Heavy Rain in Hawaii, April 25, 2004

HAWAIIAN ISLANDS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1008 AM HST SUN APR 25 2004

.SYNOPSIS...A COLD FRONT WILL BEGIN MOVING SLOWLY DOWN THE ISLAND
CHAIN LATER TODAY. OUT AHEAD OF THE FRONT...GENERALLY FAIR WEATHER
IS EXPECTED...WITH ONLY ISOLATED SHOWERS MAINLY DURING THE
AFTERNOONS AND EVENINGS. THE FRONT WILL BE ACCOMPANIED BY A BAND OF
SHOWERS AND GUSTY WINDS THAT WILL REACH KAUAI BY TONIGHT. THE FRONT
AND ITS SHOWERS ARE STILL ON SCHEDULE TO REACH THE CENTRAL ISLANDS
ON MONDAY...AND THE BIG ISLAND MONDAY NIGHT.

&&

.DISCUSSION...SATELLITE IMAGERY SHOWS THE LEADING EDGE OF A BAND OF
SHOWERS ASSOCIATED WITH A WEAK COLD FRONT ABOUT 35 MILES NORTHWEST
OF KAUAI. AS WAS EXPECTED...THIS FEATURE HAS BEEN REINVIGORATED BY
AN UPPER LEVEL TROUGH DIGGING SOUTH ALONG 150W. INFRARED IMAGERY
SHOWED COOLING CLOUD TOPS EARLY THIS MORNING WITH SOME TOWERING
CUMULUS TOPS TO 19 THOUSAND FEET. THE 12Z SOUNDINGS AND WSR-88D WIND
PROFILES INDICATE THAT THE BOUNDARY LAYER WINDS ARE STARTING TO
RESPOND WITH TRADES A LITTLE STRONGER THAN YESTERDAY...BLOWING
AROUND 15 KT. THE STRONGER TRADES AND RELATIVELY DRY AIRMASS WILL
KEEP FINE WEATHER AHEAD OF THE FRONT...THOUGH THE BIG ISLAND WILL
SEE ANOTHER DAY WITH CUMULUS CLOUDS BILLOWING OVER THE SLOPES AND A
COUPLE OF ISOLATED HEAVY SHOWERS OVER THE INTERIOR THIS AFTERNOON.

NO CHANGES WITH THE LONGER RANGE FORECAST PLAN AT THIS TIME.
ALTHOUGH CONVECTIVE PARAMETERS APPEAR TO BE PRETTY MARGINAL...THE
DIGGING UPPER LEVEL TROUGH AND MID LEVEL COOLING MAY BE ENOUGH TO
SPARK A CB OR TWO ALONG THE FRONT. HAVE ADDED A SLIGHT CHANCE OF A
THUNDERSTORM TO THE FORECAST GRIDS FOR NORTHWEST OF KAUAI FOR THE
AFTERNOON...AND WILL MONITOR CONVECTIVE TRENDS TO SEE WHETHER WE
NEED TO CONTINUE OR ENLARGE THIS AREA IN THE LATER PERIODS.

A LATE SEASON CUTOFF LOW IS EXPECTED TO TAKE SHAPE NORTHEAST OF THE
ISLANDS OVER THE NEXT FEW DAYS...NEAR 35N 147W. THIS FEATURE WILL
MEANDER AROUND FOR A FEW DAYS...KEEPING NORTHWESTERLY FLOW ALOFT
OVER THE STATE. THIS WILL TEND TO LINGER THE FRONTAL REMNANTS OVER
THE SOUTHERN MAIN ISLANDS FOR QUITE SOME TIME...AT LEAST THROUGH
MID-WEEK. ALTHOUGH THE MID LEVELS MAY START TO WARM BY TUESDAY...
BOTH GFS AND ETA SHOW THAT THE AXIS OF THE SUBTROPICAL JET WILL
SHIFT NORTH TOWARD THE ISLANDS. THUS INCREASED UPPER LEVEL
DIVERGENCE MAY COMPENSATE FOR WEAK MID LEVEL WARMING...WITH REMNANT
SHOWER AREAS CONTINUING TO GET A BIT OF A ENERGY BOOST ON TUESDAY.

&&

.MARINE...MEASUREMENTS AT THE BUOYS SOUTH OF THE ISLANDS INDICATE
THAT THE SOUTH SWELL IS CURRENTLY PEAKING. SWELLS ARE HIGHEST AT
BUOY 51004...THE EASTERN MOST BUOY IN THE ARRAY. THIS SUGGESTS THAT
THE BULK OF THE SWELL ENGERY IS PASSING JUST EAST OF THE ISLANDS.
THE HAWAIIAN ISLANDS WILL CONTINUE TO EXPERIENCE A SIGNIFICANT SOUTH
SWELL WITH SURF HEIGHTS ABOVE THE 8 FOOT ADVISORY CRITERIA.

&&

.WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY FOR ALL S FACING SHORES...AND W SHORES OF THE
BIG ISLAND.
SMALL CRAFT ADVISORY FOR HAWAIIAN COASTAL WATERS AND THE CHANNELS
BETWEEN THE ISLANDS.

R BALLARD/WROE