Small Craft Advisory 1, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1250 PM HST SAT JAN 1 2011

.UPDATE...
HAVE UPDATED THE FORECAST FOR THIS AFTERNOON THROUGH SUNDAY TO
REMOVE THUNDERSTORMS...AND TO GENERALLY DECREASE POPS AND SKY COVER.
THE WEAK SURFACE LOW NEAR MOLOKAI THIS MORNING HAS SINCE
DISSIPATED...AND TRADE WINDS ARE BUILDING OVER THE ISLANDS. AN
UPPER TROUGH AND DEVELOPING LOW ALOFT REMAINS WEST OF KAUAI...
PRODUCING CLOUDY SKIES THERE...BUT LITTLE ELSE. HAVE ALSO MODIFIED
WIND FORECAST TO BE BETTER IN LINE WITH DISCUSSION BELOW.

&&

.SYNOPSIS...
TODAY/S LIGHT TRADE WINDS WILL STRENGTHEN ON SUNDAY...AND WILL FOCUS
THEIR LIMITED MOISTURE OVER WINDWARD SLOPES AND COASTS. A DEVELOPING
LOW ALOFT WEST OF THE ISLANDS WILL BRING PERIODS OF HIGH CLOUDS
THROUGH SUNDAY...BUT LITTLE INSTABILITY. THE LOW WILL MOVE WELL
SOUTH OF THE ISLANDS BY MONDAY...AND QUIET TRADE WIND WEATHER WILL
PREVAIL FROM MONDAY THROUGH WEDNESDAY. A SHEAR LINE WILL BRING A
BRIEF PERIOD OF INCREASED WINDWARD SHOWERS WEDNESDAY NIGHT AND
THURSDAY. COOL NORTHEAST WINDS WILL FOLLOW THE SHEAR LINE...BUT
WINDS WILL VEER TO A WARMER SOUTHEAST DIRECTION BY NEXT WEEKEND.

&&

.PREV DISCUSSION ISSUED 935 AM...
A COMPLEX WEATHER PATTERN IS CURRENTLY IN PLACE NEAR THE ISLANDS.
RADAR ANIMATIONS HIGHLIGHT A WEAK AREA OF LOW PRESSURE OVER WATER
JUST N OF MOLOKAI...WHICH IS ACTING TO FOCUS CLOUDS AND SHOWERS OVER
OAHU AND MOLOKAI. A SHARPENING TROUGH ALOFT NW OF THE ISLANDS IS
MOVING SE...AND IS BRINGING INCREASED INSTABILITY AND LAYERED CLOUDS
TO KAUAI AND ADJACENT WATERS. FURTHER AFIELD...A FRONT IS ANALYZED
ABOUT 350 MILES NW OF KAUAI...WITH WEAK HIGH PRESSURE ABOUT 1250
MILES NE OF THE ISLANDS. WITH THIS SYNOPTIC SETUP...LIGHT WINDS ARE
FAVORING A NORTHERLY DIRECTION OVER WATERS WEST OF MOLOKAI...WHILE
LIGHT TO MODERATE TRADES EXIST OVER THE BIG ISLAND AND ADJACENT
WATERS.

THE FORECAST CALLS FOR THE WEAK SURFACE LOW/TROUGH NEAR MOLOKAI TO
GRADUALLY DISSIPATE THROUGH TONIGHT...WHILE TRACKING SLOWLY
WESTWARD. THEREFORE...LIGHT AND VARIABLE WINDS WILL GIVE WAY TO A
STRENGTHENING TRADE WIND FLOW...WITH MODERATE TRADES STATEWIDE BY
TOMORROW AFTERNOON. THE TRADES WILL BE SUPPORTED BY 1028 MB HIGH
CENTERED NE OF THE ISLANDS. THIS HIGH WILL MOVE SLOWLY E THROUGH
WEDNESDAY...MAINTAINING LIGHT TO MODERATE TRADE WINDS. LATEST
GUIDANCE INDICATES A SHEAR LINE MOVING OVER THE ISLANDS FROM THE N
ON WEDNESDAY NIGHT AND THURSDAY WITH MARGINAL SUPPORT ALOFT...
BRINGING A BRIEF PERIOD OF INCREASED WINDWARD SHOWERS...AND COOL NE
WINDS. THE MODERATE NE WINDS ARE EXPECTED TO WEAKEN AND VEER TO THE
E...AND THEN SE...BY NEXT WEEKEND.

