092
FXHW60 PHFO 081307
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
307 AM HST THU OCT 8 2026
SYNOPSIS
A FLASH FLOODING THREAT PERSISTS FOR KAUAI THIS MORNING AND OAHU
THROUGH THIS AFTERNOON WITH COMPARATIVELY FEW SHOWERS EXPECTED
ELSEWHERE. LIGHT TO MODERATE TRADES RETURN THIS WEEKEND.
DISCUSSION
WIDELY SCATTERED MODERATE TO LOCALLY HEAVY SHOWERS ARE ONGOING FROM
KAUAI TO OAHU WITH TENDENCY FOR INCREASED ORGANIZATION IN THE KAUAI
CHANNEL BENEATH MATURE RIGHT ENTRANCE DYNAMICS. HEAVY RAIN RATES OF
1 TO LOCALLY 2 INCHES PER HOUR HAVE BEEN QUITE ISOLATED THUS FAR,
BUT ARE BEGINNING TO ALIGN WITHIN THE FLOW-PARALLEL BAND THAT HAS
FORMED IN THE CHANNEL. CLOUD TOP COOLING ASSOCIATED WITH THIS BAND
IS ASSOCIATED WITH A MODEST INCREASE IN THUNDERSTORM ACTIVITY AND
SUGGESTS THE INTENSIFICATION PROCESS WILL CONTINUE IN THE NEAR TERM,
THOUGH IT IS CLEAR AT THIS POINT THAT ORGANIZATION WILL CONTINUE TO
STRUGGLE DUE TO THE LACK OF A SURFACE-BASED FORCING MECHANISM.
REGARDLESS, EASTWARD PROGRESS OF THIS BAND WILL CRITICAL FOR THIS
MORNING'S OAHU FORECAST AND SUBSEQUENT FLASH FLOODING POTENTIAL.
THOUGH NOT PARTICULARLY ACCURATE IN THEIR DEPICTION OF THE POSITION
OF THE PRIMARY BAND OF HEAVY RAIN, THE GUIDANCE IS GENERALLY IN
AGREEMENT THAT ONCE FORMED EASTWARD PROGRESS WILL BE MINIMAL. WHILE
CONVECTION MAY INHERENTLY DEVELOP A TENDENCY TO PROPAGATE EASTWARD
WITH TIME, THE GREATEST ORGANIZATION IS EXPECTED TO REMAIN IN THE
KAUAI CHANNEL. WITH THAT SAID, A SECONDARY SURGE OF DEEP MOISTURE
IS STILL POISED TO LIFT ACROSS OAHU DURING THE MORNING HOURS AND
THE MODEST ASCENT FIELD AWAY FROM THE PRIMARY BAND MAY STILL BE
SUFFICIENT TO MAINTAIN ELEVATED RAIN RATES FOR AT LEAST THE NEXT
SEVERAL HOURS.
TO THE SOUTHWEST, CHANNEL 10/LOW-LEVEL WATER VAPOR IMAGERY DEPICTS A
PLUME OF DRY AIR LIFTING TOWARD KAUAI WITHIN A CORRIDOR OF BACKING
MID-LEVEL SOUTHERLIES. THE ARRIVAL OF THIS DRY AIR INTRUSION WILL
BRING A QUICK RETURN TO STABILITY AND WILL SIGNAL THE END OF ANY
FLOODING THREAT FOR KAUAI UPON ITS ARRIVAL LATER THIS MORNING.
HOWEVER, THE LOSS OF A WESTERLY COMPONENT TO THE MID-LEVEL FLOW WILL
DELAY THE ARRIVAL OF THIS DRY AIR FOR OAHU WHERE PERIODS OF SHOWERS,
SOME HEAVY, WILL CONTINUE THROUGH MUCH OF THE DAY. THE LEAD EDGE
OF THIS DRY AIR IS ALSO ENHANCING MID-LEVEL CONVERGENCE AND
HELPING TO ORGANIZE CONVECTION UPSTREAM OF OAHU. THE FLOOD WATCH
REMAINS IN PLACE, THOUGH IT IS INCREASINGLY TENUOUS FOR KAUAI
WHICH MAY BE DROPPED LATER THIS MORNING.
TROPICAL MOISTURE CHARACTERIZED BY PWATS AROUND 2" WILL REMAIN IN
PLACE INTO THE FIRST HALF OF THE WEEKEND, BUT THE WAVE OF DEEP
SATURATION THAT SPREAD OVER THE ISLANDS LAST NIGHT INTO THIS MORNING
WILL BE LONG GONE TO THE NORTH BY THEN. THIS LEAVES THE ISLANDS IN
AN AREA OF VERY BROAD, WEAK ASCENT EAST OF LINGERING RIGHT ENTRANCE
DYNAMICS LIKELY WITHOUT SUFFICIENT FORCING TO GENERATE MEANINGFUL
SHOWER ACTIVITY. WHILE ISOLATED NUISANCE FLOODING CAN'T BE RULED OUT
LATE THIS EVENING INTO FRIDAY, MAINLY FROM OAHU THROUGH MAUI COUNTY,
IT IS UNLIKELY TO WARRANT AN EXTENSION IN TIME OR SPACE TO THE FLOOD
WATCH, ESPECIALLY CONSIDERING THIS EVENT'S UNDERWHELMING PERFORMANCE
THUS FAR.
