690  
FXHW60 PHFO 280634  
AFDHFO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HONOLULU HI  
834 PM HST SAT FEB 27 2021  
   
SYNOPSIS
 
 
TRADE WINDS WILL STRENGTHEN ON SUNDAY, WITH LOCALLY WINDY CONDITIONS  
EXPECTED TO PERSIST FOR THE NEXT SEVERAL DAYS, WHILE A TROUGH ALOFT  
KEEPS THE ISLAND ATMOSPHERE UNSTABLE. WHILE FAST-MOVING HEAVY  
SHOWERS WILL FOCUS OVER WINDWARD AREAS, THE STRONG TRADES WILL ALSO  
PUSH A FEW SHOWERS LEEWARD. INCREASED MOISTURE NEAR MAUI AND THE BIG  
ISLAND WILL BRING A MORE WIDESPREAD THREAT OF HEAVY WINDWARD  
SHOWERS, AND A SLIGHT CHANCE OF THUNDERSTORMS.  
 

 
   
DISCUSSION
 
 
CURRENTLY AT THE SURFACE, A 1038 MB HIGH IS CENTERED AROUND 1400  
MILES NORTHEAST OF HONOLULU, WHILE ANOTHER 1042 MB HIGH IS  
CENTERED AROUND 1250 MILES NORTH-NORTHWEST OF KAUAI. THE RESULTING  
GRADIENT IS PRODUCING BREEZY TRADE WINDS ACROSS THE ISLAND CHAIN  
THIS EVENING. INFRARED SATELLITE IMAGERY SHOWS MOSTLY CLOUDY  
CONDITIONS IN WINDWARD AREAS, WITH PARTLY CLOUDY SKIES PREVAILING  
IN MOST LEEWARD LOCALES. RADAR IMAGERY SHOWS SCATTERED TO NUMEROUS  
SHOWERS MOVING INTO WINDWARD AND MAUKA SECTIONS OF THE SMALLER  
ISLANDS, WITH WIDESPREAD RAINFALL OVER WINDWARD BIG ISLAND. A FEW  
SHOWERS ARE OCCASIONALLY MAKING IT INTO LEEWARD SECTIONS OF THE  
SMALLER ISLANDS, AND A FEW DIMINISHING SHOWERS ARE NOTED ALONG THE  
LEEWARD BIG ISLAND SLOPES. MAIN SHORT TERM CONCERNS CONTINUE TO  
REVOLVE AROUND THE ONGOING FLASH FLOOD AND WINTER WEATHER  
HEADLINES, AS WELL AS THE POTENTIAL NEED FOR WIND ADVISORIES.  
 
HIGH PRESSURE NORTHEAST OF THE STATE WILL SETTLE SOUTHWARD AND  
WEAKEN TONIGHT AND SUNDAY, WHILE THE HIGH NORTH-NORTHWEST OF THE  
STATE BUILDS EASTWARD AND STRENGTHENS TO AROUND 1044-45 MB, DUE  
NORTH OF THE ISLAND CHAIN BY SUNDAY AFTERNOON. THIS HIGH WILL  
THEN SETTLE SOUTHWARD AND WEAKEN SLIGHTLY MONDAY AND TUESDAY,  
FOLLOWED BY A NEW STRONG HIGH BUILDING NORTHWEST OF THE STATE  
WEDNESDAY THROUGH FRIDAY, THEN SHIFTING EASTWARD FAR TO THE NORTH  
OF THE ISLAND CHAIN NEXT WEEKEND. OVERALL, BREEZY TO WINDY TRADES  
WILL CONTINUE THROUGH EARLY NEXT WEEK, WITH THE TRADES PEAKING  
LATE SUNDAY THROUGH EARLY TUESDAY. WIND ADVISORIES WILL LIKELY BE  
REQUIRED ONCE AGAIN FOR PORTIONS OF THE STATE DURING THIS TIME.  
THE TRADES SHOULD EASE A BIT FOR THE MIDDLE AND LATTER PART OF  
NEXT WEEK AS THE GRADIENT RELAXES, BUT WILL LIKELY HOLD IN THE  
MODERATE TO BREEZY RANGE.  
 
