
MOST ISLANDS THROUGH THE WEEKEND.

MORNING RADAR VAD WINDS SHOW EASTERLY TRADE WINDS OF 20 KT OR
LESS...LIGHT ENOUGH TO INHIBIT WIDESPREAD LOW LEVEL TURB. AS
WINDS INCREASE TONIGHT AND SUNDAY...AIRMET TANGO MAY BE NEEDED.

&&

.MARINE...
THE SMALL CRAFT ADVISORY CONTINUES FOR ONLY THE ALENUIHAHA
CHANNEL TODAY. TRADE WINDS ARE FORECAST TO INCREASE AGAIN STARTING
TONIGHT OR SUNDAY...SO THIS ADVISORY WILL LIKELY BE POSTED AGAIN
FOR THE TYPICALLY WINDY ZONES ADJACENT TO THE ISLANDS OF MAUI
COUNTY AND THE BIG ISLAND. THIS SCA WILL LIKELY CONTINUE FOR THESE
WATERS THROUGH THE MIDDLE OF NEXT WEEK ONCE IT IS ISSUED.

A NORTHWEST SWELL WILL PEAK TODAY...THEN GRADUALLY LOWER TONIGHT.
ANOTHER REINFORCING SMALL NORTHWEST SWELL ARRIVING LATE TONIGHT
WILL LIKELY PEAK SUNDAY...THEN SLOWLY LOWER EARLY NEXT WEEK. A NEW
SMALL LONGER PERIOD WEST-NORTHWEST SWELL IS EXPECTED ON WEDNESDAY
AND THURSDAY. ELSEWHERE...EXPECT A NOTICEABLE BUMP IN SURF HEIGHTS
ALONG SOUTH FACING SHORES FROM THIS WEEKEND THROUGH EARLY NEXT
WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING FOR ALENUIHAHA
CHANNEL.

&&

$$

PUBLIC/MARINE...POWELL
AVIATION...WROE

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office