Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
352 AM EDT Mon Oct 16 2023

Valid 00Z Tue Oct 17 2023 - 00Z Tue Oct 24 2023

Continue to expect fairly light trades through midweek, supporting
some land/sea breeze influence on showers wherever the background
flow is too weak to promote a more typical windward focus.  A
lingering band of moisture over the northwestern islands early
this week will depart soon, leading to a brief drier trend before
another front likely approaches or reaches the northwestern
islands late this week.  Today's guidance has returned to better
agreement for this front/moisture axis by way of the GFS/GEFS mean
trending back to the south toward the ECMWF/ECMWF mean (and
consensus from two days ago).  This moisture axis and potential
for some rainfall enhancement over northwestern locations should
persist into the weekend.  Meanwhile high pressure to the north of
the front may help trades to rebound briefly late in the week.

From the weekend into early next week the guidance is consistent
with the general idea of significant trough amplification (with
embedded upper low) north and west of the state, pushing a front
to a position northwest of the main islands.  Leading flow across
the state should turn more southerly with while moisture/rainfall
should increase.  However there is a decent amount of
northeast-southwest spread for where the core of the upper trough
and associated low pressure will be, leading to differences in the
exact surface pattern and eventual moisture focus early next week.
 The 18Z/00Z GFS runs are on the west/southwest side of the
envelope by next Monday, leading to the most pronounced northward
surge of moisture being focused over the northwestern islands. 
The 00Z GEFS mean is closer to the average of remaining guidance
but still hints at a western moisture axis.  On the other hand the
00Z ECMWF/12Z ECens mean suggest that lower latitude moisture
should come into the Big Island and central part of the state. 
Given typical spread and forecast errors that far out in time,
while accounting for the more extreme aspects of the GFS, would
prefer a compromise approach among the 00Z GEFS mean/ECMWF and 12Z
ECMWF mean. 

Rausch