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Flash flood watch and high surf advisory for Big Island

FLOOD ADVISORY
NATIONAL WEATHER SERVICE HONOLULU HI
756 AM HST SAT NOV 14 2009

HAWAII IN HAWAII COUNTY-
756 AM HST SAT NOV 14 2009

THE NATIONAL WEATHER SERVICE IN HONOLULU HAS ISSUED A

* FLOOD ADVISORY FOR THE ISLAND OF HAWAII IN HAWAII COUNTY

* UNTIL 1045 AM HST

* AT 749 AM HST…RADAR SHOWED HEAVY RAIN MOVING ASHORE FROM HAMAKUA TO PUNA AND SOUTH TO WINDWARD PORTIONS OF KAU.

* OTHER LOCATIONS IN THE ADVISORY INCLUDE BUT ARE NOT LIMITED TO PEPEEKEO…PAHOA…OOKALA…MOUNTAIN VIEW… LAUPAHOEHOE… KEAAU…KAPOHO…HONOMU…HONOKAA…HAWAIIAN PARADISE PARK…HAWAIIAN BEACHES AND HAKALAU.

PRECAUTIONARY/PREPAREDNESS ACTIONS…

STAY AWAY FROM STREAMS…DRAINAGE DITCHES AND LOW LYING AREAS PRONE TO FLOODING.

RAINFALL AND RUNOFF WILL ALSO CAUSE HAZARDOUS DRIVING CONDITIONS DUE TO PONDING…REDUCED VISIBILITY AND POOR BRAKING ACTION.

DO NOT CROSS FAST FLOWING OR RISING WATER IN YOUR VEHICLE OR ON FOOT. TURN AROUND…DON/T DROWN.

A FLASH FLOOD WATCH REMAINS IN EFFECT.

THIS ADVISORY MAY NEED TO BE EXTENDED BEYOND 1045 AM HST IF HEAVY RAIN PERSISTS.

BIG ISLAND NORTH AND EAST-
INCLUDING…HILO…VOLCANO…HONOKAA…KAMUELA
322 AM HST SAT NOV 14 2009

HIGH SURF ADVISORY IN EFFECT UNTIL 6 PM HST THIS EVENING.

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST SAT NOV 14 2009

Synopsis
Unsettled weather continues with locally heavy rains and thunderstorms possible through today. Strong trade winds will last through the weekend…along with above average rainfall. Rainfall will taper off a bit early next week…but will still likely remain higher than normal…especially for windward areas.

Discussion
Heavy showers and thunderstorms continue to pinwheel around the main Hawaiian Islands…affecting local waters for the most part but also moving across the islands from time to time. A weakening upper low about 300 miles west of Kauai has kept our airmass unstable…while east southeasterly winds continue to bring abundant moisture across the state. The focus of heavy showers and thunderstorms is near Kauai and Oahu this morning…with the heaviest activity across the Koolau Range of Oahu. Moderate to occasionally heavy showers also form across the mauka sections of Kauai from time to time. Lighter showers persist across windward and southeast sections of the Big Island. Satellite loop shows the surface low…now near 20n170w or about 700 miles west southwest of Kauai…continues moving west. The surface low has long since decoupled from the upper low…which has not moved much over the past 24 hours. This movement of the surface low away from the islands has allowed low level winds across local waters to back to almost a trade wind direction. The pressure gradient between the surface low and surface high pressure far north of the islands remains steep enough to support strong and gusty winds this morning…at or above small craft advisory criteria for the traditionally windy waters and channels.

Since heavy showers and thunderstorms remain close by…we assess the flood threat to be high enough to continue the flash flood watch through this afternoon. However…satellite loop shows that layered clouds have moved northeast of the big island…likely removing the moisture needed for snow on the big island summits. The winter weather advisory for the big island summits is therefore cancelled.

The upper low will drift slowly west over the weekend as it fills. Boundary layer moisture should remain abundant through today as well. As trades gradually swing to a more typical northeasterly direction…showers will become more terrain focused as topography takes over the main forcing mechanism. Trades will stay breezy and increase into next week with pops remaining higher than normal through the forecast period along windward zones.

For up to date weather information see the Hawaii 24/7 Weather Page

NWS Infrared Satellite Image Loop

NWS Infrared Satellite Image Loop

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