Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
819 AM EDT Thu Aug 18 2016

Valid 00Z Fri Aug 19 2016 - 00Z Fri Aug 26 2016

There actually appear to be some significant changes occurring
during the period of the forecast.  While the typical trade flow
dominates through the weekend with periodic pulses of enhanced
moisture, a more substantial change to flow is forecast starts
Sunday and continuing into next week.  This shift is due to an
amplification of two separate upper troughs over the north central
Pacific that appear to increase precipitable water values from the
typical 1.25 to 1.5 inches closer to 2 inches as per the latest
GFS run that moves up the islands from east to west starting
Monday through Thursday. The GFS does show an increase in
precipitation values near the islands while the ECMWF does not. 
The amplification of the troughs disrupts the trade flow pattern,
weakening it as an inverted trough of sea level pressure develops
west of the islands.

Kocin