707
FXHW60 PHFO 071937
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
937 AM HST WED OCT 7 2026
SYNOPSIS
WEAKENING TRADE WINDS WILL PRODUCE LIGHT RAINFALL OVER MAINLY
WINDWARD AREAS TONIGHT. LOW PRESSURE WILL DEVELOP NORTH OF THE
STATE ON WEDNESDAY, CAUSING WINDS TO SHIFT OUT OF THE SOUTH AND
ALLOWING SEA BREEZES TO PRODUCE A FEW INTERIOR SHOWERS IN THE
AFTERNOON. DEEP SOUTHERLY WINDS WILL DRAW TROPICAL MOISTURE OVER
THE PORTIONS OF THE ISLAND CHAIN WEDNESDAY NIGHT THROUGH AT LEAST
THURSDAY, BRINGING SOME POTENTIAL FOR FLOODING RAINFALL. THE LOW
WILL WEAKEN SEVERAL HUNDRED MILES NORTHWEST OF KAUAI FRIDAY AND
SATURDAY THEN LIFT AWAY ON SUNDAY, THOUGH A FEW HEAVY SHOWERS MAY
LINGER THROUGH THE WEEKEND UNDER LIGHT WINDS. LIGHT TRADE WINDS
ARE EXPECTED TO RETURN EARLY NEXT WEEK.
UPDATE
LAND BREEZES DEVELOPED LATE LAST NIGHT AS REGION WINDS DECLINED,
LEADING TO MOSTLY CLEAR CONDITIONS EARLY THIS MORNING. SOUTHERLY
WINDS ARE BEGINNING TO DEVELOP AS OF MID MORNING, WITH LITTLE TO
NO RAINFALL EXPECTED THROUGH MIDDAY. SEA BREEZES WILL DOMINATE
THIS AFTERNOON AND WILL PRODUCE A FEW INTERIOR SHOWERS AS THE
ATMOSPHERE DESTABILIZES. FLOOD WATCH GOES INTO EFFECT THIS
EVENING FOR KAUAI AND OAHU. SEE BELOW FOR MORE DETAILS ON THE
UNFOLDING FLOOD THREAT.
PREV DISCUSSION
ISSUED AT 436 AM HST WED OCT 7 2026
STABLE AND LIGHT ESE FLOW PREVAILS BENEATH AN INVERSION AVERAGING
ABOUT 7.5KFT OVER THE ISLANDS AT PRESS TIME THIS MORNING. WINDS
WILL CONTINUE VEERING THROUGH TODAY BECOMING SSE BY THIS EVENING.
THIS IS OCCURRING IN RESPONSE TO AN APPROACHING MID-LEVEL TROUGH
PRESENTLY APPROACHING KAUAI FROM THE NW. AT THIS TIME, A FRONTAL
WAVE IS DEVELOPING IN ADVANCE OF THIS TROUGH WHILE FREQUENT
THUNDERSTORMS ARE NOTED IN THE BASE OF THE TROUGH WHERE 700-500MB
LAPSE RATES ARE FIRMLY IN EXCESS OF 7C/KM AND 500MB ARE AROUND
-14C. AS TODAY PROGRESSES, CYCLOGENESIS WILL FOCUS NEAR 30N/160W,
OR ABOUT 550 MILES DUE NORTH OF KAUAI AS ADDITIONAL ENERGY FOCUSES
IN THE BASE OF THE TROUGH. IN THE NEAR TERM, EMERGING SEA BREEZES
AGAINST A BACKGROUND OF LIGHT SOUTHERLIES WILL TEND TO FOCUS
AFTERNOON CLOUDS AND SHOWERS OVER NORTHERN PORTIONS OF THE ISLANDS
WHERE SCATTERED COVERAGE IS ANTICIPATED DURING PEAK HEATING.
BY TONIGHT, ATTENTION TURNS TOWARD THE NORTHWARD PROGRESS OF THE
TROPICAL DISTURBANCE NEAR 15N/162W, OR ABOUT 600 MILES SSW OF KAUAI.
