Drought in Hawaii, November 1 to 30, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST MON OCT 31 2011

.SYNOPSIS...
BOUTS OF UNSETTLED WEATHER ARE IN STORE THIS WEEK. AN UPPER LEVEL
DISTURBANCE PASSING OVER THE STATE WILL POSE A THREAT FOR HEAVY
SHOWERS THROUGH TUESDAY. WITH GENTLE TO MODERATE TRADE WINDS
BLOWING...SHOWERS WILL FAVOR WINDWARD AND MAUKA AREAS...THOUGH
LEEWARD AREAS MAY SEE A BRIEFLY HEAVY SHOWER. TRADE WINDS WILL
STRENGTHEN TUESDAY NIGHT AND WEDNESDAY AS HIGH PRESSURE BUILDS NORTH
OF THE STATE. THE STRENGTHENING TRADES WILL CARRY A MOIST AIR MASS
OVER THE ISLANDS...LEADING TO AN INCREASE IN SHOWERS.

&&

.DISCUSSION...
LOCALLY HEAVY RAINFALL IS POSSIBLE TONIGHT...ESPECIALLY OVER THE
EASTERN END OF THE STATE WHERE THUNDERSTORMS ARE A THREAT. A
STRONGER THAN EXPECTED UPPER LEVEL SHORTWAVE TROUGH CURRENTLY 150
MILES NORTH OF MAUI IS DROPPING SOUTHWARD. THIS FEATURE IS
TRIGGERING HEAVY SHOWERS AND THUNDERSTORMS IN A BROAD BAND OF DEEP
MOISTURE 100 MILES NORTH OF THE ISLANDS...AND ALTHOUGH THIS DEEP
MOISTURE IS NOT EXPECTED TO REACH THE ISLANDS TONIGHT...HEAVY
SHOWERS ARE POSSIBLE OVER THE ISLANDS AS THE SHORTWAVE PASSES
OVERHEAD. ISOLATED CONVECTION LEFTOVER FROM THIS AFTERNOON OVER MAUI
AND THE BIG ISLAND IS LINGERING THIS EVENING...AND WITH THE
ATMOSPHERE BECOMING INCREASINGLY UNSTABLE...AN UPDATE WAS SENT TO
INCREASE SHOWER COVERAGE AND INCLUDE A SLIGHT CHANCE OF
THUNDERSTORMS OVER THESE ISLANDS.

A CHANCE FOR ISOLATED HEAVY SHOWERS WILL PERSIST THROUGH
TUESDAY...ESPECIALLY OVER THE BIG ISLAND AND MAUI. THE UPPER LEVEL
SHORTWAVE TROUGH WILL MOVE SLOWLY OVER THE EASTERN END OF THE ISLAND
CHAIN TUESDAY...MAINTAINING UNSTABLE CONDITIONS. THE DEEP MOISTURE
CURRENTLY TO THE NORTHEAST IS CURRENTLY FORECAST TO REMAIN OFFSHORE
THROUGH THE DAY...BUT WE WILL TAKE A CLOSER LOOK AT THAT AS WELL AS
THE THUNDERSTORM THREAT.

TRADE WINDS WILL STRENGTHEN TUESDAY NIGHT AND WEDNESDAY AS HIGH
PRESSURE STRENGTHENS FAR NORTH OF THE STATE. ONCE ESTABLISHED...
LOCALLY BREEZY TRADE WINDS WILL HOD INTO THE WEEKEND.

THE STRENGTHENING TRADE WIND FLOW WILL CARRY DEEP MOISTURE OVER THE
ISLANDS TUESDAY EVENING THROUGH WEDNESDAY. UPPER LEVEL TROUGHING
WILL LINGER OVER THE STATE...AND ALTHOUGH THE ATMOSPHERE WILL NOT BE
AS UNSTABLE AS IT WILL BE TONIGHT AND TUESDAY...HEAVY SHOWERS REMAIN
A POSSIBILITY.

UNCERTAINTY IN THE RAINFALL FORECAST INCREASES TOWARD THE END OF THE
WORK WEEK AND HEADING INTO NEXT WEEKEND. THE GFS AND ECMWF MODELS
SHOW THE ABOVE-MENTIONED UPPER LOW ELONGATING AND STALLING IN THE
VICINITY OF THE STATE...BUT DETAILS REMAIN UNCLEAR. THE CURRENT
FORECAST CALLS FOR A SOMEWHAT WET TRADE WIND PATTERN...WITH
CONFIDENCE TOO LOW FOR ANY MENTION OF THUNDERSTORMS.

&&

.AVIATION...
ISOLATED THUNDERSTORMS MAY CONTINUE TO DEVELOP ALONG WINDWARD BIG
ISLAND OVERNIGHT AS AIR MASS REMAINS UNSTABLE OVER THE EASTERN
ISLANDS. IN FACT...LOCALLY HEAVY SHOWERS AFFECTING WINDWARD MAUI AS
WELL AS WEST MAUI THIS EVENING MAY CONTINUE OVERNIGHT. LOOK FOR
ISOLATED IFR CONDITIONS TO PREVAIL OVER WINDWARD BIG ISLAND AND
MAUI REST OF TONIGHT THROUGH EARLY TUESDAY MORNING...WITH MAINLY
VFR CONDITIONS FOR THE REST OF THOSE ISLANDS.

MOSTLY VFR CONDITIONS WILL PREVAIL OVER THE REST OF THE STATE...
THOUGH WITH THE LIGHT TRADE WINDS...EXPECT A FEW WINDWARD SITES MAY
EXPERIENCE MVFR CONDITIONS AT TIMES...DUE TO PASSING CLOUDS AND
SHOWERS. TRADES ARE EXPECTED TO INCREASE A BIT BY TUESDAY AFTERNOON
AS THE SURFACE PRESSURE GRADIENT IS EXPECTED TO TIGHTEN ACROSS THE
STATE.

&&

.MARINE...
THE CURRENT MODERATE NORTHWEST SWELL WILL PEAK OVERNIGHT. THIS SWELL
WILL DIMINISH TUESDAY AND WEDNESDAY. FORERUNNERS FROM ANOTHER
MODERATE NORTHWEST SWELL WILL ARRIVE LATE FRIDAY...AND FILL IN
THROUGH THE DAY ON SATURDAY. A ROUGH...SHORT PERIOD EASTERLY TRADE
SWELL WILL BUILD BY MID WEEK AS THE TRADE WINDS INCREASE.

WINDS SHOULD REMAIN BELOW THE 25 KT SMALL CRAFT ADVISORY THRESHOLD
THROUGH TUESDAY. AS TRADES INCREASE TUESDAY NIGHT/WEDNESDAY...SMALL
CRAFT WINDS ARE EXPECTED FOR THE TYPICALLY WINDY WATERS AROUND THE
BIG ISLAND AND MAUI. ALSO...AS THE TRADE SWELL BUILD BY MID-WEEK...
SEAS MAY ALSO APPROACH THE 10 FT THRESHOLD FOR SMALL CRAFT ADVISORY.

&&

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

&&

UPDATE...WROE
AVIATION...HUI