567
FXHW60 PHFO 060719
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
919 PM HST SUN OCT 5 2025
UPDATE
MARINE SECTION HAS BEEN UPDATED TO BETTER SHOW CURRENT TRENDS.
SYNOPSIS
A SURFACE TROUGH APPROACH AND THEN MOVE OVER THE WESTERN END OF
THE STATE TONIGHT THROUGH MONDAY. AS THIS OCCURS, WINDS WILL
WEAKEN AND BECOME MORE SOUTHEASTERLY, RESULTING IN A DAYTIME SEA
BREEZE AND NIGHTTIME LAND BREEZE REGIME. AS THE FEATURE MOVES
THROUGH, INCREASED CLOUDS AND SHOWERS ARE EXPECTED OVER THE
WESTERN ISLANDS THROUGH AT LEAST MONDAY. MODERATE TRADE WINDS
WILL RETURN NEAR THE END OF THE WEEK.
DISCUSSION
REGIONAL SATELLITE IMAGERY SHOWS A WELL-DEFINED BAND OF SHOWERS
ASSOCIATED WITH A TROUGH NORTH OF THE MAIN HAWAIIAN ISLANDS, JUST
INSIDE THE NORTHERN OFFSHORE WATERS THIS AFTERNOON. IN ADDITION TO
THIS SURFACE TROUGH, A DISTINCT UPPER-LOW IS LOCATED NEAR 30N
150W AS OF 0100 UTC, WHERE TOWERING CUMULUS AND HEAVIER SHOWERS
ARE OBSERVED ROUGHLY 550 TO 800 MILES NORTHEAST OF HONOLULU.
CLOSER TO THE ISLANDS, A LATE MORNING ASCAT PASS AND SURFACE
OBSERVATIONS FROM AROUND THE STATE THROUGHOUT THE DAY REVEAL
MODERATE TRADE WINDS THAT ARE SLIGHTLY MORE NORTHEASTERLY OVER THE
WESTERN END OF THE STATE IN CLOSER PROXIMITY TO THE SURFACE
TROUGH, AND MORE EASTERLY OVER THE EASTERN END OF THE STATE
FARTHER AWAY FROM THE FEATURE. RELATIVELY FEW SHOWERS AND LOW
CLOUDS ARE MOVING INTO THE ISLANDS ON THE MODERATE TRADES AT THIS
TIME, THOUGH AFTERNOON SEA-BREEZE INDUCED CLOUD BUILDUPS AND A
FEW SHOWERS HAVE DEVELOPED OVER THE BIG ISLAND AGAIN TODAY.
AS STRONG HIGH PRESSURE BUILDS BEHIND A COLD FRONT MOVING QUICKLY
EASTWARD ACROSS THE NORTH PACIFIC WELL NORTH OF THE REGION, THE
SURFACE TROUGH NEAR THE MAIN HAWAIIAN ISLANDS WILL BE DISPLACED
SOUTHWARD NEAR AND THEN OVER WESTERN ISLANDS. THE BAND OF CLOUDS
AND SHOWERS DISCUSSED EARLIER ASSOCIATED WITH THIS FEATURE IS
EXPECTED TO APPROACH KAUAI TONIGHT, REACHING AND PASSING OVER THE
GARDEN ISLE MONDAY MORNING. AS IT WEAKENS, IT COULD ALSO REACH
OAHU BY THE EARLY AFTERNOON HOURS ON MONDAY. WITH THIS AFTERNOON'S
FORECAST UPDATES, SHOWER CHANCES HAVE BEEN ADJUSTED UPWARD FOR
THE WESTERN END OF THE STATE THROUGH MONDAY, THOUGH IT IS NOTABLE
THAT NEITHER THE HREF (HIGH RESOLUTION ENSEMBLE FORECAST SYSTEM)
PROBABILITIES NOR THE NBM PQPF (PROBABILISTIC QUANTITATIVE
PRECIPITATION FORECASTS) GET TOO CARRIED AWAY WITH RAINFALL
ACCUMULATIONS, LIKELY DUE TO THE BAND'S QUICK MOVEMENT OVER THE
ISLANDS AND WEAKENING NATURE.
AS THE TROUGH APPROACHES THE WESTERN ISLANDS, THE BACKGROUND
MODERATE TRADE WIND FLOW WILL WEAKEN TO BECOME LIGHT OUT AHEAD OF
IT. THIS WILL MARK A RETURN OF DAYTIME SEA BREEZES AND OVERNIGHT
LAND BREEZES, PARTICULARLY FOR THE EASTERN ISLANDS ON MONDAY, THEN
STATEWIDE FROM MONDAY NIGHT THROUGH AT LEAST WEDNESDAY NIGHT AS
THE LIGHT BACKGROUND WINDS BECOME MORE SOUTHEASTERLY. WITH THIS
PATTERN, INCREASED LEEWARD AND INTERIOR SHOWER ACTIVITY CAN BE
EXPECTED FROM LATE MORNING THROUGH EARLY EVENING EACH DAY,
FOLLOWED BY CLEARING AND LIMITED SHOWERS EACH NIGHT.
