Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 181415
AFDHFO

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

.SYNOPSIS...
HIGH PRESSURE CENTERED NORTH OF THE ISLANDS WILL MAINTAIN LOCALLY
BREEZY TRADE WINDS THROUGH FRIDAY. THE TRADES WILL FOCUS SHOWERS
OVER WINDWARD AND MOUNTAIN AREAS. THE WINDS WILL BECOME LIGHT OVER
THE 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...
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 THE TROUGH 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 THUNDERSTORM. 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 MODEL 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 MODELS DO ALSO AGREE ON A QUIET WEEKEND. THE WEATHER PATTERN
MAY TURN SLIGHTLY CONVECTIVE WITH LOCAL DAYTIME SEA BREEZES AS THE
TRADES EASES TO LIGHT TO LOCALLY MODERATE. 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.

THE POPS AND SKY COVER HAVE BEEN TRIMMED DOWN FOR THE WINDWARD AND
MOUNTAIN AREAS OF MOLOKAI MAUI AND THE BIG ISLAND THIS MORNING. IT
LOOKS LIKE IT WON/T BE THAT SHOWERY IN THESE PLACES THIS MORNING.


&&

.AVIATION...
HIGH PRESSURE TO THE NORTH OF THE ISLANDS MAINTAINING TRADE WIND
FLOW...WITH CLOUDS AND SHOWERS MOVING OVER MOSTLY WINDWARD AND MAUKA
AREAS. SOME MVFR CONDITIONS ARE EXPECTED WITH THE CLOUDS AND SHOWERS
IN THOSE AREAS. OTHERWISE VFR CONDITIONS ARE EXPECTED TO PREVAIL.

HIGH PRESSURE BUILDING TO THE NORTH WILL STRENGTHEN TRADE WINDS
TODAY WHICH MAY REQUIRE AN AIRMET FOR MECHANICAL TURBULENCE TO
THE LEE OF THE MOUNTAINS.

&&

.MARINE...
A COUPLE OF ZONES HAVE BEEN ADDED TO THE EXISTING SMALL CRAFT
ADVISORY /SCA/. THESE TWO ZONES ARE THE WINDWARD WATERS OF KAUAI
AND OAHU AND IS DUE MAINLY TO THE BUILDING NW SWELL. THE SCA FOR THE
AFFECTED ZONES IS GOOD TILL 6 PM HST FRIDAY.

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

WE WILL BE KEEPING A CLOSE WATCH TO THIS NEW NW SWELL. SURF HEIGHTS
ARE EXPECTED TO RISE TO NEAR OR AT ADVISORY LEVELS FOR THE NORTH AND
WEST SHORES OF SOME ISLANDS TONIGHT. SO...AN ADVISORY MAY BE NEEDED
LATER THIS MORNING. THIS SWELL JUST HIT BUOY 51001 A COUPLE OF HOURS
AGO. IT WILL PEAK TONIGHT AND GRADUALLY LOWER FRIDAY.

THE UPCOMING LARGE NW SWELL 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.

&&

$$
PUBLIC/MARINE...LAU
AVIATION...M BALLARD







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