High Surf in Hawaii, November 11 to 19, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
417 AM HST WED NOV 11 2009

.SYNOPSIS...
ISLAND WEATHER WILL BE UNSETTLED THROUGH THE WEEK WITH LOCALLY
HEAVY SHOWERS AND SOME THUNDERSTORMS POSSIBLE. WINDS WILL INCREASE
OVER KAUAI TODAY AS A LOW PRESSURE FORMS JUST NORTH OF MAUI. THE LOW
WILL MOVE WEST OF THE ISLANDS THURSDAY BRINGING MOIST SOUTHEAST FLOW
OVER THE STATE. TRADE WINDS ARE EXPECTED OVER THE WEEKEND WITH
ENHANCED SHOWERS REMAINING.

&&

.DISCUSSION...
HEAVY RAINS DURING THE FIRST HALF OF LAST NIGHT PROMPTED FLOOD
ADVISORIES FOR PARTS OF OAHU...MOLOKAI...AND AREAS NEAR CAPTAIN
COOK ON THE BIG ISLAND. RAIN GAGES ALONG THE KOOLAU MOUNTAINS
RANGED FROM 1.00 TO 1.75 INCHES OF RAIN...RADAR ESTIMATES SHOW THE
NORTH COAST OF MOLOKAI RECEIVED 1 TO 3 INCHES WITHIN A 3 HOUR
PERIOD...AND RAIN FALL NEAR CAPTAIN COOK WAS ESTIMATED TO TOTAL
NEAR 1.5 INCHES. AFTER MIDNIGHT...RAINFALL EASED OVER THE STATE
BUT...AS OF 3 AM...SHOWER COVERAGE HAS INCREASED AGAIN AS MODERATE
TO HEAVY SHOWERS MOVE INTO OAHU/S NORTH SHORE...THE NORTH SHORE OF
KAUAI...AND OVER THE HANA COAST ON MAUI.

EARLY MORNING SATELLITE IMAGES SHOW AN UPPER LEVEL LOW FORMING
APPROXIMATELY 250 MILES NORTH OF MOLOKAI...AND SURFACE
OBSERVATIONS SHOW A SURFACE TROUGH HAS FORMED OVER MAUI AND
EXTENDS TOWARD THE NNW. THE DEVELOPMENT OF THE UPPER LOW AND
SURFACE TROUGH WILL DICTATE THE ISLANDS WEATHER OVER THE NEXT FEW
DAYS.

MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE UPPER LOW...FORMING
A DEEP CUT-OFF LOW JUST NORTH OF THE ISLANDS TODAY...AND MOVING
WEST TO A POSITION WEST OF THE STATE BY THURSDAY AFTERNOON. THE
UPPER LOW IS EXPECTED TO REMAIN WEST OF THE ISLANDS INTO THE
WEEKEND AS IT WEAKENS. AT THE SURFACE...THINGS ARE NOT AS CLEAN
CUT. MOST MODELS HAVE INITIALIZED THE SURFACE TROUGH NEAR MAUI
THIS MORNING...AND MOVE A DEEPENING TROUGH WEST...ACROSS THE
ISLANDS TODAY AND TONIGHT BEFORE FORMING A WEAK SURFACE ON
THURSDAY. HOWEVER...THE WRF SHOWS A DIFFERENT SCENARIO BY
DEEPENING THE CURRENT SURFACE TROUGH INTO A LOW THIS MORNING...AND
CONTINUES TO DEEPEN THE LOW INTO THURSDAY AS IT MOVES WEST ACROSS
THE ISLANDS. THE WRF HAS GAINED SOME CREDIBILITY WITH THIS
COMPLICATED SCENARIO BY CORRECTLY FORECASTING TUESDAY/S STRONG
WINDS NEAR KAUAI AND THE CURRENT STRONG WINDS ON THE BIG ISLAND
SUMMITS. THE WRF HAS ALSO DONE WELL WITH THE OVERNIGHT QPF
FIELDS...LINING UP WELL WITH RAINBANDS SEEN ON RADAR. SO...THE
SHORT TERM FORECAST GIVES A NOD TO THE WRF...WITH STRONGER WINDS
OVER AND NEAR KAUAI AS THE SURFACE LOW FORMS JUST NORTH OF MAUI
LATER THIS MORNING. THE WIND ADVISORY REMAINS OVER KAUAI AND
NIIHAU UNTIL 6 PM TODAY...AND A WIND ADVISORY IS NOW IN EFFECT FOR
THE BIG ISLAND SUMMITS WITH SW WINDS REACHING ADVISORY LEVELS.

