345
FXHW60 PHFO 181400
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST FRI APR 18 2025
SYNOPSIS
A CONVECTIVE PATTERN WITH MOSTLY LIGHT WINDS WILL HOLD IN PLACE
TODAY, WITH SHOWERS FAVORING THE ISLAND INTERIORS DURING THE
AFTERNOON AND EVENING HOURS AND ALONG WINDWARD AREAS OVERNIGHT.
LOCALLY HEAVY RAIN AND A SLIGHT CHANCE OF THUNDERSTORMS IS
FORECAST THROUGH TODAY AS AN UPPER LOW MOVES OVER THE STATE.
MODERATE TRADES ARE EXPECTED TO RETURN SATURDAY THROUGH THE
WEEKEND. LINGERING MOISTURE AND INSTABILITY WILL LIKELY KEEP A
RATHER SHOWERY PATTERN, EVEN FOR LEEWARD AREAS THROUGH THE WEEKEND.
A NEW STORM SYSTEM COULD BRING ANOTHER CHANCE FOR HEAVY RAINFALL
AND THUNDERSTORMS TO THE ISLANDS TUESDAY AND WEDNESDAY.
DISCUSSION
AN UPPER LEVEL LOW IS NOW CENTER OVER MAUI COUNTY AND CONTINUES
TO PROVIDE AMPLE INSTABILITY ACROSS THE STATE. A SURFACE TROUGH
LOCATED JUST WEST OF KAUAI IS GENERATING LIGHT TO MODERATE EAST TO
SOUTHEAST FLOW OVER THE STATE WHILE OF POOL OF PRECIPITABLE WATER
VALUES AROUND 1.5 INCHES LINGERS ACROSS THE STATE. INFRARED
SATELLITE IMAGERY SHOWS MOSTLY CLOUDY CONDITIONS ACROSS THE STATE
EXPECT FOR PARTLY CLOUDY CONDITIONS OVER OAHU. RADAR SHOWS
NUMEROUS LIGHT TO MODERATE SHOWERS ARE CURRENTLY OVER KAUAI AND
THE COASTAL WATERS WITH A FEW SHOWERS MAKING IN WINDWARD AREAS OF
OAHU AND SOUTHEAST BIG ISLAND.
THE SURFACE TROUGH IS EXPECTED TO WEAKEN AND TRACK WEST OF THE
STATE TODAY AND SATURDAY, ALLOWING LIGHT TO MODERATE EAST
SOUTHEAST WINDS TO TRANSITION TO A MORE MODERATE EASTERLY FLOW
PATTERN TONIGHT INTO SATURDAY. EXPECT A HYBRID PATTERN WHERE
SHOWERS ARE MAINLY FOCUSED ALONG WINDWARD AND MAUKA AREAS, BUT
LEEWARD AND INTERIOR AREAS WILL STILL SEE CLOUDS AND SHOWERS
DEVELOP DUE TO SEA BREEZES. THE UPPER LOW IS EXPECTED TO CONTINUE
TO MOVE EASTWARD AND WEAKEN TODAY INTO SATURDAY, BUT WILL STILL
PROVIDE ENOUGH INSTABILITY TO CONTINUE THE THREAT OF LOCALLY HEAVY
SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE EASTERN HALF OF THE
STATE. THE INSTABILITY WILL ALSO ALLOW WINDWARD SHOWERS TO SPILL
OVER TO LEEWARD AREAS. SNOW IS EXPECTED ACROSS THE HIGH ELEVATION
SUMMITS OF THE BIG ISLAND AND WINTER WEATHER ADVISORY HAS BEEN
EXTENDED THROUGH 6 AM SATURDAY FOR ELEVATIONS ABOVE 11,000 FEET.
THE UPPER LOW WILL OPEN UP TO A TROUGH AS IT WEAKENS OVER THE
WEEKEND. THUNDERSTORMS OR HEAVY SHOWERS COULD BE POSSIBLE OVER THE
WEEKEND GIVEN THE REMNANT MOISTURE AROUND THE ISLANDS AND MODEL
GUIDANCE IS ALSO HINTING AT A SHORT WAVE TROUGH DIPPING DOWN
SUNDAY THAT WILL KEEPING SO UNSTABLE CONDITIONS OVER THE STATE
EVEN AS MODERATE TRADES RETURN. AS A RESULT, EXPECT A SHOWERY
TRADEWIND PATTERN THROUGH THE WEEKEND, WITH SHOWERS SPILLING OVER
TO LEEWARD AREAS. A NEW, POTENT STORM SYSTEM WILL DISRUPT THE
TRADEWIND FLOW MUCH OF NEXT WEEK BRINGING LIGHT TO MODERATE
SOUTHERLY WINDS LATE MONDAY INTO TUESDAY AND ANOTHER ROUND OF
POTENTIALLY SIGNIFICANT RAINFALL TUESDAY THROUGH THURSDAY.
