Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
814 AM EDT Tue Apr 11 2017

Valid 00Z Wed Apr 12 2017 - 00Z Wed Apr 19 2017

A weak mid level trough initially near 170W longitude will be
drifting toward the state over the coming days.  This feature
along with somewhat above normal precipitable water values (PWATs)
should bring the potential for some moderate to locally heavy
shower activity.  With differing details among the models there
are signals that some of the trough energy may get pulled off just
west of the islands and linger through at least the weekend. 
Overall the 00z/06z GFS runs are most pronounced with this
possibility aloft as well as in forecasting higher PWATs.  From
the weekend into next week there is increasing model/ensemble
spread for mid-latitude details aloft across the central/eastern
Pacific.  The one common theme is toward a gradual sagging of
heights aloft within broadly cyclonic flow over to north/northeast
of the state.  This evolution may provide a southward push to a
band of moisture originally associated with a weakening front
north of the area.

Expect trades of varying strength through the period.  Influences
on trade flow will be high pressure initially north of the state
moving into the eastern Pacific followed by a high that weakens
north-northwest of the area around Saturday.  By early next week a
stronger mid-latitude surface high will track eastward between
30-40N latitude.  Corresponding to differences aloft, guidance
diverges significantly with timing of this high.  Based on north
Pacific guidance comparisons and faster 06z GFS trend, would
initially recommend a compromise between the 06z GFS and somewhat
faster 00z ECMWF mean.  The 00z ECMWF is on the fast side of the
spread while the 00z CMC/CMC mean are slower than the 00z GFS/GEFS
mean.

Rausch