High Surf in Hawaii, April 17 to 19, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST THU APR 17 2008

.SYNOPSIS...
A SURFACE LOW NORTHWEST OF KAUAI WILL SLOWLY MOVE NORTHEAST
TODAY...BRINGING A FRONT JUST WEST OF THE STATE. THE FRONT WILL
REMAIN WEST OF KAUAI...BUT IT WILL BRING LIGHT SOUTHEASTERLY WINDS
AND UNSETTLED WEATHER TO THE WESTERN END OF THE STATE. TRADE WINDS
ARE EXPECTED TO RETURN THIS WEEKEND.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS A TROUGH SLOWLY MOVING NORTHEAST ABOUT 400
MILES NORTHWEST OF KAUAI AND A STRONG UPPER LOW FURTHER NORTH NEAR
40N 165W MOVING SOUTH. THE TROUGH NORTHWEST OF KAUAI IS EXPECTED TO
SWING JUST NORTH OF THE STATE TODAY BEFORE BEING ABSORBED BY THE
LOW TO THE NORTH LATE TONIGHT.

WHILE THE THE FRONT ASSOCIATED WITH THE LOW EDGES CLOSER TO THE
ISLANDS OF OF NIIHAU AND KAUAI EARLY THIS MORNING. SHOWERS AND
THUNDERSTORMS ALONG THE LEADING EDGE OF THE FRONT WERE AFFECTING
KAUAI AND NIIHAU EARLY THIS MORNING. FORECAST MODELS KEEP THIS
FRONTAL BOUNDARY WEST OF THE STATE AND DRAG IT NORTH NORTHEAST
FOLLOWING THE TRACK OF THE PARENT SURFACE LOW. INGREDIENTS REMAIN IN
PLACE FOR UNSETTLED WEATHER ACROSS THE WESTERN END OF THE STATE
TODAY. SATELLITE DERIVED TOTAL PRECIPITABLE WATER SHOWS HIGHER THAN
NORMAL MOISTURE WEST OF THE STATE WITH 1.7 INCHES ALONG THE FRONT
AND TAPERING OFF TO ABOUT 1 INCH NEAR THE BIG ISLAND. THIS IS IN
GOOD CORRELATION TO THE MOISTURE MEASURED FROM THE SOUNDINGS AT
LIHUE /1.6 INCHES/ AND HILO /1.2 INCHES/. MODELS DO SHOW AN INCREASE
IN MOISTURE OVER KAUAI AND OAHU AS THE FRONT EDGES SLIGHTLY EAST
TODAY. INSTABILITY EXISTS AS TEMPERATURES AT 500MB HOVER AROUND -12
CELSIUS. ALSO...AS THE NEARBY TROUGH SWINGS THROUGH TO OUR NORTH
TODAY...AND VERTICAL MOTION WILL BE ENHANCED DUE TO DIFFLUENT FLOW
ALOFT. WITH THE PROXIMITY OF THIS SYSTEM...KAUAI WILL HAVE THE
GREATEST CHANCE FOR HEAVIER SHOWERS AND SCATTERED THUNDERSTORMS. A
SLIGHT CHANCE OF THUNDER EXISTS FOR OAHU AS WELL. A FLASH FLOOD
WATCH HAS BEEN ISSUED FOR KAUAI AND NIIHAU.

THE LOW LIFTS TO THE NORTH ON FRIDAY AND WINDS STATEWIDE SHOULD
START SWINGING AROUND TO THE EAST AS HIGH PRESSURE REBUILDS
NORTHEAST OF THE STATE. LIGHT TRADES ARE EXPECTED TO RETURN THIS
WEEKEND.

WE REMAIN ON ALERT FOR WINDS ON THE BIG ISLAND THIS MORNING AND THE
POTENTIAL FOR ELEVATED SULFUR DIOXIDE CONCENTRATIONS REACHING THE
HILO AREA. THE LATEST SOUNDING TAKEN AT 2 AM THIS MORNING SHOW
MOSTLY SOUTH WINDS AT THE SURFACE THROUGH 8000 FEET RIGHT WHERE THE
INVERSION IS SITTING. WITH THE STABLE INVERSION AND THE BIG
ISLAND...BEING  A LARGE LAND MASS WITH PEAKS TO 13000 FEET...THE
SOUTHEAST WINDS CANNOT FLOW UP AND OVER THE MOUNTAINS AND ARE FORCED
TO GO AROUND...RESULTING IN SOUTHERLY WINDS. THESE WINDS ARE THE
PRIMARY TRANSPORT MECHANISM FOR VOLCANIC ASH AND GASEOUS EMISSIONS
FROM KILAUEA. THE OZONE MONITORING INSTRUMENT /OMI/ ABOARD THE
EOS-AURA SATELLITE SHOWED A BUILDUP OF SO2 FARTHER UPSLOPE AND
FARTHER NORTH YESTERDAY. THE SOUTHERLY FLOW BETWEEN 2000 AND 7000
FEET IN CONJUNCTION WITH NIGHT TIME LAND BREEZES DOWN THE MOUNTAIN
SLOPES COULD MEAN SHARP RISES IN SO2 NEAR HILO EARLY THIS MORNING.
HOWEVER...IT SHOULD QUICKLY MIX OUT BY MID MORNING.

&&

.MARINE...
A HIGH SURF ADVISORY WILL BEGINS AT 6AM TODAY FOR SOUTH FACING
SHORES. WAVE WATCH III CONTINUES TO SHOW SWELLS 2-3 FEET ROLLING IN
TODAY AND RISING TO 4 FEET ON FRIDAY. NATURALLY...THE LONGER PERIOD
ENERGY OF 17-20 SECONDS WILL ARRIVE FIRST ON TODAY AND PERIODS WILL
DECREASE TO AROUND 15-16 SECONDS ON FRIDAY. THE SOUTH SWELLS HAVE
REACHED BUOY 51028 YESTERDAY. A BIT OF 19 SECOND ENERGY WAS REPORTED
AT BUOY 51002. HOWEVER...THE SPECTRAL DENSITY PLOTS DO INDICATE
SMALL SPIKES OF ENERGY IN THE 15 AND 20 SECOND BINS. THE SWELL
SHOULD PEAK ON FRIDAY...THEN DROP TO MODERATE LEVELS OVER THE
WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH IN EFFECT THROUGH THURSDAY NIGHT FOR KAUAI AND
NIIHAU.

HIGH SURF ADVISORY FROM 6 AM TODAY TO 6 AM HST SATURDAY FOR SOUTH
FACING SHORES OF ALL ISLANDS.

&&

ELAU