Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
358 AM EDT Sat May 27 2023

Valid 00Z Sun May 28 2023 - 00Z Sun Jun 04 2023

Today's models and ensembles agree with the forecast pattern into
Thursday but then they diverge for specifics of flow aloft late in
the week, affecting how much moisture will be over the state at
that time.  A surface trough crossing the state from east to west
around Sunday will provide a brief period of lighter trades and
some sea/land breeze influence on showers.  Trades should steadily
rebound toward moderate to brisk strength over the following days
(with windward/mountain shower focus) as high pressure persists to
the north, with strongest winds likely to be around
Wednesday-Thursday.  Guidance is consistent with precipitable
water values increasing to above normal from about Sunday onward
as an elongated east-west weakness with one or more embedded lows
develops over or just north of the islands.  This weakness may
dissipate around Wednesday or Thursday.  By Friday-Saturday the
models and ensembles develop significant spread for how upstream
shortwave energy may evolve, with corresponding differences in
moisture.  On one side of the envelope, the 00Z GFS/CMC develop
enough upper troughing in a favorable position to support an
additional increase of moisture (GFS bringing PWATs above 1.75
inches by Saturday).  On the other hand the 00Z ECMWF has a
somewhat broader/more suppressed depiction aloft and has drier air
moving in from the northeast (PWATs locally reaching as low as
1.00 inch).  The GEFS mean holds PWATs in the 1.25-1.50 inch range
while the 12Z ECMWF mean has a moderate drier trend but not to the
extent of the 00Z ECMWF.  With the prior 18Z GFS closer to the
GEFS mean in principle and the wide envelope that currently
exists, would recommend an overall solution closest to the GEFS
mean or a partial compromise between it and the ECMWF mean.

Rausch