HAWAII EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD 800 AM EDT FRI SEP 21 2012 VALID 00Z SAT SEP 22 2012 - 00Z SAT SEP 29 2012 TO BEGIN THE PERIOD...A WELL-DEVELOPED MID-LEVEL CYCLONE LOCATED NORTH OF 40N LATITUDE WILL SHIFT TOWARD THE NORTHEAST WHILE WEAKER SHORTWAVE RIDGING BUILDS IN THE WAKE. ALL OF THE 500-MB HEIGHT FALLS WILL CONCENTRATE TO REGIONS NORTH OF 35N LATITUDE WHILE A BROAD 588-DM RIDGE IMPACTS THE SUBTROPICS. THE STRONG FRONTAL PASSAGE IN THE MID-LATITUDES WILL ALLOW A STRENGTHENING SURFACE RIDGE TO BUILD WHICH WILL GRADUALLY INCREASE THE TRADE WINDS ACROSS THE HAWAIIAN ISLAND CHAIN. DURING THE WEEKEND...MODELS INDICATE NORTHEASTERLY TRADES NEARING THE 15 TO 20 KNOT RANGE. THE LOW-LEVEL NORTHEASTERLY FLOW WILL ADVECT 1 TO 1.25 INCH PWATS TOWARD THE STATE RESULTING IN NUMEROUS WINDWARD SHOWERS...WITH LOCALLY HEAVIER AMOUNTS ALONG THE FAVORED UPSLOPE TERRAIN. ON TUESDAY AND INTO WEDNESDAY...MID-LEVEL RIDGING TO THE WEST WILL GATHER STRENGTH AS THE HEIGHTS INCREASE TO ABOVE 594-DM NEARBY 30N/175E. EVENTUALLY SOME OF THESE HEIGHTS ARE FORECAST TO DECREASE AS UPPER TROUGHING TO THE NORTH BEGINS TO APPROACH. MODELS DO BECOME IN LESS AGREEMENT LATER IN THE PERIOD WITH THAT AMPLIFIED FLOW ACROSS THE ACTIVE MID-LATITUDES. THE 00Z CMC WAS DEPICTED HEIGHTS FALLING AS FAR SOUTH AS 28N ALTHOUGH THIS WAS NOT SUPPORTED BY ANY OTHER MODEL. OTHERWISE...THE HAWAIIAN ISLANDS CAN EXPECT MODERATE TRADES TO CONTINUE THROUGHOUT THE REMAINDER OF THE WEEK WITH ADDITIONAL WINDWARD SHOWER ACTIVITY. ALTHOUGH...THE 06Z GFS DOES SHOW PWATS DECREASING TO 0.75 TO 1 INCH WHICH COULD DIMINISH SOME OF THE QPF AMTS OVER THE REGION. RUBIN-OSTER