AS FOR THE REMAINING WEATHER DETAILS, A TROUGH ALOFT WILL KEEP A  
MOIST AND UNSTABLE AIRMASS OVER THE STATE TONIGHT THROUGH SUNDAY  
NIGHT. THE DEEPEST MOISTURE AND MOST UNSTABLE CONDITIONS WILL  
RESIDE OVER THE EASTERN ISLANDS OF MAUI AND THE BIG ISLAND  
HOWEVER, WHERE THE THREAT FOR LOCALLY HEAVY RAINFALL AND  
THUNDERSTORMS WILL CONTINUE, MAINLY OVER WINDWARD AREAS. THE  
FLASH FLOOD WATCH REMAINS IN EFFECT UNTIL 6 PM SUNDAY, BUT THIS  
MAY EVENTUALLY NEED TO BE EXTENDED THROUGH EARLY MONDAY MORNING.  
ACROSS THE REMAINDER OF THE STATE, A WET TRADE WIND PATTERN IS  
EXPECTED WITH SHOWERS FAVORING WINDWARD AND MAUKA AREAS AND A FEW  
SHOWERS SPREADING LEEWARD FROM TIME TO TIME.  
 
DUE TO THE MOISTURE DEPTH EXTENDING ABOVE THE HIGH ELEVATION  
SUMMITS OF MAUNA KEA AND MAUNA LOA, A WINTER WEATHER ADVISORY  
REMAINS IN EFFECT FOR A WINTRY MIX OF FREEZING RAIN/DRIZZLE AND  
SNOW THROUGH NOON MONDAY. THIS MAY BE A BIT LONG AND WE MAY BE  
ABLE TO SCALE THIS BACK TO RUN THROUGH 6 AM MONDAY WITH THE  
MORNING FORECAST PACKAGE.  
 
THE UPPER TROUGH AXIS WILL SHIFT SOUTH OF THE STATE ON MONDAY,  
THEN LINGER JUST SOUTH OF THE ISLANDS THROUGH MID WEEK. A SERIES  
OF SHORTWAVE TROUGHS MAY THEN ROTATE THROUGH THE REGION THURSDAY  
THROUGH NEXT WEEKEND. OVERALL, WITH A TROUGHING ALOFT MORE OR LESS  
BEING MAINTAINED OVER THE STATE THROUGH MUCH OF NEXT WEEK, WE  
SHOULD SEE A WETTER THAN NORMAL TRADE WIND PATTERN PREVAILING WITH  
SHOWERS FAVORING WINDWARD AND MAUKA AREAS AND A FEW SHOWERS  
REACHING LEEWARD COMMUNITIES FROM TIME TO TIME.  
 

 
   
AVIATION
 
 
A SLOW MOVING EAST TO WEST ORIENTED UPPER TROUGH LIES OVER THE  
ISLAND CHAIN THIS EVENING. THIS TROUGH IS CAUSING ADVERSE WEATHER  
OVER THE EASTERN SECTIONS OF THE BIG ISLAND, INCLUDING THE CHANCE  
FOR THUNDERSTORMS. THE WIDESPREAD MVFR CEILINGS AND SHOWERS ARE  
FORECAST TO CONTINUE THROUGH AT LEAST SUNDAY MORNING WHERE AIRMET  
SIERRA IS IN PLACE FOR TEMPO MOUNTAIN OBSCURATION. AIRMET SIERRA  
EXTENDS FROM UPOLU POINT TO CAPE KUMUKAHI TO SOUTH CAPE.  
 
BREAKS IN THE CLOUD DECK HAVE ALLOWED FOR THE CANCELLATION OF  
AIRMET SIERRA FOR THE SMALLER ISLANDS THIS EVENING, BUT THIS MAY  
BE NEEDED ONCE AGAIN LATER TONIGHT AND INTO THE EARLY MORNING  
HOURS SHOULD CLOUDS AND SHOWERS INCREASE. OVER LEEWARD BIG  
ISLAND, DAYTIME HEATING AND AN UNSTABLE AIR MASS WILL RESULT IN  
SCATTERED SHOWERS AND A CHANCE OF THUNDERSTORMS IN THE AFTERNOON  
AND EARLY EVENING HOURS. AS FOR THE SMALLER ISLANDS, SCATTERED  
SHOWERS WILL FAVOR THE WINDWARD AND MOUNTAIN AREAS, CAUSING TEMPO  
MVFR CONDITIONS.  
 
AS STRONG HIGH PRESSURE REMAINS IN PLACE NORTHEAST OF THE STATE,  
EASTERLY TRADE WINDS WILL REMAIN BREEZY TO LOCALLY STRONG TONIGHT  
BEFORE INCREASING ONCE AGAIN ON SUNDAY AS A NEW, STRONGER SURFACE  
HIGH BUILDS. AIRMET TANGO REMAINS IN EFFECT TO ACCOUNT FOR LOW-  
LEVEL MECHANICAL TURBULENCE OVER AND IMMEDIATELY SOUTH THROUGH  
WEST OF ALL ISLANDS.  
 

