999  
FXHW60 PHFO 200636  
AFDHFO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HONOLULU HI  
836 PM HST WED FEB 19 2020  
   
SYNOPSIS
 
 
GUSTY EASTERLY TRADE WINDS WILL CONTINUE THROUGH THURSDAY, THEN  
GRADUALLY DECREASE FRIDAY AND SATURDAY AS A FRONT APPROACHES FROM  
THE NORTHWEST. ALTHOUGH RAINFALL WILL FOCUS OVER WINDWARD AND  
MAUKA LOCATIONS, STRONG WINDS WILL PUSH SHOWERS INTO LEEWARD AREAS  
AT TIMES AS WELL. WINDS WILL BECOME LIGHT AND VARIABLE BY SUNDAY  
AS THE FRONT NEARS THE ISLANDS, WITH SEA AND LAND BREEZES  
EXPECTED STATEWIDE. SHOWERS WILL FAVOR INTERIOR AND MOUNTAIN  
AREAS DURING THE DAY AND LOCATIONS NEAR THE COAST AT NIGHT. TRADE  
WINDS ARE EXPECTED TO RETURN EARLY NEXT WEEK, WITH RATHER WET  
CONDITIONS POSSIBLE OVER THE WESTERN ISLANDS AS THE FRONT STALLS  
OUT IN THIS VICINITY.  
 

 
   
DISCUSSION
 
 
CURRENTLY AT THE SURFACE, A 1034 MB HIGH CENTERED AROUND 900 MILES  
NORTH OF HONOLULU IS DRIVING STRONG AND GUSTY TRADE WINDS ACROSS  
THE ISLAND CHAIN THIS EVENING. INFRARED SATELLITE IMAGERY SHOWS A  
LARGE SWATH OF LOW CLOUDS OVER AND UPSTREAM OF THE ISLANDS, WITH  
CLOUD COVER THICKEST IN WINDWARD LOCALES. RADAR IMAGERY SHOWS  
FREQUENT SHOWERS PUSHING INTO WINDWARD AREAS, WITH COVERAGE THE  
HIGHEST ACROSS MAUI COUNTY AND OAHU AT THE MOMENT. CONSIDERABLE  
LEEWARD SPILLOVER IS ALSO OCCURRING DUE TO THE STRENGTH OF THE  
TRADES. MAIN SHORT TERM CONCERNS REVOLVE AROUND TRADE WIND TRENDS  
AND RAIN CHANCES THROUGH THE REMAINDER OF THE WEEK AND INTO THE  
WEEKEND.  
 
STRONG HIGH PRESSURE WILL SLIDE EASTWARD AND WEAKEN SLIGHTLY OVER  
THE NEXT FEW DAYS AS A COLD FRONT APPROACHES FROM THE NORTHWEST.  
STRONG AND GUSTY TRADES WILL CONTINUE ACROSS THE ISLAND CHAIN  
THROUGH THURSDAY, THEN TREND LOWER FRIDAY, BEFORE SHIFTING AROUND  
TO THE EAST-SOUTHEAST ON SATURDAY AS THE FRONT MOVES CLOSER. LIGHT  
AND VARIABLE WINDS WILL LIKELY DEVELOP BY LATE SATURDAY ACROSS THE  
WESTERN ISLANDS WHILE MODERATE TRADES HOLD ON ACROSS THE EASTERN  
END OF THE STATE. THE GRADIENT WILL SLACKEN FURTHER SATURDAY  
NIGHT, ALLOWING A LAND BREEZE PATTERN TO DEVELOP STATEWIDE, WITH  
THIS SEA/LAND BREEZE PATTERN HOLDING IN PLACE THROUGH AT LEAST  
SUNDAY NIGHT. MODEL SOLUTIONS ARE IN FAIRLY GOOD AGREEMENT SHOWING  
THE FRONT OR ITS REMNANT BAND OF MOISTURE PUSHING INTO THE  
WESTERN ISLANDS MONDAY, THEN STALLING OUT IN THIS AREA THROUGH THE  
FIRST HALF OF NEXT WEEK BEFORE DISSIPATING. AS THE FRONT STALLS, A  
NEW HIGH WILL SLIDE BY WELL TO THE NORTH OF THE ISLAND CHAIN.  
TRADE WINDS MAY BEGIN TO RETURN ON MONDAY, PARTICULARLY ACROSS THE  
WESTERN ISLANDS, WITH THE TRADES THEN TAKING HOLD MONDAY NIGHT AND  
CONTINUING AT MODERATE TO BREEZY LEVELS THROUGH THE MIDDLE OF NEXT  
WEEK.  
 
