FXHW60 PHFO 221330
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST TUE DEC 22 2009
.SYNOPSIS...
A SERIES OF WEAK COLD FRONTS WILL AFFECT THE ISLANDS OVER THE NEXT
SEVEN DAYS. BRIEF BOUTS OF LIGHT TO MODERATE TRADES WILL FOLLOW EACH
FRONT...WITH ANY FRONTAL SHOWERS EXPECTED TO FOCUS ON WINDWARD AND
MAUKA AREAS.
&&
.DISCUSSION...
THE SUBTROPICAL RIDGE EXTENDS SOUTHWEST FROM A 1028 MB HIGH NEAR
38N134W THROUGH 27N141W...25N155W AND 22N180W THIS MORNING. LOWS
PASSING EASTWARD WITHIN THE WINTER MID LATITUDE STORM TRACK HAVE
STEADILY PUSHED THE RIDGE FARTHER AND FARTHER SOUTH OVER THE PAST
WEEK...WEAKENING IT IN THE PROCESS. THE NEXT SEVEN DAYS WILL SEE A
SERIES OF FRONTS PASSING ACROSS PORTIONS OF THE ISLANDS BEFORE
WASHING OUT. THESE FRONTS WILL BE WEAK AND WILL BE ACCOMPANIED BY
BRIEF BOUTS OF FRONTAL SHOWERS AND LIGHT TO MODERATE POST FRONTAL
TRADE WINDS.
A FRONT ABOUT 110 MILES NORTHWEST OF KAUAI IS RAPIDLY FALLING APART
AS IT MOVES TOWARD THE SOUTHEAST AT 20 MPH. REMNANTS OF THIS FRONT
WILL REACH KAUAI LATER TODAY...THEN CONTINUE MOVING SOUTHEAST BEFORE
STALLING IN THE VICINITY OF THE BIG ISLAND TONIGHT AND WEDNESDAY.
WINDS AHEAD OF THE FRONT ARE LIGHT...WITH WINDS ALREADY SHIFTING TO
LIGHT NORTHERLIES WEST OF MAUI. A FEW SHOWERS HAVE FORMED AHEAD OF
THE FRONT ACROSS MOLOKAI AND MAUI AS MILD LOW LEVEL CONVERGENCE SETS
UP WITHIN THE PREFRONTAL ENVIRONMENT. WE EXPECT THIS ACTIVITY TO
CONTINUE AND POSSIBLY INCREASE IN COVERAGE...BUT WIDESPREAD HEAVY
SHOWERS ARE NOT EXPECTED GIVEN THE STABILITY OF OUR AIRMASS. REMNANT
MOISTURE AND THE PROXIMITY OF AN UPPER TROUGH EAST OF THE BIG ISLAND
MAY ENHANCE SOME FRONTAL SHOWERS OVER THEM TONIGHT AND WEDNESDAY AS
THE FRONT STALLS.
POST FRONTAL TRADES WILL BE BRIEF AS THE WEAK FOLLOWING HIGH MOVES
EAST AND ANOTHER FRONT APPROACHES FROM THE NORTHWEST. WINDS WILL
AGAIN BE LIGHT AHEAD OF THE FRONT...WITH LAND AND SEA BREEZES
DOMINATING. THIS NEXT FRONT IS ALSO EXPECTED TO BE RATHER
WEAK...REACHING KAUAI EARLY THURSDAY AND PASSING ACROSS THE ISLAND
CHAIN TO NEAR THE MAUI AND THE BIG ISLAND THURSDAY NIGHT AND FRIDAY.
SHOWERS WILL FAVOR NORTH AND NORTHEAST FACING SLOPES AS TRADE WINDS
BUILD BACK IN BEHIND THE FRONT.
A THIRD FRONT IS FORECAST TO APPROACH THE STATE SUNDAY OR MONDAY.
&&
.MARINE...
A SERIES OF MODERATE TO EXTREMELY LARGE SWELLS WILL AFFECT THE
ISLANDS THIS WEEK. THE CURRENT NORTHWEST SWELL CONTINUES TO DECLINE.
HOWEVER...A LARGER NORTHWEST SWELL WILL BEGIN TO FILL IN
TODAY...PEAK TONIGHT OR EARLY WEDNESDAY WITH HEIGHTS ABOVE WARNING
LEVELS...THEN GRADUALLY LOWER INTO THURSDAY. A HIGH SURF WARNING IS
NOW IN EFFECT FOR NORTH AND WEST FACING SHORES OF THE SMALLER
ISLANDS THROUGH 6 AM THURSDAY. THIS WARNING WILL LIKELY BE EXTENDED
AS ANOTHER LARGER NORTHWEST SWELL IS EXPECTED TO BEGIN FILLING IN ON
THURSDAY...WITH WARNING LEVEL SURF EXPECTED THURSDAY NIGHT AND
FRIDAY. WAVEWATCH MODEL GUIDANCE SHOWS OPEN OCEAN SWELL HEIGHTS OF
AROUND 20 FEET WITH RATHER LONG PERIODS. THIS WOULD PRODUCE WAVE
HEIGHTS SIMILAR TO WHAT WE SAW A COUPLE OF WEEKS AGO.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING UNTIL 6 AM HST THURSDAY FOR NORTH AND WEST FACING
SHORES OF NIIHAU...KAUAI...OAHU AND MOLOKAI...AS WELL AS FOR NORTH
FACING SHORES OF MAUI.
&&
$$
POWELL
