522
FXHW60 PHFO 260121
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
321 PM HST SUN OCT 25 2026
SYNOPSIS
NORTHEASTERLY TRADE WINDS WILL WEAKEN THROUGH MONDAY. BRIEF
PASSING SHOWERS WILL DRIFT INTO THE ISLANDS ON THE TRADE WINDS,
FAVORING WINDWARD AND MOUNTAIN AREAS DURING THE OVERNIGHT TO EARLY
MORNING HOURS. DEEP TROPICAL MOISTURE WILL BRING THE POTENTIAL
FOR HEAVY RAIN AND THUNDERSTORMS ACROSS THE STATE STARTING EARLY
TUESDAY AND LASTING THROUGH AT LEAST THURSDAY. THE FORECAST FOR
NEXT WEEKEND IS A RETURN OF TRADES BUT CONTINUED ABOVE-NORMAL
RAINFALL.
DISCUSSION
TRADE WINDS WERE STILL PRESENT THIS AFTERNOON, AVERAGING 10 TO 20
MPH, WITH A FEW GUSTS AROUND 25 MPH AT THE USUAL BREEZY SPOTS.
ISOLATED SHOWERS WERE NOTED ON RADAR, MOST NUMEROUS NEAR VOLCANO
ON THE BIG ISLAND, AND OVER NORTHEAST MOLOKAI. SKIES WERE THE
USUAL MIX OF MOSTLY SUNNY ALL THE WAY TO OVERCAST, WITH THE
MAJORITY OF THE CLOUDS WINDWARD AND MAUKA.
THERE'S A COMPLICATED WEATHER PATTERN OVER THE AREA, AND IT'S
JUST GOING TO GET MORE COMPLICATED OVER THE NEXT FEW DAYS. THIS
AFTERNOON, THERE'S A LARGE CLOSED LOW ABOUT 1000 MILES TO OUR
NORTHEAST. AT THE SURFACE, A CLOSED LOW SITS DIRECTLY BENEATH IT.
A FRONT EXTENDS TO THE EAST AND THEN SOUTH OF THE LOW, AND A
TROUGH EXTENDS SOUTHWEST FROM THE DECAYING END OF THE FRONT
TOWARD HAWAII. A SEPARATE UPPER LEVEL TROUGH TO OUR NORTHWEST WILL
MOVE SOUTHEAST, HELPING TO PUSH TROPICAL STORM OLANA TOWARD US.
THE GOOD NEWS IS THAT OLANA IS FORECAST TO WEAKEN BACK INTO A
DEPRESSION BY TUESDAY, AND THE REMNANTS ARE EXPECTED TO REMAIN
WEST OF THE STATE. THE TROUGH EXTENDING FROM THE LOW TO OUR
NORTHEAST WILL EVENTUALLY EXTEND ALL THE WAY TO THE REMNANTS OF
OLANA, AND THEN DRIFT NORTH OVER THE STATE. THE TROUGH WILL BRING
A GREAT DEAL OF MOISTURE WITH IT. PW VALUES ARE STILL FORECAST TO
BE CLOSE TO 2.5 INCHES, WHICH IS EXTREMELY HIGH.
THIS TROUGH WILL REMAIN NEARLY STATIONARY OVER THE AREA FROM
TUESDAY THROUGH THE END OF THE WEEK. A SERIES OF SMALL LOWS WILL
FORM AND SLIDE EAST, WITH ONE OR MORE POTENTIALLY MOVING OVER THE
STATE. MODELS SHOW DIFFERENT TIMINGS ON THESE FEATURES, BUT THE
POINT IS THAT EACH TIME ONE OF THESE LOWS MOVES ACROSS THE
IMMEDIATE AREA, THE WINDS WILL SHIFT DIRECTION AND DIFFERENT
PARTS OF EACH ISLAND WILL BRIEFLY BECOME "WINDWARD" AND "LEEWARD".
