Flash Flood Warning 89, NWS Honolulu, HI

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HONOLULU HI
1150 AM HST TUE MAR 21 2006

.SYNOPSIS...
A PERSISTENT TROUGH ALOFT WILL REMAIN NORTHWEST OF KAUAI THROUGH
EARLY NEXT WEEK. THE TROUGH WILL KEEP THE ATMOSPHERE UNSTABLE AND
DRAW TROPICAL MOISTURE UP FROM THE SOUTH. AS A RESULT...HEAVY
SHOWERS WILL CONTINUE.

&&

.UPDATE...
WE HAVE UPDATED THE GRIDS AND TEXT FORECASTS FOR FEWERS SHOWERS THIS
AFTEROON.

.DISCUSSION...
SURFACE ANALYSES SHOW A COMPLEX LOW NORTHWEST OF THE ISLANDS WITH
LOW LEVEL FLOW VEERING FROM SOUTH SOUTHEAST NEAR THE BIG ISLAND TO
SOUTH SOUTHWEST NEAR KAUAI. RADARS SHOW SOUTHWEST TO NORTHEAST LINES
OF HEAVY SHOWERS OVER EAST KAUAI AND IN THE KAIWI CHANNEL. SATELLITE
IMAGERY SHOWS BROKEN TO OVERCAST HIGH CLOUDS OVER THE ISLANDS WITH
THICKER LAYERED CLOUDS SPREADING OVER THE ISLANDS FROM THE SOUTHWEST.

UPPER AIR ANALYSES AND WATER VAPOR IMAGERY SHOW A DEEP TROUGH ALOFT
NORTHWEST OF KAUAI WITH A COMPLEX LOW CENTERED 735 MILES NORTHWEST
OF KAUAI NEAR 29N 169W. AS LONG AS THE TROUGH REMAINS NORTHWEST OF
THE ISLANDS THERE WILL BE SOME POTENTIAL FOR HEAVY PRECIPITATION
OVER THE ISLANDS. THE COMPUTER MODELS HAVE DONE PRETTY GOOD WITH THE
LARGE-SCALE PATTERN BUT THE DIFFERENT MODELS...AND DIFFERENT RUNS OF
THE SAME MODELS HAVE BEEN INCONSISTENT WITH THE DETAILS. MODEL TO
MODEL AGREEMENT IS ACTUALLY QUITE GOOD THROUGH THURSDAY NIGHT WITH
THE MODELS DRIFTING FARTHER APART AFTER THAT.

DESPITE LOCALLY HEAVY SHOWERS THIS MORNING WE ARE NOW IN A
LULL...RELATIVELY SPEAKING...WITH HEAVIER AND MORE WIDESPREAD
RAINFALL LIKELY TOMORROW. HEAVIER RAIN WILL SPREAD OVER THE ISLANDS
FROM THE SOUTHWEST LATE TONIGHT...PROBABLY AFFECTING KAUAI FIRST
THEN SPREADING EAST. PERIODS OF VERY HEAVY RAIN ARE LIKELY THROUGH
THURSDAY. THERE IS SOME POSSIBILITY THE ATMOSPHERE COULD BECOME
UNSTABLE ENOUGH FOR SEVERE THUNDERSTORMS. IT NOW LOOKS LIKE THE BEST
CHANCE MAY BE THIS EVENING. BY TOMORROW THE ATMOSPHERE MAY BECOME
TOO UNIFORMLY MOIST AND THE WINDS ALOFT TOO UNIDIRECTIONAL TO
SUPPORT SEVERE WEATHER.

THE MODELS SHOW THE TROUGH ALOFT FLATTENING OUT THURSDAY NIGHT SO
THE ATMOSPHERE WILL BECOME A BIT LESS UNSTABLE. BUT...IT LOOKS LIKE
THE TROUGH WILL REMAIN NORTHWEST OF KAUAI THROUGH EARLY NEXT WEEK SO
SOME POSSIBILITY OF HEAVY RAIN WILL CONTINUE A WHILE LONGER. THE
LONGER RANGE MODELS SUGGEST THAT TRADE WINDS MAY FINALLY RETURN NEXT
TUESDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...

FLASH FLOOD WATCH FOR ALL ISLANDS THROUGH THURSDAY AFTERNOON.

&&

DONALDSON