306
FXHW60 PHFO 221954
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
954 AM HST TUE SEP 22 2026
SYNOPSIS
MODERATE TRADES THIS MORNING WILL GRADUALLY STRENGTHEN EACH DAY
OVER THE NEXT SEVERAL DAYS WITH WIDESPREAD STRONG TRADES EXPECTED
BY THURSDAY AND VERY WINDY CONDITIONS POSSIBLE ON FRIDAY. THE
MAIN FOCUS FOR THE WEATHER THIS WEEK WILL BE THE TROPICAL CYCLONE
DEVELOPMENT SOUTHEAST OR SOUTH OF THE BIG ISLAND OVER THE NEXT
FEW DAYS. WHILE THE POTENTIAL WIND IMPACTS REMAIN UNCERTAIN, THE
THREAT FOR FLASH FLOODING WILL INCREASE OVER THE BIG ISLAND DURING
THE SECOND HALF OF THE WEEK.
SHORT TERM UPDATE
NO CHANGES ARE PLANNED THIS MORNING. RADAR
AND SATELLITE SHOWED THE USUAL FOR A TRADE WIND REGIME...WITH
MOSTLY CLOUDY SKIES AND ISOLATED SHOWERS WINDWARD AND MAUKA, AND
MOSTLY SUNNY SKIES LEEWARD. WINDS WERE AVERAGING 5 TO 15 MPH IN
MOST AREAS, WITH THE TYPICAL WINDIEST SPOTS BLOWING 10 TO 20 MPH
WITH GUSTS 20 TO 30 MPH.
THE LATEST GUIDANCE HAS NOT REALLY CHANGED THE OVERALL
EXPECTATIONS FOR TD 15E (FUTURE NOLO). ENSEMBLES STILL SHOW A WIDE
VARIETY OF SOLUTIONS, WITH SOME MOVING OVER PART(S) OF THE STATE,
BUT MOST MISSING A DIRECT LANDFALL. SHOWERS AND/OR ISOLATED
THUNDERSTORMS MAY BEGIN TO BRING HEAVY RAIN TO THE BIG ISLAND AND
WINDWARD MAUI POTENTIALLY BEGINNING LATE WEDNESDAY. THERE IS
HIGHER CONFIDENCE IN HAVING PRECIPITATION RAMP UP WEDNESDAY NIGHT.
ONCE IT BEGINS, THE TRACK WILL DETERMINE HOW LONG IT WILL LAST AND
HOW MUCH RAIN WE SEE. AND AT THIS TIME, THERE IS A LARGE AMOUNT OF
UNCERTAINTY IN THE FORECAST TRACK. BECAUSE THE STORM IS EXPECTED
TO BEGIN TO FORM TODAY, WE SHOULD SEE SOME CONVERGENCE IN
SOLUTIONS TONIGHT AND TOMORROW, BUT WITH WEAK STEERING FLOW, WE
THINK THERE WILL CONTINUE TO BE A LARGE UNCERTAINTY IN THE TRACK
AS WE WORK THROUGH THE NEXT FEW DAYS. FOR NOW, OUR MAIN CONCERNS
ARE HEAVY RAIN AND INCREASING WINDS. A FLOOD WATCH WILL LIKELY BE
ISSUED THIS AFTERNOON, AND WIND ADVISORIES OR WARNINGS MAY BE
NEEDED LATER IN THE WEEK.
PREV DISCUSSION
ISSUED AT 414 AM HST TUE SEP 22 2026
THIS MORNING'S SATELLITE AND RADAR IMAGERY SHOWS SOME SCATTERED
SHOWERS RIDING IN WITH THE MODERATE TRADES OVER WINDWARD AND MAUKA
AREAS. FOR TODAY, WHILE CONDITIONS ARE STABLE, WE ARE SEEING
HIGHER THAN NORMAL MOISTURE LEVELS AS SEEN IN THE 12Z SOUNDINGS
FROM LIHUE AND HILO. THIS WILL ALLOW FOR SOME BRIEF DOWNPOURS AT A
FEW WINDWARD AND MOUNTAIN AREAS. OTHERWISE, WE SHOULD SEE A FAIRLY
TYPICAL TRADE WIND DAY WITH BREEZY TRADES RETURNING BY LATER THIS
AFTERNOON.
