049
FXHW60 PHFO 141359
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
359 AM HST SUN SEP 14 2025
SYNOPSIS
A HIGH PRESSURE RIDGE NORTH OF THE HAWAIIAN ISLANDS AND A WEAK
LOW DRIFTING WESTWARD JUST SOUTHEAST OF THE ISLAND CHAIN WILL
BOOST TRADE WINDS SLIGHTLY THROUGH MONDAY. A HIGH PRESSURE RIDGE
ALOFT WILL CONTINUE TO PRODUCE STABLE SUBSIDENT CONDITIONS ACROSS
THE REGION WITH LIMITED SHOWER ACTIVITY LASTING THROUGH MONDAY.
WEATHER CONDITIONS SHIFT TOWARDS THE WETTER SIDE ON TUESDAY AND
WEDNESDAY AS A WAVE MOVING THROUGH THE LOW LEVEL EASTERLIES
INCREASES CLOUDS AND SHOWERS AS THE TROUGH PASSES WESTWARD ACROSS
THE STATE. ADDITIONAL INSTABILITY WILL DEVELOP OVER THE ISLANDS
FROM THURSDAY INTO NEXT WEEKEND, INCREASING CLOUDS, SHOWERS AND
HUMIDITY LEVELS A BIT.
DISCUSSION
LOOKING AT THE LARGE SCALE WEATHER PATTERN WE SEE A HIGH PRESSURE
RIDGE ANCHORED JUST NORTH OF THE HAWAIIAN ISLANDS AND A WEAK LOW
PRESSURE SYSTEM DRIFTING WESTWARD JUST SOUTHEAST OF THE STATE.
INCREASING PRESSURE GRADIENTS FROM THESE TWO SYSTEMS WILL BOOST
WIND SPEEDS SLIGHTLY THROUGH MONDAY AS COMPARED TO SATURDAY. DRY
SUMMER WEATHER CONDITIONS WITH MODERATE TO LOCALLY BREEZY TRADE
WINDS WILL CONTINUE WITH LITTLE CHANGES TO THE OVERALL PATTERN
THROUGH MONDAY.
THE PATTERN BEGINS TO WEAVE TOWARDS THE WET SIDE ON TUESDAY AS A
WEAK WAVE DRIFTING WESTWARD THROUGH THE LOW LEVEL EASTERLIES
INCREASES CLOUDS AND SHOWERS ACROSS THE ISLANDS. THIS TROUGH
APPEARS A BIT WEAKER THAN THE LAST LOW LEVEL EASTERLY WAVE THAT
BROUGHT A DECENT AMOUNT OF RAIN TO THE ISLANDS A FEW DAYS AGO.
THIS MEANS WE ARE FORECASTING LOWER RAINFALL AMOUNTS WITH
INCREASING RAINFALL COVERAGE FAVORING THE OVERNIGHT TO EARLY
MORNING HOURS. WHILE WINDWARD AND MOUNTAIN AREAS WILL SEE THE
MAJORITY OF ENHANCED SHOWER ACTIVITY DURING THIS TIME PERIOD, SOME
OF THE STRONGER TRADE WIND SHOWERS WILL DRIFT INTO THE LEEWARD
AREAS WEST OF ISLAND MOUNTAINS.
UNSETTLED WEATHER CONDITIONS WILL LIKELY CONTINUE FROM THURSDAY
INTO NEXT WEEKEND AS A COMBINATION OF DEEP EASTERLIES UP TO AROUND
18,000 FEET WILL INTERACT WITH SUBTROPICAL JET STREAM DIVERGENCE
TO ENHANCE TYPICAL TRADE WIND SHOWERS OVER ALL ISLANDS. LONG
RANGE WEATHER MODEL SOLUTIONS ARE SUGGESTING THE SUBSIDENCE
TEMPERATURE INVERSION HEIGHTS WILL HOVER AROUND THE 7,000 FOOT
ELEVATION LEVEL, WHICH SUPPORTS ISOLATED TO SCATTERED SHOWERS
DURING THE DAY, AND SCATTERED TO NUMEROUS SHOWERS AT NIGHT WITH
WINDWARD MOUNTAIN AREAS SEEING THE HIGHER COVERAGES IN THIS RANGE.
DAY TO DAY CHANGES IN THE FORECAST SHOWER PATTERN FOR EACH ISLAND
REMAINS LIKELY THIS FAR OUT, AND THUNDERSTORMS OVER THE WESTERN
HIGHER ELEVATION SLOPES OF THE BIG ISLAND CANNOT BE RULED OUT
DURING THIS TIME PERIOD. STAY TUNED.
