Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
349 AM EDT Wed Sep 28 2022

Valid 00Z Thu Sep 29 2022 - 00Z Thu Oct 06 2022

Expect generally easterly trades through the middle of next week,
with some fluctuation between light and moderate speeds. 
Variability in the trades will be driven by an initial front just
north of the state and another that will reach close to if not
into the northwestern islands, as well as surface highs to the
north of these fronts.  The background flow will support windward
and mountain focused showers but sea breezes may also influence
showers at times when the trades are light.  Guidance continues to
show a fairly tight moisture gradient across the state, with
below-climatology precipitable water values over and near the Big
Island and above normal values over the northwestern islands which
will be closest to the fronts and could see some rainfall
enhancement at times.

As for the forecast details, moisture associated with the first
front should linger into Thursday.  Then the trades should carry a
pocket of moisture across the area around Friday.  Meaningful
differences develop with the next front that should approach
during the weekend.  The 00Z GFS has furthered the recent
southward trend, actually bringing the front and its axis of
enhanced rainfall into the northwestern islands.  On the other
hand the past two ECMWF runs through 00Z keep the front and its
heavier rainfall farther north.  Also worth noting, the 00Z ECMWF
shows a southward displacement for a central Pacific system versus
consensus by late in the period, and this could play a role in the
pattern by next Wednesday.  The 00Z GEFS mean and 12Z/27 ECMWF
mean each suggest a preferred intermediate solution that would
have the northwestern islands in the southern portion of the
moisture/rainfall shield whose axis would be aligned just to the
north.

Rausch