Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Sat Apr 15 2023

Valid 00Z Sun Apr 16 2023 - 00Z Sun Apr 23 2023

Most guidance agrees fairly well for the general themes of the
forecast through the period, though a couple differences arise for
specifics next week.  Expect moderate trades this weekend with
windward-focused showers tending to be in the light to moderate
side of the spectrum as precipitable water values over near or a
little below climatology.  Then consensus shows good continuity
with a system northwest of the islands pushing a front toward the
region early next week, turning winds more southerly.  Guidance is
similar in depicting the potential for this front to tap a
considerable amount of tropical moisture (PWATs perhaps reaching
3+ standard deviations above normal) with heaviest rainfall likely
affecting western areas on Tuesday and central locations on
Wednesday.  Rain should trend lighter over the eastern half of the
state later in the week as the front weakens.  Most solutions
suggest the lingering moisture band should return back to the
northwest by Friday-Saturday as upper ridging builds in from the
east.  Among the 00Z guidance/12Z ECMWF mean, the 00Z ECMWF is a
notable extreme in bringing the front or the remaining shear axis
just east of the Big Island by late in the week.  Remaining models
and means suggest the front should not reach any farther east than
the central islands.  By the end of the forecast next Saturday,
one other discrepancy arises involving the relative strength of
ridge to the east and an upper trough to the northwest and another
front that may approach from the northwest.  The 00Z GFS/GEFS mean
lean toward a stronger trough/weaker ridge, bringing the front
closer to the area than other solutions.  The 00Z CMC/CMCens and
12Z ECMWF mean make up the strong ridge cluster.  Similar
differences with the ridge persist from yesterday, so a compromise
appears to be a reasonable approach at this time.

Rausch