431
FXHW60 PHFO 091339
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
339 AM HST TUE SEP 9 2025
SYNOPSIS
TROPICAL STORM KIKO WILL CONTINUE TO PASS NORTH OF THE ISLANDS
TODAY AND WEDNESDAY, DISRUPTING THE TRADE WINDS, PRODUCING AREAS
OF HEAVY RAINFALL, AND GENERATING LARGE SURF ALONG EAST FACING
SHORES. MODERATE TRADE WINDS AND A TYPICAL PATTERN OF WINDWARD
RAINFALL WILL RETURN ON THURSDAY THROUGH EARLY NEXT WEEK.
DISCUSSION
THIS MORNING'S RADAR AND SATELLITE IMAGERY SHOW A BAND OF DEEP
TROPICAL MOISTURE WORKING ITS WAY ACROSS OAHU AND KAUAI. THIS
FEATURE BROUGHT A ROUND OF SHOWERS FROM EAST TO WEST ACROSS THE
ISLAND CHAIN OVERNIGHT, SOME OF WHICH PRODUCED BRIEF HEAVY
DOWNPOURS WITH SEVERAL LOCATIONS RECEIVING ABOUT A QUARTER OF AN
INCH OF RAIN.
AS OF 3:00 AM HST THIS MORNING, TROPICAL STORM KIKO WAS LOCATED
A LITTLE OVER 200 MILES NE OF HILO, MOVING WEST-NORTHWEST AND
CONTINUING TO WEAKEN. WHILE NO DIRECT IMPACTS TO HAWAII ARE
EXPECTED FROM THIS TROPICAL CYCLONE, ITS ACCOMPANYING TROPICAL
AIRMASS WILL CONTINUE TO PROVIDE DEEP MOISTURE TO THE STATE
THROUGH WEDNESDAY. AS KIKO PASSES TO THE NORTH, IT WILL SHUT DOWN
THE TRADES ACROSS THE EASTERN HALF OF THE STATE TODAY AND THE
WESTERN HALF BY THIS EVENING. THIS LIGHTER WIND PATTERN WILL ALLOW
FOR SEA BREEZES TO DEVELOP, WHICH WILL KICK OFF MIDDAY LEEWARD
AND INTERIOR SHOWERS. GIVEN THE ABUNDANT AVAILABLE MOISTURE AND
INSTABILITY PROVIDED BY A BROAD UPPER LEVEL LOW NORTHWEST OF
KAUAI, SOME OF THESE SHOWERS COULD PRODUCE BRIEF HEAVY DOWNPOURS,
WITH AN ISOLATED THUNDERSTORM OR TWO POSSIBLE OVER INTERIOR
PORTIONS OF THE BIG ISLAND.
MODERATE EAST-SOUTHEASTERLY TRADES WILL GRADUALLY REBUILD FROM
EAST TO WEST ACROSS THE ISLAND CHAIN LATE TONIGHT INTO WEDNESDAY
AS KIKO FURTHER CLEARS THE AREA AND THE SURFACE HIGH TO THE
NORTHEAST REGAINS CONTROL. HOWEVER, LINGERING TROPICAL MOISTURE
AND INSTABILITY FROM THE UPPER LEVEL LOW WILL KEEP THE ATMOSPHERE
PRIMED FOR ADDITIONAL SHOWER ACTIVITY ON WEDNESDAY. SEA BREEZE
ACTIVITY OVER THE WESTERN END OF THE STATE MAY BRING ANOTHER
ROUND OF BRIEF HEAVY AFTERNOON SHOWERS TO INTERIOR AND LEEWARD
PORTIONS OF KAUAI AND OAHU BEFORE THE TRADES BUILD BACK IN.
A MORE TYPICAL TRADE WIND PATTERN IS EXPECTED THURSDAY THROUGH
EARLY NEXT WEEK AS MID LEVEL RIDGING RETURNS AND DRIER AIR
FILTERS IN. IN THIS REGIME, MODERATE TRADES WILL FOCUS LIGHT
SHOWERS OVER WINDWARD AND MAUKA AREAS, DURING THE OVERNIGHT AND
EARLY MORNING HOURS, WITH LEEWARD AREAS REMAINING MOSTLY DRY.
AVIATION
TROPICAL STORM KIKO WILL PASS NORTH OF THE ISLAND CHAIN TODAY AND
ACT TO DISRUPT TYPICAL TRADE WIND FLOW. LIGHT WINDS, ESPECIALLY
ALONG THE LEEWARD COASTS, WILL ALLOW FOR THE DEVELOPMENT OF A
NOCTURNALLY DRIVEN SEA BREEZE/LAND BREEZE PATTERN. OUT AHEAD OF
THE TROPICAL SYSTEM, INCREASING MOISTURE AND INSTABILITY WILL AID
IN THE DEVELOPMENT OF MAINLY INTERIOR AFTERNOON AND EVENING
SHOWERS. SOME OF THE SHOWERS COULD BE HEAVY WITH ASSOCIATED
MVFR AND ISOLATED IFR CEILINGS AND VISIBILITY. IN ADDITION,
ENOUGH INSTABILITY MAY EXIST FOR SOME POP UP THUNDERSTORMS OVER
INTERIOR PORTIONS OF THE BIG ISLAND. VFR CONDITIONS EXPECTED
ELSEWHERE.
