997
FXHW60 PHFO 180610
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
810 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
AN UPPER LEVEL LOW CONTINUES TO BUILD OVER THE STATE THIS EVENING
GENERATING SIGNIFICANT AMOUNT OF INSTABILITY. A SURFACE TROUGH LOCATED
JUST WEST OF KAUAI IS GENERATING LIGHT TO MODERATE EAST TO SOUTHEAST
FLOW OVER THE STATE WITH PRECIPITABLE WATER VALUES AROUND 1.5 INCHES.
INFRARED SATELLITE IMAGERY AND RADAR SHOW MOSTLY CLOUDY CONDITIONS
IN PLACE WITH NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS MOSTLY ALONG
WINDWARD MAUI AND OAHU WITH A FEW SHOWERS DEVELOPING OVER LEEWARD BIG
ISLAND AND KAUAI. 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
LIGHT TO MODERATE EAST SOUTHEAST WINDS ALLOWING FOR NIGHTTIME LAND
AND DAYTIME SEA BREEZES. AS THE UPPER LOW SLOWLY MOVES EASTWARD TONIGHT
INTO FRIDAY, 500 MB TEMPERATURES OF -12 TO -13 C AND PRECIPITABLE WATER
VALUES AROUND 1.5 TO 1.6 INCHES WILL CONTINUE THE THREAT OF HEAVY SHOWERS
AND ISOLATED THUNDERSTORMS ACROSS ANY OF THE ISLANDS. 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 REMAINS 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
UNSTABLE EAST-SOUTHEAST WINDS WILL MAINTAIN WIDESPREAD MVFR
CONDITIONS ACROSS MOST EAST AND SOUTHEAST SLOPES WITH POCKETS OF
HEAVY SHOWERS AND THUNDERSTORMS PRODUCING IFR CONDITIONS TONIGHT.
A SURFACE TROUGH WEST OF KAUAI WILL CREEP AWAY FROM THE ISLANDS ON
FRIDAY, THOUGH WILL GENTLE TO MODERATE WINDS PERSIST OUT OF THE
EAST TO SOUTHEAST. AN UPPER-LEVEL LOW, CURRENTLY CENTERED NEAR
OAHU, WILL DRIFT EASTWARD, MAINTAINING INSTABILITY STATEWIDE
TONIGHT, AND THE GREATEST CHANCES FOR HEAVY SHOWERS AND
THUNDERSTORMS SHIFTING TO THE EASTERN HALF OF THE ISLAND CHAIN
FRIDAY.
AIRMET SIERRA IS IN EFFECT FOR MOUNTAIN OBSCURATION OVER EAST AND
SOUTH FACING AREAS OF KAUAI, OAHU, AND MAUI DUE TO REDUCED
VISIBILITY AND LOW CEILINGS IN HEAVY SHOWERS AND THUNDERSTORMS.
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 MIDNIGHT AND WILL SHIFT EASTWARD AND DIMINISH ON
FRIDAY.
MARINE
LIGHT TO MODERATE EAST-SOUTHEAST WINDS WILL PERSIST INTO FRIDAY
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
INTO FRIDAY DUE TO AN UPPER DISTURBANCE IN THE AREA.
A RETURN TO MODERATE EASTERLY TRADES IS POSSIBLE BY THE WEEKEND
AS HIGH PRESSURE BUILDS TO THE NORTH. HEAVY SHOWERS AND
THUNDERSTORMS WILL REMAIN POSSIBLE INTO FRIDAY DUE TO AN UPPER
DISTURBANCE IN THE AREA. 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 IS QUICKLY RISING
THIS EVENING AS A FRESH NORTH-NORTHWEST BUILDS DOWN THE ISLAND
CHAIN. OBSERVATIONS AT THE OFFSHORE BUOYS TO THE NORTHWEST PEAKED
ABOVE THE PREDICTED LEVELS THIS AFTERNOON, WHICH WILL CORRESPOND
TO THE SURF PEAKING OVERNIGHT AND INTO FRIDAY MORNING. HEIGHTS
COULD BRIEFLY NEAR WARNING LEVELS DURING THIS PEAK (AROUND
MIDNIGHT). A DOWNWARD TREND IS THEN EXPECTED OVER THE WEEKEND,
WITH THE SWELL SHIFTING 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
HIGH SURF ADVISORY UNTIL 6 AM HST FRIDAY FOR 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...ALMANZA
AVIATION...WROE
MARINE...GIBBS
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