AS FOR WEATHER DETAILS, DESPITE PRECIPITABLE WATER VALUES AROUND  
1 INCH, STRONG TRADES AND THE RESULTANT OROGRAPHIC LIFT WILL BE  
VERY EFFECTIVE IN WRINGING OUT A BAND OF MOISTURE AS IT PASSES  
THROUGH THE ISLAND CHAIN OVERNIGHT. RATHER WET WEATHER WILL BE THE  
RESULT, WITH WINDWARD AREAS SEEING THE SHOWERS MOST FREQUENTLY  
ALTHOUGH QUITE A BIT OF LEEWARD SPILLOVER CAN BE EXPECTED, AT  
LEAST ACROSS THE SMALLER ISLANDS. A MORE TYPICAL TRADE WIND SHOWER  
PATTERN SHOULD RESUME THURSDAY THROUGH FRIDAY NIGHT, WITH SHOWERS  
CONTINUING TO FAVOR WINDWARD AND MAUKA AREAS. A FEW SHOWERS WILL  
CONTINUE TO SPREAD LEEWARD, ALTHOUGH THERE WILL LIKELY BE A  
REDUCTION IN LEEWARD SHOWER COVERAGE DURING THIS TIME.  
 
OVER THE WEEKEND, A TRANSITION OVER TO A SEA BREEZE/LAND BREEZE  
PATTERN WILL KEEP SHOWERS FAVORING AREAS NEAR THE COAST IN AN  
EAST-SOUTHEAST TO SOUTHEAST BOUNDARY LAYER FLOW AT NIGHT, AND  
INTERIOR AND MAUKA AREAS DURING THE AFTERNOON/EARLY EVENING. A  
TRANSITION OVER TO A TRADE WIND PATTERN WILL BRING A RETURN OF  
MORE WINDWARD/MAUKA SHOWERS AND THE OCCASIONAL LEEWARD SPILLOVER  
EARLY NEXT WEEK. RATHER WET CONDITIONS COULD DEVELOP OVER THE  
WESTERN ISLANDS DURING THE FIRST HALF OF NEXT WEEK HOWEVER, AS THE  
FRONT OR ITS REMNANTS STALL OUT IN THIS VICINITY.  
 

 
   
AVIATION
 
 
GUSTY EASTERLY TRADES AND SHOWERY CONDITIONS DUE TO A BAND OF  
MOISTURE/CLOUDS IN THE AREA WILL CONTINUE INTO THURSDAY. ALTHOUGH  
MOST OF THE SHOWER COVERAGE HAS BEEN FOCUSING OVER WINDWARD  
SECTIONS OF MAUI COUNTY AND OAHU, THE TAIL-END OF THIS CLOUD BAND  
IS BEGINNING TO MOVE INTO WINDWARD AREAS OF THE BIG ISLAND THIS  
EVENING. SOME SHOWERS ARE SPILLING OVER INTO LEEWARD AREAS OF THE  
SMALLER ISLANDS, WHICH WILL CONTINUE INTO THURSDAY WITH THE STRONG  
WINDS IN PLACE.  
 
AIRMET SIERRA FOR TEMPO MOUNTAIN OBSCURATION IS IN EFFECT FOR  
WINDWARD SIDES OF KAUAI, OAHU, MOLOKAI, MAUI AND THE BIG ISLAND.  
 
AIRMET TANGO REMAINS IN EFFECT FOR TEMPO MODERATE LOW LEVEL  
TURBULENCE OVER AND DOWNWIND OF THE TERRAIN, AS WELL AS FOR STRONG  
SURFACE WINDS ACROSS THE ENTIRE STATE.  
 

