351
FXHW60 PHFO 170201
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
401 PM HST TUE DEC 16 2025
SYNOPSIS
AN APPROACHING COLD FRONT FROM THE NORTHWEST, AND PRE-FRONTAL
CONVERGENCE, WILL PROVIDE FOCUS FOR SHOWERS AND THUNDERSTORMS
THAT WILL PRIMARILY IMPACT THE WESTERN ISLANDS BEGINNING THIS
EVENING AND LASTING THOUGH THE NEXT SEVERAL DAYS. SHOWERS COULD BE
HEAVY AT TIMES, ESPECIALLY WEDNESDAY EVENING THROUGH WEDNESDAY
NIGHT. A FLOOD WATCH IS NOW IN EFFECT FOR NIIHAU, KAUAI, AND OAHU
THROUGH 6 PM HST THURSDAY. HIGH PRESSURE WILL BEGIN TO BUILD BACK
IN THIS WEEKEND, WITH A DRIER PATTERN EXPECTED HEADING INTO NEXT
WEEK. EASTERLY TRADE WINDS WILL RETURN THIS WEEKEND AS WELL,
REACHING LOCALLY STRONG SPEEDS EARLY NEXT WEEK.
DISCUSSION
REGIONAL SATELLITE IMAGERY THIS AFTERNOON SHOWS A LINE OF SHOWERS
AND THUNDERSTORMS AHEAD OF A SURFACE COLD FRONT THAT EXTENDS
SOUTHWARD ACROSS THE NORTHWEST OFFSHORE WATERS FROM A LOW THAT IS
CURRENTLY CENTERED NEAR 33N163W. RADAR IMAGERY, GOES
GEOSTATIONARY LIGHTNING MAPPER (GLM) DATA, NATIONAL LIGHTNING
DETECTION NETWORK (NLDN), AND GLOBAL LIGHTNING DETECTION (GLD)
DATA ALL SHOW THAT ROBUST THUNDERSTORMS ARE ONGOING ACROSS THE
NORTHERN OFFSHORE WATERS, AND THIS LINE OF THUNDERSTORMS HAS MOVED
CLOSER TO THE HAWAIIAN COASTAL WATERS THROUGHOUT THE DAY AS THE
FRONT APPROACHES FROM THE NORTHWEST. MEANWHILE, SOME PRE-FRONTAL
CONVERGENCE WITHIN SOUTHERLY FLOW OVER THE ISLAND CHAIN HAS
RESULTED IN SOME LIGHTER SCATTERED SHOWERS MOVING ACROSS THE
ACROSS MAINLY THE WESTERN ISLANDS THROUGHOUT THE DAY. RAINFALL
AMOUNTS TODAY HAVE GENERALLY BEEN ON THE LIGHTER SIDE WHEN
COMPARED WITH THE PAST COUPLE OF DAYS, WITH MOST ACCUMULATIONS
LESS THAN ONE QUARTER OF AN INCH OVER THE PAST 6 HOURS.
THIS EVENING AND TONIGHT, THE FRONT WILL CONTINUE ITS APPROACH
FROM THE NORTHWEST, AND CHANCES FOR RAIN AND THUNDERSTORMS WILL
INCREASE OVER THE WESTERN END OF THE STATE. HEIGHT FALLS AND
COOLING TEMPERATURES ALOFT WILL INCREASE INSTABILITY. HI-RES
GUIDANCE AND LATEST CAMS SHOW VARIATIONS OF A SIMILAR SOLUTION-
A COUPLE OF BANDS OF SHOWERS AND THUNDERSTORMS SETTING UP OVER OR
NEAR KAUAI COUNTY AND OAHU. HREF PROBABILITIES ALSO HIGHLIGHT THE
POTENTIAL FOR HIGH RAINFALL RATES GREATER THAN 0.5 INCH PER HOUR
WITHIN THESE BANDS. PERIODIC SHOWERS HAVE THE POTENTIAL TO
BECOME ORGANIZED ENOUGH TO QUICKLY PRODUCE 1 TO 2 INCHES OF RAIN
IN SPOTS. GIVEN THIS, A NEW FLOOD WATCH HAS BEEN ISSUED FOR NIIHAU,
KAUAI, AND OAHU. MAUI AND HAWAII COUNTIES WILL ALSO RECEIVE SOME
RAIN, BUT IT WILL BE MUCH MORE LIMITED AS SHOWERS THERE WILL
PRIMARILY BE A RESULT OF SURFACE-BASED CONVECTION FROM LIFT
CREATED BY THE LOCAL DIURNAL BREEZES.
