Small Craft Advisory 39, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
335 AM HST SAT NOV 22 2008

.SYNOPSIS...
UNSTABLE SOUTHEAST WIND FLOW WILL CONTINUE ACROSS THE ISLANDS
THROUGH SUNDAY MORNING...RAISING THE PROBABILITY FOR HEAVY SHOWERS
AND THUNDERSTORMS. MODERATE TO FRESH TRADE WINDS WILL RETURN SUNDAY
AFTERNOON THROUGH WEDNESDAY...THEN DECREASE AND SWITCH TO
SOUTHEASTERLIES THANKSGIVING DAY AND FRIDAY. A COLD FRONT IS
EXPECTED TO REACH THE ISLANDS DURING THE DAY FRIDAY.

&&

.DISCUSSION...
AN UPPER LOW 270 MILES NORTHWEST OF KAUAI WILL KEEP OUR AIRMASS
UNSTABLE THROUGH THE WEEKEND. AN INDUCED SURFACE TROUGH WEST OF THE
ISLANDS HAS CAUSED WINDS TO VEER TO SOUTHEASTERLIES ACROSS MOST OF
THE STATE. SATELLITE LOOP SHOWS ABUNDANT MOISTURE FROM THE DEEP
TROPICS MOVING ACROSS THE ISLANDS. LATEST COMPLETE SOUNDINGS SHOW
UP TO 2 INCHES OF PRECIPITABLE WATER ALONG WITH K-INDEX VALUES IN
THE HIGH TEENS TO THE 30S. THERE IS NO CAPPING INVERSION.

SO FAR OVER THE PAST 12 HOURS...RADAR SHOWS THAT HEAVY SHOWERS AND
THUNDERSTORMS WERE LIMITED TO WATERS AROUND KAUAI...OAHU AND
MOLOKAI. A BIT OF THIS ACTIVITY CREPT ACROSS PORTIONS OF KAUAI AND
SOUTHEAST OAHU LAST EVENING. THIS ACTIVITY DECREASED ENOUGH OVER
KAUAI TO ALLOW THE FLOOD ADVISORY TO EXPIRE FOR THAT ISLAND AT 2 AM
HST. HOWEVER...INSTABILITY...DEEP MOISTURE AND WEAK SURFACE
CONVERGENCE REMAIN. THE EASTWARD SPREAD OF HEAVY SHOWERS AND
THUNDERSTORMS IS GOVERNED BY HOW FAR EAST THE UPPER LOW WEST OF
KAUAI MOVES AND BY HOW MUCH CLEARING OCCURS ACROSS THE EASTERN
ISLANDS. CLEARER SKIES MEANS MORE DAYTIME HEATING AND THE GREATER
LIKELIHOOD FOR AFTERNOON AND EVENING CONVECTION. MODELS SHOW THE
UPPER LOW WILL MOVE CLOSER TO THE ISLANDS THROUGH TODAY...BUT IT
REMAINS UNCERTAIN HOW MUCH CLEARING WILL OCCUR ACROSS THE EASTERN
ISLANDS. BECAUSE OF THIS UNCERTAINTY...THE FLASH FLOOD WATCH WILL
REMAIN IN EFFECT FOR ALL OF THE MAIN HAWAIIAN ISLANDS UNTIL EARLY
SUNDAY MORNING.

MODELS SHOW THE UPPER LOW NORTHWEST OF KAUAI WILL MOVE WESTWARD BY
SUNDAY EVENING...DRAGGING THE SURFACE TROUGH AWAY WITH IT. THIS WILL
ALLOW A RETURN TO TRADE FLOW MONDAY THROUGH WEDNESDAY. GFS SHOWS
RETURNING TRADES MAY BE STRONG ENOUGH TO REQUIRE SMALL CRAFT
ADVISORIES FOR A PORTION OF LOCAL WATERS AND CHANNELS SUNDAY
EVENING. BY THURSDAY...A COLD FRONT APPROACHING FROM THE NORTHWEST
WILL CAUSE WINDS TO VEER BACK TO SOUTHEASTERLIES. GFS SHOWS THIS
FRONT WILL REACH KAUAI DURING THE DAY FRIDAY. IT IS TOO SOON TO TELL
HOW MUCH RAINFALL WILL OCCUR WITH THIS NEXT EVENT.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH LATE SATURDAY NIGHT FOR ALL MAIN
HAWAIIAN ISLANDS.

&&

POWELL