A CLOSED LOW ALOFT APPEARS TO BE DEVELOPING ABOUT 300 MILES NW OF
KAUAI...WITHIN A BROAD N-S TROUGH ALOFT THAT EXTENDS ALONG 162W OR
SO. THIS LOW IS FORECAST TO MOVE A POSITION WELL S OF THE ISLANDS
THROUGH MONDAY...WITH IT/S ASSOCIATED TROUGH EXTENDING NE OVER THE
ISLANDS. THIS FEATURE IS EXPECTED TO DESTABILIZE THE ATMOSPHERE...
ESPECIALLY OVER THE ISLANDS OF KAUAI AND OAHU...AND HENCE THE
INCLUSION OF THUNDERSTORMS IN THE FORECAST THROUGH SUNDAY. MOISTURE
IS SOMEWHAT LIMITED AND FORECAST CONFIDENCE IS MINIMAL...BUT WILL
WAIT TO SEE HOW THINGS DEVELOP TODAY BEFORE MAKING CHANGES TO THE
FORECAST FOR TONIGHT AND SUNDAY.

AS FAR AS SENSIBLE WEATHER...EXPECT SEA BREEZES TO DRIVE INTERIOR
CLOUDS AND SHOWERS THIS AFTERNOON...WITH THE INCREASED INSTABILITY
NEAR KAUAI LEADING TO A SLIGHT CHANCE OF A THUNDERSTORM. ATMOSPHERIC
MOISTURE CONTENT...ALTHOUGH INCREASING SOMEWHAT...APPEARS TO BE
LIMITED AND THUS THE THREAT OF PROLONGED HEAVY RAINFALL IS
MINIMIZED. BUILDING TRADE WINDS WILL FOCUS CLOUDS AND SHOWERS OVER
WINDWARD COASTS AND SLOPES TONIGHT AND SUNDAY...WITH THE PROXIMITY
OF THE LOW ALOFT BRINGING INCREASED INSTABILITY...MAINLY TO KAUAI
AND OAHU. DEEP LAYER RIDGING BUILDING OVER AND N OF THE ISLANDS WILL
BRING INCREASED STABILITY SUNDAY NIGHT AND MONDAY...AND RATHER
BENIGN TRADE WIND CONDITIONS UNTIL THE ARRIVAL OF THE AFOREMENTIONED
SHEAR LINE LATER IN THE WEEK.

WINDS OVER THE SUMMITS OF THE BIG ISLAND AND ACROSS MOUNT HALEAKALA
ON MAUI ARE EXPECTED TO INCREASE STARTING SUNDAY NIGHT DUE TO THE
BUILDING UPPER RIDGE...POSSIBLY EXCEEDING ADVISORY THRESHOLDS.

FOR THE MARINE ASPECT OF THE FORECAST...SURF ALONG NORTH AND WEST
FACING SHORES OF MOST ISLANDS WILL PEAK BELOW ADVISORY LEVELS
TODAY...DUE TO A MODERATE WNW SWELL. A LARGER LONG-PERIOD WNW SWELL
WILL BUILD TONIGHT AND PEAK SUNDAY...WITH MAX SURF HEIGHTS NEAR
WARNING LEVELS ALONG NORTH AND WEST FACING SHORES. SOME SHADOWING OF
THE SWELL BY KAUAI LOWERS CONFIDENCE IN WARNING LEVEL SURF OVER THE
ISLANDS FROM OAHU TO MAUI...BUT THIS SWELL IS EXPECTED TO BRING
WARNING LEVEL SURF TO WEST FACING SHORES OF THE BIG ISLAND...WITH
THE PEAK THERE OCCURRING SUNDAY NIGHT. THIS SWELL WILL GRADUALLY
DIMINISH ON MONDAY AND MONDAY NIGHT...BUT ANOTHER SIMILARLY SIZED
WNW SWELL WILL BUILD TUESDAY AND TUESDAY NIGHT...WITH PEAK SURF
HEIGHTS ONCE AGAIN NEAR WARNING LEVELS.

THE ANTICIPATED WNW SWELL WILL LEAD TO COMBINED SEAS IN EXCESS OF
10 FEET...WHICH IS THE LOCAL THRESHOLD FOR THE ISSUANCE OF A SMALL
CRAFT ADVISORY /SCA/...LIKELY TO BE ISSUED LATER TODAY.
STRENGTHENING TRADE WINDS SUNDAY AND MONDAY WILL LIKELY REACH SCA
THRESHOLD IN THE TYPICALLY WINDY AREAS ADJACENT TO MAUI AND THE BIG
ISLAND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

BIRCHARD