THE FRONT IS EXPECTED TO STALL OVER THE WESTERN END OF THE STATE,
WHICH WILL RESULT IN CONTINUED HEAVY RAIN AND THUNDER CHANCES
THROUGH FRIDAY. INSTABILITY, LOW LEVEL CONVERGENCE, AND LIFT
APPEAR TO BE MAXIMIZED WEDNESDAY EVENING INTO WEDNESDAY NIGHT,
WHICH PROVIDES THE BEST WINDOW FOR FLOODING CONCERNS.
THE WEAKENING BOUNDARY WILL BEGIN TO LIFT AWAY FROM THE STATE ON
FRIDAY, BEGINNING A DRIER TREND. GLOBAL MODELS INDICATE THAT LOW
LEVEL FLOW WILL BECOME MORE EASTERLY BY SATURDAY. UPPER RIDGING
WILL FORM OVER THE ISLANDS THIS WEEKEND, AND THIS SUBSIDENCE WILL
KICK OFF SEVERAL DAYS OF TYPICAL TRADE WEATHER IN THE DAYS
LEADING UP TO CHRISTMAS. MODEL GUIDANCE IS SUGGESTING THAT A LARGE
NORTH PACIFIC SURFACE HIGH WILL TIGHTEN THE PRESSURE GRADIENT
ENOUGH TO STRENGTHEN TRADES BACK TO LOCALLY STRONG SPEEDS EARLY
NEXT WEEK.
AVIATION
A COLD FRONT WILL CONTINUE TO GRADUALLY APPROACH KAUAI FROM THE
NORTHWEST, ENHANCING SHOWERS AND PRODUCING ISOLATED TO SCATTERED
THUNDERSTORMS ALONG ITS AXIS. AHEAD OF THE FRONT, MODERATE TO
LOCALLY BREEZY SOUTHERLY WINDS WILL BRING LOW CLOUDS AND ISOLATED
TO SCATTERED SHOWERS TO SOUTH FACING COASTS AND SLOPES, MOST OF
WHICH ARE BEING FUNNELED ACROSS OAHU AND THE SOUTHEAST LOWER
SLOPES OF THE BIG ISLAND THIS AFTERNOON. BRIEF MVFR CONDITIONS CAN
BE EXPECTED AS THESE SHOWERS PASS THROUGH.
OVERNIGHT, SHOWERS AND THUNDERSTORMS ALONG THE FRONTAL BOUNDARY
WILL EDGE CLOSER AND MAY MOVE OVER KAUAI BY WEDNESDAY MORNING.
OTHERWISE, SHOWERS WILL CONTINUE STREAMING ACROSS THE CENTRAL
PART OF THE STATE ON THE SOUTHERLY FLOW, WITH AN INCREASING
POTENTIAL FOR HEAVY RAIN AND THUNDERSTORM DEVELOPMENT INTO THE DAY
ON WEDNESDAY. MVFR AND EVEN IFR CONDITIONS WILL BE POSSIBLE AS
THESE SHOWERS AND POTENTIAL THUNDERSTORMS MOVE THROUGH. THE
EASTERN ISLANDS OF MAUI AND THE BIG ISLAND WILL REMAIN MORE STABLE
WITH PREVAILING VFR CONDITIONS FOR MOST AIRFIELDS.
AIRMET SIERRA IS IN EFFECT FOR TEMPO MOUNTAIN OBSCURATIONS FOR
OAHU, MOLOKAI AND LANAI THIS AFTERNOON AND KAUAI WILL LIKELY NEED
TO BE ADDED LATER THIS EVENING OR LATE TONIGHT.
AIRMET TANGO IS IN EFFECT FOR TEMPO MODERATE TURBULENCE ALOFT
FROM 140 TO FL340 ACROSS THE ISLANDS ASSOCIATED WITH THE
SUBTROPICAL JET STREAM OVER THE ISLANDS. AS THE JET WEAKENS OVER
THE STATE THIS EVENING, THIS AIRMET WILL LIKELY BE CANCELLED.
