724
FXHW60 PHFO 100155
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
355 PM HST TUE SEP 9 2025
SYNOPSIS
SHOWERS SPREAD OVER WINDWARD BIG ISLAND AND MAUI
TONIGHT AND THEN TRANSITION TO LOCALLY HEAVY INTERIOR SHOWERS OVER
MOLOKAI THROUGH KAUAI TOMORROW AFTERNOON. LOCALLY BREEZY TRADES
RETURN WEDNESDAY NIGHT.
DISCUSSION
TODAY. MODEL ANALYSIS AT 500MB PLACES THE HAWAIIAN ISLANDS UNDER THE
EASTERNMOST MID-LEVEL LOW ASSOCIATED WITH A MATURE OMEGA BLOCK
CENTERED NEAR THE INTERNATIONAL DATELINE. THIS LOW WILL WILL
STAGNATE THROUGH THE NEAR TERM AND GRADUALLY RETROGRADE WESTWARD AND
AWAY FROM THE STATE DURING THE END OF THE WEEK. BENEATH THIS UPPER
LOW RESIDES A STRONGLY SHEARED AND SUBSTANTIALLY WEAKENED TROPICAL
STORM KIKO WHICH IS ADVANCING NORTHWESTWARD WITHIN SE LOW-LEVEL FLOW
AS UPPER-LEVEL FLOW SIMULTANEOUSLY SHEARS CONVECTION OFF TO THE
NORTH. THIS AFTERNOON'S OBSERVED SOUNDINGS OUT OF LIHUE AND HILO
INDICATE AMPLE LOW-LEVEL MOISTURE IN THE LOWEST 7KFT OR SO, BUT
STILL CAPPED BY DRY MID-LEVELS. BACKING ENE TO NNE WINDS OVER THE
WESTERN END OF THE STATE INDICATE INFLUENCE FROM THE OUTER PORTION
OF KIKO'S ENVELOPE OF LOW-LEVEL CYCLONIC FLOW. THIS LIGHT NNE
GRADIENT MAY YET FORCE SEA BREEZE CONVERGENCE TOWARD THE SOUTHERN
PORTION OF OAHU WHERE LIMITED AFTERNOON SHOWERS ARE POSSIBLE
DURING THE REMAINDER OF THE AFTERNOON. MORE ROBUST CONVECTION
EXISTS ON THE BIG ISLAND WHERE TERRAIN HAS ALLOWED ACCESS
UNSTABLE MID AND UPPER LEVELS WHERE THE BULK OF THE 1000 J/KG OF
OBSERVED CAPE RESIDES. THESE SHOWERS WILL DIMINISH WITH THE LOSS
OF HEATING THIS EVENING.
TONIGHT. THE TRAILING BAND OF MOISTURE EXTENDING FROM TC KIKO TO
WATERS WELL EAST OF THE BIG ISLAND WILL ADVANCE WEST THROUGH THE
AREA TONIGHT AND WEDNESDAY. THIS BAND RESIDES ALONG THE CONVERGENT
LEAD EDGE OF HIGH PRESSURE THAT WILL BUILD INTO THE AREA DURING THE
MEDIUM RANGE. A WIDE COVERAGE OF SHOWERS OVER WINDWARD PORTIONS OF
THE BIG ISLAND AND MAUI CAN BE EXPECTED TONIGHT MAINLY AFTER
MIDNIGHT AND MAINLY OVER AREAS EXPOSED TO ESE FLOW. LOCALES SUCH
AS WESTERN MAUI AND THE HAMAKUA COAST OF THE BIG ISLAND LIKELY
OBSERVE LITTLE IN THE WAY OF RAINFALL WHILE AMOUNTS UP TO A COUPLE
OF INCHES WILL BE POSSIBLE FOR OTHER WINDWARD LOCATIONS. WEAK
CAPPING WILL FAVOR LOCALIZED HEAVY DOWNPOURS, BUT THE GENERAL
EXPECTATION IS FOR RAIN RATES TO REMAIN BELOW 1" PER HOUR.
