610
FXHW60 PHFO 060209
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
409 PM HST SUN OCT 5 2025
SYNOPSIS
A SURFACE TROUGH WILL APPROACH, AND THEN MOVE OVER, THE WESTERN
END OF THE STATE TONIGHT THROUGH MONDAY. AS THE FEATURE MOVES
THROUGH, INCREASED CLOUDS AND SHOWERS ARE EXPECTED OVER THE
WESTERN ISLANDS. AHEAD OF IT, WINDS WILL WEAKEN AND BECOME MORE
SOUTHEASTERLY, RESULTING IN A DAYTIME SEA BREEZE AND NIGHTTIME
LAND BREEZE REGIME THROUGH AT LEAST WEDNESDAY NIGHT. 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
THE CURRENT MODERATE, MEDIUM-PERIOD NORTH-NORTHWEST (330 DEGREE)
SWELL FILLED IN OVERNIGHT WELL ABOVE MODEL-PREDICTED VALUES AND IS
CURRENTLY STILL RUNNING AROUND 8 FEET AT 12 SECONDS. THEREFORE,
WILL EXTEND THE HIGH SURF ADVISORY (HSA) THROUGH MIDNIGHT TONIGHT
(HST). THE SWELL SHOULD DROP BELOW ADVISORY LEVEL LATER TONIGHT,
THEN CONTINUE TO FADE OVER THE NEXT FEW DAYS. THE SMALL CRAFT
ADVISORY HAS ALSO BEEN EXTENDED UNTIL MIDNIGHT TONIGHT FOR 10
FOOT SEAS IN AREAS EXPOSED TO THIS SWELL. A SMALL MEDIUM TO LONG-
PERIOD SWELL FROM THE NORTHWEST (320 DEG) IS EXPECTED TO FILL IN
MONDAY, PEAK TUESDAY AND DECLINE THROUGH THE MIDDLE OF NEXT WEEK.
THE CURRENT SMALL, LONG-PERIOD SOUTHWEST (210 DEG) SWELL WILL
CONTINUE TO SLOWLY DECLINE INTO EARLY NEXT WEEK. A SMALL, LONG-
PERIOD SOUTHWEST SWELL MAY ARRIVE LATE TODAY, AND BUILD INTO EARLY
NEXT WEEK BEFORE SUBSIDING. 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 OVER THE NEXT
SEVERAL DAYS, EVEN WITH THE SLIGHT BOOST TODAY WITH THE BRIEF
UPTICK IN TRADES.
HIGH PRESSURE THE NORTHEAST WILL CONTINUE TO BRING MODERATE EAST-
NORTHEAST TRADES TO THE REGION TONIGHT. A TROUGH IS EXPECTED TO
DEVELOP NORTHEAST OF THE STATE OVER THE NEXT COUPLE OF DAYS, AND
THEN MOVE TO THE SOUTHEAST, AND WILL WEAKEN WINDS TO LIGHT AND
VARIABLE THROUGH THE FIRST HALF OF NEXT WEEK.
FIRE WEATHER
LIGHT WINDS AND INCREASED SHOWERS WILL MITIGATE ANY FIRE WEATHER
CONCERNS THROUGH THE WEEK.
HFO WATCHES/WARNINGS/ADVISORIES
HIGH SURF ADVISORY UNTIL MIDNIGHT HST TONIGHT FOR NORTH AND WEST
FACING SHORES OF NIIHAU, KAUAI, OAHU, MOLOKAI, AND NORTH FACING
SHORES OF MAUI..
SMALL CRAFT ADVISORY UNTIL MIDNIGHT HST TONIGHT FOR KAUAI
NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-
KAUAI CHANNEL-OAHU WINDWARD WATERS-KAIWI CHANNEL-MAUI COUNTY
WINDWARD WATERS.
DISCUSSION...VAUGHAN
AVIATION...WALSH
MARINE...TS
FIRE WEATHER...VAUGHAN
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