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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
932 AM HST THU DEC 18 2014

.SYNOPSIS...
HIGH PRESSURE CENTERED NORTH OF THE ISLANDS WILL MAINTAIN LOCALLY 
BREEZY TRADE WINDS THROUGH FRIDAY. MOSTLY CLOUDY SKIES WITH FREQUENT 
SHOWERS WILL CONTINUE OVER MOST WINDWARD AND MOUNTAIN AREAS THROUGH 
THE REST OF THE MORNING HOURS...BECOMING SCATTERED IN THE AFTERNOON. 
ISOLATED SHOWERS ARE POSSIBLE OVER LEEWARD AREAS TODAY. THE TRADES 
ARE EXPECTED TO BECOME LIGHT OVER THE UPCOMING WEEKEND AS THE HIGH 
LEAVES THE AREA AND A FRONT APPROACHES THE ISLANDS FROM THE 
NORTHWEST. THE FRONT WILL MOVE DOWN THE ISLAND CHAIN BETWEEN SUNDAY 
NIGHT AND TUESDAY NIGHT BRINGING WITH IT SOME SHOWERY AND WINDY 
WEATHER.

&&

.DISCUSSION...
SATELLITE AND RADAR IMAGERY FROM EARLIER THIS MORNING SHOW A 
PERSISTING ACTIVE SHOWER PATTERN ACROSS WINDWARD AREAS OF ALL THE 
MAIN HAWAIIAN ISLANDS...WITH ADDITIONAL SHOWERS UPSTREAM HEADING 
TOWARDS THE ALOHA STATE. THEREFORE...POPS HAVE BEEN INCREASED FOR 
ALL WINDWARD AREAS FOR THE REST OF THE MORNING HOURS. POPS OVER 
WINDWARD MAUI COUNTY HAVE ALSO BEEN INCREASED TO SCATTERED THIS 
AFTERNOON AS THE TRADE WIND SHOWER PATTERN SHOULD REMAIN ACTIVE 
TODAY. 

DIFFERENCES REMAINS BETWEEN THE TWO GLOBAL MODELS...THE ECMWF 
/EC/ AND GFS...REGARDING THE UPPER LEVEL SHORT WAVE TROUGH AND ITS 
SUPPORT OF THE SURFACE FRONT EARLY NEXT WEEK.

THE MOST NOTABLE DIFFERENCE IS IN THE TIMING OF THE UPPER LEVEL 
TROUGH WHERE THE EC HAS THE TROUGH JUST WEST OF KAUAI MONDAY EVENING 
WHILE THE GFS HAS IT OVER KAUAI AND OAHU. 

THE EC REMAINS THE STRONGER OF THE TWO WITH A COLD 500 MB TEMP OF 
MINUS 17 C. THE GFS HAS A MINUS 14 C. NOT MUCH OF A DIFFERENCE HERE 
WHERE BOTH TEMPS ARE COLD ENOUGH TO SUPPORT AT LEAST A SLIGHT CHANCE 
OF A THUNDERSTORM AND ALMOST CERTAIN...SPOTTY HEAVY SHOWERS.

THE MODELS DIFFER THEREAFTER. THE EC KEEPS THE UPPER TROUGH OVER 
THE ISLANDS TUESDAY...THUS MAINTAINING A CHANCE OF ENHANCED SHOWERS 
AND A SLIGHT CHANCE OF A THUNDERSTORMS. ON THE OTHER HAND...THE GFS 
HAS THE UPPER TROUGH FAR NE OF THE ISLANDS...SUGGESTING MORE LIGHT 
TO MODERATE SHOWERS WITH THE FRONT. THE TWO MODELS DO AGREE ON THE 
LOCATION OF THE FRONT...OVER MAUI TUESDAY AFTERNOON. SHOULD WE 
PURSUE THE EC SOLUTION...IMPROVEMENT IN THE WEATHER WILL COME 
TUESDAY NIGHT AS THE UPPER TROUGH FINALLY LIFTS OUT.

THIS IS STILL A GOOD FEW DAYS AWAY SO WE WILL WAIT AND SEE IF THE 
MODELS MAINTAINS A SHOWERY OUTLOOK FOR MONDAY AND MONDAY NIGHT.

