996  
FXHW60 PHFO 232000  
AFDHFO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HONOLULU HI  
1000 AM HST SAT JUN 23 2018  
   
SYNOPSIS
 
 
HIGH PRESSURE NORTH AND NORTHEAST OF THE ISLANDS WILL SUPPORT BREEZY  
TRADE WINDS FOR THE NEXT WEEK. THE TRADES WILL DELIVER PASSING  
CLOUDS AND SHOWERS THAT WILL PRIMARILY AFFECT WINDWARD SLOPES AND  
COASTS, WITH A FEW BRIEF SHOWERS SPREADING TO LEEWARD AREAS OF THE  
SMALLER ISLANDS. LEEWARD SLOPES OF THE BIG ISLAND WILL SEE AFTERNOON  
AND EVENING CLOUDS THAT WILL DROP A FEW SHOWERS BEFORE GENERALLY  
CLEARING AT NIGHT.  
 

 
   
DISCUSSION
 
 
A 1034 MB SURFACE HIGH FAR N OF THE ISLANDS WILL MOVE STEADILY E  
THROUGH TUESDAY WHILE MAINTAINING A CENTRAL PRESSURE IN THE 1030'S.  
THE HIGH IS THEN EXPECTED TO WOBBLE AROUND TO THE DISTANT NE OF THE  
ISLANDS THROUGH THE END OF NEXT WEEK. THE ASSOCIATED PRESSURE  
GRADIENT WILL ENSURE SEASONABLE BREEZY TRADE WINDS REMAIN OVER THE  
ISLANDS FOR THE FORESEEABLE FUTURE, WITH SOME SUBTLE FLUCTUATIONS.  
 
WATER VAPOR IMAGERY AND MODEL ANALYSES INDICATE A MID- TO UPPER-  
LEVEL LOW CENTERED ABOUT 500 MILES NE OF THE BIG ISLAND. UPPER AIR  
SOUNDINGS AND LATEST VISIBLE SATELLITE IMAGES INDICATE THAT THIS  
FEATURE IS NOT SIGNIFICANTLY DESTABILIZING THE LOWER ATMOSPHERE, BUT  
AN INCREASE IN SHOWERY LOW CLOUDS IS NOTED JUST A LITTLE E OF THE  
ISLANDS, AND EXTENDING E OF 150W. IN THE SHORT TERM, THERE IS A BIT  
OF A BREAK IN THE LOW CLOUD FIELD IMMEDIATELY UPSTREAM OF THE  
ISLANDS FROM OAHU TO THE BIG ISLAND, WITH SHOWERY LOW CLOUDS IN  
GREATER CONCENTRATION NEAR AND E OF KAUAI. THIS SHOULD KEEP KAUAI  
SOMEWHAT SHOWERY TODAY WHILE THE OTHER ISLANDS SEE FEWER SHOWERS.  
 
MODEL GUIDANCE APPEARS TO HAVE INITIALIZED WELL, AND DEPICTS THE MID-  
LEVEL LOW GRADUALLY WEAKENING AS IT DRIFTS W OVER THE NEXT 24 TO 48  
HOURS, WHILE THE UPPER-LEVEL LOW MOVES N. THIS IS EXPECTED TO LEAD  
TO AN INCREASE IN TRADE WIND SHOWERS LATER TONIGHT AND ON SUNDAY,  
AND POTENTIALLY AGAIN AROUND MONDAY NIGHT, AS THE MID-LEVEL LOW  
WEAKENS TO A TROUGH AND MOVES OVER THE ISLANDS. MOST OF THE  
ASSOCIATED MOISTURE WILL FOCUS OVER WINDWARD SLOPES AND COASTS, BUT  
THE LOCALLY STRONG TRADE WINDS WILL PUSH A FEW SHOWERS TO LEEWARD  
AREAS ON THE SMALLER ISLANDS. LEEWARD SLOPES OF THE BIG ISLAND WILL  
SEE THE TYPICAL AFTERNOON AND EVENING CLOUDS AND SHOWERS THAT TEND  
TO GRADUALLY CLEAR OVERNIGHT.  
 
