Flash Flood Warning 9, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST WED NOV 28 2007

.SYNOPSIS...
HEAVY SHOWERS AND SCATTERED THUNDERSTORMS WILL AFFECT OAHU AND MAUI
COUNTY TODAY...WITH LOCALLY HEAVY SHOWERS POSSIBLE ELSEWHERE AS
WELL. LIGHT SOUTH TO SOUTHEAST WINDS WILL CONTINUE THROUGH THE NEXT
SEVERAL DAYS...ALONG WITH UNSETTLED WEATHER AND THE THREAT OF
LOCALLY HEAVY RAINFALL.

&&

.DISCUSSION...
REGIONAL RADARS SHOW WIDESPREAD SHOWERS WITH EMBEDDED THUNDERSTORMS
STRETCHING FROM OAHU TO WEST MAUI. CELL MOTIONS ACROSS THE CENTRAL
ISLANDS HAVE TRENDED TOWARD MORE OF AN EASTERLY DIRECTION OVER THE
PAST FEW HOURS...AND HAVE SPREAD FROM OAHU TO MAUI COUNTY.
ADDITIONAL CELLS HAVE DEVELOPED WESTWARD TOWARD KAUAI...AND THESE
ARE MOVING NORTHWARD OR NORTHEASTWARD SLOWLY. IR SATELLITE SHOWS
CONVECTION EXTENDING 100 MILES SOUTH SOUTHWEST OF HONOLULU...WITH
ADDITIONAL STORMS EXTENDING FROM A LINE FROM 400 MILES SOUTHWEST OF
HONOLULU TO 300 MILES SOUTH OF HONOLULU.

WATER VAPOR IMAGERY SHOWS AN UPPER TROUGH EXTENDING ALONG 160W...
WITH A SHARP SHORTWAVE EMBEDDED IN IT ABOUT 500 MILES NORTHWEST OF
HONOLULU. AT THE SURFACE...A TROUGH IS LOCATED 250 MILES NORTHWEST
OF KAUAI...WITH A HIGH FAR NORTHEAST OF THE STATE...LEADING TO BROAD
SOUTHEASTERLY LOW-LEVEL FLOW ACROSS THE ISLANDS. THIS FLOW
CONTINUES TO PULL TROPICAL MOISTURE TOWARDS US...WITH AMSU/SSMI
SENSORS INDICATING PRECIPITABLE WATERS AROUND TWO INCHES OVER AND
SOUTH OF THE STATE. THE POLAR SENSORS SHOW DO SHOW DRIER AIR TRYING
TO EDGE IN FROM THE EAST...WHICH CAN BE SEEN IN THE DRIER AND
SOMEWHAT MORE STABLE SOUNDING AT PHTO COMPARED TO PHLI. GIVEN THE
PERSISTENT COMBINATION OF TROPICAL MOISTURE AND UPPER-LEVEL
TROUGHING/INSTABILITY...HAVE UPDATED THE FORECAST TO CARRY
NUMEROUS/OCCASIONAL SHOWERS AND ISOLATED/SCATTERED THUNDERSTORMS
ACROSS THE SMALLER ISLANDS TODAY AND TONIGHT. GFS AND NAM HAVE
CONSISTENTLY SHOWN THAT THIS BAND OF ACTIVITY WILL SLOW ITS
EASTWARD MOVEMENT...IN PART DUE TO THE DRIER AND MORE STABLE AIR TO
THE EAST OF THE STATE. KEPT POPS SCATTERED ACROSS THE BIG ISLAND...
BUT MAINTAINED THE MENTION OF HEAVY RAINFALL.

CONDITIONS WILL BEGIN TO IMPROVE ON THURSDAY...BUT HEAVY RAINFALL
WILL STILL BE POSSIBLE DUE TO THE COMBINATION OF LINGERING MOISTURE
AND THE UPPER LEVEL TROUGH OVERHEAD. MID-LEVEL HEIGHTS START TO
REBUILD ON FRIDAY BEHIND THE TROUGH...WITH FORECAST SOUNDINGS
SHOWING MOISTURE DEPTH DIMINISHING AND A WEAK INVERSION DEVELOPING.
HOWEVER...THE AIRMASS WILL REMAIN UNSTABLE WITH WEAK LOW-LEVEL FLOW
UNDER THE SURFACE RIDGE AXIS. THE FIRST OF A PAIR OF COLD FRONTS
WILL APPROACH KAUAI AND WEAKEN ON SATURDAY...WITH A REINFORCING
FRONT REACHING THE STATE ON SUNDAY.

&&

.MARINE...
THE LATEST NORTHWEST SWELL HAS REACHED BUOY 51001...BUT ARRIVED A
FEW HOURS LATER THAN EXPECTED. SURF SHOULD REACH ADVISORY LEVELS
THIS AFTERNOON AND PEAK TONIGHT...BEFORE SLOWLY SUBSIDING. A HIGH
SURF ADVISORY CONTINUES FOR NORTH AND WEST FACING SHORES OF
NIIHAU...KAUAI...OAHU...AND MOLOKAI...AND NORTH FACING SHORES OF
MAUI. WAVEWATCH III GUIDANCE DOES SHOW SOME SWELL WRAPPING AROUND
THE SMALLER ISLANDS TO REACH THE WEST COAST OF THE BIG ISLAND...BUT
THE BULK OF THE ENERGY WILL BE BLOCKED. SURF HEIGHTS ARE EXPECTED TO
STAY BELOW ADVISORY LEVELS FOR WEST FACING SHORES OF THE BIG ISLAND.

THUNDERSTORMS CONTINUE TO DEVELOP AND AFFECT LOCAL WATERS ADJACENT
TO OAHU AND THE ISLANDS OF MAUI COUNTY. PLEASE SEE THE LATEST MARINE
WEATHER STATEMENT...ISSUED UNDER AWIPS HEADER MWSHFO AND WMO HEADER
FZHW70 PHFO...FOR THE LATEST INFORMATION ON THUNDERSTORM COVERAGE
AND MOVEMENT.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH WEDNESDAY NIGHT FOR NIIHAU-KAUAI-
OAHU-MOLOKAI-LANAI-MAUI.

HIGH SURF ADVISORY UNTIL 4 PM HST THURSDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-WAIANAE COAST-OAHU NORTH SHORE-OAHU
KOOLAU-MOLOKAI-MAUI WINDWARD WEST-WINDWARD HALEAKALA.

&&

BRAVENDER