High Surf in Hawaii, December 1 to 2, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
335 AM HST THU DEC 1 2011

.SYNOPSIS...
NORTHEAST WINDS WILL INCREASE NEAR KAUAI AND OAHU TODAY...WHILE
LIGHTER TRADE WINDS WILL PREVAIL OVER MAUI COUNTY AND THE BIG
ISLAND. PASSING SHOWERS WILL FOCUS OVER WINDWARD AND MAUKA AREAS
STATEWIDE...BUT WILL BE MORE FREQUENT OVER KAUAI AND OAHU THROUGH
TONIGHT...AS A WEAK FRONT STALLS AND DISSIPATES NEARBY. LIGHT TO
MODERATE TRADE WINDS ON FRIDAY WILL TURN TO THE SOUTHEAST OVER THE
WEEKEND...AS ANOTHER FRONT APPROACHES THE ISLANDS.

&&

.DISCUSSION...
CURRENTLY...THE ISLANDS LIE BETWEEN TWO HIGH PRESSURE SYSTEMS...ONE
FAR TO THE NW AND THE OTHER FAR TO THE NE. A SHARP N-S ORIENTED
SURFACE TROUGH MARKS THE BOUNDARY BETWEEN THESE TWO HIGHS...LOCATED
OVER WATERS N AND NE OF MAUI AND THE BIG ISLAND...WITH A DEVELOPING
SURFACE LOW NEAR THE NORTH END OF THE TROUGH...ALONG THE LONGITUDE
OF THE ISLANDS NEAR 32N. LOW LEVEL CONVERGENCE ALONG THE SURFACE
TROUGH IS BEING ENHANCED BY A PASSING TROUGH ALOFT...RESULTING IN
SCATTERED THUNDERSTORMS ABOUT 200 TO 600 MILES NE OF MAUI AND THE
BIG ISLAND.

ISLANDS FROM MAUI WESTWARD ARE PRIMARILY UNDER THE INFLUENCE OF THE
HIGH TO THE NW...WITH THE RESULTANT LOW LEVEL FLOW MORE NORTHERLY
THAN USUAL. INCREASING NE WINDS NEAR KAUAI AND OAHU WILL BRING
PASSING SHOWERS TO WINDWARD AND N SHORE COMMUNITIES TODAY AND
TONIGHT AS THE HIGH TO THE NW PUSHES A WEAKENING SHEAR LINE OVER
THESE ISLANDS. THESE NE WINDS HAVE ALREADY MADE FOR A WET NIGHT
ALONG N FACING SLOPES ON KAUAI...WITH 0.5-1.0 INCH OF RAIN MEASURED
IN THE 6 HOUR PERIOD ENDING AT 2 AM. THE SHEAR LINE IS EXPECTED TO
DISSIPATE NEAR KAUAI AND OAHU ON FRIDAY AS IT STALLS. MEANWHILE...A
SOMEWHAT DRIER...AND LIGHTER...WIND REGIME WILL PREVAIL OVER THE BIG
ISLAND...AS THE PRESSURE GRADIENT IS QUITE LOOSE S OF THE TROUGH
AXIS.

AS THE SURFACE TROUGH TO THE NE GRADUALLY DISSIPATES AND DRIFTS W
OVER THE NEXT 2 DAYS...THE HIGH TO THE NW WILL MOVE E AND WEAKEN.
END RESULT WILL BE A TREND TOWARD TYPICAL ENE TRADE WINDS STATEWIDE
ON FRIDAY...WITH SHOWERS FOCUSING OVER WINDWARD AND MAUKA AREAS.
WINDS WILL TURN TO THE SE ON SATURDAY...AS HIGH PRESSURE BECOMES
ESTABLISHED FAR NE OF THE ISLANDS...AND ITS ASSOCIATED RIDGE IS
SHUNTED S TOWARD THE ISLANDS...IN ADVANCE OF AN APPROACHING FRONT.
THESE WINDS MAY BRING INCREASED MOISTURE TO WINDWARD AND SE BIG
ISLAND...BUT THE SMALLER ISLANDS LOOK AS IF THEY/LL BE IN THE WIND
SHADOW OF THE BIG ISLAND...LIMITING WIND STRENGTH AND SHOWER
COVERAGE.

