Drought in Hawaii, November 1 to 22, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST TUE NOV 1 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 TODAY...MAINLY FOR THE BIG ISLAND AND MAUI. WITH GENTLE TO
MODERATE TRADE WINDS BLOWING...SHOWERS WILL FAVOR WINDWARD AND MAUKA
AREAS...THOUGH LEEWARD AREAS MAY SEE A BRIEFLY HEAVY SHOWER.
STRENGTHENING TRADE WINDS TONIGHT AND WEDNESDAY WILL CARRY A MOIST
AIR MASS OVER THE ISLANDS...LEADING TO AN INCREASE IN SHOWERS.
MODERATE TRADE WINDS WILL FOCUS SHOWERS OVER WINDWARD AREAS THURSDAY
THROUGH THE WEEKEND...WHILE UNSTABLE CONDITIONS MAY LEAD TO PERIODS
OF LOCALLY HEAVY SHOWERS.

&&

.DISCUSSION...
LOCALLY HEAVY RAINFALL REMAINS A THREAT FOR MAINLY THE EASTERN END
OF THE STATE TODAY. A STRONGER THAN EXPECTED UPPER LEVEL SHORTWAVE
TROUGH CURRENTLY NEARING MAUI FROM THE NORTH IS TRIGGERING HEAVY
SHOWERS AND THUNDERSTORMS IN A BROAD BAND OF DEEP MOISTURE 50 MILES
NORTH OF THE ISLANDS AND OVER MAUI AND THE BIG ISLAND AND THEIR
ADJACENT WATERS. THE 12Z HILO SOUNDING SHOWS DEEP MOISTURE WITH
PRECIPITABLE WATER VALUES AT AN IMPRESSIVE 1.71 INCHES...AND WITH
INSTABILITY OVER THE EASTERN END OF THE STATE EXPECTED TO INCREASE
IN THE SHORT TERM AS THE SHORTWAVE MOVES OVERHEAD...THE BIG ISLAND
HAS THE GREATEST CHANCE FOR THUNDERSTORMS AND HEAVY RAIN TODAY. AS A
RESULT...WE HAVE ISSUED A FLASH FLOOD WATCH FOR THE BIG ISLAND. FROM
KAUAI TO MOLOKAI...BRIEFLY HEAVY SHOWERS CANNOT BE RULED OUT...
MAINLY THIS MORNING...BUT THERE IS LITTLE FLASH FLOOD RISK AS DEEP
MOISTURE SHOULD REMAIN OFF TO THE NORTHEAST TODAY.

WET CONDITIONS ARE EXPECTED TONIGHT AND WEDNESDAY AS THE DEEP
MOISTURE CURRENTLY NORTHEAST OF THE ISLANDS RIDES IN ON A
STRENGTHENING TRADE WIND FLOW. TRADES WILL GRADUALLY STRENGTHEN AS
STRONG SURFACE HIGH PRESSURE SETS UP FAR NORTH OF THE ISLANDS. THE
STRONGER TRADES WILL FOCUS CLOUDS AND SHOWERS OVER WINDWARD AND
MAUKA AREAS...WHILE SHOWERS WILL PERIODICALLY BE BLOWN OVER LEEWARD
SECTIONS OF THE SMALLER ISLANDS. THE ATMOSPHERE WILL BE SOMEWHAT
UNSTABLE...BUT HEAVY SHOWERS WILL LIKELY BE SPOTTY.

ADDITIONAL PERIODS OF HEAVY RAINFALL REMAIN A POSSIBILITY THROUGH AT
LEAST THE WEEKEND. A REX BLOCK WILL SET UP BY THE END OF THE WORK
WEEK AND WILL REMAIN IN PLACE INTO EARLY NEXT WEEK. UNDER THIS
PATTERN...HIGH PRESSURE ALOFT REMAINS NEARLY STATIONARY IN THE MID
LATITUDES WHILE AN UPPER LEVEL TROUGH OR LOW IS PARKED DIRECTLY TO
THE SOUTH. THERE IS HIGH CONFIDENCE THAT THE HIGH PRESSURE TO THE
NORTH WILL DRIVE MODERATE TRADE WINDS OVER THE ISLANDS. HOWEVER...
THERE IS CONSIDERABLE UNCERTAINTY REGARDING THE DEGREE OF
INSTABILITY THAT WILL EXIST UNDER THE UPPER LOW...WHICH WILL LIKELY
BE PARKED NEAR THE STATE. THE CURRENT...LOW CONFIDENCE FORECAST
PAINTS A WET...TRADE-WIND SHOWER PATTERN...WITH THE BEST CHANCE OF
HEAVY SHOWERS OCCURING ON THURSDAY. THE AMOUNT OF AVAILABLE MOISTURE
APPEARS LIMITED...AND WITH TRADE WINDS BLOWING...FLOODING RAINS
APPEAR TO BE UNLIKELY.

&&

.AVIATION...
ISOLATED THUNDERSTORMS CONTINUE TO DEVELOP ALONG WINDWARD BIG
ISLAND THIS MORNING AS AIR MASS REMAINS UNSTABLE OVER THE EASTERN
ISLANDS WITH THE LIGHT TRADE WINDS. ISOLATED THUNDERSTORMS ARE ALSO
POSSIBLE FOR NORTH AND EAST OF MAUI AND MOLOKAI THROUGH THIS
MORNING. LOOK FOR ISOLATED IFR CONDITIONS TO PREVAIL OVER WINDWARD
BIG ISLAND...MAUI AND MOLOKAI AT LEAST THROUGH THIS MORNING...WHILE
MAINLY VFR CONDITIONS CONTINUE FOR THE REST OF THOSE ISLANDS.

MOSTLY VFR CONDITIONS WILL PREVAIL OVER THE REST OF THE STATE...
THOUGH TRADE WINDS WILL CARRY PASSING CLOUDS AND SHOWERS ACROSS THE
ISLANDS AT TIMES...RESULTING IN BRIEF MVFR CONDITIONS...ESPECIALLY
FOR THE WINDWARD SITES. TRADES ARE EXPECTED TO INCREASE A BIT THIS
AFTERNOON AS THE SURFACE PRESSURE GRADIENT IS EXPECTED TO TIGHTEN
ACROSS THE STATE.

&&

.MARINE...
THE CURRENT MODERATE NORTHWEST SWELL IS PEAKING AND WILL DIMINISH
TODAY 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
TODAY. AS TRADES INCREASE LATER TONIGHT AND 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...
FLASH FLOOD WATCH FOR THE BIG ISLAND THROUGH 6 PM HST TODAY.

&&

PUBLIC AND MARINE...WROE
AVIATION...HUI