280
FXHW60 PHFO 180142
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
342 PM HST WED SEP 17 2025
SYNOPSIS
LOCALLY BREEZY TRADES DELIVER LIMITED SHOWERS WINDWARD AND MAUKA
INTO THURSDAY. AN INCREASE IN SHOWERS IS THEN EXPECTED THURSDAY
NIGHT INTO THE WEEKEND FOLLOWED BY A RETURN TO DRIER AND MORE
STABLE TRADE WIND PATTERN THEREAFTER.
DISCUSSION
A CLOSED UPPER LOW POSITIONED NORTH OF KAUAI SUPPORTS A 55KT
SUBTROPICAL JET DRAPED OVER THE EASTERN END OF THE STATE AND
ASSOCIATED SOUTHWEST FLOW ALOFT IS ADVECTING HIGH CLOUDS OVER AND
SOUTH OF THE BIG ISLAND. AS THE LOW DRIFTS WESTWARD DURING THE NEXT
FEW DAYS, SO TOO WILL THE AXIS OF SW FLOW ALOFT RESULTING IN PATCHY
HIGH CLOUDS AREAWIDE FOR THE REST OF THE WEEK. THE LOW OTHERWISE
REMAINS INCONSEQUENTIAL THROUGH THE NEAR TERM AS IT RESIDES ABOVE
STRONGLY STABLE MID-LEVELS. AT THE SURFACE, A STABLE TRADE WIND
PATTERN PREVAILS WITH A FEW MODEST PATCHES OF MOISTURE POISED TO
BRING PERIODIC SHOWERS TO WINDWARD AND MAUKA AREAS THE NEXT COUPLE
OF NIGHTS.
UPSTREAM, AN ORPHANED COLD FRONT ALIGNED ALONG & SOUTH OF 30N
PRESENTS AS A NARROW RIBBON OF ENHANCED MOISTURE AVERAGING ABOUT
5KFT IN DEPTH EXCEPT WHERE DEEP CONVECTION EXISTS ALONG ITS
CONVERGENT LEAD EDGE. POCKETS OF THUNDERSTORMS HAVE BEEN COMMON
ALONG THIS BOUNDARY. AS THIS MOISTURE IS USHERED SOUTHWESTWARD
WITHIN PREVAILING TRADE WINDS, IT WILL INCREASINGLY ENCOUNTER A
HOSTILE MID-LEVEL ENVIRONMENT THAT WILL TEND TO ERODE THE DEEPEST
MOISTURE AND RESULT IN A TREND TOWARD DECREASING DEEP CONVECTION
AS IT APPROACHES THE ISLANDS. LOW-LEVEL CONVERGENCE ITSELF WILL
ALSO TEND TO DIMINISH WITH TIME GIVEN THE DEARTH OF MID-LEVEL
SUPPORT FOR THE FRONT. ONGOING BREEZY TRADES WILL FURTHER LIMIT
PROSPECTS FOR MEANINGFUL LOW-LEVEL CONVERGENCE ALONG WHICH DEEP
CONVECTION COULD ORGANIZE. WITH THAT SAID, THE RESIDENT UPPER LOW
WILL OFFER MID/UPPER LEVEL LAPSE RATES AROUND 6.5C/KM WITHIN A LOW
DENSITY CAPE PROFILE THAT WILL PROVIDE VERY MARGINAL SUPPORT FOR
ISOLATED THUNDERSTORMS WITHIN ANY POCKETS OF DEEPER MOISTURE, MOST
LIKELY OVER THE WESTERN END OF THE STATE AND AT NIGHT WHEN LAPSE
RATES ARE MAXIMIZED. LOW CONFIDENCE AT THIS JUNCTURE PRECLUDES
INCLUSION OF THUNDERSTORMS IN THE FORECAST OVER/AROUND OAHU &
KAUAI, BUT POPS HAVE BEEN BUMPED UP A BIT GIVEN HIGH CONFIDENCE IN
OVERALL SHOWER COVERAGE.
OF NOTE, GUIDANCE INDICATES ENE TO NE FLOW THROUGH 700MB FRIDAY
NIGHT WHICH IS FAVORABLE FOR DIRECTING MOISTURE TOWARD THE HAMAKUA
COAST OF THE BIG ISLAND, AN AREA IN NEED OF RAINFALL. GUIDANCE ALSO
INDICATES MOISTURE ARRIVAL PRIOR TO FULL DEVELOPMENT OF THE MOUNTAIN
BREEZE THAT WOULD OTHERWISE LIMIT RAINFALL POTENTIAL THERE.
A TYPICAL BREEZY TRADE WIND PATTERN THEN PREVAILS INTO NEXT WEEK.
