Drought in Hawaii, October 1 to 31, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST MON SEP 30 2013

.SYNOPSIS...
A COLD LOW IN THE MIDDLE ATMOSPHERE WILL DESTABILIZE THE ATMOSPHERE
OVER THE NORTHWEST END OF THE STATE TONIGHT AND TUESDAY. HEAVY RAIN
AND THUNDERSTORMS WILL BE POSSIBLE...BUT PROBABLY NOT WIDESPREAD...
MOSTLY FROM OAHU NORTH. LIGHT WINDS AND MUGGY CONDITIONS WILL
ENCOURAGE BUILDUPS EACH AFTERNOON AT LEAST THROUGH MID-WEEK...AND
TRUE TRADE WINDS ARE NOT EXPECTED TO RETURN UNTIL THE WEEKEND.

&&

.DISCUSSION...
A COMPACT BUT POWERFUL MID-LEVEL LOW SHOWED UP CLEARLY NORTH OF
KAUAI IN BOTH VISIBLE-LIGHT AND INFRARED IMAGES. VIGOROUS
THUNDERSTORMS PERSISTED ALONG THE SOUTH EDGE OF THE SEMICIRCULAR
CLOUD FEATURE SURROUNDING THE LOW CENTER. HOWEVER...THE COLD POOL
ASSOCIATED WITH THE LOW WAS BROAD ENOUGH TO DESTABILIZE THE AIR MASS
FURTHER AFIELD...PRODUCING THUNDERSTORMS OVER OAHU EARLIER TODAY.
WITH SOLAR HEATING ABSENT...LAPSE RATES OVER LAND SHOULD RELAX
ENOUGH TO LIMIT DEEP CONVECTION SOUTH OF THE KAUAI CHANNEL
OVERNIGHT...BUT THE RISK WILL NOT GO AWAY COMPLETELY UNTIL THE LOW
ITSELF DOES BY AROUND WEDNESDAY. SATELLITE IMAGES SHOWED LOW- TO
MID-LEVEL CLOUD COVER...AND CORRESPONDING PRECIPITABLE WATER...
MOVING NORTH TOWARD THE BIG ISLAND FROM THE DEEP TROPICS. OVER
KAUAI...RAINFALL DROPPED OFF THROUGH THE PAST FEW HOURS...BUT WITH
THUNDERSTORMS STILL FORMING WITHIN SIGHT OF THE NORTH SHORE...
CONTINUED VIGILANCE WILL BE NEEDED OVERNIGHT.

GUIDANCE AGREED IN PREDICTING THE LOW TO OPEN OUT AND MERGE INTO A
LARGER TROUGH AS IT MOVES NORTHWEST THROUGH THE NEXT 24 TO 36 HOURS.
ALTHOUGH THIS TIME FRAME SEEMED A LITTLE QUICK FOR A CUT-OFF LOW...
THE PATH OF THE LOW OVER THE PAST COUPLE OF DAYS SUPPORTED THE MODEL
PROJECTIONS.

IN TERMS OF WIND THROUGH MID-WEEK...THE SUBTROPICAL LOW AT THE
SURFACE TO THE NORTH WILL WEAKEN AS A FRONT ENCROACHES FROM THE
NORTHWEST. THE RESULTING SLACK PREVAILING WINDS OVER THE STATE WILL
ENCOURAGE DIURNAL CIRCULATIONS. TOGETHER WITH THE LINGERING MOIST
AIR MASS...SEA BREEZES MAY KEEP PRODUCING SUBSTANTIAL SHOWERS EVEN
BEYOND MID-WEEK. THIS ASPECT OF THE FORECAST LIKELY WILL NEED SOME
TUNING OVERNIGHT.

SOLUTIONS PREDICTED A GRADUAL RETURN TO MORE TYPICAL CONDITIONS BY
THE WEEKEND...AS RIDGING RECOVERS BOTH ALOFT AND AT THE SURFACE TO
THE NORTHEAST. IN TURN...THE RETURNING TRADE WINDS WILL SCOUR OUT
THE GREATEST CONCENTRATIONS OF WATER VAPOR. HOWEVER...TRADE WIND
SPEEDS ARE EXPECTED TO REMAIN ON THE LOW SIDE OF AVERAGE AT LEAST
UNTIL EARLY NEXT WEEK.

&&

.MARINE...
WINDS SHOULD REMAIN BELOW THE SMALL CRAFT ADVISORY /SCA/ CRITERIA
THROUGH THE FORECAST PERIOD.

A NEW NORTH SWELL ARRIVING LATE TUESDAY WILL PRODUCE MODEST SURF
ALONG NORTH-FACING SHORES OF THE ISLANDS WEDNESDAY AND THURSDAY.
THIS SWELL WILL SUBSIDE SLOWLY THURSDAY NIGHT AND FRIDAY. A
NORTH-NORTHWEST SWELL ARRIVING EARLY SATURDAY MORNING WILL PRODUCE
MODEST SURF ALONG MOST NORTH- AND WEST-FACING SHORES OF THE SMALLER
ISLANDS OVER THE WEEKEND.

TRADE-WIND SWELL WILL DIMINISH ALONG WINDWARD SHORES AND REEFS AS
WINDS WEAKEN THROUGH TUESDAY. ELSEWHERE...SMALL SWELLS FROM THE
SOUTHERN HEMISPHERE WILL MAINTAIN SMALL BACKGROUND SURF ALONG
SOUTH-FACING SHORES THIS WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH TUESDAY AFTERNOON FOR NIIHAU-KAUAI-OAHU.

&&

RYSHKO