429  
FXHW60 PHFO 201322  
AFDHFO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HONOLULU HI  
322 AM HST SAT APR 20 2019  
   
SYNOPSIS
 
 
SEASONAL TRADE WIND CONDITIONS WILL PREVAIL THROUGH THE WEEKEND AND  
MUCH OF NEXT WEEK AS HIGH PRESSURE REMAINS IN PLACE TO THE NORTH.  
CLOUDS AND SHOWERS WILL FAVOR THE TYPICAL WINDWARD LOCATIONS EACH  
DAY.  
 

 
   
DISCUSSION
 
 
THE LATEST SURFACE ANALYSIS SHOWED A 1029 MB AREA OF HIGH PRESSURE  
CENTERED OVER THE NORTHEAST PACIFIC AND A RIDGE EXTENDING WEST-  
SOUTHWEST FROM IT TO AN AREA NORTH OF THE ISLANDS. WATER VAPOR  
IMAGERY SHOWED AN UPPER RIDGE POSITIONED OVER THE REGION AND  
MOSTLY DRY AIR ALOFT. SATELLITE DATA AND UPPER AIR SOUNDINGS  
DEPICTED MOISTURE LEVELS NEAR TO SLIGHTLY BELOW NORMAL FOR THIS  
TIME OF YEAR AND A STRONG SUBSIDENCE INVERSION BETWEEN SIX AND  
EIGHT THOUSAND FEET. RAIN GAGES SUPPORT THE DRY CONDITIONS WITH  
MINIMAL ACCUMULATIONS MEASURED OVER THE PAST 12-HRS (THROUGH 2 AM  
HST). PEAK TOTALS FOR THIS PERIOD HAVE BEEN ON THE BIG ISLAND  
ALONG THE WINDWARD COAST FROM HAMAKUA TO NORTH KOHALA (.22 TO .7  
INCHES).  
 
GUIDANCE SUPPORTS THE MOSTLY DRY AND STABLE TRADE WIND PATTERN  
CONTINUING THROUGH MUCH OF NEXT WEEK. TRADES ARE FORECAST TO  
TREND UP TODAY THROUGH SUNDAY DUE TO THE RIDGE STRENGTHENING NORTH  
OF THE ISLANDS. BREEZY CONDITIONS WILL RESULT, ESPECIALLY THROUGH  
THE LATE MORNING AND AFTERNOON HOURS. THE UPPER RIDGE IS FORECAST  
TO REMAIN OVER THE REGION INTO NEXT WEEK WITH MOSTLY DRY MID- TO  
UPPER-LEVEL AIR HOLDING IN PLACE. THESE UPPER CONDITIONS COMBINED  
WITH A STRONG SUBSIDENCE INVERSION WILL LIMIT THE RAINFALL  
POTENTIAL/COVERAGE, EVEN FOR WINDWARD LOCATIONS. THE EXCEPTION  
WILL BE DUE TO POCKETS OF HIGHER MOISTURE MOVING THROUGH  
PERIODICALLY WITHIN THE TRADES, WHICH WILL TRANSLATE TO BETTER  
WINDWARD RAINFALL COVERAGE.  
 
FOR THE EXTENDED PERIOD, GUIDANCE DEPICTS LOWERING UPPER HEIGHTS AND  
THE SURFACE RIDGE TO THE NORTH WEAKENING DUE TO A WEAK SHORTWAVE  
TROUGH AND SURFACE FRONT MOVING INTO THE REGION LATE NEXT WEEK.  
FORECAST CONFIDENCE THIS FAR OUT REMAINS LOW, BUT IF THIS SCENARIO  
DOES EVOLVE, TRADES WOULD TREND DOWN, POTENTIALLY BECOMING LIGHT  
AND VARIABLE FOR SOME LOCATIONS.  
 

 
   
AVIATION
 
 
A HIGH PRESSURE RIDGE NORTH OF THE STATE WILL KEEP THE ISLANDS IN  
A MODERATE TO BREEZY TRADE WIND WEATHER PATTERN THROUGH MONDAY.  
NEAR SURFACE WIND SPEEDS ARE STRONG ENOUGH TO SUPPORT MODERATE LOW  
LEVEL TURBULENCE OVER AND SOUTH THROUGH WEST OF MOUNTAIN RANGES  
OF ALL ISLANDS. SCATTERED SHOWER ACTIVITY WILL FAVOR WINDWARD AND  
MOUNTAIN SECTIONS WITH BRIEF PERIODS OF MVFR CONDITIONS MAINLY  
DURING THE OVERNIGHT HOURS.  
 
AIRMET TANGO REMAINS IN EFFECT FOR TEMPO MODERATE TURBULENCE BELOW  
080. THIS AIRMET WILL LIKELY REMAIN IN EFFECT THROUGH THE  
WEEKEND.  
 

 
   
MARINE
 
 
NO SIGNIFICANT CHANGES TO THE FORECAST WITH THE MORNING PACKAGE.  
THE RIDGE TO THE NORTH OF THE ISLANDS WILL MAINTAIN FRESH TO  
STRONG TRADE WINDS INTO EARLY NEXT WEEK. THE SMALL CRAFT ADVISORY  
(SCA) IS IN EFFECT FOR MOST OF THE WATERS NEAR MAUI COUNTY AND THE  
BIG ISLAND THROUGH TONIGHT, AND THROUGH TOMORROW FOR THE MORE  
TYPICAL WINDIER AREAS. WILL WAIT TO SEE HOW THINGS PAN OUT TODAY  
BEFORE MAKING ANY CHANGE IN THE TIMING OF THE SCA.  
 
SURF ALONG ALL SHORES IS EXPECTED TO REMAIN BELOW ADVISORY LEVELS  
FOR THE NEXT WEEK. THE CURRENT NORTH-NORTHWEST SWELL WILL  
CONTINUE TO DECLINE THROUGH THE WEEKEND. A SMALL, WEST-NORTHWEST  
SWELL IS POSSIBLE EARLY NEXT WEEK. BACKGROUND SOUTH-SOUTHWEST  
SWELLS WILL KEEP SURF SMALL ALONG SOUTH FACING SHORES THROUGH THE  
WEEKEND. AN UPWARD TREND ALONG SOUTH FACING SHORES IS POSSIBLE  
EARLY NEXT WEEK, DUE TO RECENT ACTIVITY SOUTHEAST OF NEW ZEALAND.  
SURF ALONG EAST FACING SHORES WILL SEE A BUMP OVER THE WEEKEND  
IN RESPONSE TO THE TRADE WINDS. SEE THE LATEST OAHU SURF  
DISCUSSION (SRDHFO) FOR ADDITIONAL DETAILS ON SURF AND SWELL.  
 

 
   
HFO WATCHES/WARNINGS/ADVISORIES
 
 
SMALL CRAFT ADVISORY UNTIL 6 PM HST SUNDAY FOR MAALAEA BAY-  
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG  
ISLAND SOUTHEAST WATERS.  
 
SMALL CRAFT ADVISORY UNTIL 6 AM HST SUNDAY FOR KAIWI CHANNEL-  
MAUI COUNTY WINDWARD WATERS-BIG ISLAND WINDWARD WATERS.  
 

 
 

 
 
DISCUSSION...GIBBS  
AVIATION...BOHLIN  
MARINE...M BALLARD  
 
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