Flash Flood Warning 5, NWS Honolulu, HI

HAWAIIAN ISLANDS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
335 PM HST MON JAN 31 2005

.SYNOPSIS...
A COLD FRONT APPROACHING THE STATE WILL INTERACT WITH THE MOIST AND
UNSTABLE AIR ALREADY OVER THE ISLANDS. SHOWERS AND THUNDERSTORMS ARE
EXPECTED TO FORM ALONG...AND AHEAD OF THIS FRONT. EXCESSIVE RAINFALL
AND FLASH FLOODING IS POSSIBLE THROUGH MIDWEEK. THE RISK FOR FLASH
FLOODING WILL INITIALLY BE OVER THE WESTERN MAIN ISLANDS...THEN
SPREAD TOWARD MAUI AND THE BIG ISLAND LATER ON TUESDAY. DRIER AIR
WILL SLOWLY OVERSPREAD THE ISLANDS BEHIND THE FRONT...BUT MAY NOT
REACH THE BIG ISLAND UNTIL LATE IN THE WORK WEEK.

&&

.DISCUSSION...
THE 00Z LIHUE SOUNDING IS QUITE UNSTABLE...WITH A MOIST LAYER UP TO
ABOUT 700 MB AND DRIER AIR ABOVE THAT. THIS YIELDS A CAPE OF ABOUT
2800 J/KG AND A LIFTED INDEX OF -7. THE SOUNDING ALSO SHOW DECENT
DEEP LAYER VEERING WITH HEIGHT. WE HAVE BEEN WATCHING A COUPLE OF
SEVERE THUNDERSTORMS NORTHWEST OF KAUAI THAT HAVE LIKELY HAD HAIL
AND WATERSPOUTS BASED ON ELEVATED CORES ABOVE THE FREEZING LEVEL AND
MODERATE ROTATION. FORECAST SOUNDINGS SUGGEST THE THREAT FOR SEVERE
THUNDERSTORMS SHOULD DIMINISH TONIGHT AS THE FLOW BECOMES
UNIDIRECTIONAL WITH HEIGHT AND THE DRY LAYER ALOFT ERODES AWAY.

STRONG DEEP LAYER MOISTURE ADVECTION...AN APPROACHING FRONTAL
BOUNDARY...AND A DIGGING UPPER TROUGH WILL MAKE FOR HIGH RAIN
CHANCES NEAR KAUAI...AND LATE TONIGHT FOR OAHU. ALTHOUGH THE AIRMASS
IS RELATIVELY UNSTABLE EVEN FOR THE SOUTHERN MAIN ISLANDS...THE LACK
OF A WELL-DEFINED FOCUSING MECHANISM AND LITTLE IF ANY LOW LEVEL
MOISTURE ADVECTION SHOULD KEEP THINGS QUIETER THERE. ALTHOUGH THE
RADAR IS PROBABLY OVERESTIMATING THE RAINFALL RATES DUE TO HAIL
CONTAMINATION...THE RELATIVELY SLOW MOVEMENT OF THE CELLS MAKES FOR
SIGNIFICANT FLOOD POTENTIAL WHERE STORMS OCCUR.

THE COLD FRONT IS EXPECTED TO BE NEAR KAUAI LATE TONIGHT AND OAHU
EARLY TUESDAY. THE FRONT IS THEN PROGGED TO SLOW AND MOVE OVER MAUI
COUNTY LATER TUESDAY...STALLING NEAR THE BIG ISLAND BY WEDNESDAY.
BEST RAIN CHANCES WILL BE ALONG AND AHEAD OF THE FRONT. THE AIRMASS
BEHIND THE FRONT WILL BE DRIER...BUT STILL QUITE UNSTABLE. HAVE LEFT
IN ISOLATED THUNDERSTORMS BEHIND THE FRONT AS LONG AS THE VERY COLD
MID-LEVEL AIR IS OVER THE ISLANDS.

OUR EXPECTATION CONTINUES TO BE THAT THE FRONT WILL LIKELY GET HUNG
UP NEAR THE BIG ISLAND AS A WAVE OF LOW PRESSURE DEVELOPS NORTH OF
THE ISLANDS ON WEDNESDAY. THUS...ONLY GRADUALLY DECREASING CHANCES
OF RAIN FOR THE SOUTHERN END OF THE CHAIN AS UPPER LEVEL HEIGHTS
BEGIN TO RISE.

FORECAST SOUNDINGS INDICATE THAT THE SNOW LEVEL SHOULD LOWER TO NEAR
10000 FEET AS THE DEEP LAYERED MOISTURE APPROACHES THE BIG ISLAND.
WINTER STORM WATCH WILL CONTINUE FOR THE POSSIBILITY OF HEAVY
SNOWFALL FOR THE BIG ISLAND SUMMITS TUESDAY INTO WEDNESDAY.

&&

.MARINE...
BUOY 51001 SHOWS THAT THE NORTHWEST SWELL IS SLOWLY TRENDING DOWN AS
EXPECTED. WILL LEAVE HIGH SURF ADVISORY UP FOR TONIGHT...AND HAVE
NOT EXTENDED IT INTO WEDNESDAY. WE EXPECT TO DROP THE SMALL CRAFT
ADVISORY AT 6 PM.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH...KAUAI OAHU AND MOLOKAI THROUGH WEDNESDAY.

FLASH FLOOD WATCH...LANAI MAUI AND BIG ISLAND TUESDAY AND WEDNESDAY.

WINTER STORM WATCH...BIG ISLAND SUMMITS TUESDAY AND WEDNESDAY.

HIGH SURF ADVISORY...N AND W FACING SHORES OF NIIHAU KAUAI OAHU
                             AND MOLOKAI.
                     N FACING SHORES OF MAUI.

&&

R BALLARD