Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 759 AM EDT Sun Sep 11 2016 Valid 00Z Mon Sep 12 2016 - 00Z Mon Sep 19 2016 Early this week, a tropical wave and embedded weak area of low pressure will cross the islands, producing an increase in showers across the area. The wave departs to the west mid-week, but the mid-upper level trough remains overhead. An impressive surge of tropical moisture and anomalous precipitable water (pw) will persist over the islands, especially the Big Island. The operational gfs and ecmwf increase pw values to 2 inches, with pw anomalies reaching 2 to 5 standard deviations above normal and remaining in place through most of next week. The weakness aloft is slow to move across the Hawaiian Islands this week. This locks in the above average tropical moisture content and could lead to more enhanced shower activity the latter half of the week. Next weekend the 06z GFS/00z Canadian/00z ECMWF nudge the upper trough east and a mid-upper level ridge crests and builds to the north of the islands. Both the gfs and ecmwf produce strong advection of drier air with pw values dropping next Sun 19 Sept. This would results in a sharply reduced threat of moderate to heavy rainfall in the islands. Petersen