THIS DEVELOPING LOW ALOFT AND IT/S SURFACE REFLECTION BRING
TOGETHER THE INGREDIENTS FOR HEAVY RAINFALL. THE LOW ALOFT WILL
BRING A DESTABILIZING POOL OF COLD AIR TO THE MID- AND UPPER-
LEVELS OF THE ATMOSPHERE...WHILE ALSO INDUCING THE SURFACE LOW.
THE SURFACE LOW WILL PROVIDE LOW-LEVEL CONVERGENCE THAT WILL ALLOW
MOISTURE NEAR THE SURFACE TO TAP IN TO THE INSTABILITY ALOFT.
OROGRAPHIC LIFTING AND DAYTIME HEATING WILL ALSO ADD SOME LIFT TO
THE LOW-LEVEL MOISTURE.

THE SURFACE LOW FORMING JUST NORTH OF MAUI IS EXPECTED TO TRACK W
WITH THE SUPPORTING LOW ALOFT...AND WINDS WILL BECOME LIGHT AND
VARIABLE...AND THEN SWITCH TO THE SE...AS THE LOW PASSES W OVER
ANY ONE ISLAND. THE SURFACE LOW IS EXPECTED TO BE W OF ALL ISLANDS
BY THURSDAY...WITH A MOIST AND CONVERGENT SOUTHEASTERLY FLOW IN PLACE
OVER ALL ISLANDS.

MODEL RUNS CONTINUE TO SHOW THE BULK OF THE HEAVY PRECIP N OF THE
ISLANDS ON WEDS/WEDS NIGHT...WHERE CONVERGENCE IS MAXIMIZED ON THE
N SIDE OF THE DEVELOPING SURFACE LOW. BY LATE THURSDAY...THE
SURFACE LOW WILL BE W OF THE ISLANDS...AND SE FLOW ON THE E
SIDE OF THE LOW ALOFT/SURFACE TROUGH IS EXPECTED TO BRING BOUTS OF
WIDESPREAD HEAVY RAIN TO MOST AREAS ACROSS THE STATE. THE COLD
POOL OF AIR ASSOCIATED WITH THE LOW ALOFT ALSO BRINGS THE THREAT OF
WINTER WEATHER TO THE SUMMITS AND UPPER ELEVATIONS OF THE BIG
ISLAND... WHERE A WINTER WEATHER ADVISORY IS IN EFFECT.

THE WEAKENING OF THE UPPER LOW WILL BE SLOW...SO THE CHANCE OF
HEAVY RAIN/FLOODING AND UPPER ELEVATION WINTER WEATHER COULD
EXTEND INTO THE WEEKEND. MODELS ARE DEPICTING INCREASING TRADE
WINDS BY THE WEEKEND WITH HEAVIER THAN NORMAL SHOWERS.

&&

.MARINE...
SURF WILL REMAIN BELOW ADVISORY LEVELS TODAY. A ROUGH...SHORT-
PERIOD NE SWELL IS EXPECTED LATE TONIGHT THROUGH FRIDAY...AND A HIGH
SURF ADVISORY MAY BE REQUIRED FOR E FACING SHORES. SMALL CRAFT
ADVISORIES ARE IN PLACE FOR WATERS AROUND KAUAI DUE TO THE
EXPECTED STRONGER WINDS TODAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH LATE THURSDAY NIGHT FOR ALL HAWAII
ISLANDS.

WIND ADVISORY UNTIL 6 PM HST THIS EVENING FOR NIIHAU-KAUAI.

WINTER WEATHER ADVISORY UNTIL 10 AM HST THURSDAY FOR BIG ISLAND
SUMMITS.

WIND ADVISORY UNTIL 10 AM HST THURSDAY FOR BIG ISLAND SUMMITS.

SMALL CRAFT ADVISORY UNTIL 4 AM HST THURSDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-KAUAI CHANNEL.

&&

MORRISON