383
FXHW60 PHFO 171933
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
933 AM HST THU APR 17 2025
SYNOPSIS
A CONVECTIVE PATTERN WITH MOSTLY LIGHT WINDS WILL HOLD IN PLACE
DURING THE NEXT COUPLE DAYS, WITH SHOWERS FAVORING AREAS NEAR THE
COAST AT NIGHT AND THE ISLAND INTERIORS DURING THE AFTERNOON AND
EVENING HOURS. LOCALLY HEAVY RAIN AND A SLIGHT CHANCE OF
THUNDERSTORMS IS FORECAST THROUGH FRIDAY AS AN UPPER LOW MOVES
OVER THE STATE. LINGERING MOISTURE WILL LIKELY KEEP THE PATTERN
RATHER SHOWERY, EVEN IN LEEWARD AREAS AT TIMES THROUGH THE WEEKEND.
A NEW STORM SYSTEM COULD BRING ANOTHER CHANCE FOR HEAVY RAINFALL
AND THUNDERSTORMS TO THE ISLANDS TUESDAY AND WEDNESDAY.
DISCUSSION
WATER VAPOR IMAGERY SHOWS A DIGGING UPPER LOW EMBEDDED WITHIN A BROADER
TROUGH CENTERED JUST NORTHWEST OF KAUAI THIS MORNING. AT THE SURFACE,
A WEAKENING STATIONARY FRONT IS ALSO LOCATED JUST NORTHWEST OF
KAUAI, WITH BROAD TROUGHING NOW PRESENT OVER THE ISLAND CHAIN.
A 1030 MB HIGH IS CENTERED TO THE DISTANT NORTH-NORTHEAST. WINDS
ARE LIGHT AND VARIABLE ACROSS THE WESTERN ISLANDS, WHILE LIGHT TO
MODERATE EAST-SOUTHEASTERLIES ARE PRESENT IN UNSHELTERED SECTIONS
OF MAUI COUNTY AND THE BIG ISLAND. INFRARED SATELLITE IMAGERY
SHOWS MOSTLY CLOUDY CONDITIONS IN PLACE, WITH RADAR IMAGERY
SHOWING A FEW SHOWERS NEAR THE COASTS OF THE ISLANDS, WITH MOST
ACTIVITY OVER THE COASTAL WATERS. MAIN SHORT TERM FOCUS REVOLVES
AROUND THE POTENTIAL FOR HEAVY RAIN AND THUNDERSTORMS DURING THE
NEXT COUPLE DAYS.
THE STATIONARY FRONT WILL DISSIPATE LATER TODAY, BUT BROAD SURFACE
TROUGHING WILL HOLD IN PLACE INTO FRIDAY, CONTINUING THE NIGHTTIME
LAND AND DAYTIME SEA BREEZES WITH GENTLE TO MODERATE EAST SOUTHEAST
WINDS OVER EXPOSED PORTIONS OF THE BIG ISLAND AND MAUI COUNTY.
THROUGH FRIDAY, SHOWERS WILL FAVOR OVER THE WATER AT NIGHT AND
MORNING AND THE ISLAND INTERIORS DURING THE AFTERNOON AND EVENING
HOURS. AS THE UPPER LOW AND COLD POOL MOVE ACROSS THE STATE, 500
MB TEMPERATURES OF -12 TO -14 C AND PRECIPITABLE WATER VALUES
AROUND 1.5 INCHES WILL RESULT IN HEAVY SHOWERS POTENTIALLY ACROSS
ANY OF THE ISLANDS THIS AFTERNOON AND EVENING, AND REPEATING AGAIN
FRIDAY. ISOLATED THUNDERSTORMS WILL REMAIN POSSIBLE GIVEN THE
UNSTABLE ATMOSPHERE CAUSED BY THE COLD POOL ALOFT. SNOW IS EXPECTED
ACROSS THE HIGH ELEVATION SUMMITS OF THE BIG ISLAND AND WINTER
WEATHER ADVISORY IS NOW IN EFFECT FROM NOON TODAY THROUGH 6 PM
FRIDAY FOR ELEVATIONS ABOVE 11,000 FEET.
THE UPPER LOW WILL OPEN UP TO A TROUGH AND WEAKEN THROUGH THE
WEEKEND. THUNDERSTORMS OR HEAVY SHOWERS COULD BE POSSIBLE AFTER
FRIDAY GIVEN THE REMNANT MOISTURE AROUND THE ISLANDS, BUT THE
ATMOSPHERE OVER HAWAII WILL BEGIN TO STABILIZE AND WILL LOWER THE
CHANCES FOR THIS. PRECIPITABLE WATER VALUES CONTINUE TO HOLD
CLOSE TO 1.5 INCHES THROUGH THE WEEKEND AND THE LATEST MODEL
TRENDS HAVE BEEN FOR WEAK TRADE WINDS. AS A RESULT, THE PATTERN
LOOKS A BIT SHOWERY THROUGH THE WEEKEND, WITH BOTH WINDWARD
SHOWERS, AND CHANCES FOR SHOWERS EACH AFTERNOON AND EVENING IN
LEEWARD AREAS AS WELL. A NEW STORM SYSTEM WILL BRING SOUTHERLY
WINDS BEGINNING MONDAY AND ANOTHER ROUND OF HEAVY RAIN AND
THUNDERSTORMS TUESDAY AND WEDNESDAY.
