088  
FXHW60 PHFO 170140  
AFDHFO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HONOLULU HI  
340 PM HST TUE JUL 16 2019  
   
SYNOPSIS
 
 
A TRADE WIND WEATHER PATTERN CAN BE EXPECTED THROUGH THE  
REMAINDER OF THE WEEK AND ON INTO EARLY NEXT WEEK, THANKS TO HIGH  
PRESSURE FAR NORTH OF THE AREA. CLOUDS AND PASSING SHOWERS WILL  
TEND TO FAVOR WINDWARD AND MAUKA AREAS. LEEWARD SECTIONS OF THE  
BIG ISLAND WILL SEE CLOUDS AND SHOWERS MAINLY DURING THE AFTERNOON  
AND EVENING HOURS.  
 

 
   
DISCUSSION
 
 
AT THE SURFACE, A 1030 MB HIGH IS CENTERED FAR NORTH OF THE  
STATE. THIS PLACES THE ISLANDS IN A MODERATE TO BREEZY TRADE WIND  
ENVIRONMENT. AN ELONGATED UPPER LEVEL TROUGH IN THE VICINITY OF  
THE STATE, IS SEEN IN WATER VAPOR IMAGERY. SATELLITE IMAGERY SHOWS  
AN AREA OF ENHANCED MOISTURE EMBEDDED IN THE TRADES, WHICH HAS  
CAUSED SOME INCREASE IN SHOWER ACTIVITY ACROSS PORTIONS OF THE  
STATE INCLUDING A FEW THUNDERSTORMS OVER THE LEEWARD SLOPES OF THE  
BIG ISLAND DUE THE VICINITY OF THE UPPER TROUGH. WE EXPECT THIS  
AREA OF ENHANCED MOISTURE TO MOVE THROUGH THE AREA OVERNIGHT,  
BRINGING WITH IT SOME PASSING SHOWERS FOR WINDWARD AND MAUKA AREAS  
WITH THE TRADE WINDS SUFFICIENTLY STRONG ENOUGH TO BLOW A FEW  
SHOWERS OVER TO SELECT LEEWARD AREAS AT TIMES. THUNDERSTORM  
ACTIVITY WILL LIKELY TAPER OFF THIS EVENING AS DAYTIME HEATING  
OVER THE SLOPES DIMINISHES.  
 
THE UPPER TROUGH IS FORECAST TO WEAKEN AND LIFT OUT TO THE NORTH  
AND WEST LATER WEDNESDAY THROUGH FRIDAY. THIS WILL STABILIZE THE  
AIRMASS WITH SHOWERS BECOMING LESS PREVALENT. MEANWHILE, THE  
SURFACE HIGH FAR TO OUR NORTH WILL STRENGTHEN A BIT CAUSING A  
SLIGHT UPTICK IN TRADE WINDS SPEEDS.  
 
AS WE HEAD INTO THE WEEKEND AND ON INTO EARLY NEXT WEEK, THE HIGH  
TO OUR NORTH WILL SLOWLY WEAKEN WITH A SLIGHT DOWNWARD TREND IN  
TRADE WIND SPEEDS. THE ABOVE MENTIONED TROUGH WILL SAG BACK  
SOUTHWARD, CLOSER TO THE STATE. THIS MAY CAUSE FOR A SLIGHT UPTICK  
SHOWER ACTIVITY, MAINLY FOR WINDWARD AND MAUKA AREAS. DAYTIME  
HEATING WILL CONTINUE TO ALLOW FOR CLOUDS AND SHOWERS TO FORM OVER  
THE LEEWARD BIG ISLAND SLOPES EACH AFTERNOON AND EVENING.  
 

 
   
AVIATION
 
 
HIGH PRESSURE NORTH OF THE ISLAND CHAIN CONTINUES TO BRING  
MODERATE TO BREEZY TRADES TO THE STATE. CLOUDS AND SHOWERS  
CONTINUE TO FAVOR WINDWARD AND MAUKA SECTIONS OF THE ISLANDS,  
HOWEVER, A FEW THUNDERSTORMS HAVE POPPED UP ON LEEWARD SLOPES OF  
THE BIG ISLAND THIS AFTERNOON. THESE MAY RESULT IN OCCASIONAL MVFR  
CONDITIONS, BUT VFR CONDITIONS ARE EXPECTED TO DOMINATE.  
THUNDERSTORM ACTIVITY WILL DECREASE THIS EVENING AND CLOUDS ARE  
EXPECTED TO CLEAR OUT DURING THE OVERNIGHT HOURS, SO THE ISSUANCE  
OF AIRMET SIERRA IS NOT ANTICIPATED AT THIS TIME.  
 
AIRMET TANGO REMAINS IN EFFECT FOR SOUTH THROUGH WEST AREAS OF  
ALL ISLANDS BELOW 7000 FEET FOR TEMPO MODERATE TURBULENCE.  
 

 
   
MARINE
 
 
HIGH PRESSURE FAR NORTH OF THE STATE WILL MAINTAIN FRESH TO STRONG  
TRADES THROUGH FRIDAY. THE TRADES ARE EXPECTED TO EASE SLIGHTLY  
OVER THE WEEKEND, AS HIGH PRESSURE TO THE NORTH WEAKENS. A SMALL  
CRAFT ADVISORY (SCA) IS POSTED FOR MOST WATERS BETWEEN OAHU AND  
THE BIG ISLAND. FOR THE REMAINING WATERS NOT IN THE SCA, WINDS  
WILL REMAIN BORDERLINE WITH FRESH TRADES IN THESE AREAS. WE WILL  
CONTINUE TO MONITOR WINDS ACROSS THE COASTAL WATERS AND ADDITIONAL  
ZONES MAY BE ADDED TO THE SCA IF NEEDED.  
 
THE CURRENT SOUTH SWELL WILL CONTINUE TO SLOWLY SUBSIDE THROUGH  
MID-WEEK, WITH ONLY SMALL BACKGROUND SOUTH AND SOUTHWEST SWELLS  
EXPECTED THROUGH THE WEEKEND. LOCALLY STRONG TRADE WINDS WILL  
PRODUCE CHOPPY WAVES ALONG EAST FACING SHORES, BUT THE FETCH WILL  
BE SHORT FOR THE NEXT COUPLE OF DAYS SO WAVE HEIGHTS WILL REMAIN  
SMALL. EAST SHORE SURF WILL GET A BOOST THURSDAY AND FRIDAY AS  
THE UPSTREAM FETCH OF TRADE WINDS INCREASES. SURF IS EXPECTED TO  
STAY JUST BELOW ADVISORY LEVELS ALONG EAST FACING SHORES THURSDAY  
AND FRIDAY AND SLOWLY EASE OVER THE WEEKEND AS TRADES WEAKEN  
SLIGHTLY.  
 

 
   
HFO WATCHES/WARNINGS/ADVISORIES
 
 
SMALL CRAFT ADVISORY UNTIL 6 AM HST SATURDAY FOR MAALAEA BAY-  
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG  
ISLAND SOUTHEAST WATERS.  
 
SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 PM HST  
WEDNESDAY FOR OAHU LEEWARD WATERS-KAIWI CHANNEL-MAUI COUNTY  
WINDWARD WATERS.  
 

 
 

 
 
DISCUSSION...BURKE  
AVIATION...DYE  
MARINE...KINO  
 
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