029
FXHW60 PHFO 200119
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
319 PM HST MON OCT 19 2026
SYNOPSIS
HIGH PRESSURE FAR NORTH OF THE MAIN HAWAIIAN ISLANDS WILL MAINTAIN
A MODERATE TO LOCALLY WINDY TRADE WIND PATTERN OVER THE REGION
INTO THE MIDDLE OF THE WEEK. AN AREA OF SHOWERS MOVING IN ON THE
TRADES TONIGHT WILL MAINTAIN PASSING SHOWERS OVER THE WINDWARD AND
MOUNTAINS INTO TUESDAY. MODERATE TRADES AND FEWER SHOWERS ARE
EXPECTED DURING THE SECOND HALF OF THE WEEK, WITH AN INCREASE IN
SHOWERS DURING THE WEEKEND.
DISCUSSION
THE FORECAST FOR TONIGHT HAS BEEN UPDATED TO INCREASE POPS AND
ASSOCIATED FIELDS FOR THE WINDWARD SIDES OF THE ISLANDS,
PARTICULARLY OVER MAUI COUNTY AND THE BIG ISLAND WITH AN AREA OF
SHOWERY LOW CLOUDS RIDING IN ON THE TRADE WIND FLOW. SATELLITE
DERIVED PRECIPITABLE WATER (PW) SHOWS VALUES 1.3 INCHES UPSTREAM
OF THE ISLANDS. THE AFTERNOON SOUNDINGS AT LIHUE AND HILO HAD 1.19
AND 1.06 INCHES OF PW RESPECTIVELY. THE 1.3 IS NEAR NORMAL FOR
THIS TIME OF YEAR, SO JUST EXPECTING A FEW MORE SHOWERS THAN WE
HAVE BEEN SEEING IN THE LAST COUPLE OF DAYS.
HIGH PRESSURE FAR TO THE NORTH WILL LINGER INTO WEDNESDAY, WITH A
TIGHT PRESSURE GRADIENT OVER THE ISLANDS MAINTAINING THE MODERATE
TO LOCALLY BREEZY TRADES. A FEW SITES IN THE WINDIEST LOCATIONS
(ALONG RIDGES) HAVE SEEN WINDS BRIEFLY REACH ADVISORY LEVELS, BUT
NOT EXPECTING ANY WIDESPREAD OR PERSISTENT ADVISORY CONDITIONS SO
HAVE HELD OFF ON ANY HEADLINES. THERE IS GOOD MODEL AGREEMENT
WITH THE ECMWF AND GFS MODELS THAT THE HIGH WILL WEAKEN WEDNESDAY
AS A STRONG LOW, CURRENTLY FAR TO THE NORTHWEST IN THE WESTERN
PACIFIC, MOVES TO THE EAST AND SETS UP FAR NORTH-NORTHWEST OF THE
ISLANDS. THE HIGH WILL WEAKEN AND MOVE TO THE EAST, AS THE LOW
DEEPENS, AND AN ASSOCIATED FRONT MOVES CLOSER TO THE ISLANDS OVER
THE WEEKEND.
WITH THE HIGH WEAKENING, THE PRESSURE GRADIENT OVER THE ISLANDS
WILL WEAKEN, AND WINDS ARE EXPECTED TO RETURN TO MODERATE LEVELS.
A DRIER AIRMASS MOVING OVER THE ISLANDS WILL RESULT IN FEWER
SHOWERS DURING THE WEDNESDAY THROUGH FRIDAY TIME PERIOD.
AS THE ABOVE MENTIONED FRONT MOVES CLOSER TO THE ISLANDS THIS
WEEKEND, MOISTURE WILL BE DRAWN NORTHWARD OVER THE ISLANDS,
INCREASING SHOWER ACTIVITY. AND THEN THE SECOND HALF OF THE
WEEKEND AND INTO NEXT WEEK, THE TAIL END OF A FRONT MAY IMPACT THE
NORTHERN ISLANDS BY INCREASING SHOWER ACTIVITY.
