707
FXHW60 PHFO 170602 AAA
AFDHFO
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HONOLULU HI
802 PM HST TUE DEC 16 2025
UPDATE
UPDATE MARINE SECTION TO EXPAND SMALL CRAFT ADVISORY IN AREA AND
TIME.
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.
PREV DISCUSSION
/ISSUED 401 PM HST TUE DEC 16 2025/
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 KAUAI WATERS WILL ADVANCE SOUTHEASTWARD
AND STALL NEAR OAHU WEDNESDAY NIGHT. MODERATE TO LOCALLY STRONG
SOUTHERLY WINDS WILL STRENGTHEN OVER THE WESTERN HALF OF THE STATE
AHEAD OF THE FRONT BEFORE EASING TO LIGHT TO GENTLE SPEEDS
WEDNESDAY NIGHT AND THURSDAY. A SMALL CRAFT ADVISORY (SCA) IS NOW
IN EFFECT FOR STRENGTHENING WINDS AND BACK TO BACK LARGE WNW AND
NNW SWELLS BUILDING SEAS TO 10 FT TONIGHT WITH ANOTHER
REINFORCEMENT THURSDAY. HEAVY SHOWERS AND THUNDERSTORMS ARE
POSSIBLE OVER KAUAI AND OAHU WATERS THROUGH THURSDAY. A STRONG
HIGH PRESSURE SYSTEM WILL BUILD N OF THE STATE FRIDAY ALLOWING
LIGHT TO MODERATE TRADES TO RETURN AND GRADUALLY STRENGTHEN TO
MODERATE TO STRONG SPEEDS SUNDAY INTO EARLY NEXT WEEK.
A LARGE, SHORT TO MEDIUM PERIOD WNW SWELL FILLS IN TONIGHT
THROUGH WEDNESDAY FROM A LOW TO THE NW. THIS SWELL WILL ELEVATE
SURF ALONG NORTH AND WEST FACING SHORES TO JUST BELOW THE HSA
THRESHOLD AND WILL BE FAIRLY CHOPPY. SEAS WILL BUILD TO 10 FEET
AND HIGHER AROUND KAUAI AND OAHU WATERS. A LARGE, MEDIUM PERIOD
NNW SWELL WILL FILL IN WEDNESDAY NIGHT AND PEAK THURSDAY RIGHT
AROUND ADVISORY LEVELS. THIS SWELL WILL KEEP SCA LEVEL SEAS (10
FEET OR GREATER) OVER THE WESTERN HALF OF THE STATE AND POSSIBLY
EXPAND WINDWARD MAUI WATERS. 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 WILL REMAIN SMALL EXCEPT WHERE NW-N SWELL ENERGY WRAPS
THROUGH THE WEEK. BY NEXT WEEK, NE SWELL COULD ELEVATE SURF ALONG
E FACING SHORES AND WILL BECOME MORE CHOPPY AS STRONG TRADE WINDS
RETURN. S SHORE SURF WILL REMAIN CHOPPY AS PERSISTENT S-SW WINDS
HOLD THROUGH WEDNESDAY, BEFORE GRADUALLY EASING THROUGH THE
SECOND HALF WEEK AND SWINGING AROUND TO THE NE.
HFO WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR NIIHAU-KAUAI LEEWARD-
KAUAI MOUNTAINS-WAIANAE COAST-OAHU NORTH SHORE-OLOMANA-CENTRAL
OAHU-WAIANAE MOUNTAINS-KAUAI NORTH-KAUAI EAST-KAUAI SOUTH-EAST
HONOLULU-HONOLULU METRO-EWA PLAIN-KOOLAU WINDWARD-KOOLAU
LEEWARD.
SMALL CRAFT ADVISORY UNTIL 6 AM HST THURSDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-KAUAI CHANNEL-
OAHU WINDWARD WATERS-OAHU LEEWARD WATERS-KAIWI CHANNEL.
UPDATE...ALMANZA
MARINE...ALMANZA
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