Flash Flood Warning 25, NWS Honolulu, HI

HAWAIIAN ISLANDS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST THU SEP 15 2005

.SYNOPSIS...HEAVY RAIN AND THUNDERSTORMS WILL CONTINUE OVER PARTS OF
THE STATE TODAY...WITH A FLASH FLOOD WATCH IN EFFECT FOR THE ENTIRE
STATE. COLD TEMPERATURES ALOFT WITH MOIST...UNSTABLE AIR NEAR THE
SURFACE IS PRODUCING THE HEAVY RAINFALL. DRIER CONDITIONS SHOULD
EASE THE THREAT OF FLOODING LATE FRIDAY AND OVER THE WEEKEND.

&&

.DISCUSSION...A FAIRLY STRONG TROUGH SEEN AT 500 AND 250 MB ALOFT
WITH ITS COLD TEMPERATURES HAS DESTABILIZED A WARM...MOIST MASS OF
AIR MOVING BY IN THE TRADE WINDS. THIS IS CAUSING VERY HEAVY
RAINFALL OVER PARTS OF THE STATE TODAY...WHICH MAY LAST INTO
TONIGHT...ESPECIALLY OVER KAUAI AND OAHU. THE HEAVIEST RAINFALL
OVERNIGHT WAS ALONG THE WINDWARD COAST AND HALEAKALA SLOPES OF MAUI
AND OVER MOUNT WAIALEALE AND THE NORTHEAST SLOPES ON KAUAI. THIS
RAINFALL CAUSED THE HANALEI RIVER TO FLOOD AND CLOSE THE ROAD ALONG
THE NORTH SHORE OF KAUAI OVERNIGHT. A FLASH FLOOD WARNING HAS BEEN
ISSUED FOR WINDWARD BIG ISLAND...WHERE HEAVY RAIN IS FALLING OVER
HILO...PUNA AND PARTS OF HAMAKUA AT THE MOMENT. GIVEN THE MOIST
UNSTABLE AIRMASS CURRENTLY OVER THE MAIN HAWAIIAN ISLANDS...HEAVY
RAIN AND FLASH FLOODING REMAINS A POSSIBILITY FOR ALL THE ISLANDS
THROUGH THE DAY TODAY.

THE 06Z GFS75 SHOWS THE UPPER TROUGH WILL REMAIN NEAR THE ISLANDS
THROUGH LATE TODAY...ENHANCING SHOWERS OVER MAINLY WINDWARD AND
MAUKA AREAS. LEEWARD SLOPES OF THE BIG ISLAND MAY SEE SOME
ENHANCEMENT AS WELL IN THE AFTERNOON AND EVENING. HOWEVER...EVEN
AFTER LIFTING NORTHWARD FRIDAY...MODELS SHOW THE TROUGH CUTS OFF
INTO AN UPPER LOW WHICH NEVER REALLY STRAYS MORE THAN 600 MILES
AWAY...ALTHOUGH THIS IS APPARENTLY FAR ENOUGH AWAY FOR GFS TO SHOW
SIGNIFICANT DRYING FOR THE ISLANDS FRIDAY AND THROUGH THE WEEKEND.
AS THE UPPER TROUGH LIFTS NORTHWARD...WEAK RIDGING ALOFT WILL BUILD
OVER THE STATE FROM THE EAST. THIS WILL INCREASE STABILITY...THUS
REDUCING THE THREAT OF HEAVY SHOWERS THROUGH THE WEEKEND. IN
ADDITION...THE REFORMATION OF THE INTERTROPICAL CONVERGENCE ZONE 500
TO 600 MILES SOUTH OF THE ISLANDS WILL PUT A CORK IN THE FLOW OF
DEEP TROPICAL MOISTURE NORTHWARD. THIS WILL REDUCE THE LIKELIHOOD
OF A REPEAT OF THE HEAVY RAINFALL SUNDAY NIGHT INTO EARLY NEXT WEEK
WHEN THE GFS IS SUGGESTING A RETURN OF THE UPPER TROUGH TO A
POSITION NORTHWEST OF THE MAIN HAWAIIAN ISLANDS SINCE THERE WILL BE
LESS FUEL...OR LOW-LEVEL MOISTURE...AROUND TO FEED HEAVY SHOWER AND
THUNDERSTORM DEVELOPMENT. MODERATE TO LOCALLY FRESH TRADE WINDS WILL
PERSIST THROUGH THE WEEKEND AS HIGH PRESSURE PERSISTS NORTH OF THE
STATE. TRADES MAY DECREASE SLIGHTLY EARLY NEXT WEEK AS THE HIGH
MOVES OFF TO THE NORTHEAST.

TROPICAL STORM JOVA IS LOCATED ABOUT 1600 MILES EAST SOUTHEAST OF
HILO. THE OFFICIAL FORECAST...ISSUED BY THE NATIONAL HURRICANE
CENTER IN MIAMI...HAS JOVA STRENGTHENING INTO A MINIMAL HURRICANE
FRIDAY EVENING AS IT REACHES 13.6N 137.7W...ABOUT 1080 MILES EAST
SOUTHEAST OF HILO. JOVA IS THEN FORECAST TO WEAKEN BACK TO TROPICAL
STORM STRENGTH SATURDAY AFTERNOON WHILE STILL FAR SOUTHEAST OF THE
MAIN HAWAIIAN ISLANDS. GIVEN THE UNCERTAINTY INVOLVED IN TRACK AND
INTENSITY FORECASTING AT DAY FIVE...WE WILL HOLD OFF MAKING ANY
CHANGES IN THE LOCAL FORECAST AT THIS TIME AND WILL MAINTAIN A TRADE
WIND FORECAST. JOVA WILL BE CLOSELY MONITORED AS IT APPROACHES THE
REGION. THE CENTRAL PACIFIC HURRICANE CENTER WILL ASSUME FORECAST
RESPONSIBILITY FOR JOVA WHEN IT CROSSES 140W ON SATURDAY.

&&

.MARINE...SURF ALONG SOUTH FACING SHORES WILL REMAIN ELEVATED AT THE
15 FOOT WARNING LEVEL THROUGH NOON TODAY...BUT IS EXPECTED TO
SUBSIDE BELOW WARNING LEVEL THIS AFTERNOON. SURF ALONG SOUTH SHORES
IS EXPECTED TO REMAIN ABOVE THE ADVISORY LEVEL OF 8 FEET INTO EARLY
SATURDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY...ALL HAWAIIAN WATERS
HIGH SURF WARNING...SOUTH FACING SHORES
FLOOD WATCH...KAUAI OAHU MOLOKAI MAUI AND BIG ISLAND

&&

FARRELL