836
FXHW60 PHFO 091415
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
415 AM HST SUN MAR 9 2025
SYNOPSIS
HIGH PRESSURE NORTH OF THE ISLANDS WILL MAINTAIN STRONG TRADE
WINDS INTO THE MIDDLE OF THE WEEK. EXPECT PERIODS OF WINDWARD AND
MAUKA SHOWERS, PARTICULARLY OVERNIGHT AND DURING THE EARLY
MORNING HOURS. WINDS WILL EASE A LITTLE DURING THE SECOND HALF OF
THE WEEK AS THE HIGH MOVES CLOSER TO THE ISLANDS.
DISCUSSION
AS ANTICIPATED, MADE SOME TWEAKS TO THE FORECAST TO KEEP IT IN
LINEWITH THE LATEST NATIONAL BLEND OF MODELS (NBM). THE OVERALL
FORECAST PHILOSOPHY REMAINS THE SAME. THAT BEING SAID, THE POPS
WERE INCREASED A BIT OVER WINDWARD PORTIONS OF THE BIG ISLAND
DURING THE SECOND HALF OF TONIGHT AND TOMORROW. THE OTHER CHANGE
WAS TO THE WINDS TODAY. THE NBM, INFLUENCED BY SEVERAL OF THE HIGH
RESOLUTION MODELS, WOULD SUGGEST SOME AREAS OF THE BIG ISLAND AND
MAUI COUNTY COULD REACH WIND ADVISORY THRESHOLDS TODAY. HOWEVER
GIVEN THAT CURRENT OBSERVATIONS DO NOT MATCH WELL WITH THE INITIAL
STEPS OF THESE MODELS, HAVE DECIDED TO LIMIT WIND SPEEDS OVER
THOSE AREAS TO JUST BELOW ADVISORY LEVELS FOR TODAY.
AS EXPECTED, THE DISSIPATING COLD FRONT NORTH OF THE ISLANDS
EARLIER HAS WEAKENED. WHAT REMAINS OF THE DISSIPATING FRONT IS TO
THE NORTHEAST OF THE ISLANDS DURING THE PRE-DAWN HOURS. MEANWHILE
A LINGERING CLOUD BAND THAT WAS ONCE PART OF THE FRONT IS BEING
CARRIED INTO THE ISLANDS ON THE TRADE WIND FLOW GENERATED BY THE
STRONG HIGH PRESSURE SYSTEM FAR NORTH OF THE ISLANDS. THIS CLOUD
BAND IS MOVING OVER KAUAI AND IS EXPECTED TO SINK SOUTHWARD TO
OAHU LATER TODAY, BEFORE MOVING TOWARDS MAUI COUNTY AND THE BIG
ISLAND TONIGHT AND TOMORROW. EXPECT AN UPTICK IN WINDWARD AND
MAUKA SHOWERS WITH THIS CLOUD BAND, AND THE STRONG TRADE WINDS
COULD CARRY SOME OF THE SHOWERS TO LEEWARD AREAS.
THE OVERNIGHT SOUNDINGS FROM LIHUE AND HILO SHOW THE INVERSION
BETWEEN 8500 AND 9000 FEET RESPECTIVELY. BOTH SITES REPORTED
PRECIPITABLE WATER (PW) AROUND 1.1 INCHES, WHICH IS NEAR NORMAL
FOR MARCH. IN FACT 500MB AND 700MB TEMPERATURES FROM BOTH SITES
ARE ALSO NEAR NORMAL FOR THIS TIME OF YEAR.
SATELLITE DERIVED PW SHOWS LOWER VALUES BEHIND THE CLOUD BAND
MENTIONED ABOVE THAT IS MOVING TOWARDS KAUAI EARLY THIS MORNING.
THE GFS AND ECWMF BOTH SHOW A MID LEVEL RIDGE MOVING NORTH OF THE
ISLANDS LATER TODAY, WHICH WILL LIKELY RESULT IN A LOWER TRADE
WIND INVERSION LATER TODAY AT LEAST OVER KAUAI. THIS WILL LIKELY
RESULT IN FEWER SHOWERS OVER THE EASTERN END OF THE STATE.
MEANWHILE, A MID LEVEL TROUGH LOOKS TO REMAIN OVER OR JUST SOUTH
OF THE BIG ISLAND, WHICH COULD HELP TO ENHANCE SOME OF THE SHOWERS
THAT ARE ASSOCIATED WITH THE BAND AS IT REACHES THE SOUTHERN END
OF THE STATE TONIGHT AND TOMORROW.
A STRONG HIGH PRESSURE SYSTEM FAR NORTH OF THE ISLANDS WILL
CONTINUE TO DRIVE STRONG TRADES TO THE ISLANDS INTO THE MIDDLE OF
THE WEEK. WITH THE DRIER AIR BEHIND THE CLOUD BAND, SOME GUSTY
WINDS ARE POSSIBLE, AND THERE IS A CHANCE SOME OF THE TYPICAL
WINDIER AREAS OF MAUI COUNTY AND THE BIG ISLAND COULD SEE WINDS
APPROACH WIND ADVISORY LEVELS TONIGHT AND TOMORROW. AS MENTIONED
ABOVE, SOME OF THE HIGH RESOLUTION MODELS WOULD SUGGEST SOME OF
THOSE AREA COULD REACH ADVISORY LEVELS THIS MORNING, BUT
CONFIDENCE IS LOW GIVEN THE LATEST OBSERVATIONS. WILL CONTINUE TO
MONITOR THE SITUATION THROUGHOUT THE DAY.
