599  
FXHW60 PHFO 061937  
AFDHFO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HONOLULU HI  
937 AM HST MON APR 6 2020  
   
SYNOPSIS
 
 
LIGHT WINDS WILL PERSIST THROUGH THE WEEK. A WEAKENING FRONT  
MOVING TOWARDS THE ISLANDS THROUGH TUESDAY WILL BRING SOME  
LOCALLY HEAVY DOWNPOURS AND A FEW THUNDERSTORMS. SCATTERED  
SHOWERS WILL CONTINUE ACROSS THROUGH THE REMAINDER OF THE WEEK,  
AS THE FRONT SLOWLY DISSIPATES OVER THE CENTRAL AND EASTERN  
ISLANDS.  
 

 
   
DISCUSSION
 
 
NO CHANGES TO THE FORECAST THIS MORNING. WIND REPORTS ACROSS THE  
ISLANDS SHOW LIGHT WINDS PREVAILING AND THAT IS EXPECTED TO  
CONTINUE FOR MUCH OF THE WEEK. THE LIGHTNING NETWORKS THIS MORNING  
HAVE DETECTED THUNDERSTORMS NEAR KAUAI, IN THE KAUAI CHANNEL AND  
NEAR MOLOKAI OVER THE LAST COUPLE OF HOURS. MORE THUNDERSTORMS ARE  
POSSIBLE ACROSS THE REGION TODAY, AND AGAIN TOMORROW DURING THE  
DAY.  
 
A LOW PRESSURE SYSTEM ABOUT 1000 MILES NORTH-NORTHWEST OF KAUAI  
WILL BE MOVING TO THE NORTHEAST OVER THE NEXT 24 HOURS OR SO. THE  
OVERNIGHT SURFACE ANALYSIS SHOWED A RIDGE OVER THE ISLANDS, WITH A  
TROUGH TO THE NORTHWEST OF KAUAI, AND A COLD FRONT ABOUT 500 MILES  
NORTHWEST OF KAUAI. THE RIDGE IS HELPING TO KEEP WINDS LIGHT OVER  
THE ISLANDS, WHILE AN UPPER LEVEL TROUGH ASSOCIATED WITH THE  
SURFACE TROUGH AND FRONT ARE HELPING TO DESTABILIZE THE  
ATMOSPHERE. THIS COMBINATION HAS LED TO THE THUNDERSTORM AND  
LOCALLY HEAVY RAIN THAT HAS OCCURRED OVER AND NEAR THE ISLANDS IN  
THE DAYTIME HEATING. A DRIER AIRMASS COMBINED WITH WARMER  
TEMPERATURES ALOFT MOVING IN TUESDAY NIGHT WILL LIMIT ANY  
THUNDERSTORM DEVELOPMENT BY WEDNESDAY. HOWEVER THE LIGHT WINDS  
WILL PERSIST, WHICH WILL LEAD TO CLOUD AND SHOWER DEVELOPMENT OVER  
THE ISLANDS, MAINLY DURING THE DAY DURING THE SECOND HALF OF THE  
WEEK.  
 
THE LOW MENTIONED ABOVE WILL CONTINUE TO MOVE TO THE NORTHEAST  
THROUGH THE WEEK, KEEPING THE RIDGE OVER OR SOUTH OF THE ISLANDS,  
RESULTING IN THE LIGHTER WINDS. ANOTHER LOW FORMS THURSDAY TO THE  
NORTHWEST OF THE ISLANDS AND MOVES TO THE EAST BEFORE LIFTING TO  
THE NORTH FRIDAY NIGHT. ANOTHER COLD FRONT ASSOCIATED WITH THIS  
LOW LOOKS TO APPROACH THE ISLANDS NEXT WEEKEND. AT THIS TIME, THE  
MODELS SHOW UPPER LEVEL DYNAMICS WILL NOT BE CONDUCIVE TO HEAVY  
RAIN OR THUNDERSTORMS, BUT OF COURSE WE WILL CONTINUE TO MONITOR  
THE SITUATION WITH FUTURE MODEL RUNS.  
 