 
   
MARINE
 
 
HIGH PRESSURE WILL BE THE DOMINANT FEATURE FOR THE NEXT SEVERAL  
DAYS, PRODUCING STRONG TRADES ACROSS THE COASTAL WATERS. A 1038  
MB HIGH FAR TO THE NORTHEAST OF THE REGION WILL BECOME REINFORCED  
WITH A 1044-45 MB HIGH CURRENTLY FAR TO THE NORTH-NORTHWEST OF  
THE REGION OVER THE REMAINDER OF THE WEEKEND. THE TRADE WINDS ARE  
EXPECTED TO GET A BOOST OVER THE NEXT 24 HOURS AS THE HIGH TO THE  
NORTH-NORTHWEST BECOMES THE DOMINANT HIGH IMPACTING OUR WEATHER.  
 
THE PERSISTENT TRADE WIND PATTERN WE HAVE BEEN EXPERIENCING OVER  
THE LAST SEVERAL DAYS HAS ALREADY BEEN GENERATING ADVISORY LEVEL  
SURF ALONG EAST FACING SHORES. THE CURRENT HIGH SURF ADVISORY FOR  
EAST FACING SHORES CONTINUES THROUGH TUESDAY, ALTHOUGH ITS  
POSSIBLE THAT IT MAY NEED TO BE EXTENDED.  
 
THIS SUPPORTS THE SMALL CRAFT ADVISORY (SCA) CURRENTLY OUT FOR  
ALL COASTAL WATERS FOR A COMBINATION OF WINDS AND SEAS. AS THE  
WINDS PICK UP, GALE FORCE WINDS ARE POSSIBLE IN THE ALENUIHAHA  
CHANNEL. AS A RESULT, A GALE WATCH IS IN PLACE FOR THE ALENUIHAHA  
CHANNEL STARTING SUNDAY NIGHT. THE SCA AND GALES ARE CURRENTLY  
EXPECTED TO CONTINUE THROUGH TUESDAY, WITH SOME WEAKENING OF THE  
WINDS POSSIBLE TUESDAY NIGHT AND WEDNESDAY WHICH WOULD ALLOW FOR  
SOME AREAS TO BE DROPPED.  
 
A SMALL TO MODERATE NORTHWEST SWELL IS FILLING IN, AND EXPECTED TO  
PEAK TOMORROW. THE NEXT NORTHWEST SWELL IS EXPECTED TO ARRIVE  
WEDNESDAY NIGHT AND CURRENTLY IS EXPECTED TO RUN HIGHER THAN THE  
CURRENT SWELL. THIS SWELL COULD RAISE SURF TO NEAR ADVISORY LEVELS  
AS IT PEAKS THURSDAY. A SMALL BUMP IS LIKELY ALONG SOUTH FACING  
SHORES MONDAY NIGHT INTO WEDNESDAY, AND AGAIN AT THE END OF THE  
WEEK.  
 

 
   
HFO WATCHES/WARNINGS/ADVISORIES
 
 
HIGH SURF ADVISORY UNTIL 6 PM HST TUESDAY FOR KAUAI WINDWARD-  
OAHU KOOLAU-OLOMANA-MOLOKAI WINDWARD-MAUI WINDWARD WEST-WINDWARD  
HALEAKALA-SOUTH BIG ISLAND-BIG ISLAND NORTH AND EAST.  
 
FLASH FLOOD WATCH THROUGH SUNDAY AFTERNOON FOR MAUI WINDWARD  
WEST-WINDWARD HALEAKALA-HALEAKALA SUMMIT-SOUTH BIG ISLAND-BIG  
ISLAND NORTH AND EAST-BIG ISLAND INTERIOR.  
 
WINTER WEATHER ADVISORY UNTIL NOON HST MONDAY FOR BIG ISLAND  
SUMMITS.  
 
SMALL CRAFT ADVISORY UNTIL 6 PM HST TUESDAY FOR KAUAI NORTHWEST  
WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-KAUAI CHANNEL-  
OAHU WINDWARD WATERS-OAHU LEEWARD WATERS-KAIWI CHANNEL-MAUI  
COUNTY WINDWARD WATERS-MAUI COUNTY LEEWARD WATERS-MAALAEA BAY-  
PAILOLO CHANNEL-BIG ISLAND WINDWARD WATERS-BIG ISLAND LEEWARD  
WATERS-BIG ISLAND SOUTHEAST WATERS.  
 
GALE WATCH FROM SUNDAY EVENING THROUGH TUESDAY AFTERNOON FOR  
ALENUIHAHA CHANNEL.  
 
SMALL CRAFT ADVISORY UNTIL 6 PM HST SUNDAY FOR ALENUIHAHA  
CHANNEL.  
 

 
 

 
 
DISCUSSION...JELSEMA  
AVIATION...VAUGHAN/LAU  
MARINE...M BALLARD  
 
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