604
FXHW60 PHFO 301346
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
346 AM HST FRI MAY 30 2025
SYNOPSIS
WIND SPEEDS WILL INCREASE TODAY AND SATURDAY AS THE HIGH PRESSURE
RIDGE BUILDS IN NORTH OF THE STATE. TRADE WINDS WILL DECREASE A
BIT ON SUNDAY AND BRIEFLY VEER OUT OF THE EAST-SOUTHEAST DIRECTION,
WITH EASTERLIES STRENGTHENING OVER THE ISLANDS INTO THE MODERATE
TO BREEZY RANGE FROM SUNDAY NIGHT INTO WEDNESDAY. WEATHER
CONDITIONS APPEAR TO TREND TOWARDS THE WETTER SIDE STARTING TODAY
WITH INCREASING SHOWER ACTIVITY IN THE FORECAST LASTING INTO THE
MIDDLE OF NEXT WEEK.
DISCUSSION
LOOKING INTO THE SATELLITE IMAGERY THIS MORNING WE SEE AN
INCREASING TREND TOWARDS THE WET SIDE. A WEAK LOW LEVEL TROUGH
JUST EAST OF THE BIG ISLAND WILL BRING SOME ADDITIONAL CLOUDS AND
SHOWERS TO EACH ISLAND THROUGH FRIDAY. THIS TROUGH IS COMING INTO
THE ISLANDS A BIT STRONGER THAN WE ANTICIPATED BASED ON AVAILABLE
GUIDANCE FROM 24 HOURS AGO. IN THE UPPER LEVEL GOES WATER VAPOR
IMAGERY THE SUBSIDENCE ALOFT HAS WEAKENED AS THE SUBTROPICAL JET
STREAM DRIFTS NORTHWARD, BRINGING A BIT MORE INSTABILITY INTO THE
HAWAII REGION. THE UPPER AIR BALLOON SOUNDINGS OBSERVED AT 2 AM
HST (12Z) THIS MORNING FROM LIHUE AND HILO BOTH SHOW TEMPERATURE
INVERSION HEIGHTS AROUND THE 6,500 TO 7,000 FEET ELEVATION LEVEL.
THESE TEMPERATURE INVERSION HEIGHTS WILL LIKELY RISE TO AROUND
8,000 TO 10,000 FEET LATER TODAY AS THIS LOW LEVEL TROUGH MOVES
FROM EAST TO WEST THROUGH THE HAWAIIAN ISLANDS. THE FORECAST
RAINFALL COVERAGE INCREASED IN THIS MORNINGS FORECAST GRID PACKAGE
TO REFLECT THESE HIGHER SHOWER TRENDS.
EXPECT MODERATE TO BREEZY TRADE WINDS TODAY THROUGH SATURDAY AS
THE RIDGE BRIEFLY BUILDS IN NORTH OF THE ISLAND CHAIN. PERIODS OF
SHOWERS WILL REMAIN IN THE FORECAST AS LOW LEVEL CONVERGENT
FORCING WITH THE PASSING 700 MB TROUGH COMBINES FORCES WITH WEAK
DIVERGENCE ALOFT FROM A WEAK UPPER TROUGH AND UPPER LEVEL
DIVERGENCE UNDER THE SUBTROPICAL JET STREAM. AN UPPER LEVEL LOW
WILL WEAKEN AS IT APPROACHES THE ISLANDS FROM THE WEST ON SUNDAY,
AND THEN MERGE WITH A STRONGER UPPER LEVEL LOW DRIFTING IN FROM
THE FAR NORTH. THE BOUNDARY LAYER STEERING FLOW AROUND 5,000 FEET
SHOW EAST-SOUTHEASTERLY WINDS, WHICH MAY PRODUCE SOME LEEWARD
ISLAND MOUNTAIN PLUMES IN A LESS STABLE ENVIRONMENT. THESE ISLAND
PLUMES TEND TO FORM LONG BANDS OF SHOWERS DUE TO CONVERGING WINDS IN
THE LEE OR WEST OF ISLAND MOUNTAINS. THESE BANDS THAT FORM JUST
WEST OF MAUI, MOLOKAI AND LANAI COULD DRIFT INTO OAHU OR EVEN
NEAR KAUAI, PRODUCING BRIEF PERIODS OF ENHANCED SHOWERS FROM
SUNDAY TO MONDAY.
AT THE SURFACE WIND LEVEL, BREEZY EASTERLY TRADE WINDS WILL
RETURN BY SUNDAY NIGHT AND LAST INTO WEDNESDAY. WEAK UPPER LEVEL
DIVERGENCE WILL KEEP MODEST INSTABILITY OVER THE HAWAIIAN ISLANDS
THROUGH WEDNESDAY. MODEL CROSS SECTIONS SUGGEST TEMPERATURE
INVERSION HEIGHTS WILL RANGE FROM 7,000 TO 8,000 FEET, A FAIRLY
WET PATTERN FOR THIS TIME OF YEAR. EXPECT PERIODS OF SHOWERS
FAVORING WINDWARD AND MOUNTAIN AREAS, WITH SOME OF THE STRONGER
SHOWERS BRINGING A FEW PERIODS OF RAINFALL TO THE TYPICALLY DRIER
WESTERN LEEWARD AREAS.