THIS WEEK'S FORECAST REMAINS VERY CHALLENGING AND WILL BE HIGHLY
DEPENDENT ON THE FORMATION OF A TROPICAL CYCLONE NEAR THE BIG
ISLAND OVER THE NEXT SEVERAL DAYS. LATEST TROPICAL WEATHER OUTLOOK
FROM THE NATIONAL HURRICANE CENTER HAS A HIGH CHANCE OF FORMATION
OVER THE NEXT 48 HOURS. WHILE STRONG SHEAR HAS BEEN KEEPING THE
SYSTEM FROM GETTING ORGANIZED, THE MODELS DO SHOW A DECREASE OF
WINDSHEAR OVER THE NEXT 24 TO 36 HOURS. SO THE EXPECTATION IS FOR
THE THUNDERSTORMS SOUTHEAST OF THE BIG ISLAND TO BECOME BETTER
ORGANIZED WITH A TROPICAL DEPRESSION LIKELY TO FORM OVER THE NEXT
DAY OR TWO.
AROUND THURSDAY, GLOBAL MODELS AND THE LATEST ENSEMBLES ARE
SHOWING THE POTENTIAL TROPICAL CYCLONE DRIFTING NORTHWARD TOWARDS
THE BIG ISLAND AS IT REACHES THE WESTERN PERIPHERY OF A
SUBTROPICAL RIDGE OF HIGH PRESSURE. AT THIS TIME, THERE IS STILL
HIGH UNCERTAINTY ON THE STRENGTH AND POSITION OF THIS POTENTIAL
TROPICAL CYCLONE AS IT SLOWLY DRIFTS NORTHWARD. WHILE THERE IS A
GREAT DEAL OF UNCERTAINTY, THERE IS A SIGNIFICANT POTENTIAL FOR A
PROLONGED HEAVY RAIN EVENT OVER WINDWARD AND SOUTHEAST BIG ISLAND
DUE TO THE DEEP TROPICAL MOISTURE AND WEAK STEERING FLOW. WHILE
THERE IS A LOT OF MOISTURE AVAILABLE, DUE TO THE HIGH UNCERTAINTY
ON THE INTENSITY OF THE POTENTIAL TROPICAL CYCLONE, RAINFALL RATES
REMAIN VERY UNCERTAIN. WHILE TROPICAL MOISTURE COULD BEGIN
IMPACTING WINDWARD AND SOUTHEAST BIG ISLAND AS EARLY AS WEDNESDAY,
THE HEAVIER RAIN RATES LOOKS TO BE MORE THURSDAY INTO FRIDAY, THUS
WE HELD OFF ON A FLOOD WATCH FOR THE BIG ISLAND FOR NOW. A FLOOD
WATCH WILL BE ISSUED FOR THE BIG ISLAND EVENTUALLY, AS WE GET A
BETTER HANDLE ON THE POTENTIAL TROPICAL CYCLONE DEVELOPMENT.
AS FOR THE POTENTIAL WIND IMPACTS, WHILE THERE IS HIGH
UNCERTAINTY, THERE IS A HIGH LIKELIHOOD OF AT LEAST WINDY TRADES
BY FRIDAY OF THIS WEEK WITH GUSTS OF 50 MPH TO EVEN 60 MPH
POSSIBLE OVER THE TYPICAL WINDY AREAS AROUND THE EASTERN HALF OF
THE STATE. THE POTENTIAL FOR STRONGER WIND GUSTS WILL BE HIGHLY
DEPENDENT ON THE TROPICAL CYCLONE DEVELOPMENT.
AVIATION
BREEZY TRADE WINDS CONTINUE TODAY. MOISTURE GRADUALLY INCREASES
TONIGHT INTO TOMORROW DUE TO A DISTURBANCE SOUTHEAST OF HAWAII.