AVIATION
A HIGH PRESSURE RIDGE NORTH OF THE ISLANDS AND A WEAK LOW
SOUTHEAST OF THE BIG ISLAND WILL KEEP MODERATE TO BREEZY EASTERLY
TRADE WINDS IN THE FORECAST THROUGH MONDAY. STABLE CONDITIONS
ALOFT WILL KEEP CLOUDS AND SHOWERS TO A MINIMUM WITH WINDWARD
AIRFIELDS SEEING BRIEF PERIODS OF SHOWER ACTIVITY.
NO AIRMETS ARE IN EFFECT. AN AIRMET FOR MODERATE LOW LEVEL
TURBULENCE OVER AND SOUTH THROUGH WEST OF ISLAND MOUNTAINS MAY
BE NEEDED LATER TODAY DUE TO INCREASING WINDS.
MARINE
WEAK SURFACE HIGH PRESSURE WILL REMAIN NEARLY STATIONARY NORTH OF
THE ISLANDS TODAY. A LOW SLOWLY MOVING WEST SOUTHEAST OF THE STATE
WILL CREATE A TIGHT ENOUGH PRESSURE GRADIENT ACROSS THE NEARSHORE
WATERS TO RESULT IN ANOTHER COUPLE OF DAYS OF MODERATE TO LOCALLY
STRONG TRADES. THE SMALL CRAFT ADVISORY (SCA) HAS BEEN EXTENDED
FOR THE WINDIER WATERS SURROUNDING MAUI COUNTY AND BIG ISLAND
THROUGH MONDAY AFTERNOON. A COLD FRONT PASSING ATOP THIS HIGH
NORTH OF THE STATE WILL SLIGHTLY WEAKEN IT BEFORE THE BACKING HIGH
BEHIND THE FRONT RE-TIGHTENS THE DOWNSTREAM PRESSURE GRADIENT.
HOWEVER, THE WEAKENING LOW DRIFTING WESTWARD JUST SOUTH OF THE
ISLANDS WILL KEEP TRADE WINDS AT SIMILAR SPEEDS THROUGH MONDAY.
EXPECT A BRIEF DROP OFF IN WIND SPEEDS BY TUESDAY, WITH TRADES
PICKING BACK UP TO MORE FRESH TO LOCALLY STRONG MAGNITUDES BY
WEDNESDAY.
THE RECENT SMALL, MEDIUM PERIOD NORTH SWELL WILL SIGNIFICANTLY FALL
OFF TODAY AND PRODUCE WAIST HIGH SURF BY LATE AFTERNOON. ANOTHER
MEDIUM PERIOD NORTH SWELL ARRIVAL THURSDAY MAY CAUSE A SLIGHT BUMP
IN LATE WEEK SURF ALONG NORTH-FACING SHORES. SURF ALONG SOUTH-FACING
SHORES WILL REMAIN NEAR OR SLIGHTLY ABOVE LATE SUMMER NORMS TODAY.
A SMALL, LONGER PERIOD SOUTH SWELL REINFORCEMENT ARRIVING EARLY
THIS MORNING WILL HOLD TODAY'S SOUTH SHORE SURF TO AROUND WAIST
HIGH. TYPICAL EAST-FACING SHORE SHORT PERIOD WIND WAVE CHOP WILL
HOLD THROUGH MONDAY AS THE ISLANDS REMAIN UNDER A MODERATE TRADE
FETCH OVER AND JUST UPSTREAM OF THE ISLANDS.
FIRE WEATHER
LOW HUMIDITY LEVELS WILL CONTINUE TODAY WITH SUSTAINED WIND SPEEDS
APPROACHING CRITICAL FIRE WEATHER THRESHOLDS FOR A FEW HOURS EACH
AFTERNOON THROUGH MONDAY. EXPECT DECREASING FIRE WEATHER THREATS
FROM TUESDAY INTO NEXT WEEKEND DUE TO HIGHER AFTERNOON MINIMUM
HUMIDITY LEVELS. TEMPERATURE INVERSION HEIGHTS NEAR THE BIG ISLAND
AND MAUI WILL RANGE FROM 5,000 TO 6,500 FEET TODAY.
HFO WATCHES/WARNINGS/ADVISORIES
SMALL CRAFT ADVISORY UNTIL 6 PM HST MONDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.
DISCUSSION...BOHLIN
AVIATION...BOHLIN
MARINE...BLOOD
FIRE WEATHER...BOHLIN
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