AIRMET SIERRA FOR MTN OBSC IS IN EFFECT FOR NORTH THROUGH EAST
SECTIONS OF KAUAI, OAHU, MOLOKAI, AND MAUI ABOVE 2000 FT. SOME
IMPROVEMENT IS EXPECTED LATER THIS MORNING, THOUGH AIRMET SIERRA
MAY BE NEEDED FOR INTERIOR SECTIONS OF THE ISLANDS THIS AFTERNOON.
MARINE
NO SIGNIFICANT CHANGES TO THE FORECAST THIS MORNING. TROPICAL
CYCLONE KIKO REMAINS THE FOCUS WEATHER IN THE SHORT TERM WITH
REGARDS TO THE SWELL GENERATED BY THE SYSTEM. THE HILO BUOY SAW AN
INCREASE IN SWELL SHORTLY AFTER SUNSET, AND ADDITIONAL INCREASES
ARE EXPECTED THROUGH TONIGHT.
TROPICAL STORM KIKO IS ABOUT 180 NM NE OF HILO DURING THE PRE-DAWN
HOURS, AND IS EXPECTED TO CONTINUE TO TRACK TO THE NW TODAY. AS IT
DOES SO, IT IS DISRUPTING THE TRADE WIND FLOW, CAUSING WINDS OVER
THE COASTAL WATERS TO WEAKEN TO GENTLE TO MODERATE BACKGROUND
NORTHEAST FLOW.
KIKO IS MOVING THROUGH THE OFFSHORE WATERS TO THE NORTHEAST OF THE
ISLANDS. A TROPICAL STORM WARNING IS IN EFFECT FOR THE OFFSHORE
WATERS WITH TROPICAL STORM CONDITIONS EXPECTED OVER THE E AND NE
OFFSHORE WATERS THROUGH WEDNESDAY. ALTHOUGH NO WIND IMPACTS ARE
EXPECTED OVER THE COASTAL WATERS, A QUICK RISE OF WAVE HEIGHTS ARE
EXPECTED TONIGHT INTO TUESDAY AS KIKO PASSES.
THE LATEST BUOY OBSERVATIONS FROM HILO SHOWED A RISE IN ENERGY
ACROSS THE 12-14 SECOND SPECTRAL BANDS DURING THE EVENING, AND
THROUGHOUT THE NIGHT. WITH KIKO EXPECTED TO MAKE ITS CLOSEST
APPROACH TO THE HAWAIIAN ISLANDS DURING THE NEXT 12-24 HOURS, WE
EXPECT ANOTHER QUICK RISE IN WAVE HEIGHTS OVER THE WESTERN HALF
OF THE STATE TODAY. ALTHOUGH PEAK SURF HEIGHTS ARE EXPECTED TO BE
SHORT-LIVED, A RAPID RISE OF EAST SWELL SHOULD PRODUCE DANGEROUS
CONDITIONS ALONG EAST FACING SHORES. A HIGH SURF WARNING REMAINS
IN EFFECT FOR THE BIG ISLAND, MAUI, AND MOLOKAI, AND STARTS FOR
OAHU AND KAUAI THIS MORNING. SURF HEIGHTS ARE EXPECTED TO HAVE
PEAKED FOR THE BIG ISLAND OVER THE NEXT COUPLE OF HOURS, FOR MAUI
COUNTY IN THE NEXT FEW HOURS, AND MID DAY INTO THE AFTERNOON FOR
OAHU AND KAUAI.
A REINFORCING SWELL OUT OF THE SOUTH-SOUTHWEST IS EXPECTED TODAY.
THIS SHOULD HELP MAINTAIN SURF NEAR OR SLIGHTLY ABOVE THE SUMMER
AVERAGE THROUGHOUT THE FIRST HALF OF THE WEEK. ADDITIONALLY,
MULTIPLE SMALL PULES OF NORTHWEST SWELL ENERGY WILL GENERATE SMALL
SURF ALONG NORTH FACING BEACHES THROUGHOUT THE WEEK. A SHORT-
LIVED NORTHEAST SWELL IS POSSIBLE FOR SELECT EXPOSURES AS KIKO
PASSES TO OUR NORTH.
FIRE WEATHER
DECREASED WINDS AND INCREASED HUMIDITY WITH HIGHER CHANCES FOR
RAINFALL ARE EXPECTED THROUGH WEDNESDAY AS TROPICAL STORM KIKO
PASSES NORTHEAST AND NORTH OF THE STATE. A RETURN TO MODERATE AND
STABLE TRADE WINDS WILL OCCUR ON THURSDAY, THOUGH CONDITIONS ARE
EXPECTED TO REMAIN BELOW CRITICAL FIRE WEATHER THRESHOLDS.
HFO WATCHES/WARNINGS/ADVISORIES
HIGH SURF WARNING UNTIL 6 PM HST THIS EVENING FOR OLOMANA-KAUAI
EAST-KAUAI SOUTH-EAST HONOLULU-KOOLAU WINDWARD.
HIGH SURF WARNING UNTIL 6 PM HST THIS EVENING FOR MAUI WINDWARD
WEST-MOLOKAI WINDWARD-MOLOKAI SOUTHEAST-WINDWARD HALEAKALA-
KIPAHULU-BIG ISLAND SOUTHEAST-BIG ISLAND EAST-BIG ISLAND NORTH.
DISCUSSION...FARRIS
AVIATION...THOMAS
MARINE...M BALLARD
FIRE WEATHER...FARRIS
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