Flash Flood Warning 25, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
335 AM HST THU NOV 26 2009

.SYNOPSIS...
TRADE WINDS WILL DOMINATE THE WEATHER SCENE THROUGH THE WEEKEND AND
INTO THE FIRST COUPLE OF DAYS OF THE NEW WEEK. ALONG WITH THE TRADE
WINDS ARE THE SHOWERS THAT USUALLY FAVORS THE WINDWARD AND MOUNTAIN
AREAS. WITH THE STIFFER TRADES...DO EXPECT THE SHOWERS TO VENTURE
DOWNWIND INTO THE LEEWARD AREAS FROM TIME TO TIME.

&&

.DISCUSSION...
A SURPRISE DRENCHING HAS COME AND GONE FOR OAHU WHO WAS THE MAIN
RECIPIENT OF SOME BENEFICIAL RAINS WEDNESDAY AFTERNOON AND EVENING.
THESE SHOWERS STEMMED FROM AN AREA OF ORGANIZED SHOWERS CAUGHT IN
THE TRADE WIND FLOW THAT WAS BEING ENHANCED BY AN UPPER LEVEL
SHORTWAVE TROUGH OR DISTURBANCE. JUST ABOUT EVERY PART OF OAHU GOT
SOME RAIN. THERE WILL STILL BE SOME LINGERING SHOWERS OVER ON THE
LEEWARD SIDE EARLY THIS MORNING...BUT THESE SHOWERS SHOULD BE
RETREATING BACK TO THE WINDWARD AND MOUNTAIN AREAS BY MID MORNING
WITH AMPLE SUNSHINE ON TAP ON THIS THANKSGIVING DAY 2009.

HERE ARE SOME OUTSTANDING RAINFALL FIGURES DURING A 12 HOUR PERIOD
ENDING AT 2 AM HST. AMOUNTS ARE IN INCHES
MANOA - 6.63. NUUANU UPPER - 6.32. OAHU FORREST RESERVE 4.78.
MOANALUA - 2.91. MAKAHA STREAM - 1.11. HONOLULU AIRPORT - 1.02.

THE TRICKY ASPECT IS THE AMOUNT OF LOW LEVEL MOISTURE. THERE IS
CURRENTLY A LACK AS NOTED BY THE LACK OF TRADE SHOWERS AFFECTING
MAUI COUNTY AND WINDWARD BIG ISLAND THE PAST COUPLE OF HOURS. THE
HILO SOUNDING IS DRIER AS WELL AS COMPARED TO YESTERDAY AFTERNOON.
THE NEXT SOURCE OF TRADE WIND SHOWERS IS ABOUT 500 MILES EAST OF
THE BIG ISLAND WHERE SATELLITE IMAGERY SHOWS THE LEADING EDGE OF A
FIELD OF STRATOCUMULUS CLOUDS. THESE CLOUDS IS EXPECTED TO REACH THE
ISLANDS TONIGHT.

WITH THIS IN MIND...THE GENERAL CONSENSUS OF THE FORECAST MODELS
POINTS TO THE SHORTWAVE TROUGH TO MOVE THROUGH THE CENTRAL ISLANDS
THIS AFTERNOON AND EVENING AND CLEARING THE BIG ISLAND BY FRIDAY
EVENING. THE INTERACTION OF THIS TROUGH ON THE LOW LEVEL MOISTURE
COMING IN...IS WE ANTICIPATE AT LEAST SCATTERED TRADE SHOWERS
STARTING TONIGHT WITH A FEW OF THEM BLOWN DOWNWIND INTO THE LEEWARD
ZONE. WE DO NOT EXPECT THEM TO BE HEAVY NOR DO WE EXPECT A REPEAT OF
WEDNESDAY EVENING ON OAHU. ONCE THE TROUGH IS EAST OF THE BIG
ISLAND...WE EXPECT MORE OF THE SCATTERED VARIETY ACROSS THE WINDWARD
AND MOUNTAIN AREAS. ADDITIONALLY THE INVERSION GETS LOWERED FROM
12000 TO 9000 FEET. THIS DRIER TREND IS ONLY TEMPORARILY AS ANOTHER
SHORTWAVE TROUGH DESCEND ON THE ISLANDS SUNDAY.

&&

.MARINE...
THE CURRENT LARGE NORTHWEST SWELL CONTINUES TO SUBSIDE BUT NOT
ENOUGH TO LIFT THE HIGH SURF WARNING. THE WAIMEA BUOY SUGGEST THE
SURF STILL TOPPING 25 FEET FROM TIME TO TIME. WILL THEREFORE EXTEND
TO HIGH SURF WARNING TO NOON TODAY. THIS SHOULD BE MORE THAN ENOUGH
TIME TO ALLOW THE SURF TO DROP AND STAY BELOW 25 FEET...THE
THRESHOLD FOR WARNING. ONCE THIS HAPPENS...THE WARNING WILL BE
REPLACED WITH AN ADVISORY.

A SMALL CRAFT ADVISORY IS IN EFFECT FOR BOTH THE LARGE NORTHWEST
SWELL AND FOR INCREASING TRADE WINDS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF WARNING UNTIL 12 PM HST TODAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-WAIANAE COAST-OAHU NORTH SHORE-OAHU
KOOLAU-MOLOKAI-MAUI WINDWARD WEST-MAUI CENTRAL VALLEY-WINDWARD
HALEAKALA.

SMALL CRAFT ADVISORY IN EFFECT UNTIL 6 PM HST FRIDAY FOR ALL
HAWAIIAN WATERS.

&&

H LAU