 
   
AVIATION
 
 
VFR CONDITIONS PREVAIL AT ALL TAF SITES BUT OCCASIONAL MVFR  
CONDITIONS CAN BE EXPECTED AT TIMES ESPECIALLY FROM MAUI COUNTY  
WESTWARD, AS BANDS OF SHOWERS MOVE UP FROM THE SOUTH. A MOIST AND  
UNSTABLE AIRMASS ACROSS THE AREA WILL ALLOW FOR A SLIGHT CHANCE OF  
THUNDERSTORMS THROUGH THIS EVENING.  
 
AIRMET SIERRA REMAINS IN EFFECT FOR TEMPO MOUNTAIN OBSCURATION  
FOR KAUAI, MOLOKAI, LANAI, AND MAUI. THIS AIRMET MAY BE EXPANDED  
OR CANCELLED ACROSS SOME AREAS AS BAND OF SHOWERS MOVE UP FROM THE  
SOUTH.  
 
AIRMET TANGO REMAINS IN EFFECT FOR TEMPO MODERATE TURBULENCE  
BETWEEN FL230-340 ACROSS THE AREA. THIS AIRMET MAY BE DISCONTINUED  
LATER TODAY OR TONIGHT.  
 

 
   
MARINE
 
 
A WEAKENING TROUGH NEAR KAUAI AND A FRONT NORTHWEST WILL SLOWLY  
MAKE ITS WAY THROUGH THE HAWAIIAN WATERS OVER THE NEXT FEW DAYS,  
THEN STALL NEAR THE EASTERN WATERS DURING THE SECOND HALF OF THE  
WEEK. THIS WILL LEAD TO A LIGHT TO MODERATE WIND REGIME WITH A  
SOUTHERLY FLOW EXPECTED AHEAD OF THE FRONT AND A WESTERLY FLOW  
BEHIND IT.  
 
LATEST SATELLITE IMAGERY IS SHOWING A BROAD AREA OF CONVERGENT  
SOUTHERLY FLOW NEAR KAUAI WITH ISOLATED THUNDERSTORMS DEVELOPING  
OVER THE NORTHERN WATERS AND IN THE KAUAI CHANNEL. AS A UPPER  
LEVEL SHORT-WAVE PASSES THROUGH THE AREA, WE SHOULD SEE AN INCREASE  
IN SHOWERS AND SOME THUNDERSTORMS OVER THE AREA THROUGH TUESDAY.  
WITH SEAS AND SWELLS EXPECTED TO STAY BELOW SMALL CRAFT ADVISORY  
THRESHOLDS FOR MUCH OF THIS WEEK, THE MAIN THREAT TO MARINERS  
WILL BE THUNDERSTORM DEVELOPMENT.  
 
A SMALL LONG-PERIOD NORTHWEST SWELL WILL FILL IN TODAY AND PEAK  
TONIGHT AROUND 4 TO 5 FEET. THIS SWELL WILL BE FOLLOWED BY A  
SLIGHTLY LARGER NORTHWEST SWELL ARRIVING LATE TUESDAY, WHICH IS  
EXPECTED TO PEAK TUESDAY NIGHT OR EARLY WEDNESDAY BELOW ADVISORY  
LEVEL FOR NORTH AND WEST FACING SHORES. A SERIES OF SMALL SOUTH  
TO SOUTHEAST SWELLS ARE EXPECTED THIS WEEK, WITH SURF EXPECTED TO  
REACH THE SUMMER AVERAGE BY TUESDAY. SURF ALONG EAST FACING SHORES  
WILL REMAIN SMALL THIS WEEK DUE TO THE LACK OF TRADES.  
 

 
   
HFO WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  
 

 
 

 
 
DISCUSSION...M BALLARD  
AVIATION...BURKE  
MARINE...TS  
 
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