AVIATION
BREEZY TRADES WILL PERSIST THROUGH TOMORROW. PASSING SHOWERS WILL
MAINLY BE CONCENTRATED IN WINDWARD AND MOUNTAIN AREAS. THESE
SHOWERS MAY PRODUCE SHORT-LIVED MVFR CEILINGS AND VISIBILITY.
AIRMET TANGO REMAINS IN EFFECT FOR TEMPO MODERATE TURBULENCE
DOWNWIND OF TERRAIN BELOW FLIGHT LEVEL 090.
MARINE
HIGH PRESSURE CENTERED FAR NORTH OF HAWAII WILL MAINTAIN FRESH TO
STRONG TRADE WINDS FOR THE NEXT FEW DAYS, AND A SMALL CRAFT
ADVISORY (SCA) REMAINS IN EFFECT FOR ALL WATERS EXCEPT WINDWARD
BIG ISLAND THROUGH TUESDAY AFTERNOON. TRADES WILL STEADILY
DECREASE EARLY WEDNESDAY MORNING AS THE HIGH WEAKENS AND IS
DISPLACED EASTWARD BY AN APPROACHING LOW FAR NORTHWEST OF THE
ISLANDS. THE SCA WILL LIKELY BE TRIMMED BACK TO THE TYPICALLY
WINDY WATERS AROUND BIG ISLAND AND MAUI AT THAT TIME. TRADE WINDS
WILL LOWER TO GENTLE STRENGTH, OR MAY BECOME DISRUPTED ENTIRELY,
AS THE LOW PASSES TO THE NORTH THURSDAY AND FRIDAY. TRADES COULD
THEN TURN MORE NORTHEASTERLY THIS WEEKEND.
DECLINING NORTH-NORTHWEST AND WEST-NORTHWEST SWELLS WILL KEEP
SMALL TO TINY SURF IN PLACE OVER THE NEXT FEW DAYS BEFORE A SMALL
NORTHWEST SWELL GIVES A SLIGHT BUMP TO NORTH SHORES ON THURSDAY
AND FRIDAY. THIS WILL THEN BE FOLLOWED BY A SLIGHTLY LARGER NORTH-
NORTHWEST SWELL THIS WEEKEND AND A POTENTIALLY LARGER LONG PERIOD
WEST- NORTHWEST SWELL EARLY NEXT WEEK FROM A FORECASTED STORM
FORCE LOW DEVELOPING NORTHEAST OF JAPAN IN THE NEXT FEW DAYS.
SMALL BACKGROUND SOUTH SWELLS WILL KEEP RELATIVELY SMALL SURF FOR
SOUTH FACING SHORES THROUGH MUCH OF THE WEEK. A MODERATE SOUTH-
SOUTHWEST SWELL IS EXPECTED THIS WEEKEND, AND COULD BRING SURF
HEIGHTS ABOVE SEASONAL AVERAGES.
ROUGH TRADE WIND SWELL WILL PRODUCE EAST SHORE SURF JUST ABOVE
SEASONAL AVERAGE THROUGH TUESDAY, THEN DECLINE LATER IN THE WEEK
AS TRADE WINDS DECREASE.
FIRE WEATHER
FIRE WEATHER WILL REMAIN BELOW CRITICAL LEVELS FOR THE NEXT
SEVERAL DAYS. THE SUBSIDENCE TEMPERATURE INVERSION NEAR MAUI AND
THE BIG ISLAND WILL REMAIN IN THE 7000 TO 8000 FOOT RANGE.
HFO WATCHES/WARNINGS/ADVISORIES
SMALL CRAFT ADVISORY UNTIL 6 PM HST TUESDAY FOR ALENUIHAHA
CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS-
KAIWI CHANNEL-KAUAI CHANNEL-KAUAI LEEWARD WATERS-KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-MAALAEA BAY-MAUI COUNTY LEEWARD
WATERS-MAUI COUNTY WINDWARD WATERS-OAHU LEEWARD WATERS-OAHU
WINDWARD WATERS-PAILOLO CHANNEL.
DISCUSSION...M BALLARD
AVIATION...PECHACEK
MARINE...TSAMOUS
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