Heavy Rain in Hawaii, May 4, 2002

HAWAIIAN ISLANDS SYNOPTIC DISCUSSION AND GUIDANCE
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST FRI MAY 3 2002

SUMMARY...A HEAVY RAIN SCENARIO IS SETTING ITSELF UP FOR PARTS OF
THE STATE TONIGHT. LOCALLY HEAVY RAINFALL ON WINDWARD OAHU...MAINLY
NEAR PUNALUU AND KANEOHE...AND MORE WIDESPREAD HEAVY RAINFALL ON THE
BIG ISLAND OF HAWAII FOR TONIGHT...WITH HEAVY SHOWERS AND POSSIBLE
THUNDERSTORMS INCREASING STATEWIDE OVER THE WEEKEND. WINDS WILL BE
LIGHT BUT SHOULD BE INCREASING FROM THE SOUTH AND SOUTHEAST OVER THE
WEKEND.

DISCUSSION...COMPUTER MODELS HAVE BEEN SUGGESTING A HEAVY RAIN EVENT
FOR THE STATE OF HAWAII BEGINNING THIS WEEKEND FOR NEARLY A WEEK
NOW. TONIGHT HEAVY RAINFALL HAS BEGUN OVER HILO AND PUNA ON THE BIG
ISLAND...WITH LOCALLY HEAVY RAINFALL AMOUNTS ON WINDWARD OAHU AS
WELL. EXTREMELY HEAVY RAINFALL IS SHOWING UP ON DOPPLER RADAR TO THE
SOUTH OF SOUTH POINT ON THE BIG ISLAND...AND THIS HAS PROMPTED THE
ISSUANCE OF A FLASH FLOOD WATCH FOR THE BIG ISLAND FOR TONIGHT AS
THAT AREA OF HEAVY RAINFALL IS MOVING NORTHWARD. MOIST AIR MOVING IN
FROM THE SOUTHEAST NEAR THE BIG ISLAND IS CONVERGING WITH MOIST AIR
ABOVE 10000 FEET MOVING IN FROM THE SOUTHWEST IN THIS SHOWER AREA...
AND THIS BAND IS PROPOGATING TOWARD THE BIG ISLAND TO ITS NORTH.
FORECASTS HAVE BEEN MODIFIED TO REFLECT THESE REALITIES...AND
COMPUTER MODELS WILL BE COMPARED TO THE ACTUALITIES AS WELL.

COMPUTER MODELS CONTINUE TO PREDICT MOISTURE CONVERGENCE OVER THE
ISLANDS AND RESULTANT HEAVY RAINFALL AND POSSIBLE THUNDERSTORMS
THROUGH MONDAY AT LEAST. THE AVIATION MODEL IS STILL TRYING TO
DEVELOP A SURFACE LOW PRESSURE SYSTEM OR STRONG TROUGH SOUTH OF THE
STATE...AND MOVE IT NORTHWARD JUST WEST OF KAUAI. THIS WILL PLACE
STRONG SURFACE MOISTURE CONVERGENCE OVER THE STATE IN THE SOUTHEAST
FLOW INTO THE LOW OR TROUGH...AND MAINTAIN THE POSSIBILITY OF
LOCALLY HEAVY RAINFALL FOR ALL ISLANDS INTO EARLY NEXT WEEK. THIS
MODEL IS ALSO STRENGTHENING THE WINDS...BUT THIS MAY BE OVERDONE IN
THE SOUTHEASTERLY FLOW DUE TO BLOCKING EFFECTS OF THE ISLANDS
THEMSELVES.

ON ANOTHER FRONT...A STRONG LOW IN THE SOUTHERN HEMISPHERE SOUTHEAST
OF NEW ZEALAND WILL SEND A SUBSTANTIAL SWELL IN OUR DIRECTION. THE
SWELL SHOULD REACH HAWAII WEDNESDAY OR THURSDAY PROBABLY REQUIRING A
HIGH SURF ADVISORY OR EVEN A HIGH SURF WARNING FOR SOUTH FACING
SHORES. FARRELL

.HFO...WARNINGS...NONE
.      WATCHES...FLASH FLOOD BIG ISLAND
.      ADVISORIES...SMALL STREAM EAST BIG ISLAND AND WINDWARD OAHU