Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
745 AM EDT Sat Sep 10 2016

Valid 00Z Sun Sep 11 2016 - 00Z Sun Sep 18 2016

Typical trade winds and windward showers with easterly flow will
remain intact through today. On Sunday, a tropical wave and
embedded weak area of low pressure approach from the southeast. 
The wave/low pressure 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 its mean suggest
standardized 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 next
week. This locks in the above average tropical moisture content
and could lead to more enhanced shower activity.

Next weekend the 06z GFS/00z Canadian/00z ECMWF nudge the upper
trough east and an upper level ridge crests and builds south
across the islands. This would signal a drying trend and turn
towards a reduced threat of moderate to heavy rainfall in the
islands.

Petersen