158
FXHW60 PHFO 181309
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
309 AM HST TUE NOV 18 2025
SYNOPSIS
AN UPPER LEVEL LOW SOUTHWEST OF THE ISLANDS WILL PULL MOISTURE
OVER THE EASTERN HALF OF THE STATE THROUGH TUESDAY. THIS FEATURE,
ALONG WITH A DEVELOPING SURFACE TROUGH, WILL BRING AN INCREASED
CHANCE OF HEAVIER SHOWERS TUESDAY NIGHT THROUGH WEDNESDAY,
ESPECIALLY FOR WINDWARD PORTIONS OF MAUI AND THE BIG ISLAND.
THE CHANCE OF HEAVY RAINFALL DIMINISHES LATE WEDNESDAY INTO
THURSDAY, THOUGH BREEZY SHOWERY TRADES WILL PERSIST. A BRIEF
PERIOD OF STABLE AND DRIER TRADE WIND CONDITIONS IS EXPECTED ON
FRIDAY, FOLLOWED BY MORE SHOWERY WEATHER INTO THE WEEKEND AS A
COLD FRONT ADVANCES TOWARD THE ISLAND CHAIN.
DISCUSSION
LATEST SATELLITE IMAGERY SHOWS THICK MID TO UPPER LEVEL CLOUDS
STREAMING IN FROM THE SOUTHWEST FROM OAHU TO THE BIG ISLAND
CAUSING OVERCAST CONDITIONS. NEAR THE SURFACE, MODERATE TRADES
CONTINUE TO PUSH TYPICAL SCATTERED SHOWERS ALONG WINDWARD AND
MAUKA AREAS ESPECIALLY OVER THE WESTERN END OF THE STATE AS
EVIDENT ON RADAR. MEANWHILE ON THE EASTERN END OF THE STATE SOME
SHOWERS ARE BEGINNING TO FALL ACROSS EAST AND SOUTHEAST PORTIONS
OF THE BIG ISLAND. WITH FREEZING LEVELS AROUND 13KFT TO 14KFT
A WINTRY MIX OF RAIN AND SNOW AT THE SUMMITS OF MAUNA LOA AND
MAUNA KEA IS POSSIBLE. A WINTER WEATHER ADVISORY REMAINS IN EFFECT
THROUGH 6PM THIS EVENING.
AN UPPER LEVEL TROUGH TO THE NORTHWEST DEEPENS AND A SURFACE
TROUGH TO THE SOUTHWEST OF THE BIG ISLAND, WILL CONTINUE TO
PRODUCE UNSTABLE CONDITIONS ALOFT. THIS IS CONDUCIVE TO SOME HEAVY
RAIN DEVELOPING SOUTH OF THE BIG ISLAND, IN ASSOCIATION WITH THE
AFOREMENTIONED SURFACE TROUGH. HOWEVER, UNCERTAINTY REMAINS AN
ISSUE. THE GFS IS STILL A LITTLE MORE BULLISH WITH THE INTENSITY
THAN THE ECWMF, THOUGH IT HAS BEEN TRENDING SLIGHTLY WEAKER WITH
THE LAST COUPLE RUNS. THIS POCKET OF DEEP MOISTURE SHOULD LIFT
NORTHWARD LATE TONIGHT INTO WEDNESDAY, CAUSING CONDITIONS TO
DETERIORATE FURTHER FOR WINDWARD PORTIONS OF THE BIG ISLAND AND
MAUI. STRONG TRADES, COMBINED WITH DEEP MOISTURE AND INSTABILITY
ALOFT, MAY LEAD TO A PERIODS OF HEAVY RAINFALL FOR THESE AREAS AND
A FLOOD WATCH MAY BE NEEDED LATE TONIGHT THROUGH WEDNESDAY. THE
LIMITING FACTOR WILL BE IF CURRENT TRENDS HOLD, FLOODING WILL BE
LIMITED AND THE FLOOD WATCH WOULDN'T BE NECESSARY. FORECAST
RAINFALL TOTALS CURRENTLY RANGE FROM AROUND AN INCH WITH THE
ECMWF'S WEAKER FORCING TO AROUND TWO INCHES FROM THE GFS.
