Weather Service Report


661 
FXHW60 PHFO 211340
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
338 AM HST SUN DEC 21 2014

.SYNOPSIS...
LIGHT WINDS WILL CONTINUE TODAY...ALLOWING FOR SEA BREEZES TO 
RETURN THIS AFTERNOON AND GENERATING A FEW SHOWERS OVER LEEWARD AND 
INTERIOR AREAS. A COLD FRONT WILL APPROACH THE ISLANDS FROM THE 
NORTHWEST...BRINGING AN INCREASE IN SHOWERS STARTING LATER TONIGHT. 
THERE IS POTENTIAL FOR HEAVY RAIN AND A FEW THUNDERSTORMS ACROSS THE 
ALOHA STATE FROM MONDAY AFTERNOON THROUGH TUESDAY. STRONG NORTHERLY 
WINDS WILL DEVELOP BEHIND THE FRONT BY MID WEEK. 

&&

.DISCUSSION...
A FEW SHOWERS HAVE BEEN MOVING ACROSS WINDWARD AND MOUNTAIN AREAS 
DURING THE EARLY MORNING HOURS...WITH SFC WINDS REMAINING GENERALLY 
LIGHT. WINDS OVER THE BIG ISLAND ARE NOW VEERING TO A MORE SE FLOW. 
AN UPPER LEVEL RIDGE OVER THE ALOHA STATE WILL HELP IN KEEPING A 
RELATIVELY STABLE AIRMASS ALOFT WITH SHOWER ACTIVITY REMAINING LOW 
TODAY. AT THE SFC...A BROAD HIGH FAR ENE OF THE ISLANDS WILL 
CONTINUE TO MIGRATE E...WHICH WILL MAINTAIN WINDS ON THE LIGHT SIDE 
TODAY AND TONIGHT.  

MEANWHILE...A DEEPENING TROUGH FAR NW OF THE ISLAND CHAIN CONTINUES 
TO GRADUALLY APPROACH THE ALOHA STATE...WITH AN ASSOCIATED COLD 
FRONT ABOUT 250 MILES NW OF KAUAI ALSO MOVING TOWARDS THE ISLANDS. 
WITH THIS OVERALL SYNOPTIC SETUP...EXPECT ANOTHER ROUND OF SEA 
BREEZES DEVELOPING THIS AFTERNOON WITH CLOUDS AND SHOWERS AFFECTING 
SOME LEEWARD AND INTERIOR AREAS. RAINFALL SHOULD REMAIN LIGHT. 

THE TROUGH/LOW COMPLEX WILL APPROACH THE W EDGE OF THE ISLAND CHAIN 
TONIGHT WITH SHOWER COVERAGE INCREASING ACROSS THE AREA...AND WITH 
POSSIBLY ENOUGH UPPER LVL SUPPORT FOR SOME DEEP CONVECTION TO 
DEVELOP. A COLDER AIRMASS ALOFT WILL ARRIVE WITH THE TROUGH AND 
FURTHER DESTABILIZE THE ATMOSPHERE OVER THE ISLANDS. LATEST MODEL 
ANALYSES SHOW 500 MB TEMPS DROPPING TO -12C TO -14C. HOWEVER...
COMPARED TO PREVIOUS RUNS...THE MOST RECENT TRENDS IN THE GLOBAL 
MODEL SOLUTIONS SEEM LESS AGGRESSIVE IN TERMS OF OVERALL AVAILABLE 
MOISTURE FOR SIGNIFICANT CONVECTION TO DEVELOP WITH THE FROPA. X-SEC 
ANALYSES DEPICT A RATHER DRY SWATH OF AIR ABOVE 700 MB MON THROUGH 
TUE. BUT THE TROUGH SHOULD PROVIDE ENOUGH INSTABILITY TO ERODE LOW 
LVL INVERSIONS AND ALLOW FOR SOME VERTICAL DEVELOPMENT OF SHOWERS 
AND ANY THUNDERSTORM CELLS THAT MAY FORM. 