AVIATION
LOCALLY BREEZY TRADE WINDS WILL CONTINUE FOR THE NEXT SEVERAL
DAYS. ALTHOUGH SOME CLOUDS AND SHOWERS EMBEDDED WITHIN THE TRADES
WILL BE POSSIBLE FOR WINDWARD AND MOUNTAIN AREAS, VFR FLIGHT
CONDITIONS ARE EXPECTED TO PREVAIL FOR MOST LOCATIONS.
AIRMET TANGO HAS BEEN ISSUED FOR MODERATE LOW LEVEL TURBULENCE
DOWNWIND OF ISLAND TERRAIN. THIS AIRMET WILL LIKELY BE NEEDED FOR
THE NEXT SEVERAL DAYS AS BREEZY TRADES PERSIST.
MARINE
SURFACE HIGH PRESSURE WILL REMAIN ANCHORED NORTH OF THE STATE FOR
THE NEXT SEVERAL DAYS AND BRING MODERATE TO LOCALLY STRONG TRADE
WINDS ACROSS THE WATERS. A BRIEF UPTICK OF WIND SPEEDS ARE
EXPECTED TONIGHT INTO THURSDAY WITH FRESH TO STRONG TRADES
EXPECTED ACROSS MANY COASTAL WATERS. HOWEVER, WINDS ARE EXPECTED
TO DECREASE BACK TO MODERATE TO LOCALLY STRONG SPEEDS BY FRIDAY
AS A FRONT DROPS SOUTH AND WEAKENS THE HIGH. WITH THE LATEST
HIGH-RES MODELS SHOWING A SLIGHT INCREASE OF WIND SPEEDS, THE
SMALL CRAFT ADVISORY HAS BEEN ADJUSTED TO INCLUDE MAUI WINDWARD
WATERS TONIGHT AND MAY NEED TO BE EXPANDED TO THE KAIWI CHANNEL
FOR THURSDAY. THESE ADVISORIES WILL LIKELY BE SCALED BACK TO THE
JUST THE TYPICAL WINDY AREAS AROUND MAUI AND THE BIG ISLAND FROM
FRIDAY ONWARD.
SURF ALONG SOUTH FACING SHORES WILL BE SMALL OVER THE NEXT FEW
DAYS WITH MAINLY BACKGROUND SOUTH AND SOUTHEAST ENERGY. A SMALL TO
MODERATE, LONG-PERIOD, SOUTH SOUTHWEST SWELL WILL BUILD SATURDAY
INTO SUNDAY AND HELP BOOST SOUTH SHORE SURF HEIGHTS BACK UP TO
NEAR OR ABOVE THE SEPTEMBER AVERAGE.
SURF ALONG NORTH FACING SHORES SHOULD SEE A SMALL INCREASE
TOMORROW AS A SHORT PERIOD NORTHERLY SWELL FILLS IN. THIS SMALL
BUMP IS EXPECTED TO PEAK ON FRIDAY OUT OF THE NORTH TO NORTH-
NORTHEAST DIRECTION, FOLLOWED BY A SHORT PERIOD NORTH NORTHWEST
SWELL THIS WEEKEND. MODERATE TO LOCALLY STRONG TRADES NEAR AND
UPSTREAM OF THE AREA WILL LEAD TO CHOPPY CONDITIONS ALONG EAST
FACING SHORES OVER THE NEXT SEVERAL DAYS. A SLIGHT INCREASE OF
WINDSWELL IS EXPECTED OVER THE WEEKEND DUE TO A FETCH OF STRONG
WINDS NORTHEAST OF THE STATE.
FIRE WEATHER
DECREASING FIRE WEATHER RISK AS HUMIDITY GRADUALLY INCREASES
THROUGH THE WEEK AND INTO THE WEEKEND. SHOWERS INCREASE IN
COVERAGE THURSDAY NIGHT INTO THE WEEKEND AS DEEP POCKETS OF
MOISTURE FILTER IN ON THE TRADES HELPING TO ALLEVIATE FIRE
WEATHER CONCERNS. SUSTAINED WINDS BRIEFLY HOVER NEAR TO BELOW THE
CRITICAL FIRE WEATHER THRESHOLD THROUGH THURSDAY AFTERNOON THEN
TREND SLIGHTLY LIGHTER FOR THE WEEKEND.
HFO WATCHES/WARNINGS/ADVISORIES
SMALL CRAFT ADVISORY UNTIL 6 AM HST THURSDAY FOR KAUAI LEEWARD
WATERS-KAUAI CHANNEL.
SMALL CRAFT ADVISORY UNTIL 6 PM HST THURSDAY FOR MAUI COUNTY
WINDWARD WATERS-MAALAEA BAY-PAILOLO CHANNEL-ALENUIHAHA CHANNEL-
BIG ISLAND LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.
DISCUSSION...JVC
AVIATION...VAUGHAN
MARINE...KINO
FIRE WEATHER...JVC
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