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Hawaiian Islands Synoptic Discussion and Guidance

507
FXHW60 PHFO 070637
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST FRI NOV 6 2009

.SYNOPSIS...
HIGH PRESSURE TO THE NORTH WILL KEEP TRADE WINDS BLOWING INTO NEXT
WEEK. A SHOWER BAND WILL SAG SOUTH OVER THE ISLANDS TONIGHT AND
PROVIDE AN UPTICK IN WINDWARD SHOWERS OVER THE WEEKEND. HIGH
CLOUDS WILL COVER HAWAIIAN SKIES OVER MUCH OF THE WEEKEND AND
EARLY NEXT WEEK. TRADE SHOWERS WILL INCREASE LATE IN THE WEEKEND
AND CONTINUE THROUGH THE WORK-WEEK AS THE UPPER ATMOSPHERE BECOMES
UNSTABLE.
&&

.DISCUSSION...
NO BIG SURPRISES IN THE SHORT TERM FORECAST TONIGHT. WATCHING THE
BAND OF LOW CLOUDS UPSTREAM OF THE ISLANDS MOVE IN...BUT FEEL THE
GRIDS PROPERLY REFLECT THIS FEATURE AT THIS TIME.

PREVIOUS DISCUSSION FOLLOWS.

&&

.PREV DISCUSSION...
ISSUED AT 345 PM
RAINFALL TODAY HAS BEEN MINIMAL WITH ONLY A FEW HUNDREDTHS
FALLING OVER WINDWARD AND MAUKA LOCATIONS. A CLOUD BAND ABOUT 50
MILES NORTH OF THE ISLANDS WILL CONTINUE MOVING SOUTH SLOWLY AND
SPREAD OVER WINDWARD ISLAND LOCATIONS TONIGHT. RIDGING ALOFT WILL
KEEP THE ATMOSPHERE RATHER STABLE...AND ONLY LIGHT TO MODERATE
SHOWERS ARE EXPECTED OVER WINDWARD AREAS.

AT THE SURFACE...MODERATE TO FRESH TRADE WINDS ARE EXPECTED TO
CONTINUE NEXT WEEK AS HIGH PRESSURE REMAINS FAR NORTH OF THE
STATE WITH THE RIDGE REMAINING BETWEEN 30N AND 35N.

MID AND UPPER LEVEL CLOUD COVER WILL INCREASE FROM WEST TO EAST
BEGINNING SATURDAY AS CLOUDS FORMED BY A TROUGH 750 MILES WEST OF
KAUAI ARE ADVECTED OVER THE STATE. RIDGING ALOFT LOCATED SOUTHEAST
OF THE STATE AND THE UPPER TROUGH TO THE WEST WILL CREATE A
CONVEYOR BELT EFFECT...ALLOWING MID AND UPPER CLOUDS TO STREAM OVER
THE ALOHA STATE. THE TROUGH ALOFT IS EXPECTED TO PUSH EAST OVER
THE NEXT FEW DAYS REACHING KAUAI SUNDAY NIGHT. MODELS SHOW THE
TROUGH WILL BRING SOME INSTABILITY TO THE ATMOSPHERE SUNDAY NIGHT
THROUGH TUESDAY...ALLOWING FOR AN INCREASE IN COVERAGE AND
INTENSITY OF THE TRADE SHOWERS. AS THE UPPER TROUGH MOVES
EAST...THE ENHANCED UPPER CLOUD COVER WILL MOVE EAST OF THE STATE
TUESDAY.

THE GLOBAL COMPUTER MODELS CONTINUE TO SHOW A STRONGER UPPER TROUGH
DIGGING TOWARD THE ISLANDS FROM THE NORTH WEDNESDAY AND THURSDAY.
THE MODELS HAVE BEEN INCONSISTENT IN THEIR FORECASTS FOR THIS
SYSTEM...AND SOME DIFFERENCES REMAIN IN THE LATEST RUNS OF THE GFS
AND ECMWF. BOTH CONTINUE TO SHOW TRADE WINDS PERSISTING THROUGH THE
PERIOD AS THE TROUGH ALOFT APPROACHES FROM THE NORTH DURING THE
SECOND HALF OF THE WEEK. THE DIFFERENCES COME IN THE LOCATION OF
THE UPPER TROUGH WEDNESDAY THROUGH FRIDAY. THE GFS KEEPS THE
TROUGH CLOSE ENOUGH TO THE STATE TO PROVIDE ATMOSPHERIC
INSTABILITY...WHILE THE ECMWF KEEPS THE TROUGH FAR ENOUGH EAST TO
KEEP THE STATE UNDER A MORE STABLE ATMOSPHERE. THE FORECAST FOR
THE SECOND HALF OF NEXT WEEK CALLS FOR WET TRADES...WHICH IS A LEAN
TOWARD THE GFS SOLUTION. CONFIDENCE IN THIS LONG TERM FORECAST
REMAINS LOW WITH SMALL PERTURBATIONS IN THE MODELS CONTINUING TO
CAUSE LARGE CHANGES IN THE FORECAST SOLUTION.

&&

.MARINE...
A SMALL CRAFT ADVISORY CONTINUES FOR COASTAL AREAS AROUND KAUAI
DUE TO COMBINED SEAS...AND AROUND THE WINDIER AREAS NEAR THE BIG
ISLAND AND MAUI FOR WINDS. THE CURRENT NORTH NORTHWEST SWELL WILL
SLOWLY DIMINISH. THIS SWELL WILL BE REINFORCED BY A NEW NORTH
NORTHWEST SWELL ARRIVING TONIGHT...BUT SURF WILL REMAIN BELOW THE
ADVISORY THRESHOLD.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL NOON HST SATURDAY FOR KAUAI WINDWARD
WATERS-KAUAI LEEWARD WATERS-OAHU WINDWARD WATERS-KAIWI CHANNEL-
MAUI COUNTY WINDWARD WATERS-BIG ISLAND LEEWARD WATERS.

SMALL CRAFT ADVISORY UNTIL 6 AM HST SUNDAY FOR KAUAI NORTHWEST
WATERS-KAUAI CHANNEL-MAALAEA BAY-PAILOLO CHANNEL-ALENUIHAHA
CHANNEL-BIG ISLAND SOUTHEAST WATERS.

&&

$$

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office

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RH		27 %
Wind		NE 10 mph
Road		Open