676
FXHW60 PHFO 122118
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1118 AM HST SAT JUL 12 2025
UPDATE
THE BAND OF MOISTURE MOVING OVER THE ISLANDS HAS PROMPTED THE
ISSUANCE OF AIRMET SIERRA FOR MOUNTAIN OBSCURATION ON WINDWARD
BIG ISLAND, WITH OTHER ISLANDS POSSIBLY IN NEED OF AN AIRMET LATER
TODAY. SEE THE AVIATION SECTION BELOW FOR MORE DETAILS.
SYNOPSIS
HIGH PRESSURE WELL NORTHEAST OF THE ISLANDS WILL MAINTAIN
MODERATE TO LOCALLY BREEZY TRADES, WEAKENING SLIGHTLY AS THE HIGH
BEGINS TO DRIFT FURTHER AWAY FROM THE ISLANDS. EXPECT PASSING
CLOUDS AND SHOWERS TO FAVOR WINDWARD AND MAUKA AREAS, WITH A
SLIGHT UPTICK IN SHOWER ACTIVITY THROUGH THE WEEKEND AND INTO
EARLY NEXT WEEK.
PREV DISCUSSION
/ISSUED 339 AM HST SAT JUL 12 2025/
HIGH PRESSURE PERSIST NORTHEAST OF THE ISLANDS, MAINTAINING
MODERATE TO LOCALLY BREEZY TRADES THROUGH THE NEXT SEVERAL DAYS.
MODEL GUIDANCE OF THE GFS AND ECMWF CONTINUES TO SUPPORT THE HIGH
DRIFTING FURTHER NORTHEASTWARD THROUGHOUT THE WEEKEND AND INTO
EARLY NEXT WEEK, ALLOWING TRADES TO WEAKEN SLIGHTLY, THOUGH WIND-
PRONE LOCATIONS WILL TEND TO REMAIN ON THE BREEZIER SIDE. ON THE
CONTRARY, AN INCREASE IN SEA BREEZE ACTIVITY WILL BE POSSIBLE FOR
SHELTERED WESTERN SLOPES OF ISLAND MOUNTAINS.
LATEST OBSERVATIONS FROM LOW-LEVEL WATER VAPOR IMAGERY CONTINUES
TO DISPLAY A COMPACT LOW JUST NORTH OF THE ISLANDS SLOWLY
MEANDERING WESTWARD. DESPITE ITS QUASI-STATIONARY STATUS, AN
ASSOCIATED SHORTWAVE TROUGH WILL MIGRATE INTO THE VICINITY OF THE
ISLANDS, ASSISTING IN RAISING INVERSION HEIGHTS A BIT THROUGHOUT
THE WEEKEND. THE 12Z INVERSION HEIGHTS AT LIHUE AND HILO ARE 7000
TO 8000 FEET, RESPECTIVELY. THIS, IN CONJUNCTION WITH AN AREA OF
MOISTURE EAST OF THE OFFSHORE WATERS, MAY RESULT IN ENHANCED
SHOWER ACTIVITY, ESPECIALLY ACROSS WINDWARD AND MAUKA AREAS, BUT
CAN STILL LINGER INTO LEEWARD AREAS AS WELL.
BY EARLY NEXT WEEK, MODEL GUIDANCE IS DEPICTING ANOTHER AREA OF
MOISTURE MOVING EAST TO WEST TRACKING TOWARD THE ISLANDS. WHILE
THE ECMWF HINTS AT THIS MOISTURE MISSING NORTH OF THE ISLANDS, THE
GFS IS MUCH MORE AGGRESSIVE, SUGGESTING A SLIGHT UPTICK IN
WINDWARD AND MAUKA SHOWER ACTIVITY THROUGH THE EARLY PORTION OF
NEXT WEEK.
THEREAFTER BY TUESDAY EVENING, A RESUMPTION OF TYPICAL SUMMERTIME
TRADES IS IN ORDER AS GUIDANCE HINTS AT THE AFOREMENTIONED HIGH
PRESSURE BUILDING BACK UP, INCREASING THE LOCAL PRESSURE
GRADIENT. AS A RESULT, TRADES MAY INCREASE SLIGHTLY FOR THE LATTER
HALF OF NEXT WEEK, BUT CONFIDENCE IS TOO LOW AT THIS TIME TO SAY
ANYTHING WITH ABSOLUTE CERTAINTY THIS FAR OUT IN TIME.