MARINE
A COLD FRONT JUST NW OF THE ISLANDS WITHIN THE OFFSHORE WATERS WILL
ADVANCE SOUTHEASTWARD AND IS EXPECTED TO STALL BETWEEN KAUAI AND
OAHU TOMORROW. THE FRONT WILL MAINTAIN MODERATE TO FRESH SOUTH
SOUTHWESTERN WINDS THROUGH WEDNESDAY AS WELL AS BRING HEAVY
SHOWERS AND THUNDERSTORMS TO THE COASTAL WATERS AROUND KAUAI AND
OAHU. THUNDERSTORMS EMBEDDED WITHIN THE HEAVIER SHOWERS WILL
REMAIN POSSIBLE THROUGH THURSDAY MORNING AND COULD BE STRONG AT
TIMES DUE TO STRONG UPPER LEVEL SUPPORT. BY THURSDAY MORNING THE
SOUTHERLY WINDS ARE EXPECTED TO DECREASE AS THE FRONT WEAKENS
INTO A LOW LEVEL CONVERGENCE ZONE OR TROUGH OVER THE WESTERN
ISLANDS. WINDS WILL REMAIN LIGHT AND VARIABLE FROM THURSDAY NIGHT
THROUGH SATURDAY AS THE WEAK FEATURE GETS PUSHED WEST BY A
DEVELOPING RIDGE. AND BY SUNDAY, STRONG HIGH PRESSURE TO THE FAR
N WILL MOVE S AND GREATLY STRENGTHEN TRADE WINDS INTO NEXT WEEK.
N SWELL WILL GRADUALLY DECLINE THROUGH TONIGHT BEFORE A MID
PERIOD WNW SWELL FILLS IN TONIGHT THROUGH WEDNESDAY FROM A LOW TO
THE NW. THIS SWELL WILL ELEVATE SURF TO JUST BELOW THE HSA
THRESHOLD BUT IS EXPECTED TO BRING SEAS TO 10 FEET AROUND OAHU AND
KAUAI. THIS MEANS THAT NORTH SHORES SHOULD SEE RELATIVELY JUMBLED
SURF ON WEDNESDAY WITH THE SHORT TO MID PERIOD ENERGY MIXING IN.
AND A SMALL CRAFT ADVISORY (SCA) HAS BEEN ISSUED FOR THE NW
WATERS OF KAUAI AND OAHU. A LARGER NW SWELL WILL THEN BEGIN
FILLING IN BY WEDNESDAY NIGHT AND PEAK ON THURSDAY RIGHT AROUND
ADVISORY LEVELS. THIS SWELL COULD ALSO BRIEFLY BRING SCA LEVEL
SEAS (10 FEET) TO THE NW WATERS OF KAUAI. THIS SWELL WILL
GRADUALLY FADE OUT THROUGH THE REMAINDER OF THE WEEK WITH SMALL TO
MODERATE N AND NW SWELLS MIXED IN THROUGH THE WEEKEND.
E SHORES REMAIN SMALL EXCEPT WHERE NW-N SWELL ENERGY WRAPS
THROUGH THE WEEK. BY NEXT WEEK, NE SWELL COULD ELEVATE E SHORES
AND TRADE WINDS INCREASE. S SHORES SHOULD SEE SHORT PERIOD S
SWELL DUE TO PERSISTENT S-SW WINDS THROUGH AT LEAST THE FIRST HALF
OF THE WEEK, THEN DECREASE DURING THE SECOND HALF AS THE S-SW
WINDS DECREASE.
FIRE WEATHER
INCREASED MOISTURE AND SHOWER CHANCES, COMBINED WITH LIGHT WINDS,
WILL PREVENT CRITICAL FIRE WEATHER CONCERNS OVER THE NEXT FEW
DAYS.
HFO WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR NIIHAU, KAUAI, AND OAHU.
SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO MIDNIGHT HST
WEDNESDAY NIGHT FOR KAUAI NORTHWEST WATERS-KAUAI WINDWARD WATERS-
KAUAI LEEWARD WATERS-OAHU WINDWARD WATERS.
DISCUSSION...VAUGHAN
AVIATION...FARRIS
MARINE...TSAMOUS
FIRE WEATHER...VAUGHAN
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