378  
FXHW60 PHFO 200256 AAC  
AFDHFO  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE HONOLULU HI  
456 PM HST FRI JAN 19 2018  
   
SYNOPSIS
 
 
A RIDGE NORTH OF THE ISLANDS WILL PRODUCE TRADE WINDS OVER THE  
ISLANDS. A BAND OF SHOWERY LOW CLOUDS ALONG A DISSIPATING FRONT  
WILL REMAIN NEARLY STATIONARY OVER THE ISLANDS, KEEPING WINDWARD  
AREAS RATHER WET THROUGH EARLY NEXT WEEK. A NEW FRONT APPROACHING  
FROM THE NORTHWEST WILL WEAKEN THE RIDGE AND MAKE THE ATMOSPHERE  
MORE MOIST AND LESS STABLE. DAYTIME SEA BREEZES AND NIGHTTIME LAND  
BREEZES WILL BECOME MORE WIDESPREAD EARLY NEXT WEEK WITH AFTERNOON  
CLOUDS AND SHOWERS POSSIBLE OVER INTERIOR AREAS. TRADE WINDS AND  
WINDWARD SHOWERS WILL RETURN BY THE MIDDLE OF NEXT WEEK.  
 

 
   
DISCUSSION
 
 
A 1034 MB HIGH ABOUT 1350 MILES NORTHEAST OF OAHU IS FORECAST TO  
MOVE EAST AROUND 20 MPH. A RIDGE EXTENDS WEST SOUTHWEST FROM THE  
HIGH. THE PRESSURE GRADIENT SOUTH OF THE HIGH HAD BEEN PRODUCING  
STRONG EASTERLY TRADE WINDS OVER THE ISLANDS. WITH THE HIGH NOW  
FARTHER AWAY, THE PRESSURE GRADIENT HAS WEAKENED. WINDS AROUND THE  
ISLANDS HAVE SUBSIDED, AND WILL CONTINUE TO WEAKEN THROUGH THE  
WEEKEND.  
 
AN EAST TO WEST BAND OF SHOWERY LOW CLOUDS ALONG A DISSIPATING  
STATIONARY FRONT CONTINUES TO MOVE OVER THE ISLANDS IN THE TRADE  
WINDS AND KEEP WINDWARD AREAS QUITE RAINY THROUGH TONIGHT.  
 
A TROUGH ALOFT AND A COLD FRONT WILL MOVE TOWARD THE ISLANDS FROM  
THE NORTHWEST OVER THE WEEKEND. AS THE FRONT APPROACHES, THE WINDS  
OVER THE ISLANDS WILL WEAKEN FURTHER AND VEER OUT OF THE SOUTHEAST  
NEAR KAUAI AND OAHU. THE OLD FRONTAL BAND MAY SHIFT NORTH OF  
KAUAI AND OAHU, BUT WILL LIKELY REMAIN OVER THE BIG ISLAND. THE  
SOUTHEAST FLOW WILL BE PARTLY BLOCKED BY THE BIG ISLAND AND WINDS  
MAY BE LIGHT ENOUGH OVER THE SMALLER ISLANDS FOR DAYTIME SEA  
BREEZES AND NIGHTTIME LAND BREEZES.AS THE TROUGH ALOFT MOVES  
CLOSER AND THE ATMOSPHERE BECOMES MORE UNSTABLE, HEAVIER SHOWERS  
ARE POSSIBLE AND THERE COULD BE SNOW OVER THE SUMMITS ON THE BIG  
ISLAND.  
 
THE FRONT IS FORECAST TO STALL NORTHWEST OF THE ISLANDS ON  
TUESDAY. THE SURFACE RIDGE WILL REBUILD NORTH OF THE ISLANDS. THE  
ATMOSPHERE WILL BECOME MORE STABLE AND TRADE WINDS WILL STRENGTHEN  
AGAIN AROUND THE MIDDLE OF NEXT WEEK.  
 
