990
FXHW60 PHFO 180704
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
904 PM HST WED OCT 17 2018
SYNOPSIS
LIGHT TO MODERATE TRADES WILL CONTINUE THROUGH THE REMAINDER OF
THE WORK WEEK. THE TRADES WILL THEN STRENGTHEN TO MODERATE LEVELS
OVER THE WEEKEND AND POSSIBLY REACH LOCALLY BREEZE LEVELS NEXT
WEEK AS HIGH PRESSURE BUILDS NORTH OF THE ISLANDS. CLOUDS AND
SHOWERS ASSOCIATED WITH AND OLD FRONT WILL LINGER NEAR THE BIG
ISLAND AND MAUI THROUGH THE WEEKEND, KEEPING A SHOWERY TRADE WIND
PATTERN IN PLACE. MEANWHILE, DRIER CONDITIONS SHOULD PREVAIL
ACROSS THE WESTERN HALF OF THE STATE WITH MAINLY WINDWARD AND
MAUKA SHOWERS THROUGH SATURDAY, WITH A MORE SHOWERY TRADE WIND
PATTERN EXPECTED SUNDAY THROUGH EARLY NEXT WEEK. A DISTURBANCE
ALOFT WILL BRING UNSTABLE CONDITIONS AND THE POTENTIAL FOR HEAVY
RAIN AND THUNDERSTORMS TO MAUI AND THE BIG ISLAND FRIDAY NIGHT
THROUGH SUNDAY AS WELL, WHICH COULD CONTINUE INTO EARLY NEXT WEEK.
DISCUSSION
CURRENTLY AT THE SURFACE, A WEAK RIDGE OF HIGH PRESSURE IS
CENTERED AROUND 475 MILES NORTH OF KAUAI, DRIVING LIGHT TO
MODERATE TRADE WINDS ACROSS THE ISLAND CHAIN THIS EVENING.
MEANWHILE, A WEAKENING COLD FRONT IS LOCATED AROUND 550 MILES
NORTHWEST OF KAUAI. INFRARED SATELLITE IMAGERY SHOWS A BAND OF
CLOUDS ASSOCIATED WITH AN OLD FRONT OVER AND UPSTREAM OF THE BIG
ISLAND. MOSTLY CLOUDY SKIES PREVAIL OVER WINDWARD AREAS, WITH
PARTLY CLOUDY SKIES IN PLACE IN MOST LEEWARD LOCALES. RADAR
IMAGERY SHOWS ISOLATED TO SCATTERED SHOWERS DRIFTING INTO WINDWARD
SECTIONS OF THE SMALLER ISLANDS, WITH NUMEROUS SHOWERS AFFECTING
WINDWARD SECTIONS OF THE BIG ISLAND. MEANWHILE, ASIDE FROM AN
ISOLATED SHOWER OR TWO OVER LEEWARD AREAS, MOST AREAS ARE RAIN
FREE.
THE RIDGE OF HIGH PRESSURE NORTH OF THE STATE WILL WEAKEN OVER
THE NEXT COUPLE DAYS AS A COLD FRONT PASSES BY WELL TO THE NORTH
OF THE ISLAND CHAIN. LIGHT TO MODERATE TRADES ARE EXPECTED TO
PREVAIL TONIGHT AND THURSDAY, THEN EASE SLIGHTLY THURSDAY NIGHT
THROUGH FRIDAY NIGHT WITH LOCAL LAND AND SEA BREEZES POSSIBLE IN
SOME OF THE MORE SHELTERED AREAS. A RIDGE OF HIGH PRESSURE WILL
THEN BECOME RE-ESTABLISHED NORTH OF THE STATE OVER THE WEEKEND,
BRINGING A RETURN OF MODERATE TRADE WINDS, WITH THE TRADES
STRENGTHENING TO MODERATE AND LOCALLY BREEZY LEVELS DURING THE
FIRST HALF OF NEXT WEEK.
AS FOR SENSIBLE WEATHER DETAILS, A PLUME OF DEEP MOISTURE
ASSOCIATED WITH THE REMNANTS OF AN OLD FRONT, WILL LINGER OVER THE
BIG ISLAND THROUGH THE WEEKEND AND POSSIBLY INTO EARLY NEXT WEEK.