WHILE THE TRADE WINDS WILL KEEP THE BIG ISLAND'S VOLCANIC EMISSIONS  
AWAY FROM THE SMALLER ISLANDS, THEY WILL CONTINUE TO STREAM OVER  
PORTIONS OF THE PUNA AND KAU DISTRICTS. ADDITIONALLY, EDDIES THAT  
DEVELOP TO THE LEE OF THE BIG ISLAND WILL OCCASIONALLY LEAD TO VOG  
MOVING ASHORE OVER THE KONA AND KOHALA DISTRICTS.  
 

 
   
AVIATION
 
 
BREEZY, OCCASIONALLY STRONG, TRADE WINDS WILL PERSIST THROUGH THE  
DAY AS A RIDGE OF HIGH PRESSURE REMAINS NORTH OF THE STATE. VFR WILL  
PREDOMINATE, WITH PASSING SHOWERS BRINGING BRIEF MVFR CONDITIONS TO  
WINDWARD AND MAUKA SECTIONS OF THE ISLANDS.  
 
AIRMET TANGO REMAINS IN EFFECT FOR LOW LEVEL TURBULENCE OVER AND SW  
OF ALL ISLANDS.  
 

 
   
MARINE
 
 
TRADES ARE FORECAST TO STEADILY INCREASE THROUGH THE WEEKEND AND  
HOLD IN THE FRESH TO STRONG CATEGORY AS HIGH PRESSURE BUILDS NORTH  
OF THE STATE. A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR MOST  
WATERS EAST OF OAHU THROUGH SUNDAY DUE TO THE BREEZY WINDS. ALTHOUGH  
THE TRADES MAY SLIGHTLY BACK OFF BRIEFLY BY MONDAY, LOCALLY STRONG  
TRADES WILL REMAIN LIKELY OVER THE TYPICAL CHANNELS AROUND MAUI  
COUNTY AND SOUTH OF THE BIG ISLAND.  
 
SURF ALONG EAST FACING SHORES WILL BECOME ROUGH THROUGH THE WEEKEND  
AS THE TRADES INCREASE LOCALLY AND UPSTREAM ACROSS THE EASTERN  
PACIFIC. AFTER THE TRADES BRIEFLY WEAKEN AROUND MONDAY, A SURGE  
UPSTREAM AND LOCALLY WILL LIKELY TRANSLATE TO INCREASING SURF THAT  
MAY NEAR THE ADVISORY LEVEL BY MIDWEEK.  
 
SURF ALONG SOUTH FACING SHORES IS EXPECTED TO TREND BACK UP NEXT  
WEEK AS OVERLAPPING LONG-PERIOD SOUTH SWELLS FILL IN DUE TO RECENT  
ACTIVITY ACROSS THE SOUTHERN PACIFIC. THE FIRST SWELL IS CURRENTLY  
BUILDING AT THE AMERICAN SAMOA BUOY WITHIN THE 14-16 SECOND BANDS  
THIS MORNING, WHICH SHOULD CONTINUE THROUGH THE WEEKEND AS THE  
SECOND SOURCE FILLS IN. THE LATEST WAVEWATCH III GUIDANCE DEPICTS  
THIS SOURCE PEAKING MONDAY AT THE SAMOA BUOY AT 7 FT 15 SECONDS.  
LOCALLY, SURF WILL BEGIN TO BUILD ALONG SOUTH FACING SHORES FROM THE  
FIRST SOURCE TUESDAY, THEN BECOME REINFORCED BY THURSDAY AS THE  
SECOND/LARGER SOURCE FILLS IN. SURF MAY REACH THE SOUTH SHORE  
ADVISORY LEVEL AT THE PEAK OF THIS REINFORCEMENT BY THURSDAY.  
 
LOOKING AHEAD INTO THE FIRST WEEK OF JULY, THE ACTIVE TREND COULD  
PERSIST ALONG SOUTH FACING SHORES. THE LATEST ECMWF AND GFS GUIDANCE  
SUPPORTS A GALE-FORCE LOW PASSING JUST SOUTH OF THE TASMAN SEA AND  
NEW ZEALAND TODAY THROUGH MONDAY WITH GALES SETTING UP WITHIN  
HAWAII'S SWELL WINDOW.  
 

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

 
 

 
 
SYNOPSIS/DISCUSSION...BIRCHARD  
AVIATION...TS  
MARINE...FOSTER  
 
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