AS FOR THE REST OF THE ISLANDS, TONIGHT THROUGH WEDNESDAY, THE
SURFACE HIGH BUILDING FAR NORTH OF THE STATE WILL BRING STRONG
TRADES WITH SCATTERED TO NUMEROUS SHOWERS THAT WILL AFFECT BOTH
WINDWARD AND LEEWARD SIDES OF THE ISLANDS. THE FLOODING THREAT
REMAINS LOW OVER THE SMALLER ISLANDS DUE TO THE SPEED THESE
SHOWERS WILL BE MOVING AND THE LACK OF FORCING.
ANY POTENTIAL THREAT FOR HEAVY RAIN WILL DECREASE LATE WEDNESDAY,
BUT BREEZY AND WET CONDITIONS ARE EXPECTED INTO THURSDAY. THE
STRONG SURFACE HIGH PASSING TO THE NORTH WILL MAINTAIN BREEZY
TRADE WINDS, AND EVEN THOUGH PWATS WILL BE DECREASING, BOTH THE
GFS AND ECMWF KEEP ABUNDANT MOISTURE AROUND THE ISLANDS,
POINTING TO A RATHER WET PATTERN.
A BRIEF PERIOD OF STABLE AND DRIER TRADE WIND CONDITIONS IS
EXPECTED ON FRIDAY, FOLLOWED BY THE POTENTIAL FOR MORE SHOWERY
WEATHER INTO THE WEEKEND AND EARLY NEXT WEEK AS A COLD FRONT
APPROACHES THE ISLAND CHAIN. ONCE AGAIN MODELS VARY ON TIMING AND
LOCATION SO PLEASE PAY ATTENTION FOR FURTHER UPDATES.
AVIATION
TRADES WILL STRENGTHEN AND BACK TO THE EAST NORTHEAST. LOW CIGS
AND TRADE WIND SHRA WILL BE FOCUSED OVER WINDWARD AND MAUKA
LOCATIONS. AS DEEPER MOISTURE STREAMS UP FROM THE SOUTHEAST, SHRA
WILL INCREASE ACROSS THE ISLAND CHAIN. IFR/MVFR CONDS ARE POSSIBLE
IN THESE HEAVIER SHRA. SOME LOCATIONS ON THE WESTERN SIDE OF THE
STATE MAY STAY VFR.
AIRMET SIERRA WHILE NOT IN EFFECT AT THIS TIME, WILL LIKELY BE
NEEDED FOR PORTIONS OF THE ISLAND CHAIN THROUGH THURSDAY.
AIRMET TANGO IS IN EFFECT FOR MOD TURB IN THE MID TO UPPER
LEVELS.
AIRMET ZULU IS IN EFFECT FOR SOME LIGHT ICING DUE TO THE INFLUX
OF HIGH CLOUDS.
MARINE
A FRONT ABOUT 600 NM MILES NORTHWEST OF THE KAUAI COASTAL WATERS
(ABOUT 450 NM NORTHWEST OF THE OFFSHORE WATERS) WILL CONTINUE TO
MOVE TO THE EAST AND APPROACHING THE REGION OVER THE NEXT COUPLE
OF DAYS. THE FRONT IS PUSHING THE RIDGE TO THE NORTH OF THE REGION
TO THE EAST WHICH WILL RESULT IN A WEAKENING OF THE WINDS TODAY,
AS THE WINDS ALSO VEER TO THE EAST-SOUTHEAST. THE FRONT IS
EXPECTED TO WEAKEN AS IT ENTERS THE NORTHWEST OFFSHORE WATERS
LATER TODAY, AND THEN LIFT TO THE NORTH TONIGHT AND TOMORROW. NEAR
GALE-FORCE WINDS ARE POSSIBLE BEHIND THE FRONT IN THE NORTHWEST
OFFSHORE WATERS. AN UPPER LEVEL TROUGH OVER THE ISLANDS, COMBINED
WITH MOISTURE SURGING NORTHWARD ON THE EAST SIDE OF SAID UPPER
TROUGH COULD PRODUCE THUNDERSTORMS OVER THE OFFSHORE WATERS.