THIS DISTURBANCE IS EMBEDDED WITHIN A BROADER TROPICAL AIRMASS
CHARACTERIZED BY SURFACE DEWPOINTS WELL INTO THE 70S, PWAT VALUES IN
EXCESS OF 2", AND IS SURROUNDED BY SHOWER ACTIVITY. POCKETS OF
THUNDERSTORMS ARE ALSO NOTED NEAR ITS CORE WHERE CONDITIONAL
INSTABILITY IS IS APPARENTLY SUFFICIENT FOR MODERATELY INTENSE
UPDRAFTS IN SPITE OF WARM 500MB TEMPERATURES AROUND -4C AND SUB
6C/KM LAPSE RATES. SOUTHERLY FLOW IN ADVANCE OF THE DEVELOPING
EXTRATROPICAL CYCLONE NORTH OF THE AREA WILL DRAW THIS FEATURE NORTH
AND SHEAR IT ACROSS THE ISLANDS TONIGHT INTO THURSDAY. THE PRESENCE
OF THUNDERSTORMS AT THIS TIME INCREASES CONFIDENCE IN THEIR
INCLUSION IN THE OFFICIAL FORECAST SEEING AS HOW INSTABILITY WILL
ONLY INCREASE WITH NORTHWARD EXTENT AS 500MB TEMPS OVER KAUAI & OAHU
WILL TURN AT LEAST 2-4C COLDER THAN WHAT THE SYSTEM IS CURRENTLY
EXPERIENCING. IN ADDITION, FACT THAT CONVECTION IS ALREADY FAIRLY
WIDESPREAD SOUTH OF THE ISLANDS SUGGESTS THE INCOMING ATMOSPHERE
WILL BE PRIMED FOR SHOWER AND ISOLATED THUNDERSTORM ACTIVITY IN
SPITE OF THE RESIDENT HOSTILE STABLE/DRY ENVIRONMENT WHICH SHOULD
IN TURN BE DISPLACED RATHER EASILY.
HI-RES GUIDANCE SUGGESTS SHOWERS, SOME HEAVY, WILL BECOME
INCREASINGLY WIDESPREAD BETWEEN SUNSET AND MIDNIGHT TONIGHT. AT THE
SAME TIME, THE DIGGING TROUGH WILL RESULT IN OUTSTANDING RIGHT
ENTRANCE JET DYNAMICS PARKED OVER KAUAI LATE TONIGHT THROUGH MUCH OF
THURSDAY. AT THE LEAST, THIS WILL FAVOR STEADY, BROAD ASCENT FROM
MAUI COUNTY THROUGH KAUAI IN MAINTENANCE OF INCREASING SHOWER
COVERAGE AS MOISTURE STEADILY DEEPENS. HOWEVER, WHILE DIFFERING ON
EXACT LOCATION, THE EC AND GFS BOTH ALLOW A BAND OF PARTICULARLY
INTENSE RAINFALL TO DEVELOP ALONG THIS DEVELOPING JET-FRONT FEATURE,
THOUGH THE FRONT WILL BE WASHED OUT AT THE SURFACE SUBSEQUENTLY
LIMITING LOW-LEVEL CONVERGENCE. NONETHELESS, ANY CORRIDOR OF
ENHANCED CONFLUENT FLOW AROUND KAUAI OR OAHU SHOULD BE MORE THAN
SUFFICIENT TO TRIGGER BANDING OF DEEP CONVECTION, HEAVY RAIN, AND
ISOLATED THUNDERSTORMS. THE HEAVIEST RAIN IS ANTICIPATED FROM AROUND
SUNRISE THURSDAY THROUGH THURSDAY EVENING FOCUSED MAINLY OVER KAUAI
AND OAHU. AT THIS TIME, IT APPEARS THAT ONCE THE INCREASINGLY STRUNG
OUT TROPICAL DISTURBANCE, OR REMNANT THEREOF, ADVANCES THROUGH THE
AREA, SHOWER COVERAGE SHOULD DECREASE CONSIDERABLY THURSDAY NIGHT
INTO FRIDAY. WITH THAT SAID, RIGHT ENTRANCE DYNAMICS WILL PERSIST
OVER THE WESTERN END OF THE STATE THROUGH AT LEAST FRIDAY AS THE
UPPER TROUGH CLOSES OFF AND STAYS NEARLY STATIONARY NW OF KAUAI.
THIS SHOULD SUFFICIENT FOR SHOWERS TO CAPITALIZE ON RICH LOW-LEVEL
MOISTURE AND PRODUCE POCKETS OF HEAVY SHOWERS THURSDAY NIGHT INTO
EARLY FRIDAY NIGHT, ESPECIALLY OVER LEEWARD ZONES.