WEDNESDAY. THIS BAND OF MOISTURE WILL BE POSITIONED OVER THE CENTRAL
PORTION OF THE STATE DURING THE DAY WEDNESDAY. EMERGING ESE FLOW
POSES THE PRIMARY UNCERTAINTY IN THE FORECAST AS IT IS MODELED TO BE
NEARLY STRONG ENOUGH TO WIPE OUT THE SEA BREEZE INFLUENCE, A
NECESSITY FOR LOW-LEVEL FORCING TOMORROW. EVEN SO, THE GFS, EC AND
THE SUITE OF HI-RES MODELS MAINTAIN A STRONG CONSENSUS THAT
AFTERNOON CONVECTION OVER THE WESTERN END OF THE STATE, PARTICULARLY
OAHU, COULD BE FAIRLY VIGOROUS DURING PEAK HEATING WEDNESDAY
AFTERNOON. FORECAST SOUNDINGS INDICATE PLENTY OF DRY AIR IN THE
COLUMN THAT WILL NEED TO BE OVERCOME, BUT AREAS OF PREFERENTIALLY
STRONG CONVERGENCE OR PERSISTENT CONVECTION COULD NONTEHLESS
CAPITALIZE ON RESIDENT ELEVATED INSTABILITY AND PRODUCE LOCALLY VERY
HEAVY DOWNPOURS. THIS IS BORNE OUT IN EXPLICIT DEPICTIONS FROM THE
CAMS AS WELL, WHICH SIMULATE ECHO TOPS TO OVER 35KFT. WEAKLY
CONVERGENT ESE FLOW THROUGH ABOUT 700MB ALSO POSES THE THREAT FOR
ISLAND PLUME INTERACTION FROM MOLOKAI WHICH WOULD ELEVATE ANY
FLOODING THREAT OVER OAHU. AT THIS TIME, WILL HOLD OFF ON INCLUSION
OF THUNDER OVER OAHU AND KAUAI ON WEDNESDAY, BUT IT IS WITHIN THE
REALM OF POSSIBILITY. ALL TOLD, AN UNCERTAIN FLOODING THREAT PERHAPS
6 HOURS IN DURATION DURING PEAK HEATING WILL EXIST OVER OAHU AND
KAUAI ON WEDNESDAY.
EXTENDED. LOCALLY BREEZY TRADES THEN RETURN FROM WEDNESDAY NIGHT
ONWARD WHILE BUILDING UPPER RIDING PROVIDES AMPLE STABILITY. SHOWERS
FOCUSED WINDWARD AND MAUKA DURING THIS TIME, MAINLY DURING THE
OVERNIGHT AND EARLY MORNING HOURS.
AVIATION
AS TROPICAL STORM KIKO CONTINUES TO PASS NORTH OF THE ISLANDS
THROUGH WEDNESDAY, TRADE WINDS WILL REMAIN DISRUPTED IN PLACES,
AND A MOIST AND SOMEWHAT UNSTABLE AIR MASS WILL PERSIST. DAYTIME
SEA BREEZES ARE PRODUCING AREAS OF MVFR CEILINGS AND VISIBILITY IN
ISOLATED +SHRA/TSRA OVER INTERIOR BIG ISLAND AND MAUI THIS
AFTERNOON, BUT SO FAR, AIRMET SIERRA FOR MOUNTAIN OBSCURATION IS
NOT NEEDED. THIS SHOWER ACTIVITY IS EXPECTED TO DIMINISH OVERNIGHT
AS DIURNALLY DRIVEN CONVECTION DIMINISHES. A SLIGHTLY DRIER NORTH
TO NORTHEASTERLY FLOW OVER OAHU AND KAUAI HAS NOT BEEN AS ACTIVE
WITH SHOWERS AND MVFR CONDITIONS TODAY. WINDS ON THESE ISLANDS
WILL BECOME VARIABLE OVERNIGHT, AND SOME MVFR CONDITIONS COULD
FORM ALONG WINDWARD AND NORTH FACING TERRAIN. ON WEDNESDAY, EXPECT
SHOWERS AND POTENTIAL FOR MVFR CONDITIONS IN +SHRA TO BE GREATEST
OVER KAUAI AND OAHU, WHILE TRADES SLOWLY REBUILD OVER BIG ISLAND
AND MAUI.
MARINE
TROPICAL STORM KIKO IS ABOUT 125 NM NE OF OAHU THIS AFTERNOON AND
CONTINUES TO TRACK WEST-NORTHWEST. KIKO CONTINUES TO DISRUPT THE
TRADEWIND FLOW WITH GENTLE TO MODERATE WINDS EXPECTED ACROSS MOST
OF THE COASTAL WATERS TONIGHT. AS KIKO CONTINUES TO TRACK
WESTWARD, MODERATE TO LOCALLY FRESH EAST TO SOUTHEAST TRADES WILL
RETURN STARTING WITH THE BIG ISLAND LATE TONIGHT INTO WEDNESDAY
MORNING AND GRADUALLY SPREAD WESTWARD.