AS THE WIND BLOWS TOWARD THE MOUNTAINS, RAIN EFFICIENCY WILL
INCREASE, GIVING BRIEF INCREASES IN RAIN RATE AND THE POTENTIAL
FOR FLOODING. THE EXACT LOCATIONS AND TIMINGS OF THESE SUBTLE
FEATURES ARE NOT YET PREDICTABLE WITH ANY CONFIDENCE. THEREFORE,
THE QPF WILL UNDERGO (PERHAPS SIGNIFICANT) REVISION OVER THE NEXT
COUPLE OF DAYS. WE HAVE OPTED TO GO WITH ANOTHER HYDROLOGIC
STATEMENT TODAY DISCUSSING THE POTENTIAL FOR HEAVY RAIN, AS
OPPOSED TO A FLOOD WATCH. ONE OTHER CONSIDERATION IN THIS DECISION
IS THAT THE LATEST MODELS ARE SLOWER TO BRING HEAVY RAIN TO THE
STATE. IT NOW LOOKS LIKE IT SHOULD ARRIVE TUESDAY AS OPPOSED TO
MONDAY NIGHT.
AT THIS TIME, IT APPEARS THE THREAT OF HEAVY RAIN WILL EXTEND FROM
TUESDAY THROUGH THE END OF THE WEEK, AND POSSIBLY INTO THE
WEEKEND. OBVIOUSLY OUR CONFIDENCE GETS LOWER WITH TIME, SO THE
CURRENT FORECAST DOES NOT EXPLICITLY DEPICT HIGH POPS AND HEAVY
RAIN BEYOND THURSDAY. THE BEST CHANCE FOR HEAVY RAIN APPEARS TO BE
FROM TUESDAY AFTERNOON THROUGH WEDNESDAY AFTERNOON, BUT I WOULDN'T
BE SURPRISED IF THAT ENDED UP BEING EXTENDED INTO THURSDAY OR EVEN
FRIDAY. TOTAL RAINFALL AMOUNTS IN OUR QPF GRIDS FROM TUESDAY
THROUGH THURSDAY, USING BROAD NUMBERS, CURRENTLY RANGE FROM 2 TO 8
INCHES, WITH THE HIGHEST AMOUNTS IN THE HIGHER ELEVATIONS. THESE
NUMBERS WILL CHANGE OVER THE NEXT FEW DAYS AS HIGHER RESOLUTION
GUIDANCE BECOMES AVAILABLE (WHEN THE FORECAST IS WITHIN 48 HOURS,
GENERALLY).
THERE IS ALSO A CHANCE OF THUNDERSTORMS AT TIMES DURING THIS
PERIOD, BUT WE HAVE ADJUSTED THE WORDING FROM "SCATTERED" TO
"ISOLATED", INDICATING A SLIGHT LESSENING OF THE THREAT BASED ON
THE LATEST GUIDANCE. UPPER LEVEL TEMPERATURES ARE COLD ENOUGH FOR
THUNDERSTORMS, ESPECIALLY CONSIDERING THE HIGH MOISTURE CONTENT OF
THE ATMOSPHERE, BUT IT'S CLOSE. WE FEEL THAT ISOLATED SHOULD BEST
CONVEY WHAT WE'RE THINKING AT THIS TIME. AS WITH ANY THUNDERSTORM,
BRIEF GUSTY WINDS ARE POSSIBLE, BUT OVERALL THIS SETUP SHOULD NOT
BRING STRONG WINDS TO LARGE AREAS OF THE STATE.
AVIATION
MODERATE TRADE WINDS WILL PREVAIL THE REST OF TODAY WITH SOME
ISOLATED BREEZY CONDITIONS AT PNHY AND PHMK. OTHERWISE, WINDWARD
AND MOUNTAIN AREAS ON BIG ISLAND WILL SEE AN INCREASE IN SHOWERS
WHICH MAY CAUSE TEMPORARY MVFR CEILINGS AND VISIBILITIES IN ANY
SHOWER THAT PASSES THROUGH.