THE WEATHER PATTERN MAY TURN SLIGHTLY CONVECTIVE WITH LOCAL DAYTIME 
SEA BREEZES AS THE TRADES EASES TO LIGHT TO LOCALLY MODERATE DURING 
THE WEEKEND. A STRONG AND STABLE AIR MASS WILL PUT A LID ON THESE 
CONVECTIVE CLOUDS. THERE WILL BE ENOUGH OF AN EASTERLY WIND FLOW TO 
CARRY A FEW SHOWER BEARING CLOUDS TO THE WINDWARD AREAS OF ALL THE 
ISLANDS.


&&

.AVIATION...
CLOUDS AND SHOWERS CARRYING IN WITH THE TRADE WINDS ARE CAUSING MVFR 
CIGS AND TEMPO MTN OBSC THIS MORNING. THEREFORE...AIRMET SIERRA HAS 
BEEN ISSUED FOR MTN OBSC ON THE WINDWARD SIDES OF OAHU...MOLOKAI AND 
MAUI THROUGH 22Z. THE CLOUDS AND SHOWERS ARE EXPECTED TO DECREASE BY 
AFTERNOON AS THE CLOUD TOPS WARM AND MIXING INCREASES. 
ELSEWHERE...VFR CONDITIONS WILL PREVAIL.

BREEZY TRADE WINDS ARE ALSO RESULTING IN LEEWARD MECHANICAL 
TURBULENCE OVER ALL ISLANDS. AIRMET TANGO IS IN EFFECT FOR THIS...
AND WILL LIKELY CARRY ON UNTIL FRIDAY.

&&

.MARINE...
A SMALL CRAFT ADVISORY /SCA/ REMAINS IN EFFECT FOR THE WINDWARD 
WATERS OF KAUAI AND OAHU...DUE MAINLY TO A LARGE NW SWELL...AND FOR 
MAALAEA BAY...THE WATERS SOUTH OF THE BIG ISLAND...AND THE PAILOLO 
AND ALENUIHAHA CHANNELS DUE TO STRONG GUSTY WINDS. THE SCA IS VALID 
THROUGH 6 PM HST FRIDAY.

WE DO LOOK FORWARD TO THE SCA BEING LOWER LATE FRIDAY AFTERNOON.
THIS WILL BE SHORT LIVE HOWEVER. SCA CONDITIONS ARE AGAIN EXPECTED 
SATURDAY NIGHT FOR THE ANTICIPATED LARGE NW SWELL. 

SURF HEIGHTS ARE EXPECTED TO RISE TO ADVISORY LEVELS FOR THE NORTH 
AND WEST SHORES OF MOST OF THE SMALLER ISLANDS TONIGHT. SO...A SURF 
ADVISORY WILL BE IN EFFECT FROM 4 PM HST THIS AFTERNOON THROUGH 
FRIDAY. THIS SWELL WILL PEAK TONIGHT AND GRADUALLY LOWER FRIDAY.

AN UPCOMING LARGE NW SWELL ON SUNDAY WILL LIKELY NEED A HIGH SURF 
WARNING INVOLVING BOTH NORTH AND WEST FACING SHORES OF MOST ISLANDS. 
THE SOURCE OF THIS SWELL IS FROM A RATHER BROAD STORM LOW CURRENTLY 
LOCATED OFF THE EAST COAST OF JAPAN. ANOTHER STORM LOW IS PREDICTED 
BY THE MODELS TO FORM NORTH OF THE ISLANDS THE MIDDLE OF NEXT WEEK 
WHICH MAY KEEP SURF ELEVATED IN AT LEAST THE ADVISORY RANGE THROUGH 
CHRISTMAS.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 600 PM HST FRIDAY FOR WINDWARD WATERS OF 
KAUAI AND OAHU...MAALAEA BAY...THE WATERS SOUTH OF THE BIG ISLAND... 
AND THE PAILOLO AND ALENUIHAHA CHANNELS.

HIGH SURF ADVISORY FROM 4 PM THIS AFTERNOON TO 6 PM HST FRIDAY 
FOR NIIHAU-KAUAI WINDWARD-KAUAI LEEWARD-WAIANAE COAST-OAHU NORTH 
SHORE-OAHU KOOLAU-MOLOKAI-MAUI WINDWARD WEST-WINDWARD HALEAKALA.

&&

$$

DISCUSSION/MARINE...REYNES/LAU
AVIATION...FOSTER




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