THE LONG RANGE FORECAST FOR THE SECOND HALF OF NEXT WEEK SUGGESTS
LINGERING INSTABILITY ALOFT WITH A WEAK DIVERGENT PATTERN. NOT
MUCH CHANGE TO THE MODERATE EASTERLY TRADE WINDS. SHOWER ACTIVITY
ON THURSDAY AND FRIDAY WILL FAVOR THE WINDWARD AND MOUNTAIN AREAS
IN THE OVERNIGHT TO EARLY MORNING HOURS IN THIS WEATHER PATTERN.
AVIATION
BANDS OF LOW LEVEL CLOUDS ARE RIDING INTO EACH ISLAND ON THE TRADE
WINDS THIS MORNING. PERIODS OF MVFR CONDITIONS WITH LOW CEILINGS
AND SHOWERS SHOULD BE EXPECTED FOR WINDWARD AREAS TODAY AND
TONIGHT. PASSING SHOWERS WILL ALSO AFFECT LEEWARD AIRFIELDS TODAY
AND TONIGHT WITH BRIEF PERIODS OF MVFR CONDITIONS IN SHOWERS POSSIBLE.
AIRMET SIERRA WAS ISSUED THIS MORNING FOR MOUNTAIN OBSCURATIONS
OVER NORTH THOUGH EAST SECTIONS OF OAHU MOLOKAI MAUI AND THE BIG
ISLAND. THESE CONDITIONS WILL LIKELY EXPAND TO KAUAI LATER THIS
MORNING. THESE PERIODS OF MVFR CEILINGS AND SHOWERS SHOULD LAST
THROUGH TONIGHT FOR MOST OF THESE ISLANDS.
MARINE
FRESH TO STRONG TRADES WILL FILL IN TODAY AS THE SURFACE RIDGE
BUILDS NORTH OF THE ISLANDS. EXPECT THE STRONGEST WINDS OVER THE
TYPICALLY WINDIER CHANNELS AND WATERS AROUND MAUI COUNTY AND THE
BIG ISLAND TO PERSIST THROUGH SATURDAY. FORECAST GUIDANCE
SUGGESTS THE RIDGE WILL BRIEFLY WEAKEN THROUGH THE LATTER HALF OF
THE WEEKEND AND AS A BROAD SURFACE TROUGH DEVELOPS FAR NORTHWEST
OF THE AREA. THIS WILL LEAD TO THE TRADES VEERING OUT OF THE
EAST-SOUTHEAST BY SUNDAY, WITH LIGHTER WINDS OVER THE WESTERN END
OF THE STATE AND FRESH TRADES CONTINUING OVER THE EASTERN END.
TRADES WILL SHIFT BACK OUT OF THE EAST AND STRENGTHEN EARLY NEXT
WEEK AS THE TROUGH WEAKENS AND TRACKS AWAY FROM THE AREA.
SURF ALONG EXPOSED SOUTH-FACING SHORES WILL HOLD AROUND AVERAGE
LEVELS TODAY, THEN EASE OVER THE WEEKEND AS A SOUTH SWELL FADES.
THROUGH MUCH OF NEXT WEEK, EXPECT A MIX OF LONG-PERIOD BACKGROUND
SOUTH-SOUTHWEST AND SHORTER-PERIOD SOUTHEAST SWELL. ANOTHER LONG-
PERIOD SOUTH-SOUTHWEST SWELL IS POSSIBLE LATE NEXT WEEK DUE TO A
SYSTEM PASSING THROUGH OUR SWELL WINDOW NEAR NEW ZEALAND. IF THIS
MATERIALIZES, SURF COULD CLIMB TO ABOVE AVERAGE LEVELS BY NEXT
WEEKEND.
SURF ALONG EXPOSED NORTH- AND WEST-FACING SHORES WILL LOWER
THROUGH THE DAY TODAY, THEN CLIMB WELL ABOVE AVERAGE FOR THIS TIME
OF YEAR SATURDAY AS A FRESH, MEDIUM-PERIOD NORTH-NORTHWEST SWELL
ARRIVES. THIS NORTH-NORTHWEST SOURCE WILL LOWER INTO SUNDAY, THEN
RETURN TO SEASONAL LEVELS EARLY NEXT WEEK.
SURF ALONG EAST-FACING SHORES WILL GRADUALLY BUILD OVER THE
WEEKEND AND INTO EARLY NEXT WEEK AS TRADE WINDS RETURN.
HFO WATCHES/WARNINGS/ADVISORIES
SMALL CRAFT ADVISORY UNTIL 6 PM HST SATURDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.
DISCUSSION...BOHLIN
AVIATION...BOHLIN
MARINE...GIBBS
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page