Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Tue Feb 14 2023

Valid 00Z Wed Feb 15 2023 - 00Z Wed Feb 22 2023

...Heavy rainfall threat especially during Thursday-Saturday
within a potentially longer term wet pattern...

Guidance continues to show a pattern evolution that favors an
extended period of enhanced rainfall potential, though with
ongoing differences in some of the specifics.  Between now and
early Thursday the models and ensemble means have converged fairly
well for the depiction of the upper low initially over/east of the
state tracking back to the north and then west of the islands.  As
this occurs, a surface trough should track westward across the
area with an embedded low tracking just to the north of the main
islands.  This feature should push a moderate band of moisture
westward across the state.

Guidance continues to show the upper low dropping southward from
Thursday into the weekend, with the deep-layer southeasterly flow
between this upper low and the ridge to the northeast bringing in
abundant moisture late this week into the weekend.  Model
forecasts indicate the potential for heavy rainfall during this
period, with particular focus over southeastward facing locations
on the Big Island.  The GFS continues to show the deepest upper
low and weakest southwestward extent of the upper ridge, along
with seemingly spurious surface lows within the enhanced moisture
axis.  While the GFS is in the minority in this regard, the CMC
now shows a brief northward shift in the moisture by the weekend
as suggested in the GFS (before this axis shifts back
southwestward).  As in past days, the GEFS mean tones down some of
the most extreme aspects of the GFS.  On the other hand, the 00Z
ECMWF has adjusted toward keeping the moisture axis over the state
for a longer time than previous runs and the 12Z ECMWF mean before
nudging a bit west.

Adding some complexity to the forecast, guidance is now suggesting
that energy in the southern part of a trough approaching from the
west may try to amplify west of the state by next Monday-Tuesday. 
The GFS appears quite quick to drop energy southward, so prefer to
lean away from the GFS for that exact detail.  However there is
otherwise general agreement on existence of the trough and the
majority cluster of guidance suggests that this latter trough
could ultimately support enhanced moisture/rainfall focus over the
western islands by next Monday-Tuesday while surface troughing
just to the west of the state maintains a general southeasterly
low level flow.

Based on the relative distribution of the guidance after early
Thursday, overall forecast preference would be a compromise among
the GEFS mean and other non-GFS models/means.

Rausch