Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
717 AM EST Sat Jan 27 2018

Valid 00Z Sun Jan 28 2018 - 00Z Sun Feb 04 2018

Ahead of a shortwave trough aloft and weakening surface front
crossing the state this weekend, the Big Island and vicinity will
continue to be on the western edge of an area containing enhanced
deep moisture which will promote rainfall of varying intensity. 
Models still vary with precise westward extent of highest
moisture, favoring an intermediate solution.  Progression of these
features will bring a drying trend over the state for most of
Monday-Tuesday with relatively light easterly low level winds
turning southeasterly, and then strengthening somewhat from the
south/southwest as a front approaches from the west.

For this late Tuesday-Wednesday front supported by developing mean
troughing aloft northwest of the state, the 00z ECMWF is faster
than 00z/06z GFS runs but with differences aloft not completely
matching up with respective surface details and other guidance
averaging a little slower than the ECMWF.  Thus a compromise
timing appears reasonable.  The front should bring some locally
moderate-heavy rainfall into the far northwestern islands but
activity spreading southeast will likely trend a bit lighter for a
time as dynamics lift northeastward.

However in spite of this brief lighter trend, stalling of this
front along with the approach of upstream energy aloft and another
cold front should be a favorable setup to maintain moist flow over
the islands for the latter half of the week.  Thus more episodes
of enhanced rainfall are possible.  As was the case yesterday,
significant timing differences develop for this latter front with
the GFS continuing to be more progressive than most other
guidance.  Today the 00z GEFS mean is more similar to GFS runs
though.  The GFS has slowed significantly from its runs of 24
hours ago, seemingly providing more support for maintaining a
solution perhaps 2/3 toward the slower cluster of guidance.

Rausch