GLOBAL MODELS REMAIN IN FAIR AGREEMENT ON THE WEATHER FEATURES
DISCUSSED ABOVE...LEADING TO INCREASED CONFIDENCE...BUT SOLUTIONS
DIVERGE PRETTY RAPIDLY FROM SUNDAY ONWARD...WHERE CONFIDENCE IS MUCH
LOWER. THE MODEL DIFFERENCES PRIMARILY HINGE ON THE EVOLUTION OF AN
UPPER TROUGH THAT DRIVES A FRONT TOWARD KAUAI ON SUNDAY. GFS AND
NOGAPS PINCH OFF A SLOW-MOVING CUT-OFF LOW TO THE NW OF THE
ISLANDS...ALONG 165W BETWEEN 25N AND 30N...INDICATING A TENDENCY FOR
A WET SE LOW LEVEL FLOW OVER MOST OF THE ISLANDS FOR THE EARLY PART
OF NEXT WEEK. THE ECMWF INDICATES A MORE PROGRESSIVE PATTERN WITH A
CLOSED LOW DEVELOPING FAR NE OF THE ISLANDS...NEAR 38N ALONG
155W...WITH A TENDENCY TOWARD LIGHT TO MODERATE TRADE WINDS AND
RELATIVELY SETTLED WEATHER. THE FORECAST PLACES MORE WEIGHT ON THE
ECMWF SOLUTION...BUT DRAMATIC REVISIONS MAY BE NECESSARY IF THE GFS/
NOGAPS SOLUTION TURNS OUT TO BE CLOSER TO REALITY.

&&

.MARINE...
LONG PERIOD NNW SWELL HAS BEEN BUILDING AT BUOY 51101 TO THE NW OF
KAUAI OVERNIGHT...WITH LATEST OBS SUPPORTING RESULTANT SURF WELL
ABOVE ADVISORY LEVELS...AND A HIGH SURF ADVISORY REMAINS IN EFFECT
FOR EXPOSED N AND W SHORES. THE BUILDING SWELL WILL COMBINE WITH
MODERATE TO FRESH NE WINDS TO DRIVE SEAS ABOVE 10 FEET AROUND KAUAI
AND OAHU...WHERE A SMALL CRAFT ADVISORY /SCA/ IS IN EFFECT. WITH
COMBINED SEAS OF 10 FEET OR MORE SPREADING TO ADDITIONAL MARINE
ZONES...THE SCA HAS BEEN EXPANDED. SEAS ARE EXPECTED TO DIMINISH
BELOW SCA VALUES ON SATURDAY.

&&

.AVIATION...
THE LATEST SFC OBS FROM AROUND THE STATE SUGGEST PREVAILING LOW
CLOUD BASES MOSTLY ABV 030...OR VFR. WEATHER RADAR SHOW SHOWERS MOST
ABUNDANT IN THE KAUAI CHANNEL. THIS SAME AREA OF SHOWERS LIKELY
PRODUCED SOME GENEROUS RAINFALL TOTALS ACROSS WINDWARD KAUAI EARLIER
IN THE EVENING. NOW THIS AREA OF SHOWERS APPEARS TO BE HEADING
TOWARDS OAHU. RADAR IS DETECTING SMALL POCKETS OF SHOWERS SCATTERED
ACROSS THE REMAINING WINDWARD WATERS OF THE SMALLER ISLANDS AND THE
ALENUIHAHA CHANNEL. A FEW OF THESE SHOWERS BLEW THROUGH EAST OAHU
WITH EASE. PATCHY LOW CLOUDS WITH CEILINGS ABOVE 3 THOUSAND FEET
CONTINUED TO LOITER ALONG PARTS OF THE KONA COAST AND THE KOHALA
DISTRICTS OF THE BIG ISLAND AND ADJACENT WATERS.

WITH LOW CLOUDS AND SHRA SPREADING OVER KAUAI...AN AIRMET FOR MT
OBSC ABV 025 ALONG N AND E FACING SLOPES WILL BE ISSUED WITH THE
1540Z WA0HI. WL KEEP AN EYE OUT FOR OAHU AS THE SHOWERS IN THE KAUAI
CHANNEL SPREAD IN THAT DIRECTION. AIRMET FOR LOW LEVEL TURBULENCE IS
THUS FAR NOT NECESSARY. WIND SPEEDS HAVE TONED DOWN IN THE PAST FEW
HOURS OVR KAUAI.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST FRIDAY FOR NORTH AND WEST FACING
SHORES OF KAUAI NIIHAU AND OAHU AND FOR NORTH FACING SHORES OF
MOLOKAI AND MAUI.

SMALL CRAFT ADVISORY UNTIL 6 PM HST FRIDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-KAUAI CHANNEL-OAHU
WINDWARD WATERS-OAHU LEEWARD WATERS-KAIWI CHANNEL-MAUI COUNTY
WINDWARD WATERS.

&&

DISCUSSION/MARINE...BIRCHARD
AVIATION...LAU