IN THE NEAR TERM THROUGH FRIDAY, SHOWERY TRADE WIND WEATHER IS
EXPECTED TO PERSIST OVER THE BIG ISLAND, WITH DRIER TRADE WIND
WEATHER EXPECTED ACROSS THE SMALLER ISLANDS. CLOUDS AND SHOWERS
WILL FAVOR WINDWARD AND MAUKA AREAS, BUT WE SHOULD SEE SOME
INTERIOR AND LEEWARD SHOWER DEVELOPMENT AS A RESULT OF THE
WEAKENING TRADES ON FRIDAY. ADDITIONALLY, WITH THE AIRMASS
REMAINING UNSTABLE OVER THE BIG ISLAND THROUGH THE REMAINDER OF
THE WORK WEEK, WILL KEEP A SLIGHT CHANCE OF THUNDERSTORMS IN THE
FORECAST EACH AFTERNOON.
THE MODELS ARE ADVERTISING QUITE A DIFFERENT SCENARIO THAN THEY
WERE 24 HOURS AGO DURING THE WEEKEND AND INTO EARLY NEXT WEEK.
BOTH THE GFS AND ECMWF NOW SHOW A SHARP UPPER TROUGH DIGGING
SOUTHWARD OVER THE WESTERN ISLANDS FRIDAY NIGHT, THEN CLOSING OFF
OVER THE CENTRAL AND EASTERN ISLANDS SATURDAY THROUGH SUNDAY. THE
MODELS TO DIFFERING DEGREES, THEN SHOW THE WEAKNESS ALOFT
LINGERING OVER ON IN THE VICINITY OF THE ISLAND CHAIN THROUGH THE
FIRST HALF OF NEXT WEEK.
DEEP MOISTURE ASSOCIATED WITH THE FRONTAL REMNANTS IS EXPECTED TO
LINGER OVER THE EASTERN END OF THE STATE THROUGH THE MIDDLE OF
NEXT WEEK, SO THIS SHOULD KEEP A SHOWERY TRADE WIND PATTERN IN
PLACE HERE. ACROSS THE WESTERN ISLANDS THE MOISTURE WON'T BE QUITE
AS DEEP THROUGH SATURDAY NIGHT, SO EXPECT THE SHOWER COVERAGE TO
NOT BE AS GREAT HERE AT LEAST INITIALLY. THIS WILL LIKELY CHANGE
ON SUNDAY AS THE DEEPER MOISTURE BEGINS TO LIFT BACK ACROSS
WESTERN ISLANDS, MAKING FOR A MORE SHOWERY TRADE WIND PATTERN
WHICH COULD CONTINUE THROUGH THE MIDDLE OF NEXT WEEK.
THE UPPER TROUGH/LOW OVERHEAD COULD ALSO CREATE A FAIRLY UNSTABLE
AIRMASS FRIDAY NIGHT THROUGH SUNDAY, PARTICULARLY ACROSS MAUI
COUNTY AND THE BIG ISLAND. THE MAIN HAZARDS WOULD LIKELY BE HEAVY
RAINFALL AND THUNDERSTORMS. WE'LL NEED TO MONITOR MODEL TRENDS
CLOSELY OVER THE NEXT COUPLE DAYS HOWEVER, AS THERE IS THE
POTENTIAL THAT WE COULD SEE SOME SEVERE WEATHER PARTICULARLY
DURING THE SATURDAY AFTERNOON AND SATURDAY EVENING TIME FRAME AS
THE COLDEST AIR ALOFT ROTATES OVERHEAD. AT THIS TIME THE MAIN
SEVERE WEATHER THREATS IF THEY MATERIALIZE, APPEAR TO BE STRONG
GUSTY WINDS AND HAIL.
AVIATION
LIGHT TO OCCASIONALLY MODERATE TRADE WINDS WILL CONTINUE ACROSS
THE ISLAND CHAIN THROUGH THURSDAY. BRIEF TO TEMPO MVFR CONDITIONS
WILL MAINLY AFFECT WINDWARD AND MAUKA SECTIONS OVER ALL ISLES.
