Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
359 AM EDT Fri Mar 17 2023

Valid 00Z Sat Mar 18 2023 - 00Z Sat Mar 25 2023

Most guidance agrees upon a wavy front and associated heavy
rainfall staying to the north/northwest of the state over the
coming days.  By Monday-Tuesday the model and ensemble mean
consensus shows an upper low closing off to the northwest, leading
to low pressure development along with a surface trough to the
south.  While the divergence in guidance for the ultimate
evolution/track of this system next week is fairly typical for
forecasts several days out in time, the differences for sensible
weather specifically over the islands are significant.

From late this week into the weekend, expect fairly light
southerly flow on average with showers on the light side and
influenced by a combination of terrain and sea breezes.  The
northwestern islands will be closer to the greater moisture so
slightly higher rainfall totals could be possible there.  As for
next week's spread in the guidance for the upper low and surface
reflection, the 00Z GFS or slight compromise with the farther east
GEFS mean would provide a reasonable intermediate solution at this
time.  The 00Z ECMWF and 12Z ECMWF mean are farthest northwest,
leading to trades that are on the stronger side of the spectrum
and the only moisture enhancement being from a pocket of higher
precipitable water values carried along by the trade flow.  On the
other extreme, the 00Z CMC eventually strays east of the GEFS mean
(and even reforms its upper low via upstream energy) and brings a
surface trough eastward into the state, disrupting the trades. 
Note that the GEFS mean brings the initial front rather far
southeast as well, hence the overall preference being tilted
somewhat more in the GFS direction.  Based on this preference,
expect some increase in moisture/rainfall mid-late week with
southeasterly winds being most likely.

Rausch