 
   
MARINE
 
 
A STRONG SURFACE HIGH PRESSURE SYSTEM IS MOVING STEADILY EAST FAR  
NORTH OF THE AREA. THE VERY TIGHT PRESSURE GRADIENT SOUTH OF THIS  
FEATURE IS PRODUCING STRONG TO NEAR-GALE FORCE EASTERLY TRADE  
WINDS OVER HAWAIIAN WATERS, WITH WINDS REACHING GALE FORCE IN  
AREAS WHERE THE WIND ACCELERATES AROUND THE ISLANDS. A GALE  
WARNING REMAINS IN EFFECT THROUGH THURSDAY AFTERNOON FOR THE  
TYPICALLY WINDIER WATERS ADJACENT TO THE ISLANDS OF MAUI COUNTY  
AND THE BIG ISLAND. A SMALL CRAFT ADVISORY (SCA) ALSO REMAINS IN  
EFFECT FOR ALL OTHER HAWAIIAN WATERS. THE SCA WILL LIKELY NEED TO  
BE EXTENDED FOR MOST WATERS THROUGH THURSDAY NIGHT. AFTER THAT,  
IT MAY BE SCALED BACK AS WINDS AND SEAS SLOWLY DIMINISH FROM  
FRIDAY THROUGH FRIDAY NIGHT.  
 
BY THIS WEEKEND, THE SURFACE HIGH WILL MOVE FARTHER AWAY TO THE  
EAST, AS A FRONT APPROACHES THE STATE FROM THE NORTHWEST. THIS  
WILL ALLOW THE TRADE WINDS TO WEAKEN, AND START TO SHIFT OUT OF  
THE EAST-SOUTHEAST OVER MOST AREAS BY SATURDAY. THE FRONT IS  
EXPECTED TO MOVE INTO THE FAR NORTHWEST HAWAIIAN OFFSHORE WATERS  
SUNDAY, WITH STRONG NORTHEAST TRADE WINDS RETURNING BEHIND THE  
FRONT.  
 
THE STRONG TRADE WINDS WILL MAINTAIN SURF ABOVE THE HIGH SURF  
ADVISORY THRESHOLD OF 8 FEET ALONG EAST FACING SHORES THROUGH  
FRIDAY. THIS SURF WILL SUBSIDE OVER THE WEEKEND AS THE TRADE  
WINDS WEAKEN.  
 
A NEW SMALL NORTHWEST SWELL IS EXPECTED TO PEAK LATER TONIGHT OR  
EARLY THURSDAY MORNING, THEN GRADUALLY LOWER FROM THURSDAY NIGHT  
THROUGH FRIDAY. A SLIGHTLY LARGER, LONG-PERIOD NORTHWEST SWELL  
ARRIVING LATE FRIDAY WILL LIKELY PEAK ON SATURDAY, THEN GRADUALLY  
LOWER FROM SUNDAY THROUGH MONDAY. A NEW LARGE NORTHWEST SWELL IS  
POSSIBLE EARLY NEXT WEEK. ELSEWHERE, A SERIES OF SMALL SOUTH AND  
SOUTH-SOUTHWEST SWELLS WILL MAINTAIN SMALL BACKGROUND SURF ALONG  
SOUTH FACING SHORES THROUGH THIS WEEKEND.  
 

 
   
HFO WATCHES/WARNINGS/ADVISORIES
 
 
WIND ADVISORY UNTIL 6 AM HST THURSDAY FOR KAUAI-OAHU.  
 
HIGH SURF ADVISORY UNTIL 6 PM HST FRIDAY FOR KAUAI WINDWARD-OAHU  
KOOLAU-OLOMANA-MOLOKAI WINDWARD-MAUI WINDWARD WEST-WINDWARD  
HALEAKALA-SOUTH BIG ISLAND-BIG ISLAND NORTH AND EAST.  
 
WIND ADVISORY UNTIL 6 PM HST THURSDAY FOR MOLOKAI-LANAI-  
KAHOOLAWE-MAUI WINDWARD WEST-MAUI LEEWARD WEST-MAUI CENTRAL  
VALLEY-WINDWARD HALEAKALA-LEEWARD HALEAKALA-SOUTH BIG ISLAND-BIG  
ISLAND NORTH AND EAST-KOHALA.  
 
GALE WARNING UNTIL 6 PM HST THURSDAY FOR MAALAEA BAY-PAILOLO  
CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND  
SOUTHEAST WATERS.  
 
SMALL CRAFT ADVISORY UNTIL 6 PM HST THURSDAY 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-BIG ISLAND  
WINDWARD WATERS.  
 

 
 

 
 
DISCUSSION...JELSEMA  
AVIATION...GIBBS  
MARINE...HOUSTON  
 
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