THIS WILL ESPECIALLY BE THE CASE OVER THE BIG ISLAND, AND, TO A
LESSER EXTENT, MAUI, WHERE MORE WIDESPREAD AND PERSISTENT MVFR
WILL EXIST. LOW LEVEL REMNANT MOISTURE FROM AN OLD FRONT WILL
AFFECT THOSE ISLES. AN ISOLATED THUNDERSTORM IS STILL A
POSSIBILITY TOWARD THE EASTERN END OF THE STATE AS WELL. ELSEWHERE
VFR WILL HOLD SWAY.
AN AIRMET FOR MOUNTAIN OBSCURATION REMAINS IN EFFECT FOR THE
WINDWARD AREAS OF THE BIG ISLAND.
MARINE
TRADE WINDS ARE EXPECTED TO CONTINUE WEAKENING THROUGH FRIDAY.
THE TRADE WINDS ARE EXPECTED TO STRENGTHEN OVER THE WEEKEND INTO
EARLY NEXT WEEK, BUT THE CURRENT FORECAST DOES NOT HAVE SMALL
CRAFT ADVISORY (SCA) CONDITIONS OVER ANY OF THE COASTAL WATERS OR
CHANNELS THROUGH MONDAY.
UNSTABLE ATMOSPHERIC CONDITIONS MAY DEVELOP OVER THE EASTERN
ISLANDS TOWARD THE END OF THE WORK WEEK. THIS MAY CAUSE LOCALLY
HEAVY DOWNPOURS, AND ALLOW THUNDERSTORMS TO DEVELOP ACROSS THE
EASTERN PART OF THE STATE FROM LATE FRIDAY INTO THIS WEEKEND.
MARINERS SHOULD MONITOR FUTURE WEATHER FORECASTS AS THIS
SITUATION EVOLVES, PARTICULARLY NEAR MAUI AND THE BIG ISLAND.
THE CURRENT NORTH-NORTHWEST SWELL IS GRADUALLY DECLINING, BUT
SURF REMAINS ELEVATED THIS EVENING. THEREFORE, A HIGH SURF
ADVISORY (HSA) REMAINS IN EFFECT ALONG MOST NORTH AND WEST FACING
SHORES THROUGH EARLY THURSDAY MORNING. THE NORTH-NORTHWEST SWELL
WILL CONTINUE TO SLOWLY SUBSIDE FROM THURSDAY THROUGH THIS
WEEKEND. AS THE TRADE WINDS CONTINUE TO WEAKEN, EXPECT SURF TO
SLOWLY DECREASE ALONG MOST EAST FACING SHORES. HOWEVER, SOME EAST
FACING SHORES WITH A NORTHERLY EXPOSURE MAY CONTINUE TO SEE SMALL
BREAKERS FROM THE NORTH-NORTHWEST SWELL ENERGY DURING THE NEXT
COUPLE OF DAYS.
A NEW LONG-PERIOD SOUTH SWELL ARRIVING FRIDAY, IS EXPECTED TO
PEAK THIS WEEKEND. BASED ON THE LATEST GUIDANCE, SURF WILL LIKELY
REACH THE HSA CRITERIA ALONG SOUTH FACING SHORES STARTING SATURDAY.
THERE IS ALSO A POSSIBILITY SURF MAY APPROACH THE HIGH SURF
WARNING THRESHOLD ALONG SOUTH FACING SHORES THIS WEEKEND, BEFORE
THE SWELL BEGINS TO GRADUALLY DECLINE EARLY NEXT WEEK.
SEE THE LATEST COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST FOR
OAHU (SRDHFO), WHICH WAS UPDATED EARLIER THIS AFTERNOON, FOR MORE
DETAILS ON SWELLS AND SURF.
HFO WATCHES/WARNINGS/ADVISORIES
HIGH SURF ADVISORY UNTIL 6 AM HST THURSDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-WAIANAE COAST-OAHU NORTH SHORE-OAHU
KOOLAU-OLOMANA-MOLOKAI-MAUI WINDWARD WEST-MAUI CENTRAL VALLEY-
WINDWARD HALEAKALA-BIG ISLAND NORTH AND EAST.
DISCUSSION...JELSEMA
AVIATION...KINEL
MARINE...HOUSTON
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