477
FXHW60 PHFO 180146
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
346 PM 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 AN UPPER LOW EMBEDDED WITHIN A BROADER
TROUGH CENTERED NEAR OAHU THIS AFTERNOON. AT THE SURFACE, A BROAD
TROUGH IS PRESENT OVER HAWAII, AND A 1030 MB HIGH IS CENTERED TO
THE DISTANT NORTH-NORTHEAST. WINDS ARE GENERALLY LIGHT TO MODERATE
OUT OF THE EAST SOUTHEAST. PARTIAL BLOCKING FROM THE BIG ISLAND
AND MAUI COUNTY IS KEEPING LEEWARD WINDS LIGHTER AND ALLOWING FOR
ONSHORE SEA BREEZES THIS AFTERNOON. VISIBLE SATELLITE IMAGERY AND
RADAR SHOW MOSTLY CLOUDY CONDITIONS IN PLACE WITH NUMEROUS
SHOWERS ACROSS THE SMALLER ISLANDS, AND ISOLATED SHOWERS OVER THE
BIG ISLAND. MAIN SHORT TERM FOCUS REVOLVES AROUND THE POTENTIAL
FOR HEAVY RAIN AND THUNDERSTORMS DURING THE NEXT COUPLE DAYS.
THE 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. AS THE UPPER LOW MOVES EASTWARD TONIGHT, 500 MB
TEMPERATURES OF -12 TO -13 C AND PRECIPITABLE WATER VALUES AROUND
1.5 TO 1.6 INCHES WILL RESULT IN HEAVY SHOWERS AND ISOLATED
THUNDERSTORMS ACROSS ANY OF THE ISLANDS THROUGH FRIDAY. LAND
BREEZES MAY HELP SUPPRESS THE HEAVY RAIN OVER THE ISLANDS BY LATE
TONIGHT INTO FRIDAY MORNING, BUT THE FOCUS WILL SHIFT BACK OVER
THE ISLANDS BY MIDDAY FRIDAY. SNOW IS EXPECTED ACROSS THE HIGH
ELEVATION SUMMITS OF THE BIG ISLAND AND WINTER WEATHER ADVISORY IS
NOW IN EFFECT 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, POTENT STORM SYSTEM WILL BRING
SOUTHERLY WINDS BEGINNING MONDAY AND ANOTHER ROUND OF POTENTIALLY
SIGNIFICANT RAINFALL TUESDAY THROUGH THURSDAY.
AVIATION
A STATIONARY FRONT WEST OF THE ISLANDS AND UPPER LEVEL TROUGHING
WILL ALLOW UNSTABLE CONDITIONS TO CONTINUE STATEWIDE THROUGH
TOMORROW. A MOIST LIGHT SOUTHEASTERLY FLOW WITH LOCALIZED LAND/SEA
BREEZES ARE CURRENTLY BRINGING MODERATE TO HEAVY SHOWERS AND
THUNDERSTORMS OVER THE ISLANDS. THIS PATTERN WILL CONTINUE THROUGH
TOMORROW AS UPPER LEVEL TROUGHING LINGERS WITH WIDESPREAD MVFR
AND LOCALIZED IFR CIG/VIS IN +TSRA/+SHRA.
AIRMET SIERRA IS IN EFFECT FOR MOUNTAIN OBSCURATION OVER SOUTH AND
EAST FACING AREAS OF KAUAI, OAHU, AND MAUI DUE TO PERSISTENT HEAVY
SHOWERS AND THUNDERSTORMS.
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 SHOULD GRADUALLY DECREASE LATER TONIGHT.
MARINE
LIGHT TO MODERATE EAST-SOUTHEAST WINDS WILL PERSIST. 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 CONTINUE, PARTICULARLY AROUND THE BIG
ISLAND. MODERATE TRADE WIND FLOW IS EXPECTED TO RETURN ON SATURDAY
OR SUNDAY ONCE HIGH PRESSURE TO THE NORTHEAST OF THE STATE BUILDS
AND STRENGTHENS.
AN UPPER LEVEL DISTURBANCE SLOWLY MOVING OVER THE AREA WILL
TRIGGER LOCALLY HEAVY SHOWERS OR THUNDERSTORMS OVER THE SMALLER
ISLAND THIS EVENING. CONDITIONS ARE EXPECTED TO SPREAD ACROSS THE
BIG ISLAND LATE TONIGHT OR FRIDAY MORNING.
RECENT REPORTS FROM OFFSHORE BUOYS INDICATE THE NEW NORTHWEST
SWELL IS COMING IN TWO TO THREE FEET ABOVE MODEL GUIDANCE. SURF
HEIGHTS ALONG EXPOSED NORTH AND WEST FACING SHORES ARE NOW EXPECTED
TO PEAK JUST ABOVE ADVISORY CRITERIA DURING THE OVERNIGHT HOURS.
A HIGH SURF ADVISORY HAS BEEN ISSUED FOR NORTH AND WEST FACING
SHORES OF NIIHAU, KAUAI, OAHU, AND MOLOKAI AND ALSO NORTH FACING
SHORES OF MAUI. ON FRIDAY, THE SWELL WILL BEGIN TO GRADUALLY FADE
AND VEER TO THE NORTH. NO FURTHER LARGE NORTH OR NORTHWEST SWELLS
ARE ANTICIPATED FOR THE WEEKEND OR IN THE COMING WEEK.
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
HIGH SURF ADVISORY UNTIL 6 AM HST FRIDAY FOR NIIHAU-WAIANAE
COAST-OAHU NORTH SHORE-MAUI WINDWARD WEST-KAUAI NORTH-MOLOKAI
WINDWARD- MOLOKAI NORTH-MOLOKAI WEST-MAUI CENTRAL VALLEY NORTH-
WINDWARD HALEAKALA.
WINTER WEATHER ADVISORY UNTIL 6 PM HST FRIDAY FOR BIG ISLAND
SUMMITS.
DISCUSSION...FOSTER
AVIATION...TSAMOUS
MARINE...BEDAL
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