MODERATE TURBULENCE HAS BEEN REPORTED BETWEEN 23,000 AND 34,000
FEET OVER THE OPEN WATER AREAS NORTH AND EAST OF THE ISLANDS. THE
MODERATE NATURE AND FORECAST FOR CONTINUED WEAKENING OF THE WINDS
PRECLUDE ANY AIRMET OR SIGMET HEADLINES AT THIS TIME.
LOOKING AHEAD, WIDESPREAD MVFR/IFR CONDITIONS IN HEAVY SHOWERS AND
LOW CEILINGS ARE POSSIBLE BEGINNING LATE MONDAY NIGHT INTO
TUESDAY MORNING; SEE THE MAIN DISCUSSION FOR DETAILS ON THE
UPCOMING HEAVY RAIN AND FLOODING POTENTIAL.
MARINE
A SURFACE LOW FAR NORTHEAST OF THE HAWAIIAN ISLANDS WILL CONTINUE
TO DIG SOUTH TONIGHT AND STALL ROUGHLY 800 NM NORTHEAST OF THE
STATE BY MONDAY, RESULTING IN RELATIVELY WEAK WIND FLOW ACROSS THE
AREA THIS WEEK. A LOW PRESSURE TROUGH WILL THEN APPROACH THE AREA
FROM THE SOUTHWEST LATE MONDAY AND BRING HEAVY SHOWERS WITH EMBEDDED
THUNDERSTORMS TO THE WATERS OVER THE NEXT SEVERAL DAYS. WINDS MAY
BECOME LOCALLY BREEZY ALONG THE TROUGH AND AROUND SHOWERS.
A SHORT PERIOD NORTH NORTHWEST SWELL WILL GRADUALLY LOWER OVER
THE NEXT COUPLE OF DAYS. AN OVERLAPPING, MODERATE, MID-PERIOD
NORTHWEST SWELL IS EXPECTED TO BUILD THROUGH THE DAY MONDAY, WITH
SURF REACHING NEAR ADVISORY ALONG NORTH AND WEST FACING SHORES
THROUGH WEDNESDAY. A SMALL NORTH NORTHEAST SWELL SHOULD ARRIVE
DURING THE SECOND HALF OF THE WEEK.
OVERLAPPING SOUTH-SOUTHWEST SWELLS WILL KEEP SURF ALONG SOUTH-FACING
SHORES TO AROUND SEASONAL AVERAGES THROUGH TUESDAY. A LARGER SOUTH
SWELL MAY PUSH SURF UP TO NEAR ADVISORY LEVELS THURSDAY AND FRIDAY.
SURF ALONG MOST EAST-FACING SHORES WILL BE SMALL THROUGH EARLY
NEXT WEEK, BUT AREAS EXPOSED TO WRAPPING NORTHERLY SWELLS WILL
EXPERIENCE PERIODS OF MODERATE SURF THROUGH MONDAY. EAST-FACING
SHORES SHOULD ALSO SEE A BUMP IN SURF IF THE NORTH-NORTHEAST
SWELL MATERIALIZES DURING THE LATTER HALF OF THIS WEEK.
FIRE WEATHER
MODERATE TRADE WINDS WITH MOSTLY DRY CONDITIONS OVER LEEWARD
AREAS WILL CONTINUE TO PRODUCE LOW TO MODERATE FIRE WEATHER
CONDITIONS THROUGH MONDAY. DEEP TROPICAL MOISTURE WILL MOVE IN
MONDAY NIGHT OR TUESDAY, BRINGING A THREAT FOR HEAVY RAIN THROUGH
AT LEAST THURSDAY. AS A RESULT, FIRE WEATHER CONCERNS WILL BE LOW
THROUGH MOST OF NEXT WEEK. INVERSION HEIGHTS WILL RANGE FROM
8000-9000 FEET FROM MAUI TO THE BIG ISLAND TONIGHT.
HFO WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...PARKER
AVIATION...PECHACEK
MARINE...FOSTER
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