A DEVELOPING TROUGH TO THE WEST OF THE ISLANDS WILL HELP PUSH THE
HIGH PRESSURE SYSTEM CLOSER TO THE ISLANDS DURING THE SECOND HALF
OF THE WEEK. THIS WILL LEAD TO WEAKENING TRADES, AND THE
POSSIBILITY OF SOUTHEASTERLY WINDS BY NEXT WEEKEND.
AVIATION
BREEZY TO LOCALLY STRONG TRADE WINDS WILL PERSIST OVER THE NEXT
SEVERAL DAYS. REMNANT MOISTURE FROM A DISSIPATED FRONTAL BOUNDARY
WILL SAG SOUTHWARD OVER THE ISLANDS THROUGH THIS AFTERNOON AND
GENERATE SCATTERED TO NUMEROUS SHOWERS ALONG MAINLY WINDWARD
LOCATIONS. PERIODS OF MVFR CEILINGS AND VISIBILITY WILL LIKELY BE
ASSOCIATED WITH THIS ACTIVITY. AN ISOLATED SHOWER OR TWO COULD
PASS OVER THE TERRAIN AND AFFECT LEEWARD AREAS, THOUGH VFR
CONDITIONS SHOULD GENERALLY PREVAIL.
AIRMET SIERRA MAY BE NEEDED FOR THE SMALLER ISLANDS LATER THIS
MORNING TO ACCOUNT FOR LOW CEILINGS AND REDUCED VISIBILITY AS THE
BAND OF MOISTURE BEGINS TO PUSH DOWN THE ISLAND CHAIN.
AIRMET TANGO REMAINS IN EFFECT FOR MODERATE LOW-LEVEL TURBULENCE
OVER AND DOWNWIND OF ISLAND TERRAIN. THIS AIRMET IS EXPECTED TO
CONTINUE OVER THE NEXT SEVERAL DAYS.
MARINE
HIGH PRESSURE CENTERED APPROXIMATELY 750 NAUTICAL MILES NORTH OF
OAHU IS MAINTAINING A VERY TIGHT PRESSURE GRADIENT BETWEEN ITSELF
AND LOWER EQUATORIAL PRESSURE. THIS HAS RESULTED IN SEVERAL DAYS
OF FRESH TO LOCALLY STRONG TRADE WINDS. AS THIS HIGH MOVES EAST
AND IS REPLACED BY A HIGH JUST TO ITS NORTHWEST LATER THIS WEEK,
THE DOWNSTREAM PRESSURE GRADIENT WILL STILL REMAIN TIGHT ENOUGH
TO SUPPORT FRESH TO NEAR GALE FORCE TRADES. GALE FORCE WINDS ARE
POSSIBLE OVER THE NOTORIOUSLY WINDIER CHANNELS AND BAYS
SURROUNDING MAUI COUNTY AND BIG ISLAND, AS WELL AS SOUTH OF BIG
ISLAND, FROM MONDAY THROUGH THURSDAY. AN ALL-WATER SMALL CRAFT
ADVISORY FOR THESE STRONG WINDS AND RESULTANT ELEVATED SEAS WILL
REMAIN IN THE EFFECT FOR THE NEAR FUTURE.
YESTERDAY'S MODERATE SIZE, MEDIUM PERIOD NORTHWEST (310-330 DEGREE)
SWELL THAT PRODUCED THE HIGH SURF ADVISORY (HSA) IS VEERING AND
LOWERING THIS MORNING. SURF HAS FALLEN BELOW HSA HEIGHTS AND THE
ADVISORY HAS BEEN CANCELLED. THIS SWELL WILL PROGRESSIVELY DECLINE
THROUGH THE DAY. A SLIGHTLY SMALLER, MEDIUM PERIOD NORTH NORTHWEST
(330 DEGREE) SWELL WILL ARRIVE AT MID WEEK WITH A REINFORCING
LONGER PERIOD SWELL ON ITS HEELS TO CLOSE OUT THE WEEK.
EAST-FACING SHORE ROUGH, SHORT PERIOD WIND-DRIVEN SEAS WILL HOLD
THROUGH MOST OF THE WEEK IN RESPONSE TO THIS PERSISTENT FRESH TO
STRONG TRADE FETCH OVER AND UPSTREAM OF THE ISLANDS. TRADES MAY
STRENGTHEN TUESDAY AND WEDNESDAY. THIS WILL FURTHER AGITATE SEAS
AND CREATE AN EVEN ROUGHER CHOP TO EASTERN SEAS THROUGH THE MIDDLE
OF THE WEEK.
SURF ALONG SOUTH-FACING SHORES WILL REMAIN SMALL. LINGERING MEDIUM
PERIOD NORTHERLY SWELL, ALONG WITH THE EAST WIND WAVE SWELL, WILL
LIKELY WRAP INTO MORE EASTERN-FACING SOUTHERN EXPOSURES.
FIRE WEATHER
HFO WATCHES/WARNINGS/ADVISORIES
SMALL CRAFT ADVISORY UNTIL 6 AM HST TUESDAY FOR ALL HAWAIIAN
WATERS-
DISCUSSION...M BALLARD
AVIATION...THOMAS
MARINE...BLOOD
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