High Wind Watch 3, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1010 AM HST TUE NOV 10 2009

.SYNOPSIS...
ISLAND WEATHER WILL BECOME INCREASINGLY UNSETTLED THE NEXT COUPLE
OF DAYS...AS A STRONG LOW ALOFT DEVELOPS NEAR THE ISLAND CHAIN. A
SURFACE TROUGH WILL DEVELOP NORTHEAST OF THE ISLANDS TONIGHT IN
RESPONSE TO THE DEVELOPING LOW ALOFT...WITH NORTHEAST WINDS BECOMING
RATHER STRONG NEAR KAUAI. THE SURFACE TROUGH WILL TRACK FROM EAST TO
WEST ACROSS THE ISLAND CHAIN WEDNESDAY NIGHT AND THURSDAY...AND THEN
LINGER WEST OF THE ISLANDS INTO THE WEEKEND. THIS COMBINATION WILL
KEEP WEATHER UNSETTLED...WITH HEAVY SHOWERS AND THUNDERSTORMS
POSSIBLE OVER ALL ISLANDS TONIGHT THROUGH THURSDAY...AND POSSIBLY
INTO THE WEEKEND.

&&

.DISCUSSION...
A DYNAMIC WEATHER PATTERN IS EVOLVING IN THE VICINITY OF THE
HAWAIIAN ISLANDS THIS MORNING...AS A DEEP LOW ALOFT IS IN THE
PROCESS OF CARVING ITSELF OUT IN THE MIDDLE AND UPPER ATMOSPHERE.
WATER VAPOR IMAGERY HIGHLIGHTS BOTH AN EXITING AND WEAKENING TROUGH
ALOFT SW OF THE BIG ISLAND...AND AN E-W ORIENTED...DEEPENING AND
DEVELOPING TROUGH DIGGING SOUTHWARD ALONG 25/26N AND 158W.

ALTHOUGH THE DEVELOPING LOW ALOFT AND IT/S SURFACE REFLECTION WILL
BE THE MAIN PLAYERS IN ISLAND WEATHER OVER THE NEXT COUPLE OF
DAYS...A HIGH PRESSURE CELL CENTERED WELL N OF THE ISLANDS IS
CURRENTLY PROVIDING MODERATE E TO NE TRADE WINDS TO THE
ISLANDS...WITH A FAIRLY BENIGN WEATHER PATTERN IN PLACE OVER MOST
ISLANDS THIS MORNING. ISOLATED LOCALLY HEAVY SHOWERS/THUNDERSTORMS
OVER THE WINDWARD WATERS OF MAUI AND THE BIG ISLAND THIS MORNING
HAVE EASED IN THE PAST COUPLE OF HOURS...WHILE A NEW CELL HAS
RECENTLY ERUPTED OVER WATERS 50 NM SW OF THE BIG ISLAND. HIGH CLOUDS
ARE EXPECTED TO CLEAR THE BIG ISLAND AS THE DAY PROGRESSES...
ALLOWING DAYTIME HEATING TO RELEASE THE INSTABILITY SEEN IN THE
OVERNIGHT SOUNDING DATA FROM PHTO. THUS THE FLASH FLOOD WATCH FOR
THE BIG ISLAND STARTS THIS AFTERNOON.

THE APPROACHING TROUGH ALOFT IS FORECAST TO DEVELOP INTO A CUT-OFF
LOW A COUPLE HUNDRED MILES TO THE NE OF THE ISLANDS TONIGHT...TRACK
STEADILY WSW TO A POSITION JUST W OF THE ISLANDS THROUGH THURSDAY...
THEN REMAIN NEARLY STATIONARY INTO THE WEEKEND WHILE GRADUALLY
FILLING. THIS WILL INDUCE THE DEVELOPMENT OF A SURFACE TROUGH/WEAK
SURFACE LOW TO THE E OF THE ISLANDS TONIGHT. WITH STRONG HIGH
PRESSURE FAR N OF THE ISLANDS...THE PRESSURE GRADIENT BETWEEN THE
TROUGH AND THE HIGH WILL RESULT IN BRISK NE WINDS...WHICH HAVE BEEN
ADDED TO THE FORECAST FOR KAUAI AND SURROUNDING WATERS FROM LATER
TODAY INTO THURSDAY.

