Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
353 AM EDT Mon Oct 31 2022

Valid 00Z Tue Nov 01 2022 - 00Z Tue Nov 08 2022

Today's models/means still show some variation in trades over the
coming seven days.  Moderate winds should prevail early this week,
and possibly into Wednesday when a weak surface trough may pass
just to the north of the islands.  Trades will likely become more
brisk by Thursday-Friday as a surface high settling over the
east-central Pacific reaches its peak strength.  Most guidance
still shows a weakening and more southeasterly tilt of the trades
during the weekend into early next week as the surface high
weakens and a front approaches from the west.  Similar to the GFS
from 24 hours ago, now the 00Z CMC is the one extreme solution
with a farther west overall pattern and greater persistence of
trades.  Even among the other models and individual ensemble
members, there is a rapid increase of spread for specifics of the
supporting upper trough by Sunday-Monday.  As of Monday the 00Z
ECMWF and 18Z GFS are the deepest while the 00Z GFS is on the weak
side.  This spread lowers confidence in exactly how close to the
western islands the front reaches.

Generally windward/mountain-focused showers should be lightest
during the first part of the week as guidance maintains below
average precipitable water values over most of the state, except
for the Big Island at times.  Moisture should increase from the
latter half of the week onward.  Overall the GFS depicts somewhat
greater moisture than the ECMWF with the ensemble means supporting
their respective models in relative terms, favoring a compromise
at this time.  Also an upper level weakness should develop over
the area as a strong ridge prevails to the north, but with low
confidence for existence/details of any embedded weak lows.  The
combination of moisture and upper level evolution should lead to
higher trends for rainfall amounts.  By the weekend the rainfall
focus could shift more to southeast-facing terrain, and possibly
other locations, given the lighter/southeasterly trends for winds.
 The approaching upper trough/surface front could start to pull
additional moisture from the south early next week.  However the
magnitude of this moisture increase is very uncertain given the
widening spread for upper trough details.

Rausch