BY FRIDAY, THE GRADIENT MAY BE SUFFICIENTLY LIGHT TO SUPPORT SEA
BREEZE DEVELOPMENT AND POCKETS OF HEAVY DOWNPOURS ON ANY/ALL ISLANDS
DURING THE AFTERNOON AND THEN MAUI AND THE BIG ISLAND AGAIN OVER THE
WEEKEND. RETURNING MODERATE TRADES DURING THIS TIME WILL EVENTUALLY
LIMIT AFTERNOON CONVERGENCE OVER MOLOKAI, OAHU, AND KAUAI FAVORING A
RETURN TO A MODEST COVERAGE OF CLOUDS AND SHOWERS OVER WINDWARD AND
MAUKA ZONES AS EARLY AS SATURDAY. DEWPOINTS RETURN TO MORE TYPICAL
VALUES IN THE 60S SATURDAY NIGHT INTO SUNDAY.
AVIATION
LIGHT SOUTHERLY WINDS WILL INCREASE IN SPEED AND BECOME MORE
SOUTHERLY THROUGH THE DAY TODAY AS A SURFACE TROUGH EDGES OVER
THE WESTERN END OF THE STATE. HEAVY SHOWERS AND ISOLATED
THUNDERSTORMS WILL CONTINUE TO FORM IN THE VICINITY OF THIS
SURFACE TROUGH AS AN AREA OF ENHANCED MOISTURE MOVES UP FROM THE
SOUTH AND INSTABILITY INCREASES ALOFT. THE MAIN BAND OF HEAVY
SHOWERS WITH A FEW ISOLATED THUNDERSTORMS IS CURRENTLY OVER THE
KAUAI CHANNEL AND IS EXPECTED TO GRADUALLY EDGE FURTHER EASTWARD
AND IMPACT OAHU LATER THIS MORNING. MVFR CONDITIONS ARE LIKELY AND
IFR CONDITIONS POSSIBLE WITHIN HEAVIER SHOWERS AND THUNDERSTORMS.
VFR CONDITIONS WILL PREVAIL ELSEWHERE.
AIRMET SIERRA IS IN EFFECT FOR TEMPO MOUNTAIN OBSCURATION ACROSS
ALL OF KAUAI AND OAHU AND SOUTH THROUGH WEST FACING PORTIONS OF
MOLOKAI AND LANAI. THIS AIRMET, AND POSSIBLY ONE FOR IFR
CONDITIONS, WILL BE NEEDED FOR PORTIONS OF THE ISLAND CHAIN
THROUGH THE DAY.
MARINE
GENTLE TO MODERATE SOUTH TO SOUTHEAST WINDS WILL CONTINUE THROUGH
FRIDAY AS A LOW PRESSURE SYSTEM DEEPENS NORTH TO NORTHWEST OF
HAWAII. SOUTHERLY TO SOUTHEASTERLY SURFACE WINDS WILL CONTINUE TO
DRAW UP TROPICAL MOISTURE OVER THE ISLANDS UNDER THE COLD UPPER
LOW, PRODUCING PERIODS ENHANCED SHOWERS, HEAVY AT TIMES, WITH THE
POTENTIAL FOR A FEW THUNDERSTORMS NEAR NIIHAU, KAUAI AND OAHU
DURING THIS TIME. A PASSING LOW LEVEL TROUGH WILL THEN DRIFT FROM
EAST TO WEST THROUGH THE ISLANDS FROM SUNDAY INTO THE FIRST HALF
OF NEXT WEEK, POTENTIALLY EXTENDING THESE UNSTABLE WET WEATHER
TRENDS.
SOUTH SWELL WILL MAINTAIN INTO NEXT WEEK WITH PULSES OF LONG
PERIOD REINFORCEMENT ARRIVING THURSDAY AND SATURDAY. SURF WILL
REMAIN A FEW FEET BELOW ADVISORY LEVELS ALONG SOUTH FACING
SHORES.
SMALL TO MODERATE SURF ALONG NORTH AND WEST FACING SHORES WILL
CONTINUE THROUGH THE REST OF THE WEEK AS SWELL ENERGY IS
REINFORCED BY THE SLOWLY MOVING SURFACE LOW NORTH TO NORTHWEST OF
THE HAWAIIAN ISLANDS. A LARGER SWELL WILL ARRIVE AROUND TUESDAY,
BOOSTING NORTH AND WEST SHORE SURF TO JUST BELOW ADVISORY
THRESHOLDS. SURF ALONG EAST FACING SHORES WILL REMAIN SMALL AS
LOCAL WINDS REMAIN FAIRLY WEAK.
FIRE WEATHER
MOIST AND HUMID CONDITIONS UNDER MODERATE SOUTH WINDS CONTINUE
THROUGH TODAY. THE CHANCE FOR WIDESPREAD RAINFALL WILL DIMINISH
ON FRIDAY WHILE HUMID AND LIGHT SOUTHEAST WINDS PREVAIL. LIGHT TO
MODERATE EASTERLY TRADE WINDS ARE EXPECTED THIS WEEKEND. THE
INVERSION HAS BEEN WIPED OUT AND WILL REDEVELOP AS TRADES
RETURN THIS WEEKEND.
HFO WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH THROUGH 6 PM HST THIS AFTERNOON FOR NIIHAU, KAUAI,
AND OAHU.
DISCUSSION...JVC
AVIATION...FARRIS
MARINE...BOHLIN
FIRE WEATHER...JVC
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