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Hawaiian Islands Synoptic Discussion and Guidance

077
FXHW60 PHFO 220149
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST SUN DEC 21 2014

.SYNOPSIS...
A SHEAR LINE WILL MOVE SOUTHEAST OVER KAUAI THIS EVENING AND
CONTINUE DOWN TO THE BIG ISLAND BY WEDNESDAY MORNING. IT WILL BRING
WIDESPREAD SHOWERS AND STRONG TRADE WINDS. RAINFALL WILL BE MODEST
AT FIRST BUT A TROUGH ALOFT MAY PRODUCE LOCALLY HEAVY SHOWERS...OR
EVEN THUNDERSTORMS MONDAY NIGHT. RAINFALL AMOUNTS WILL TAPER OFF ON
CHRISTMAS EVE. TRADE WINDS WILL GRADUALLY WEAKEN THROUGH THE SECOND
HALF OF THE WEEK.

&&

.DISCUSSION...
OBSERVATIONS AROUND THE ISLANDS SHOW DRY WEATHER WITH LIGHT AND
VARIABLE WINDS OVER MOST AREAS. HOWEVER...NORTH WINDS HAVE DEVELOPED
OVER KAUAI COUNTY AHEAD OF AN APPROACHING SHEAR LINE. SHOWERS ALONG
THE SHEAR LINE WILL REACH KAUAI COUNTY SOON.

THE COMPUTER MODELS ARE IN GOOD AGREEMENT SHOWING THE CLOUD BAND
ALONG THE SHEAR LINE CONTINUING TO MOVE SOUTHEAST ACROSS THROUGH
WEDNESDAY MORNING. GENTLE NORTH WINDS AHEAD OF THE SHEAR LINE WILL
GIVE WAY TO STRONG NORTH TO NORTHEAST WINDS BEHIND IT. THE CLOUD
BAND WILL PRODUCE WIDESPREAD SHOWERS AS IT MOVES OVER KAUAI COUNTY
AND OAHU THROUGH MONDAY AFTERNOON BUT THE ATMOSPHERE WILL NOT BE
UNSTABLE ENOUGH TO ALLOW EXCESSIVE RAINFALL.

A TROUGH ALOFT WILL BE MOVING SOUTHEAST ACROSS THE MAIN HAWAIIAN
ISLANDS AND A STRONG SHORTWAVE WILL BE DROPPING SOUTHEAST WITHIN THE
TROUGH MONDAY EVENING THROUGH TUESDAY MORNING. THIS FEATURE WILL
DESTABILIZE THE ATMOSPHERE AND GENERATE HEAVY RAIN AND POSSIBLY
THUNDERSTORMS OVER THE ISLANDS. THE ATMOSPHERE SHOULD STABILIZE
AGAIN TUESDAY NIGHT AS THE SHORT WAVE MOVES OFF TO THE EAST.

A STRONG HIGH WITH A CENTRAL PRESSURE NEAR 1030 MB WILL BE MOVING
EAST BEHIND THE FRONT. THE HIGH WILL BE NORTH OF THE MAIN HAWAIIAN
ISLANDS BY TUESDAY EVENING. A TIGHT PRESSURE GRADIENT BETWEEN THE
HIGH AND THE FRONT WILL PRODUCE STRONG NORTH TO NORTHEAST WINDS AND
COULD REQUIRE WIND ADVISORIES. THE TRADES WILL GRADUALLY SUBSIDE
THROUGH THE WEEK BUT WILL REMAIN LOCALLY BREEZY THROUGH CHRISTMAS
EVE.

&&

.AVIATION...
A BAND OF SHOWERY LOW CLOUDS ALONG A SHEAR LINE IS EXPECTED TO REACH
KAUAI SOON BRINGING STRONG N TO NE WINDS AND WIDESPREAD MVFR
CEILINGS AND VIS WITH LOCALIZED IFR. AIRMETS FOR MT OBSC AND LOW
LEVEL TURB S THRU SW OF THE ISLANDS WILL LIKELY BE NEEDED. THE SHEAR
LINE IS EXPECTED TO REACH OAHU LATE TONIGHT AND MAUI COUNTY ON
MONDAY.

&&

.MARINE...
A NEW NORTHWEST SWELL REACHED BUOY 51101...NEAR NIHOA...AFTER
MIDNIGHT LAST NIGHT AND ROSE OVER 10 FEET BY 900 AM. SURF FROM THIS
SWELL WILL REACH WARNING LEVELS TONIGHT. A HIGH SURF WARNING IS IN
EFFECT FOR NORTH AND WEST FACING SHORES OF THE SMALLER ISLANDS AND
FOR WEST FACING SHORES OF THE BIG ISLAND. THE BIG NORTHWEST SWELL
WILL ALSO GENERATE SMALL CRAFT ADVISORY CONDITIONS OVER MOST COASTAL
WATERS DUE TO HAZARDOUS SEAS.

STRONG NORTH TO NORTHEAST WINDS WILL MOVE OVER THE AREA STARTING
THIS EVENING. THERE WILL BE WIDESPREAD SMALL CRAFT ADVISORY STRENGTH
WINDS WITH NEAR-GALE FORCE WINDS IN THE CHANNELS WITH SOME GALES
POSSIBLE. WINDS WILL GRADUALLY SUBSIDE STARTING CHRISTMAS EVE.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING UNTIL 600 AM TUESDAY FOR NORTH AND WEST FACING
SHORES OF NIIHAU KAUAI OAHU AND MOLOKAI AND FOR NORTH FACING SHORES
OF MAUI.

HIGH SURF WARNING FROM 1000 AM TODAY TO 600 AM TUESDAY FOR WEST
FACING SHORES OF THE BIG ISLAND.

SMALL CRAFT ADVISORY UNTIL 600 AM TUESDAY FOR ALL HAWAIIAN WATERS
EXCEPT MAALAEA BAY.

&&

$$
DONALDSON



Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office