Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
841 AM EDT Thu Sep 13 2018

Valid 00Z Fri Sep 14 2018 - 00Z Fri Sep 21 2018

Olivia has weakened to tropical depression status and is moving
away from the state.  However the combination of an upper low
tracking just northwest of the main islands and a lingering band
of enhanced deep moisture will continue the threat of heavy
rainfall especially over the central and northwestern islands into
late this week.  Guidance agrees that drier air will move into the
area for the weekend into early next week, yielding generally
light windward-focused showers during that time frame.  By
Wednesday-Thursday the latest GFS/ECMWF and their means show minor
differences in timing and magnitude but are similar in principle
regarding an area of enhanced moisture that may reach the islands,
with precipitable water values reaching or exceeding two inches at
some locations.  This is fairly consistent with what guidance was
showing yesterday.  During that time period the models and
ensembles show a fairly strong signal toward higher rainfall
amounts focused over the Big Island in particular.  This activity
may be enhanced by a surface trough which most guidance suggests
may reach the state from the east. 

Expect trades of varying strength to prevail through the period. 
Mid-latitude Pacific high pressure will likely support strongest
trades from late this week into the weekend.  From Monday onward
the trades may be somewhat weaker due to wave development over the
central Pacific and then the aforementioned surface trough.

Rausch