BEHIND THE FRONT, A NEW HIGH BUILDING NORTH OF THE ISLANDS WILL
HELP TRADES STRENGTHEN ACROSS THE REGION TO FRESH TO LOCALLY NEAR
GALE SPEEDS. COMBINED WITH INCOMING NORTHWESTERLY SWELLS, EXPECT
WINDS AND SEAS TO EXCEED SMALL CRAFT ADVISORY (SCA) THRESHOLDS
FOR EXPOSED COASTAL WATERS WEDNESDAY INTO THURSDAY. SOME OF THE
HIGH RESOLUTION MODELS SUGGEST THAT SCA LEVEL WINDS COULD REACH
SOME OF THE TYPICAL WINDIER WATERS LATER TODAY, HOWEVER WITH
CONFIDENCE LOW, AM HOLDING OFF ON ISSUING THE SCA AT THIS TIME.
A SMALL, SHORT PERIOD NE AND SMALL, MEDIUM PERIOD NW SWELL WILL
CONTINUE TO SLOWLY DECLINE THIS MORNING. OVERLAPPING NW TO NNW
SWELLS REST OF THIS WEEK WILL KEEP SURF HEIGHTS BOOSTED ALONG
EXPOSED N AND W FACING SHORES. A PAIR OF SMALL TO MODERATE, LONG
PERIOD NNW (310-340 DEGREE) SWELLS WILL ARRIVE TODAY, PEAKING
WEDNESDAY NEAR OR ABOVE HIGH SURF ADVISORY (HSA) LEVELS. BUOY
51001 STARTED TO PICK UP THE 16 SECOND ENERGY AROUND 1AM, AROUND
THE SAME TIME THE WAVEWATCH GUIDANCE SUGGESTED, BUT A LITTLE
SMALLER THAN GUIDANCE. SURF IS THEN EXPECTED TO GRADUALLY
DECLINING WEDNESDAY NIGHT THROUGH THE END OF THE WEEK. ANOTHER
OVERLAPPING SMALL, SHORT TO MEDIUM PERIOD N (350-010 DEGREE) SWELL
ARRIVES FROM THURSDAY INTO FRIDAY. THEN ANOTHER MODERATE, LONG
PERIOD NW (310-330 DEGREE) SWELL ARRIVES FRIDAY, PEAKING NEAR HSA
THRESHOLDS OVER THE WEEKEND.
SURF ALONG E FACING SHORES WILL CONTINUE THIS MORNING DUE TO THE
WEAKENING OF THE LOCAL AND UPSTREAM TRADE WINDS. AS A NEW HIGH
PRESSURE BUILDS N OF THE STATE WEDNESDAY THROUGH THURSDAY, ROUGH
AND CHOPPY SURF ALONG E SHORES COULD NEAR HSA LEVELS. FOR S
SHORES, PERIODS OF TINY BACKGROUND SOUTH SWELL ENERGY WILL
CONTINUE TO MOVE THROUGH KEEPING SURF FROM GOING FLAT.
FIRE WEATHER
MODERATE TRADES AND HIGHER HUMIDITIES WILL MAINTAIN CONDITIONS
BELOW CRITICAL FIRE WEATHER THRESHOLDS. WET CONDITIONS ARE
EXPECTED INTO THURSDAY, WITH HEAVY RAINFALL POSSIBLE OVER RECENT
BURN AREAS ON THE BIG ISLAND.
HFO WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL 6 PM HST THIS EVENING FOR BIG
ISLAND SUMMITS.
DISCUSSION...WALSH
AVIATION...WALSH
MARINE...M BALLARD
FIRE WEATHER...WALSH
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