Flash Flood in Hawaii, January 29, 2005

HAWAIIAN ISLANDS FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HONOLULU HI
1040 AM HST SAT JAN 29 2005

.SYNOPSIS...
A SHEARLINE...THE TRAILING END OF A FRONTAL BAND...WILL STALL NEAR
KAUAI AND OAHU TODAY...BRINGING CLOUDS AND SHOWERS TO KAUAI TODAY.
CLOUDS AND SHOWERS FORMING AHEAD OF THE WEAKENING SHEAR LINE WILL
ALSO AFFECT OAHU AND WESTERN BIG ISLAND TODAY. FAIR WEATHER WILL
RETURN TOMORROW AS THE SHEARLINE WEAKENS AND MOVES NORTH. A FRONT
WILL BE NEAR THE ISLANDS BEGINNING TUESDAY...AND WILL BRING IN A
PERIOD OF UNSETTLED WEATHER. ALTHOUGH DETAILS REMAIN UNCLEAR...THERE
IS A POTENTIAL FOR HEAVY SHOWERS AND THUNDERSTORMS FOR MOST OF THE
UPCOMING WEEK.

&&
.UPDATE...
HAVE UPDATED FORECAST/GRIDS TO INCREASE CLOUDS AND POPS FROM OAHU
TO THE BIG ISLAND FOR TODAY...AND TO LOWER SLIGHTLY THE POPS ON
KAUAI.

&&

.DISCUSSION...
A WEAKENING SHEAR LINE NEAR KAUAI AND OAHU IS LOSING ITS
CHARACTERISTICS AS AN IDENTIFIABLE FEATURE IN SATELLITE IMAGERY.
HOWEVER...LOW LEVEL CONVERGENCE ASSOCIATED WITH THIS FEATURE IS
PRODUCING LOTS OF CLOUDS...AND A FEW AREAS OF HEAVY SHOWERS ACROSS
THE MAIN HAWAIIAN ISLANDS THIS MORNING. SOME WEAK SURFACE BOUNDARIES
INTERSECTING NEAR OAHU ARE/WERE RESPONSIBLE FOR THE SHOWERS THAT
HAVE FALLEN OVER THE SOUTHERN PART OF THE ISLAND...BRINGING RAINFALL
RATES AS HIGH AS ONE AND A HALF INCHES PER HOUR TO RAIN GAGES IN
HAWAII KAI WITHIN THE LAST HOUR. WIDESPREAD CLOUDS AND SHOWERS TO
THE WEST OF THE BIG ISLAND APPEAR TO HAVE ORIGINATED FAR SOUTHEAST
OF THE ISLANDS SEVERAL DAYS AGO. GFS INDICATES THAT THE BULK OF THIS
MOISTURE WEST OF THE BIG ISLAND WILL REMAIN OFFSHORE...AT LEAST FOR
THE NEXT COUPLE OF DAYS. HOWEVER...HIGH LEVEL WINDS ARE CARRYING
SOME OF THIS CLOUDINESS..AND LIGHT TO MODERATE RAIN FROM A MID-LEVEL
CLOUD DECK...EASTWARD OVER THE BIG ISLAND.

THE WEAKENING AND DIFFUSE CLOUD BAND MARKING THE SHEAR LINE NEAR
KAUAI WILL WEAKEN AND MOVE NORTH OF THE ISLANDS BY SUNDAY MORNING AS
WINDS OVER THE ISLANDS SHIFT TO SOUTHEAST ONCE AGAIN IN RESPONSE TO
A DEEP TROUGH ALOFT AND AN ASSOCIATED COLD FRONT/SHEAR LINE THAT
WILL BE MOVING TOWARDS THE ISLANDS FROM THE NORTHWEST. THE FRONT
WILL REACH KAUAI TUESDAY MORNING AND THEN THE FORECAST BEGINS TO GET
RATHER COMPLICATED. THE FRONT APPEARS MORE LIKE A SHEAR LINE AT THE
LATITUDE OF THE ISLANDS BY TUESDAY AFTERNOON...WITH THE ACTUAL
FRONTAL PASSING THE ISLANDS TO THE NORTH. HOWEVER...A SURFACE LOW IS
FORECAST TO FORM ALONG THE SHEAR LINE BOUNDARY NEAR...OR EVEN
SOUTHWEST OF...THE ISLANDS ON TUESDAY...AND THEN MOVE NORTHEAST
ACROSS THE ISLANDS...BRINGING BOUTS OF HEAVY RAIN AND THUNDERSTORMS
THROUGH THURSDAY. THE CYCLOGENESIS NEAR THE ISLANDS ALONG A SURFACE
BOUNDARY SEEMS PLAUSIBLE AT THIS TIME...GIVEN THE FACT THAT GLOBAL
MODELS ARE DEVELOPING A SHARP MID LEVEL TROUGH NEAR THE ISLANDS.

AS IS USUALLY THE CASE WHEN VIEWING CYCLOGENESIS NEAR THE ISLANDS IN
THE 3 TO 5 DAY TIME PERIOD...SIGNIFICANT DIFFERENCES ARE SEEN FROM
ONE MODEL RUN TO THE NEXT...WITH JUST A SLIGHT CHANGE IN THE
INTENSITY OR PLACEMENT OF THE SURFACE LOW HAVING MAJOR IMPLICATIONS
FOR THE FORECAST. THEREFORE...UNDERSTAND THAT THE FORECAST FOR THE
UPCOMING WEEK CONTAINS A SOMEWHAT EXTENDED PERIOD OF UNSETTLED
WEATHER...BUT THE DETAILS ARE NOT CLEAR WHATSOEVER.

&&

.MARINE...
A NORTHWEST SWELL REACHED THE ISLANDS LAST EVENING AND WILL CONTINUE
TO PRODUCE SURF ABOVE ADVISORY LEVELS THROUGH MONDAY. PLEASE SEE
HIGH SURF MESSAGES AND OAHU SURF FORECASTS FOR FURTHER DETAILS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FOR MAUNA KEA AND MAUNA LOA THROUGH TODAY.
HIGH SURF ADVISORY FOR NORTH AND WEST FACING SHORES OF NIIHAU...
KAUAI...OAHU AND MOLOKAI.
HIGH SURF ADVISORY FOR NORTH FACING SHORES OF MAUI.
HIGH SURF ADVISORY FOR WEST FACING SHORES OF THE BIG ISLAND.
&&

BIRCHARD