AVIATION
A STATIONARY FRONT LINGERING WEST OF THE ISLANDS AND UPPER LEVEL
TROUGHING HAS LEAD TO UNSTABLE CONDITIONS STATEWIDE. LIGHT
SOUTHEASTERLY FLOW WITH LOCALIZED LAND/SEA BREEZES IS CURRENTLY
BRINGING SPOTTY MODERATE TO HEAVY SHOWERS OVER SOUTH AND EAST
FACING AREAS OF EACH ISLAND. SOME OF THE HEAVIER SHOWERS HAVE BEEN
DEVELOPING INTO THUNDERSTORMS DUE TO THE INSTABILITY. THIS
PATTERN WILL CONTINUE THROUGH TOMORROW AND COULD FURTHER
DETERIORATE TODAY, LEADING TO WIDESPREAD MVFR WITH LOCALIZED IFR
CIG/VIS IN +TSRA/+SHRA. DUE TO THE DISORGANIZED NATURE OF THIS
SYSTEM, IT IS NOT KNOWN EXACTLY WHERE THE THUNDERSTORMS OR THE
HEAVIEST SHOWERS WILL SET UP.
AIRMET SIERRA IS IN EFFECT FOR MOUNTAIN OBSCURATION OVER EAST
FACING AREAS OF KAUAI AND OAHU DUE TO PERSISTENT HEAVY SHOWERS
AND THUNDERSTORMS OVER KAUAI.
THERE ALSO IS A CHANCE FOR MODERATE UPPER LEVEL TURBULENCE OVER
THE WESTERN HALF OF THE STATE DUE TO THE UPPER LEVEL TROUGH. THIS
THREAT COULD CONTINUE THROUGH TODAY.
MARINE
LIGHT TO MODERATE EAST-SOUTHEAST WINDS WILL PERSIST INTO FRIDAY
AS A STALLED FRONT SLOWLY DIMINISHES TO THE WEST. OVER THE
WESTERN END OF THE ISLANDS, THE LIGHT WINDS WILL ALLOW A LAND AND
SEA BREEZE PATTERN TO DEVELOP 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. A RETURN TO MODERATE EASTERLY TRADES IS POSSIBLE BY THE
WEEKEND AS HIGH PRESSURE BUILDS TO THE NORTH.
AN UPPER LEVEL DISTURBANCE SLOWLY MOVING OVER THE AREA WILL
TRIGGER OCCASIONAL HEAVY SHOWERS OR THUNDERSTORMS OVER THE WESTERN
END OF THE STATE TODAY. CONDITIONS ARE EXPECTED TO SPREAD TO THE
REMAINDER OF THE SMALLER ISLANDS THIS EVENING AND THE WHOLE OF THE
STATE BY FRIDAY MORNING.
SURF ALONG EXPOSED NORTH AND WEST FACING SHORES WILL TREND UP
TODAY AS A FRESH NORTH-NORTHWEST ARRIVES AND BUILDS DOWN THE
ISLAND CHAIN. OBSERVATIONS AT THE OFFSHORE BUOYS TO THE NORTHWEST
STARTED TRENDING UP AROUND MIDNIGHT, WHICH SHOULD START SHOWING AT
EXPOSED SHORES ON KAUAI AROUND NOON, THEN TO OAHU AND MAUI COUNTY
THIS AFTERNOON BY THIS EVENING. SURF IS EXPECTED TO PEAK JUST
BELOW ADVISORY LEVELS FOR EXPOSED NORTH AND WEST FACING SHORES
LATE TONIGHT. A DOWNWARD TREND IS THEN EXPECTED OVER THE WEEKEND,
WITH THE SWELL SHIFTING TO BE OUT OF NORTH.
SURF ALONG EAST FACING SHORES WILL REMAIN BELOW THE APRIL AVERAGE
THROUGH AT LEAST SATURDAY, THEN STEADILY RISE TO AROUND AVERAGE
BY EARLY NEXT WEEK.
SURF ALONG SOUTH FACING SHORES WILL REMAIN SMALL, WITH MAINLY
OVERLAPPING BACKGROUND SOUTH SWELLS MOVING THROUGH. A LARGER PULSE
OF SOUTH-SOUTHWEST SWELL MAY ARRIVE TUESDAY.
HFO WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY FROM NOON TODAY TO 6 PM HST FRIDAY FOR
BIG ISLAND SUMMITS.
DISCUSSION...FOSTER
AVIATION...TSAMOUS
MARINE...BEDAL
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