Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
253 AM EST Mon Jan 16 2023

Valid 00Z Tue Jan 17 2023 - 00Z Tue Jan 24 2023

At least into Sunday, guidance has come into rather good agreement
for most aspects of the forecast.  Through midweek precipitable
water values will tend to stay near or slightly below climatology
while upper ridging across the area steadily weakens.  Expect
light southeasterly background flow with some land/sea breeze
influence on showers that should be on the light side.  A front
forecast to stall near the northwestern islands by Thursday should
increase moisture and rainfall in its vicinity.  The front should
dissipate and/or lift northward soon thereafter as southeasterly
(and eventually more southerly) winds strengthen while a stronger
front approaches from the west.  Given typical spread six days out
in time, the 00Z operational models are remarkably similar in
showing this latter front reaching the northwestern islands as of
early Sunday with the ensemble means fairly close as well.  Expect
a more focused band of heavier rain along this front, though
models have varied quite a bit for exact amounts.  By Monday the
guidance begins to diverge for the upper pattern over the islands,
affecting the front over the area.  The 00Z CMC/CMCens/GFS show an
upper ridge beginning to build in from the west/southwest, leading
to the front stalling/weakening.  On the other hand the 00Z ECMWF,
00Z GEFS mean, and 12Z ECMWF mean all hold onto more upper
troughing and as a result keep the front better defined and
progressing gradually eastward.  This aspect of the forecast has
fairly low predictability seven days out, lending itself to a
compromise of the 00Z GFS/ECMWF (the most moderate members of the
two respective clusters) for arriving at a specific forecast.

Rausch