A FLOOD WATCH HAS BEEN ISSUED FOR TONIGHT THROUGH THURSDAY FOR KAUAI
AND OAHU. GIVEN THE POTENTIAL FOR FLOW-PARALLEL BANDS OF CONVECTION
TO DEVELOP, THERE IS CONCERN FOR TRAINING OF HEAVY SHOWERS. RAIN
RATES COULD ALSO BE INTENSE AT TIMES GIVEN THE COMBINATION OF
FORCING AND DEEP TROPICAL MOISTURE. SUBSEQUENT SHIFTS WILL EVALUATE
THE POTENTIAL FOR AN EXPANSION TO MAUI COUNTY PENDING ADDITIONAL
DATA.
MID-LEVEL RIDGING BECOMES INCREASINGLY PROMINENT BEGINNING FRIDAY
NIGHT WITH LIGHT TO MODERATE TRADES AND INCREASING STABILITY MAKING
A PUSH INTO THE AREA FOR THE WEEKEND. SHOULD TRADES REMAIN
SUFFICIENTLY LIGHT, THEN AFTERNOON SEA BREEZES WILL STILL HAVE
PLENTY OF MOISTURE TO WORK WITH FOR AFTERNOON SHOWERS OVER ISLAND
INTERIORS THIS WEEKEND POTENTIALLY LEADING TO POCKETS OF NUISANCE
FLOODING DURING PEAK HEATING.
AVIATION
LIGHT SOUTHEAST WINDS EXPECTED THROUGH THE FORECAST PERIOD DUE TO
A SURFACE TROUGH JUST WEST OF KAUAI COUNTY. INCREASING SHRA AND A
FEW ISOLATED TSTMS ARE POSSIBLE THROUGH THURSDAY AS THE SURFACE
TROUGH MOVES EVEN CLOSER. IFR/MVFR CONDS LIKELY WITHIN HEAVIER
SHRA AND TSTMS. VFR PREVAILS ELSEWHERE.
NO AIRMETS ARE IN EFFECT.
MARINE
GENTLE TO MODERATE SOUTH TO SOUTHEAST WINDS WILL CONTINUE OVER
THE NEXT SEVERAL DAYS AS A LOW PRESSURE SYSTEM DEVELOPS NORTH OF
HAWAII. ENHANCED SHOWERS WITH THE POTENTIAL FOR A FEW THUNDERSTORMS
ARE FORECAST FOR THE WESTERN HALF OF THE STATE THROUGH THURSDAY.
A SURFACE TROUGH WILL LINGER NEAR THE AREA THROUGH THE WEEKEND AND
EARLY NEXT WEEK KEEPING POTENTIAL FOR VARIABLE WINDS AND
UNSETTLED WEATHER.
SOUTH SWELL WILL MAINTAIN INTO NEXT WEEK WITH PULSES OF LONG
PERIOD REINFORCEMENT ARRIVING THURSDAY AND SATURDAY. SURF WILL
STAY 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 NORTHWEST OF THE
HAWAIIAN ISLANDS. A LARGER SWELL WILL ARRIVE AROUND TUESDAY,
BRINGING 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
ISSUED AT 436 AM HST WED OCT 7 2026
LIGHT TO MODERATE ESE WINDS VEER TO SSE AS THE DAY PROGRESSES. FIRE
WEATHER RISK DIMINISHES THROUGH FRIDAY AS SOUTHERLY WINDS BRING
INCREASED MOISTURE AND HUMIDITY. THE INVERSION RANGE FROM 6 KFT TO
8 KFT THROUGH THE EVENING AND WILL DETERIORATE THIS EVENING AS
DEEPER MOISTURE ARRIVES.
HFO WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH FROM 6 PM HST THIS EVENING THROUGH THURSDAY
AFTERNOON FOR CENTRAL OAHU-EAST HONOLULU-EWA PLAIN-HONOLULU
METRO-KAUAI EAST-KAUAI MOUNTAINS-KAUAI NORTH-KAUAI SOUTH-KAUAI
SOUTHWEST-KOOLAU LEEWARD-KOOLAU WINDWARD-NIIHAU-OAHU NORTH SHORE-
OLOMANA-WAIANAE COAST-WAIANAE MOUNTAINS.
DISCUSSION...JVC
AVIATION...PARKER
MARINE...FOSTER
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