AVIATION
MODERATE TRADES WILL PERSIST THROUGH THE WEEKEND. CLOUDS AND
SHOWERS WILL FAVOR WINDWARD AND MOUNTAIN AREAS ACROSS ALL ISLANDS
AND MAY RESULT IN MVFR CONDITIONS AT TIMES. LOW CLOUDS AND SHOWERS
WILL LIKELY INCREASE FOR WINDWARD AREAS OF MOST ISLANDS THROUGH
THE AFTERNOON AND EVENING AS A BAND OF MOISTURE MOVES INTO THE
ISLAND CHAIN FROM THE EAST. OTHERWISE, VFR CONDITIONS WILL
GENERALLY PREVAIL.
AIRMET SIERRA IS IN EFFECT FOR MOUNTAIN OBSCURATION FOR THE
WINDWARD AREAS OF THE BIG ISLAND FROM UPOLU POINT AROUND CAPE
KUMUKAHI TO APUA POINT DUE TO A LINE OF SHOWERY LOW CLOUDS MOVING
THROUGH LATE THIS MORNING. ADDITIONAL ISLANDS MAY NEED TO BE ADDED
TO THE AIRMET LATER TODAY.
MARINE
THE HIGH PRESSURE RIDGE WILL WEAKEN NORTH OF THE HAWAIIAN ISLANDS,
DECREASING TRADE WINDS SPEEDS THROUGH MONDAY. THE RIDGE WILL
STRENGTHEN FROM TUESDAY ONWARD INCREASING TRADE WIND SPEEDS BACK
INTO THE MODERATE TO LOCALLY STRONG RANGE THROUGH THE END OF NEXT
WEEK. WIND SPEEDS HAVE FALLEN BELOW SMALL CRAFT ADVISORY (SCA) LEVELS
THIS MORNING AND THUS THE ADVISORY WAS CANCELLED. SCA CONDITIONS
MAY RETURN BY TUESDAY AS WIND SPEEDS INCREASE ONCE AGAIN.
SURF ALONG SOUTH FACING SHORES WILL REMAIN SMALL THROUGH THE
WEEKEND AS A SMALL BACKGROUND SOUTH SOUTHWEST SWELL MOVES
THROUGH. A SMALL, LONG PERIOD SOUTH SWELL WILL BUILD IN FROM
SUNDAY NIGHT INTO MONDAY MORNING, AND THEN DIMINISH TO BACKGROUND
LEVELS FROM TUESDAY TO WEDNESDAY.
WIND WAVE DRIVEN SURF HEIGHTS ALONG EAST FACING SHORES WILL
REMAIN ON THE SMALL CHOPPY SIDE THROUGH TUESDAY, THEN INCREASE
SLIGHTLY AS TRADE WIND SPEEDS PICKUP BY WEDNESDAY. A VERY SMALL
NORTHWEST SWELL MAY PASS THROUGH EARLY NEXT WEEK, PROVIDING TINY
SURF ALONG NORTH FACING SHORES ON MONDAY AND TUESDAY BEFORE
BECOMING NEARLY FLAT THROUGH THE REMAIN FORECAST PERIOD.
FIRE WEATHER
MODERATE TO LOCALLY BREEZY TRADES WILL DECREASE SLIGHTLY OVER THE
WEEKEND BEFORE BECOMING LOCALLY BREEZY AGAIN NEXT WEEK. DESPITE
THE TRADE WIND SHOWERS PICKING UP ACROSS WINDWARD SECTIONS THIS
WEEKEND AND EARLY NEXT WEEK, AFTERNOON RELATIVE HUMIDITIES ACROSS
LEEWARD SECTIONS REMAIN NEAR SUMMERTIME NORMALS. FAIRLY TYPICAL
FIRE WEATHER CONDITIONS ARE EXPECTED.
HFO WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...WROE
DISCUSSION...PIERCE
AVIATION...TS
MARINE...BOHLIN
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