Flash Flood Warning 22, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST SAT MAY 7 2011

.SYNOPSIS...
UNSETTLED WEATHER WITH LOCALLY HEAVY SHOWERS AND A SLIGHT CHANCE OF
THUNDERSTORMS WILL PERSIST OVER THE ISLANDS THROUGH EARLY NEXT WEEK
AS AN UPPER LEVEL LOW PRESSURE SYSTEM LINGERS NEAR THE STATE.
THE WINDS WILL DECREASE AND TURN MORE SOUTHEASTERLY FROM SUNDAY
THROUGH MIDDLE OF NEXT WEEK AS A SURFACE TROUGH DEVELOPS JUST WEST
OF THE ISLANDS.

&&

.DISCUSSION...
NOT MUCH CHANGES IN TERM OF WEATHER THIS EVENING AS UNSETTLED
WEATHER CONTINUES OVER THE STATE. EXTENSIVE CLOUDS AND PASSING
SHOWERS ARE AFFECTING THE AREA THIS EVENING...ESPECIALLY OVER THE
WESTERN ISLANDS. NOT SURPRISING...KAUAI AND OAHU GOT THE MOST
RAINFALL IN THE PAST 12 HOURS...THOUGH MOST NUMBERS STAYED BELOW AN
INCH. THERE ARE FEW THUNDERSTORMS FIRING UP AT TIMES SOUTH OF THE
ISLANDS...AND SO FAR THESE STAYED FAR OFFSHORE. LOOKS LIKE THAT
WILL NOT BE CHANGING MUCH TONIGHT AND SUNDAY...AS A PERSISTENT UPPER
LEVEL LOW LINGERS NEAR THE WESTERN ISLANDS. BREEZY TRADES CONTINUE
OVER THE ISLANDS ALSO...AS A STRONG HIGH PRESSURE REMAINS NORTH OF
THE ISLAND TONIGHT. HENCE WET AND BREEZY WEATHER WILL PREVAIL OVER
THE ISLANDS THROUGH REST OF THE NIGHT INTO EARLY SUNDAY
MORNING...WITH THE WESTERN ISLANDS...AS WELL AS THE WINDWARD AND
MOUNTAIN SECTIONS OF THE REST OF THE ISLANDS PROBABLY SEEING THE
MOST PRECIPITATION. A SLIGHT CHANCE OF THUNDERSTORMS OVER THE
ISLANDS CONTINUES AS WELL...AS AIR MASS REMAINS QUITE UNSTABLE.

A SURFACE TROUGH IS STILL EXPECTED TO DEVELOP JUST WEST OF THE
ISLANDS FROM SUNDAY...AND IN RESPONSE TRADE WINDS WILL SLOWLY
DECREASE AND TURNING SOUTHEAST. THIS SURFACE TROUGH DEVELOPS IN
RESPONSE TO A DEEPENING UPPER LEVEL TROUGH JUST NORTHWEST OF THE
ISLANDS. THE SOUTHEAST WINDS WILL DRAW ADDITIONAL TROPICAL MOISTURE
UP TO THE ISLANDS THROUGH THE MIDDLE OF NEXT WEEK. GIVEN THE GROUND
IS ALMOST SATURATED FROM THE ONGOING SHOWERS...THE THREAT OF FLASH
FLOOD INCREASES. A FLASH FLOOD WATCH HAS BEEN ISSUED FOR SUNDAY AND
MONDAY FOR THE SMALLER ISLANDS. REGARDLESS...UNSETTLED WEATHER IS
STILL EXPECTED TO PREVAIL THROUGH THE MIDDLE OF NEXT WEEK...WITH
LOCALLY HEAVY SHOWERS AND A SLIGHT CHANCE OF THUNDERSTORMS AFFECTING
ALL ISLANDS.

LATEST FORECAST CHARTS STILL POINT TO A RETURN OF TRADE WINDS AND
IMPROVING WEATHER TOWARDS THE NEXT WEEKEND AS THE SURFACE TROUGH IS
FORECAST TO MOVE WEST AWAY FROM THE ISLANDS...WITH A WEAK UPPER
LEVEL RIDGE BUILDS OVERHEAD.

&&

.AVIATION...
WIDESPREAD CLOUDS AND RA WILL CONTINUE TO BRING MVFR CONDITIONS AS
WELL AS MTN OBSCURATION AT TIMES TO KAUAI AND OAHU...AS WELL AS
WINDWARD SITES OF THE OTHER ISLANDS. AIR MASS REMAINS UNSTABLE
ENOUGH FOR ISOL TSRA TO DEVELOP...WITH CB TOPS TO 35 THOUSAND FEET.
AIRMET REMAIN POSTED FOR ICING WITH PERSISTENT DEEP LAYER MOISTURE
WHILE WINDS REMAIN STRONG ENOUGH TO WARRANT THE AIRMET TURBULENCE
OVER THE ISLANDS TONIGHT...THOUGH DECREASING WINDS IN THE COMING
DAYS MAY EASE THE WIND CONDITIONS.

&&

.MARINE...
ELEVATED SEAS UNDER THE BREEZY WINDS CONTINUE TO BRING SMALL CRAFT
CONDITIONS TO THE WINDY ALENUIHAHA CHANNEL AND WATERS SOUTH OF THE
BIG ISLAND. THE SMALL CRAFT ADVISORY MAY BE NEEDED TO EXTEND IF THE
CONDITIONS CONTINUE TO HOLD EARLY SUNDAY...THOUGH WINDS SHOULD BE
WEAKENED ENOUGH BY LATE SUNDAY FOR THE CONDITIONS TO DIMINISH.

THE PRESENT SMALL SOUTH SWELL WILL BE FOLLOWED BY A SLIGHTLY LARGER
SOUTH SWELL SUNDAY THROUGH TUESDAY. A SMALL NORTHWEST SWELL MAY
BOOST SURF INTO THE HEAD HIGH RANGE SUNDAY...THEN DECLINE MONDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM 6 AM HST SUNDAY TO 6 PM HST MONDAY FOR NIIHAU
KAUAI OAHU MOLOKAI LANAI AND MAUI.

WINTER WEATHER ADVISORY UNTIL 8 AM HST SUNDAY FOR THE BIG ISLAND
SUMMITS.

SMALL CRAFT ADVISORY FOR THE ALENUIHAHA CHANNEL AND WATERS SOUTH OF
THE BIG ISLAND UNTIL 6 AM HST SUNDAY.

&&

HUI