THE SURFACE TROUGH IS FORECAST TO TRACK W WITH THE SUPPORTING LOW
ALOFT...AND WINDS WILL BECOME LIGHT AND VARIABLE...AND THEN SWITCH
TO THE SE...AS THE TROUGH PASSES W OVER ANY ONE ISLAND. THE TROUGH
IS EXPECTED TO BE W OF ALL ISLANDS BY THURSDAY...WITH A MOIST AND
CONVERGENT SOUTHERLY FLOW IN PLACE OVER ALL ISLANDS. LATEST MODEL
RUNS INDICATE THE POSSIBILITY OF A PERIOD OF DISTURBED WEATHER OVER
THE ISLANDS TONIGHT AS THE SHORT WAVE TO THE N DIGS S...BUT THEN
FOCUS THE BULK OF THE HEAVY PRECIP WELL N OF THE ISLANDS ON WEDS/
WEDS NIGHT...WHERE CONVERGENCE IS MAXIMIZED ON THE N SIDE OF THE
DEVELOPING SURFACE TROUGH. BY LATE THURSDAY...THE SURFACE TROUGH
WILL BE W OF THE ISLANDS...AND DEEP S/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 WILL BRING THE THREAT OF WINTER
WEATHER TO THE SUMMITS AND UPPER ELEVATIONS OF THE BIG ISLAND...
WHERE A WINTER STORM WATCH REMAINS IN PLACE.

THE MOVEMENT AND PLACEMENT OF THE LOW ALOFT/LOW-LEVEL TROUGH WILL
HAVE MAJOR IMPACTS ON WINDS AND WEATHER EXPERIENCED OVER THE
ISLANDS...AND WE WILL LIKELY BE MODIFYING FORECASTS...POSSIBLY
DRAMATICALLY AT TIMES...AS THE EVENT EVOLVES OVER THE NEXT COUPLE OF
DAYS.

THE WEAKENING OF THE LOW INTO A TROUGH AND THE WARMING OF THE UPPER
ATMOSPHERE WILL BE SLOW...SO THE CHANCE OF HEAVY RAIN/FLOODING AND
UPPER ELEVATION WINTER WEATHER COULD EASILY EXTEND INTO THE WEEKEND.
MODELS ARE NOT BEING CONSISTENT WITH THEIR REPRESENTATION WITH
WEEKEND WEATHER OVER THE ISLANDS...AND CONFIDENCE IS A LOT LOWER
THAN NORMAL...GIVEN FORECAST MODELS INABILITY TO CORRECTLY
PARAMETRIZE ALL THE CONVECTION THAT IS SLATED TO OCCUR BETWEEN NOW
AND THEN.

&&

.MARINE...
SURF WILL REMAIN BELOW ADVISORY LEVELS INTO WEDNESDAY. A NE SWELL IS
EXPECTED LATE WEDNESDAY THROUGH FRIDAY...AND A HIGH SURF ADVISORY
MAY BE REQUIRED FOR E FACING SHORES. SMALL CRAFT ADVISORIES ARE
ANTICIPATED/IN PLACE FOR WATERS AROUND KAUAI DUE TO THE EXPECTED
EVOLUTION OF STRONG NE WINDS TONIGHT THROUGH WEDNESDAY NIGHT.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FOR THE BIG ISLAND THIS AFTERNOON THROUGH THURSDAY
NIGHT.

FLASH FLOOD WATCH FOR ALL OTHER ISLANDS TONIGHT THROUGH THURSDAY
NIGHT.

WINTER STORM WATCH FOR THE BIG ISLAND SUMMITS WEDNESDAY THROUGH
THURSDAY MORNING.

SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 4 AM HST THURSDAY
FOR KAUAI NORTHWEST WATERS-KAUAI LEEWARD WATERS.

SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 4 AM HST THURSDAY
FOR KAUAI WINDWARD WATERS-KAUAI CHANNEL.

&&

BIRCHARD