AVIATION
UNSTABLE EAST-SOUTHEAST WINDS WILL MAINTAIN MVFR CONDITIONS
ACROSS SOME EAST AND SOUTHEAST SLOPES WITH POCKETS OF HEAVY
SHOWERS AND THUNDERSTORMS PRODUCING IFR CONDITIONS TODAY. GENTLE
TO MODERATE EAST TO SOUTHEAST WINDS WILL GRADUALLY SHIFT OUT OF
THE EAST TONIGHT AND SATURDAY AS A SURFACE TROUGH WEST OF KAUAI
DRIFTS AWAY FROM THE STATE. AN UPPER-LEVEL LOW, CURRENTLY
CENTERED NEAR MAUI COUNTY, WILL DRIFT EASTWARD, MAINTAINING
INSTABILITY OVER ALL ISLANDS THROUGH THE MORNING, WITH THE
GREATEST CHANCES FOR HEAVY SHOWERS AND THUNDERSTORMS SHIFTING TO
THE EASTERN HALF OF THE ISLAND CHAIN DURING THE AFTERNOON AND
EVENING.
AIRMET SIERRA IS IN EFFECT FOR MOUNTAIN OBSCURATION OVER EAST AND
SOUTH FACING TERRAIN OF KAUAI, OAHU, AND MAUI DUE TO REDUCED
VISIBILITY AND LOW CEILINGS IN HEAVY SHOWERS. AS INSTABILITY
SHIFTS EASTWARD LATER IN THE DAY, THE AIRMET MAY NEED TO BE
EXPANDED TO THE BIG ISLAND, AND KAUAI AND OAHU MAY EXPERIENCE
SOME IMPROVEMENT.
MODERATE UPPER-LEVEL TURBULENCE WILL BE POSSIBLE NEAR AND WEST OF
THE UPPER LOW CENTER. AIRMET TANGO REMAINS IN EFFECT FOR KAUAI
AND OAHU THROUGH THE PREDAWN HOURS AND WILL SHIFT EASTWARD AND
DIMINISH ON FRIDAY.
MARINE
LIGHT TO MODERATE EAST-SOUTHEAST WINDS WILL PERSIST TODAY DUE TO
A BROAD SURFACE TROUGH LOCATED WEST OF KAUAI. OVER THE WESTERN END
OF THE ISLANDS, THE LIGHT WINDS WILL ALLOW A LAND AND SEA BREEZE
PATTERN TO CONTINUE NEAR THE COASTS. FOR THE EASTERN END, LIGHT TO
MODERATE EAST TO SOUTHEAST BREEZES, WITH LOCALIZED FRESH POCKETS,
WILL LIKELY PERSIST, PARTICULARLY AROUND THE BIG ISLAND. EXPECT
SPOTTY HEAVY SHOWERS AND THUNDERSTORMS TO CONTINUE TODAY DUE TO AN
UPPER DISTURBANCE IN THE AREA. A RETURN TO MODERATE EASTERLY
TRADES IS EXPECTED OVER THE WEEKEND AS HIGH PRESSURE BUILDS TO THE
NORTHEAST. GUIDANCE CONTINUES TO SHOW THE TRADES BECOMING
DISRUPTED AND SHIFTING OUT OF THE SOUTH EARLY NEXT WEEK AS DEEP
LOW PRESSURE SETS UP NEARBY TO THE WEST.
SURF ALONG EXPOSED NORTH AND WEST FACING SHORES PEAKED OVERNIGHT
AND WILL STEADILY LOWER TODAY THROUGH THE WEEKEND, WITH THE SWELL
DIRECTION SHIFTING OUT OF THE NORTH-NORTHWEST. SURF WILL DIP
BELOW AVERAGE BY SUNDAY, THEN CONTINUE WELL INTO NEXT WEEK, WITH
MAINLY A BACKGROUND LEVEL NORTHWEST SWELL POSSIBLE BY TUESDAY.
GUIDANCE DOES DEPICT A GALE FORMING MONDAY NEAR THE KURILS, THEN
TRACKING NORTHEAST TO THE WESTERN ALEUTIANS BY WEDNESDAY. IF THIS
MATERIALIZES, WE COULD SEE A SLIGHT UPWARD TREND AS A SMALL
NORTHWEST SWELL ARRIVES NEXT WEEKEND.
SURF ALONG EAST FACING SHORES WILL REMAIN BELOW THE APRIL AVERAGE
THROUGH EARLY NEXT WEEK DUE TO THE LACK OF TRADES LOCALLY AND
UPSTREAM.
SURF ALONG SOUTH FACING SHORES WILL REMAIN SMALL THIS WEEKEND,
AS A BACKGROUND SOUTH SWELL MOVES THROUGH. A LARGER PULSE OF
SOUTH-SOUTHWEST SWELL MAY ARRIVE EARLY NEXT WEEK.
HFO WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL 6 AM HST SATURDAY FOR BIG ISLAND
SUMMITS.
DISCUSSION...ALMANZA
AVIATION...WROE
MARINE...GIBBS
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page