Flash Flood Warning 61, NWS Honolulu, HI

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HONOLULU HI
915 PM HST MON MAR 13 2006

.SYNOPSIS...
A WET PATTERN WITH A THREAT OF HEAVY RAINFALL LASTING THROUGH MOST
OF THE WEEK.

&&

.UPDATE...
HAVE UPDATED FORECAST FOR TONIGHT TO REMOVE THUNDERSTORMS ALL AREAS
AND REMOVE HEAVY RAINFALL WORDING FOR ISLANDS EAST OF OAHU. ALSO
LOWERED POPS FOR LEEWARD PORTIONS OF ISLANDS EAST OF OAHU.

&&

.DISCUSSION...
A LINE OF HEAVY SHOWERS IS CURRENTLY MOVING OVER KAUAI FROM THE
SOUTHEAST...HAVING CLIPPED OAHU WITH ITS WEAKER EASTERN PORTION A
LITTLE EARLIER. THE EARLIER FLASH FLOOD WARNING FOR WINDWARD OAHU
WAS MORE BASED ON THE APPEARANCE OF TERRAIN ANCHORED ECHOES...BUT
THOSE HAVE SINCE DISSIPATED. WITH THE DEVELOPING SOUTHEAST
FLOW...HOWEVER...THESE TERRAIN ANCHORED ECHOES COULD REDEVELOP
AGAIN ANYTIME. THE LINE OF HEAVY RAIN APPEARS TO HAVE ITS ORIGINS
IN THE BIG ISLAND PLUME...HAVING BEEN BROUGHT NORTHWARD IN THE
RECENTLY DEVELOPED SOUTHEAST FLOW ALONG THE WESTERN END OF THE
ISLAND CHAIN. IMPRESSIVE 24 HOUR PRESSURE FALLS CONTINUE STATEWIDE
THIS EVENING...WITH THE GREATEST FALLS OF 3 TO 4 MB OCCURRING OVER
KAUAI AND OAHU. WATER VAPOR IMAGERY SHOWS A SHARP UPPER TROUGH WEST
THROUGH NORTH OF KAUAI...WITH A DIGGING SHORTWAVE NEAR 31M 169W.

THE SHORT WAVE TO THE NORTHWEST IS FORECAST TO DEVELOP INTO A CUT
OFF LOW THAT WILL DIG TOWARDS THE ISLANDS IN THE TUESDAY THROUGH
THURSDAY TIME FRAME...ENHANCING THE THREAT OF HEAVY RAINFALL. INTO
FRIDAY THIS CUT OFF WILL BEGIN TO MOVE NORTHEAST...AND WILL LIKELY
PROVIDE A BRIEF RESPITE FROM THE HEAVY RAIN. IN RESPONSE TO THIS
DIGGING CUT OFF LOW...MODELS DEVELOP A TROUGH WEST OF THE ISLANDS
AND MOVE IT EASTWARD OVER THE ISLAND CHAIN...WHICH WILL ACT TO BRING
A DEEP SOUTHERLY FLOW OVER ALL ISLANDS. GFS DEVELOPS AN ENTIRE
SERIES OF LOWS ALONG THIS TROUGH ALONG THE LONGITUDE OF THE ISLANDS
AROUND MIDWEEK...AND THE OTHER GLOBAL MODELS HAVE A SIMILAR FLAVOR
AS WELL. SO WHILE IT WILL BE DIFFICULT TO PINPOINT WHEN AND WHERE
HEAVY RAINFALL WILL OCCUR THE NEXT COUPLE OF DAYS...IT IS NOT
DIFFICULT TO SAY THAT HEAVY RAINFALL WILL OCCUR...WHICH WILL LIKELY
LEAD TO FLASH FLOODING. NO CHANGES THERE.

MODELS MOVE THE DEEP LAYER LOW EAST OF THE ISLANDS TOWARDS THE END
OF THE WEEK...ALLOWING A DRYING TREND AT THAT POINT...BUT LONGER
RANGE PROGS INDICATE ANOTHER CUT OFF LOW WILL DEVELOP NORTHWEST OF
THE ISLANDS BY THE END OF THE WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH...ALL ISLANDS THRU THURSDAY.

&&

BIRCHARD