LATE NEXT WEEK ANOTHER TROUGH ALOFT AND FRONT MAY APPROACH THE  
ISLANDS FROM THE NORTHWEST AND BRING ANOTHER PERIOD OF DISRUPTED  
TRADE WINDS AND RAINY WEATHER.  
 

 
   
AVIATION
 
 
AIRMET TANGO IS IN EFFECT THROUGH THIS EVENING FOR TEMPO MODERATE  
TURBULENCE LEEWARD OF ALL ISLANDS DUE TO FRESH TO STRONG TRADE  
WINDS. TRADE WINDS ARE EXPECTED TO WEAKEN LATER TONIGHT INTO  
SATURDAY MORNING, AND WE MAY CANCEL THIS AIRMET SOMETIME TONIGHT.  
 
AIRMET SIERRA IS IN EFFECT FOR TEMPO MOUNTAIN OBSCURATION ACROSS  
WINDWARD SECTIONS OF KAUAI, OAHU, MOLOKAI AND LANAI THROUGH 10Z  
TONIGHT. THIS IS DUE TO PASSING CLOUDS AND SHOWERS ASSOCIATED WITH  
A WEAKENING FRONT PUSHING ONTO THESE ISLANDS WITH THE TRADE WIND  
FLOW. AIRMET SIERRA MAY CONTINUE TONIGHT FOR SOME WINDWARD  
SECTIONS BEYOND 10Z.  
 
NO OTHER AIRMETS ARE ANTICIPATED AT THIS TIME.  
 

 
   
MARINE
 
 
TRADE WINDS HAVE STARTED TO WEAKEN AREA-WIDE AS THE SURFACE HIGH  
NORTH OF THE STATE MOVES EAST, BUT WILL REMAIN AROUND ADVISORY  
LEVELS THROUGH TONIGHT BEFORE DROPPING BELOW ADVISORY SATURDAY.  
ELEVATED SEAS GENERATED EAST OF THE BIG ISLAND WILL ALSO KEEP WAVE  
HEIGHTS ABOVE THE ADVISORY THRESHOLD OF 10 FEET, THEREFORE, THE  
SMALL CRAFT ADVISORY HAS BEEN EXTENDED THROUGH SATURDAY FOR MOST  
ZONES. SEAS ARE EXPECTED TO SUBSIDE BELOW ADVISORY LEVEL BEGINNING  
SATURDAY NIGHT.  
 
THE HIGH SURF ADVISORY (HSA) FOR EAST FACING SHORES HAS BEEN  
EXTENDED THROUGH SUNDAY. SURF WILL REMAIN BELOW ADVISORY LEVELS  
FOR THE REMAINING SHORES THROUGH THIS WEEKEND. A SMALL NORTHWEST  
SWELL (330 DEGREES) IS EXPECTED TO ARRIVE SATURDAY NIGHT, AND BE  
REINFORCED WITH A MODERATE WEST-NORTHWEST (300 DEGREES) SWELL  
ARRIVING SUNDAY NIGHT, PEAKING MONDAY NIGHT AND GRADUALLY  
DECLINING THROUGH WEDNESDAY. THIS SECOND SWELL MAY WARRANT A HSA  
FOR THE NORTH FACING SHORES OF SOME OF THE SMALLER ISLANDS.  
 

 
   
HFO WATCHES/WARNINGS/ADVISORIES
 
 
HIGH SURF ADVISORY UNTIL 600 PM HST SUNDAY FOR EAST FACING SHORES  
OF KAUAI, OAHU, MOLOKAI, MAUI AND THE BIG ISLAND  
 
SMALL CRAFT ADVISORY UNTIL 600 PM HST SATURDAY FOR ALL AREAS  
EXCEPT LEEWARD KAUAI, LEEWARD OAHU AND LEEWARD MAUI COUNTY WATERS.  
 

 
 

 
 
DISCUSSION...DONALDSON  
AVIATION...ALMANZA/FOSTER  
MARINE...TS  
 
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