RAIN SHOWERS ARE LIKELY TO IMPACT EASTERN AND WINDWARD AREAS OF
THE BIG ISLAND EARLY TOMORROW MORNING WITH PERIODS OF MVFR
CEILINGS AND VISIBILITY POSSIBLE IN HEAVIER SHOWERS. HIGHEST
CONFIDENCE IN IMPACTS AT PHTO EARLY WEDNESDAY WITH IMPACTS
GRADUALLY SPREADING NORTHWARDS LATE WEDNESDAY INTO THURSDAY.
AIRMET SIERRA IS IN EFFECT FOR MOUNTAIN OBSCURATION AND WILL
LIKELY BE EXTENDED.
AIRMET TANGO IS IN EFFECT FOR LOW LEVEL TURBULENCE DOWNWIND OF
ISLAND TERRAIN AND WILL LIKELY BE NEEDED THROUGH THE DAY.
MARINE
THE GRADIENT BETWEEN THE SUBTROPICAL HIGH TO THE NORTHEAST A LOW
PRESSURE SYSTEM (A DEVELOPING TROPICAL CYCLONE) TO THE SOUTHEAST
IS CAUSING MODERATE TO FRESH TRADE WINDS ACROSS THE HAWAIIAN
COASTAL WATERS TODAY. A SMALL CRAFT ADVISORY (SCA) IS IN EFFECT
FOR THE TYPICAL WINDY WATERS OF MAUI COUNTY AND THE BIG ISLAND
THROUGH EARLY WEDNESDAY EVENING. THE SCA WILL LIKELY BE EXTENDED
AND EXPANDED TO ALL COASTAL WATERS AS TRADE WINDS STRENGTHEN
DURING THE SECOND HALF OF THE WEEK AND THIS WEEKEND AS THE
TROPICAL CYCLONE ORGANIZES AND APPROACHES THE COASTAL WATERS FROM
THE SOUTHEAST. SHOWERS AND THUNDERSTORMS WILL INCREASE AS THE
SYSTEM NEARS, PARTICULARLY ACROSS THE EASTERN WATERS.
SURF ALONG SOUTH FACING SHORES WILL DECREASE INTO MIDWEEK AS THE
CURRENT SOUTH-SOUTHWEST SWELL FADES. A MODERATE SOUTHWEST SWELL
WILL BUILD IN AROUND FRIDAY INTO THE WEEKEND BUILDING SURF BACK UP
ACROSS SOUTH AND WEST FACING SHORES.
A SMALL, SHORT PERIOD, NORTH NORTHWEST SWELL WILL FADE THROUGH
WEDNESDAY. ANOTHER SMALL NORTHWEST SWELL WILL FILL IN THIS WEEKEND
KEEPING SURF SLIGHTLY ELEVATED ALONG NORTH AND WEST FACING SHORES.
EAST FACING SHORES WILL MAINTAIN ROUGH, SHORT PERIOD WINDWAVES
GENERATED FROM THE BREEZY TRADE WINDS. AS TRADES STRENGTHEN ON THURSDAY
THROUGH THE WEEKEND, SURF WILL INCREASE AND BECOME VERY ROUGH AND
CHOPPY, POSSIBLY NEARING ADVISORY LEVELS.
FIRE WEATHER
ISSUED AT 414 AM HST TUE SEP 22 2026
BREEZY TRADES WILL RETURN BY THIS AFTERNOON AND STEADILY
STRENGTHEN EACH DAY OVER THE NEXT SEVERAL DAYS. WITH WINDS
STRENGTHENING, MODERATE FIRE WEATHER CONDITIONS WILL BE POSSIBLE
THIS WEEK MAINLY OVER DRIER LEEWARD AREAS. THE INVERSION IS AROUND
5000 FEET THIS MORNING, BUT WILL RISE OVER THE EASTERN END OF THE
STATE WEDNESDAY AS DEEPER MOISTURE MOVES IN.
HFO WATCHES/WARNINGS/ADVISORIES
SMALL CRAFT ADVISORY UNTIL 6 PM HST WEDNESDAY FOR ALENUIHAHA
CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS-
MAALAEA BAY-PAILOLO CHANNEL.
SHORT TERM UPDATE...PARKER
DISCUSSION...KINO
AVIATION...KENNEDY
MARINE...FOSTER
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