Flash Flood in Hawaii, March 18, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST SAT MAR 18 2006

.SYNOPSIS...
AN UPPER TROUGH TO THE WEST OF THE ISLANDS WILL CONTINUE THROUGH THE
FORECAST PERIOD. THIS WILL KEEP WINDS GENERALLY LIGHT WITH LOCALLY
HEAVY SHOWERS POSSIBLE.
&&

.DISCUSSION...
AN UPPER TROUGH TO THE WEST OF THE STATE IS KEEPING THE ATMOSPHERE
UNSTABLE OVER THE STATE. A STRONG SHORTWAVE IS MOVING THROUGH THE
FLOW TOWARDS THE ISLAND CHAIN. THIS IS ENHANCING THE SHOWERS AND
THUNDERSTORMS OVER THE WESTERN HALF OF THE FORECAST AREA. THE
UNSTABLE ATMOSPHERE HAS ALLOWED SHOWERS TO DEVELOP THIS AFTERNOON
ACROSS ALMOST ALL OF THE ISLANDS.

FIRST ORDER OF BUSINESS THIS AFTERNOON IS TO DEAL WITH THE FLOOD
WATCH. THE FORECAST TEAM HAS DECIDED BASED ON CURRENT TRENDS TO
EXTEND THE FLOOD WATCH STATEWIDE THROUGH 8 PM HST ON MONDAY. STILL
KAUAI...NIIHAU AND OAHU REMAIN THE MAIN TARGETS FOR THE HEAVIEST
SHOWERS THROUGH MONDAY...HOWEVER THE REMAINING ISLANDS STILL HAVE
ENOUGH OF THREAT TO MAINTAIN THE WATCH.

ANOTHER FORECAST PROBLEM FOR TONIGHT INVOLVES THE SEVERE WEATHER
POTENTIAL FOR THE ISLANDS. THIS AFTERNOON A COUPLE OF VERY NASTY
THUNDERSTORMS DEVELOPED OFF THE COAST OF KAUAI...HOWEVER WERE VERY
SHORT LIVED. LOOKING AT THE UPPER WIND FIELD AND OTHER SEVERE
PARAMETERS INDICATE THAT THE RISK FOR ORGANIZED SEVERE IS
MINIMAL...THEREFORE TOP CONCERN WILL BE ADDITIONAL FLOODING. WILL
NOT ISSUE A SEVERE THUNDERSTORM WATCH FOR THIS AFTERNOON AND
EVENING...HOWEVER THERE WILL BE A THREAT OF SOME GUSTY WINDS AND
SMALL HAIL WITH STRONGER STORMS LATE THIS AFTERNOON AND
EVENING...MAINLY OVER OAHU KAUAI AND NIIHAU.

FOR SEVERAL DAYS THE GFS HAS BEEN...ALTHOUGH INITIALLY
QUESTIONABLE...DEVELOPING A LOW TO THE SOUTHWEST OF KAUAI AND
MOVING IT NORTHWARD. LOOKING AT THE SATELLITE SHOTS THERE IS A HINT
THAT A LOW MIGHT BE FORMING DOWN THERE. WILL NOT HAVE A QUICKSCAT
VIEW UNTIL 5 OR 6Z TONIGHT THEREFORE WILL HAVE TO GO WITH A BEST
GUESS. THE PROBLEM RESIDES WITH THAT THE NAM AND ECMWF ARE HOLDING
TO THEIR OWN SOLUTIONS OF ONLY A TROUGH OVER THE WESTERN ISLANDS.
THIS IS MAKING IT VERY DIFFICULT TO GET A GOOD HANDLE ON THE
FORECAST PACKAGE. THE PRIMARY DIFFERENCES BETWEEN A CLOSE
CIRCULATION AND AN OPEN WAVE IN THE LOW LEVELS WILL BE THE AMOUNT OF
CONVERGENCE AND LOCAL WIND FIELDS. ITS HARD TO DISCOUNT THE
SATELLITE DATA. STILL THE PROBABILITY THAT A CLOSED SURFACE LOW WILL
FORM IS LOW. WILL HOLD WITH A TROUGH SOLUTION WHICH STILL SUPPORTS
SHOWERS AND THUNDERSTORMS...JUST NOT AS MANY.

SUNDAY THROUGH MONDAY THE THREAT CONTINUES WITH A TROUGH IN PLACE AT
ALL LEVELS. THIS WILL CONTINUE THE THREAT OF LOCALIZED HEAVY SHOWERS
AND THUNDERSTORMS.

TUESDAY AND BEYOND...UPPER TROUGH REMAINS TO THE WEST...A SURFACE
BOUNDARY WILL BE HANGING AROUND THE ISLANDS. EACH ONE OF THE LONG
RANGE MODELS DOES THEIR OWN THING...HOWEVER KEEP THE THEME OF A WET
PATTERN GOING THROUGH FRIDAY.  DO NOT SEE ANY REASON AT THIS TIME TO
CHANGE THE CURRENT FORECAST. GOING TO HOLD ONTO THE LIGHT WINDS AND
CONVECTIVE PATTERN THROUGH FRIDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...

FLASH FLOOD WATCH...ALL ISLANDS THROUGH MONDAY EVENING.

&&

PROTON