Flash Flood Warning 24, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST FRI DEC 7 2007

.SYNOPSIS...
WIDESPREAD RAIN WITH LOCALLY HEAVY SHOWERS...AND STRONG SOUTHERLY
WIND OVER ISLAND SUMMITS AND COASTAL WATERS...WILL CONTINUE AT
LEAST THROUGH SATURDAY MORNING. AFTER ANOTHER ROUND OF HEAVIER
SHOWERS ON SATURDAY AFTERNOON...MOST RAINFALL WILL SHIFT TO
NORTHEAST SLOPES AS TRADE WINDS RETURN BY THE MIDDLE OF THE COMING
WEEK.

&&

.DISCUSSION...
A DEEPLY STACKED LOW JUST NORTH OF THE MAIN HAWAIIAN ISLANDS FINALLY
SHOWED SIGNS OF MOVING NORTH AND REJOINING THE GENERAL CIRCULATION.
THOUGH IT DID NOT APPEAR TO FILL SIGNIFICANTLY YET...THE NEXT SIX TO
EIGHT HOURS LIKELY WILL REVEAL WHETHER THIS TREND MATERIALIZES. A
SHORT WAVE ROTATING AROUND THE BASE OF THE LOW INTENSIFIED SHOWER
DEVELOPMENT...MAINLY FROM MAUI COUNTY SOUTHEAST. THE ALENUIHAHA
CHANNEL AND WATERS SOUTHEAST OF THE BIG ISLAND IN PARTICULAR
EXPERIENCED THE EFFECTS OF THIS UPPER FEATURE COMBINING WITH SPEED
CONVERGENCE IN THE PREDOMINANTLY SOUTHERLY LOW-LEVEL FLOW...THUS
PRODUCING LOCALLY EXPLOSIVE DEVELOPMENT.

ALTHOUGH THE HEAVIEST PRECIPITATION HAD SHIFTED AWAY FROM OAHU AND
KAUAI COUNTY...THE BOUNDARY BETWEEN PREVAILING SOUTHERLIES OVER MOST
OF THE STATE AND SOUTHWESTERLIES FURTHER TO THE WEST STILL SERVED AS
A FOCUS TO SQUEEZE CONTINUING RAINFALL FROM THE MOIST AIRMASS OVER
THESE ISLANDS. CONSIDERING THE SOGGY STATE OF THE SOIL AFTER THE
PAST FEW DAYS...THE FLASH FLOOD WATCH AND THE WIDESPREAD FLOOD
ADVISORIES CERTAINLY REMAINED RELEVANT FOR THE WHOLE STATE. THOUGH
MOST OF THE NON-ROUTINE PRODUCTS ARE SET TO EXPIRE BY SATURDAY
MORNING...THE ARRIVAL OF A LAST SHORT WAVE AROUND NOON ON SATURDAY
MAY REQUIRE SOME EXTENSIONS.

WIND SPEED WAS DOWN ACROSS THE BOARD...AND THE CURRENT FORECAST MAY
BE A LITTLE HIGH OVER THE COASTAL WATERS...THOUGH THE SPARSE IN SITU
OBSERVATIONS PROVIDED ONLY A LIMITED PICTURE. GIVEN THE STRONG
DYNAMICS VISIBLE FROM SATELLITE...IT WOULD BE HASTY TO DROP THE
SMALL CRAFT ADVISORY...THOUGH GUIDANCE PAINTS A VERY DIFFERENT
PICTURE IN 24 HOURS. WITH THE UPPER PORTION OF THE LOW DEPARTING...
WIND OVER THE SUMMITS MAY WELL DROP BELOW THE WIND ADVISORY
CRITERION BEFORE SATURDAY MORNING.

ON THE WHOLE...THE FORECAST APPEARS TO BE ON TRACK. THE MODELS AGREE
FAIRLY WELL WITH SATELLITE AND SURFACE DATA...AND WITH ONE ANOTHER.
THE RSM AND GFS IN PARTICULAR SHOW GOOD AGREEMENT WITH SMALLER-SCALE
FEATURES OF THE WIND FIELD...SUCH AS THE SMALL SIZE OF THE HIGH-
SPEED AREA AT UPPER ELEVATIONS...AND THE COMPLEXITIES OVER THE
COASTAL WATERS. THE PROBLEM OF THE NIGHT...ASIDE FROM THE SHORT-TERM
EMERGENCIES...MAY WELL CONSIST OF MANAGING THE TRANSITION TO TRADE
WINDS BY THE BEGINNING OF THE COMING WEEK. MODELS AS A RULE ARE TOO
EAGER IN LIFTING OUT CUTOFF LOWS...AND SINCE THE CURRENT GRIDS
FOLLOW THE MODELS FAIRLY CLOSELY...A LINGERING LOW COULD DERAIL MUCH
OF THE FORECAST FOR THE NEXT 72 HOURS. ON THE BRIGHT SIDE...
AVAILABLE DATA DOES INDEED SUPPORT GUIDANCE...SO FAR AT LEAST. THE
TRANSITION TO TRADES FROM SUNDAY TO TUESDAY...WHILE FOLLOWING THE
MODELS...SEEMS A BIT ABRUPT THOUGH... AND LOOKS LIKE THE PART OF THE
FORECAST MOST IN NEED OF A LITTLE HOUSECLEANING.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...

WIND ADVISORY FOR SUMMITS OF HALEAKALA AND BIG ISLAND THROUGH 6 AM
SATURDAY.

FLASH FLOOD WATCH FOR ALL ISLANDS THROUGH 6 AM HST SATURDAY.

SMALL CRAFT ADVISORY FOR ALL AREAS THROUGH 6 AM HST SATURDAY.

&&

RYSHKO