Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
812 AM EDT Wed Apr 12 2017

Valid 00Z Thu Apr 13 2017 - 00Z Thu Apr 20 2017

Latest models and ensembles agree that a shortwave trough west of
the state will drift toward/over the islands in coming days.  This
trough will likely consist of two impulses, the initial one now
observed and expected to reach the islands by Thursday-Friday
followed by an upstream one arriving by Saturday.  There is better
consensus today that the shearing energy should settle southward
to a position over or just south of the Big Island Sunday onward. 
The overall trough along with precipitable water values that may
reach at least one standard deviation above normal should promote
shower activity that may be locally moderate to heavy.  Best focus
for rainfall should be over windward locales but during the latter
half of the week trades may weaken enough to allow for some sea
breeze focus as well.

From Sunday into next week guidance indicates a period of stronger
trades in association with surface high pressure reaching the
central Pacific Sunday-Monday.  However as was the case yesterday,
beyond early Monday models and ensembles rapidly diverge with the
progression of this high and thus with the time frame for stronger
trades.  The 00z ECMWF and slightly farther north ECMWF mean are
fastest with the high while the 00z CMC/06z GFS become slowest. 
The 00z GEFS/CMC means are slightly faster than the 00z GFS and at
this time offer the best intermediate solution among the wide
guidance spread.  In spite of the differing surface forecasts,
both the GFS and ECMWF runs are suggesting that an axis of
relatively higher moisture could align over the islands early-mid
week.  The 00z GEFS mean is more suppressed so confidence in next
week's forecast remains below average.

Rausch