Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
820 AM EDT Tue May 19 2015

Valid 00Z Wed May 20 2015 - 00Z Wed May 27 2015

The persistent positive anomaly over western Canada remains
conducive for allowing the upstream westerlies to occasionally
separate into one or more pieces, which is depicted by most of the
current guidance across the northern Pacific by this weekend.  The
separation of the westerlies will result in a small closed low
forming just east of the islands by Saturday, which will support a
weakening of the trades and a weak cold frontal passage.  The
solution spread regarding the shortwave pattern increases
noticeably by early next week, although any differences in
sensible weather appear small.  Regarding rainfall probabilities,
other than primarily scattered windward showers through the
period, moisture anomalies are generally negative and too low to
support much rainfall.  Almost any model or combination of models
will provide a reasonable starting point for any forecast, with
more of a combination recommended by early next week, due to the
growing spread.

James