Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 AM EST Sat Jan 11 2025

Valid 00Z Sun Jan 12 2025 - 00Z Sun Jan 19 2025

Latest models and ensembles agree fairly well with the forecast
into Thursday.  Expect moderate to brisk trades from this weekend
into Monday with a corresponding windward/mountain rainfall focus.
A front approaching if not quite reaching the 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.  A guidance compromise still looks good for
resolving exact precipitable water values.  Showers should be
lighter 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
the western islands.

Guidance details diverge from late Thursday through Saturday.  The
most prominent discrepancy involves the 00Z GFS which pushes the
overall upper trough axis farther east than most other
dynamical/ML guidance (including the GEFS mean).  This pushes the
cold front farther eastward as well, with enough surface ridging
building in behind to support northeasterly winds by Saturday. 
Other dynamical guidance and ML models keep high pressure farther
west, maintaining more northerly or northwesterly winds on
Saturday.  Meanwhile, the 00Z ECMWF scenario initially appears a
little extreme with its close upper low proximity to the northeast
late in the period, but three of five 00Z ML models actually
depict an upper low similar to the ECMWF (actually two near the
ECMWF and one farther west) so it seems to be plausible enough to
include as part of a compromise with the ensemble means for an
overall preference.  This front may produce a band of at least
moderate rainfall, but with guidance still fairly diverse between
light and somewhat heavy activity.

Rausch