Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EST Sun Jan 12 2025

Valid 00Z Mon Jan 13 2025 - 00Z Mon Jan 20 2025

Not much has changed in the guidance for the period from now into
Thursday.  Moderate to brisk trades from late this weekend into
Monday will provide a windward/mountain shower focus. A front
approaching area should briefly disrupt the trades around Tuesday.
 Consensus shows good continuity in showing an upper low just
south of the Big Island into early Monday, leading to a moderate
increase of moisture and periods of enhanced rainfall especially
over the eastern side of the Big Island. Expect lighter showers
Tuesday-Wednesday as an upper ridge builds in and PWATs decrease
somewhat.  Then during the day Thursday, guidance continues to
show a central Pacific upper trough beginning to amplify toward
the state with an associated cold front approaching/reaching the
western islands.

Most of the models and ensembles have made some adjustments from
late Thursday onward, with some low-predictability detail spread
as well. The primary change in the latest guidance is toward
faster progression of the front crossing the region late this
week, with somewhat less accompanying moisture, which is seconded
by the machine learning (ML) models.  The impetus behind this
change is the introduction of a trailing cold front that most
solutions have reaching the main islands by next Sunday, also with
fairly modest moisture.  This rapid succession of features allows
for a brief return of trades around Saturday before being
interrupted again by the Sunday front.  There is still some
ambiguity with the details of upper troughing that may linger just
east of the state, with a couple 00Z ML models hanging on to the
idea of an upper low closing off to the east or northeast and
supporting a more pronounced inverted surface trough just east of
150W longitude.  For now an average of the GFS/ECMWF and their
means would be a reasonable starting point but with somewhat below
average confidence given recent guidance behavior.  Consensus
precipitable water values suggest light to moderate showers in
general by the weekend, with focus depending on wind specifics at
any particular time. 

Rausch