MODERATE TRADES MAY BEGIN TO FILL BACK INTO THE REGION BY THURSDAY
OR FRIDAY AS STRONG HIGH PRESSURE BUILDS FAR TO THE NORTHEAST OF
THE REGION AND THEN MOVES SOUTHWARD NEAR THE END OF THE WEEK.
THERE IS SOME UNCERTAINTY IN THIS, HOWEVER, AS THERE ARE SOME
DIFFERENCES BETWEEN GLOBAL MODELS REGARDING ANOTHER SURFACE TROUGH
THAT COULD DEVELOP NORTH OF THE ISLANDS MID- TO LATE-WEEK.
AVIATION
LIGHT TO LOCALLY MODERATE TRADES BRINGING PERIODS OF MVFR
COND IN ISOL SHRA ACROSS WINDWARD AND MAUKA LOCATIONS. WINDS WILL
DIMINISH INTO A LAND/SEA BREEZE PATTERN INCREASING CLDS AND
SHRA ACROSS LEEWARD AND INTERIORS OF THE ISLANDS. MVFR POSSIBLE
IN ANY SHRA, OTHERWISE VFR PREVAILS.
NO AIRMETS IN EFFECT.
MARINE
A TROUGH JUST NORTH OF THE COASTAL WATERS IS MOVING SOUTHEAST AND
WILL MOVE OVER THE KAUAI MONDAY. AS THE TROUGH MOVES OVER KAUAI,
MODERATE NORTHEAST TRADE WINDS WILL FILL IN OVER KAUAI WATERS,
WHILE ELSEWHERE LIGHT TO GENTLE EAST TO SOUTHEAST WINDS ARE
EXPECTED THROUGH MONDAY NIGHT. TUESDAY THROUGH THURSDAY LIGHT TO
GENTLE SOUTHEAST FLOW ACROSS THE ZONES WILL ALSO GIVE WAY TO
LOCALIZED LAND AND SEA BREEZES. MODERATE TRADES WILL FILL BACK
FROM EAST TO WEST AT THE END OF THE WEAK AS STRONG HIGH PRESSURE
BUILDS FAR NORTHEAST AND DRIFTS SOUTH.
THE CURRENT MODERATE NORTH-NORTHWEST SWELL THAT PEAKED WELL ABOVE
HIGH SURF ADVISORY (HSA) LEVELS TODAY HAS BEGUN TO DECLINE
QUICKLY THIS EVENING AND WILL CONTINUE TO DECLINE THROUGH MONDAY.
THE HSA AND THE SMALL CRAFT ADVISORY FOR SEAS ABOVE 10 FEET HAS
BEEN CANCELLED.
A SMALL MEDIUM TO LONG PERIOD NORTHWEST (320 DEG) SWELL IS EXPECTED
TO FILL IN THROUGH THE DAY MONDAY, PEAK MONDAY NIGHT AND SLOWLY
DECLINE THROUGH THE WEEK. A SMALL, LONG- PERIOD SOUTHWEST SWELL
HAS STARTED TO FILL IN WITH LONG PERIOD 16 SECOND FORERUNNERS. THE
SWELL IS EXPECTED TO PEAK MONDAY BEFORE SUBSIDING TUESDAY.
ANOTHER SMALL LONG- PERIOD SOUTHWEST (200 DEG) SWELL IS POSSIBLE
BY THE LATER HALF OF NEXT WEEK. SURF ALONG EAST- FACING SHORES
WILL REMAIN BELOW AVERAGE THROUGH THE WEEK.
PEAK HIGH TIDES ASSOCIATED WITH THE LUNAR CYCLE WILL LEAD TO MINOR
COASTAL FLOODING ALONG SHORELINES AND LOW LYING COASTAL AREAS
STARTING TUESDAY THROUGH THE WEEKEND. COASTAL FLOODING WILL
COINCIDE WITH THE DAILY PEAK TIDE EACH AFTERNOON.
FIRE WEATHER
LIGHT WINDS AND INCREASED SHOWERS WILL MITIGATE ANY FIRE WEATHER
CONCERNS THROUGH THE WEEK.
HFO WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...PIERCE
DISCUSSION...VAUGHAN
AVIATION...WALSH
MARINE...SHIGESATO
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