Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
809 AM EDT Tue Jul 18 2017

Valid 00Z Wed Jul 19 2017 - 00Z Wed Jul 26 2017

Moderate to brisk trades will prevail over the state as one
surface high center to the northwest tracks westward into the
western Pacific while another high develops to the northeast. 
From now into at least Thursday expect primarily windward-focused
shower activity of varying intensity with precipitable water
values fluctuating on either side of climatological values.  By
Friday-Saturday guidance begins to differ regarding westward
progression of a leading pocket of moisture associated with
Fernanda which is currently a hurricane but forecast to weaken
steadily to post-tropical/remnant low status as it reaches
145-150W by 06z Sunday as per current NHC advisory.  The 00z ECMWF
was faster with this area of moisture than GFS runs but the 06z
GFS has trended toward earlier arrival of this moisture and with
higher values than the 00z run.  The Sunday-Tuesday period is the
most likely time frame when the state may see potential for some
heavy rainfall from the remnants of Fernanda.  Specifics will be
sensitive to the exact track of the lingering surface reflection. 
For the time being there is better than average clustering for
latitude of the remnant low from Sunday onward but greater spread
for timing. 

Rausch