KIKO CONTINUES TO PRODUCE TROPICAL STORM CONDITIONS ACROSS THE
NORTHERN OFFSHORE WATERS. A TROPICAL STORM WARNING REMAINS IN
EFFECT THROUGH TONIGHT BUT THERE ARE STILL SOME UNCERTAINTY ON
THE INTENSITY OF KIKO FOR WEDNESDAY. LATEST FORECAST FROM NHC
SHOWS KIKO WEAKENING TO A TROPICAL DEPRESSION BY WEDNESDAY
MORNING. FOR THE COASTAL WATERS, DUE TO THE SWELLS FROM KIKO
COMING IN ABOVE GUIDANCE AROUND KAUAI AND OAHU, A SMALL CRAFT
ADVISORY IS IN EFFECT FOR THE EXPOSED WATERS AROUND KAUAI AND OAHU
THROUGH TONIGHT. ALTHOUGH NO WIND IMPACTS ARE EXPECTED OVER THE
COASTAL WATERS, SMALL CRAFT ADVISORY LEVEL WINDS COULD RETURN
FOR OUR TYPICAL WINDY AREAS AROUND MAUI AND THE BIG ISLAND LATE
WEDNESDAY AFTERNOON INTO THURSDAY.
THE LATEST BUOY OBSERVATIONS FROM MOKAPU SHOW THE MAIN SWELL
ENERGY FOCUSED ACROSS THE 10-14 SECOND SPECTRAL BANDS THIS
AFTERNOON. THIS SWELL WILL LIKELY PEAK LATE THIS AFTERNOON INTO
THE EVENING ACROSS OAHU AND PEAK ACROSS KAUAI LATER TONIGHT. THE
HIGH SURF WARNING HAS BEEN EXTENDED FOR KAUAI AND OAHU THROUGH
TONIGHT. SURF HEIGHTS SHOULD DROP BELOW WARNING THRESHOLDS BY
WEDNESDAY MORNING, BUT ADVISORY LEVEL SURF COULD LINGER AROUND
KAUAI THROUGH PARTS OF THE WEDNESDAY (ON A STEADY DECLINE).
MEANWHILE OVER THE BIG ISLAND, THE SWELL FROM KIKO DID NOT GET AS
LARGE AS ANTICIPATED AND IS ON A STEADY DECLINE THIS AFTERNOON.
THUS, THE HIGH SURF WARNING WAS CANCELLED FOR THE BIG ISLAND. FOR
MAUI COUNTY, SURF HEIGHTS ARE LIKELY CURRENTLY PEAKING AT ADVISORY
THRESHOLDS, THUS A HIGH SURF ADVISORY HAS BEEN ISSUED THROUGH
TONIGHT.
A REINFORCING SWELL OUT OF THE SOUTH-SOUTHWEST ARRIVED TODAY AND
WILL BE ON A SLOW DECLINE WEDNESDAY INTO THURSDAY. SURF HEIGHTS
SHOULD HOLD NEAR THE SUMMER AVERAGE THROUGH WEDNESDAY THEN DROP
BELOW AVERAGE BY THURSDAY. ANOTHER SMALL BUMP FROM THE SOUTH IS
POSSIBLE ON FRIDAY. ADDITIONALLY, MULTIPLE SMALL PULES OF
NORTHWEST TO NORTH-NORTHWEST SWELL ENERGY WILL GENERATE SMALL
SURF ALONG NORTH FACING BEACHES THROUGHOUT THE WEEK AND INTO THE
WEEKEND. A SHORT- LIVED NORTHEAST SWELL IS POSSIBLE FOR SELECT
EXPOSURES AS KIKO PASSES TO OUR NORTH.
FIRE WEATHER
HIGH HUMIDITY AND LIGHT TO MODERATE WINDS CONTINUE FOR THE NEXT
COUPLE OF DAYS WITH SCATTERED SHOWERS FOCUSED OVER ISLAND
INTERIORS DURING THE AFTERNOON. LOCALLY BREEZY TRADES THEN RETURN
WEDNESDAY NIGHT AS HUMIDITY FALLS TO TYPICAL VALUES.
HFO WATCHES/WARNINGS/ADVISORIES
HIGH SURF WARNING UNTIL 6 AM HST WEDNESDAY FOR OLOMANA-KAUAI
EAST-KAUAI SOUTH-EAST HONOLULU-KOOLAU WINDWARD.
HIGH SURF ADVISORY UNTIL 6 AM HST WEDNESDAY FOR MAUI WINDWARD
WEST-MOLOKAI WINDWARD-MOLOKAI SOUTHEAST-WINDWARD HALEAKALA-
KIPAHULU.
SMALL CRAFT ADVISORY UNTIL 6 AM HST WEDNESDAY FOR KAUAI
NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI CHANNEL-OAHU
WINDWARD WATERS.
DISCUSSION...JVC
AVIATION...WROE
MARINE...KINO
FIRE WEATHER...JVC
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