IN GENERAL...GFS AND ECMWF SHOW FAIR AGREEMENT IN TERMS OF THE 
TIMING AND OVERALL SCENARIO...BRINGING A FROPA THROUGH THE ISLAND 
CHAIN AND A CUTOFF LOW DEVELOPING NE OF THE ALOHA STATE MON THROUGH 
TUE. SO FAR IT SEEMS THE HIGHEST IMPACTS WEATHERWISE ARE EXPECTED 
OVER KAUAI COUNTY AND OAHU...WHERE THE HIGHEST POPS AND CHANCES FOR 
LOCALIZED HEAVY RAINFALL COVERAGE RESIDE. THERE IS ALSO A SLIGHT 
CHANCE OF THUNDERSTORMS FROM MON AFTERNOON TO TUE NIGHT. 

STRONG NNE WINDS WILL ARRIVE IN THE WAKE OF THE FROPA BY MID 
WEEK...THEN GRADUALLY RELAX THROUGH THE SECOND HALF OF THE WEEK. 
WIND WILL FINALLY VEER TO A MORE TYPICAL NE FLOW NEXT WEEKEND AS 
HIGH PRESSURE BUILDS NW OF THE ALOHA STATE.  

&&

.AVIATION...
LIGHT WINDS WILL ALLOW SEA BREEZES TO DEVELOP OVER THE ISLANDS LATER 
THIS MORNING...LEADING TO INCREASED CLOUDINESS OVER INTERIOR AREAS. 
A STABLE ATMOSPHERE WILL LIMIT CLOUD AND SHRA DEVELOPMENT...WITH 
ISOL MVFR VIS/CIG EXPECTED. IN THE MEAN TIME...A LIGHT BUT 
PERSISTENT E/SE LOW-LEVEL FLOW OVER MOST AREAS WILL DELIVER ISOL 
MVFR VIS/CIG IN SHRA TO WINDWARD AREAS OF THE ISLANDS...MAINLY FROM 
OAHU TO THE BIG ISLAND. A FRONT ARRIVING FROM THE NW TONIGHT WILL 
BRING INCREASING N TO NE WINDS AND MVFR VIS/CIG IN SHRA...AFFECTING 
KAUAI INITIALLY...BEFORE SPREADING TO OAHU ON MONDAY. THE INCREASING 
WINDS AND SHRA WILL LIKELY REQUIRE AIRMETS FOR LOW LEVEL TURBULENCE 
TO THE LEE OF THE MOUNTAINS...AND MOUNTAIN OBSCURATION ALONG N 
FACING SLOPES.

&&

.MARINE...
A LONG PERIOD NORTHWEST SWELL GENERATED BY A LARGE AND POWERFUL LOW 
PRESSURE SYSTEM WILL BRING INCREASING SURF HEIGHTS TODAY...REACHING 
WARNING LEVELS TONIGHT. A HIGH SURF WARNING IS IN EFFECT UNTIL 
TUESDAY MORNING FOR NORTH AND WEST FACING SHORES OF THE SMALLER 
ISLANDS...AND STARTING LATER THIS MORNING FOR WEST FACING SHORES OF 
THE BIG ISLAND. 

A HIGH SURF ADVISORY ALSO REMAINS IN EFFECT FOR EAST FACING SHORES 
OF THE BIG ISLAND THROUGH 6 PM HST TODAY.   

THIS INCREASING SWELL WILL ALSO GENERATE SMALL CRAFT ADVISORY 
CONDITIONS OVER MOST COASTAL WATERS DUE TO HAZARDOUS SEAS. 

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING UNTIL 6 AM HST TUESDAY FOR NORTH AND WEST FACING 
SHORES OF NIIHAU KAUAI OAHU AND MOLOKAI AND FOR NORTH FACING SHORES 
OF MAUI.

HIGH SURF WARNING FROM 10 AM HST TODAY TO 6 AM HST TUESDAY FOR WEST 
FACING SHORES OF THE BIG ISLAND.  

HIGH SURF ADVISORY UNTIL 6 PM HST TODAY FOR EAST FACING SHORES OF 
THE BIG ISLAND.

SMALL CRAFT ADVISORY UNTIL 6 AM HST TUESDAY FOR ALL HAWAIIAN WATERS 
EXCEPT MAALAEA BAY. 

&&

$$

DISCUSSION/MARINE...REYNES
AVIATION...BIRCHARD





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