Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
350 AM EDT Mon May 10 2021

Valid 00Z Tue May 11 2021 - 00Z Tue May 18 2021

Models and ensemble means continue to show precipitable water at
near to moderately below average values for the time of year, with
a tendency for a gradual decrease over the course of the week and
then stabilization into early next week.  Thus expect most
rainfall to be in the lighter half of the spectrum.  Trades are
likely to be in the light to moderate range into midweek, and in
some locations possibly close to being light enough at times for
land/sea breeze influence on showers while remaining rainfall
focuses over windward/mountain areas.  Guidance consensus still
shows high pressure to the north strengthening somewhat after
Wednesday, promoting stronger trades and more pronounced windward
shower focus.  An upper trough developing to the north/northeast
of the state mid-late week appears likely to deposit an upper low
that lingers northeast of the area through the weekend.  The upper
trough/low and any shortwaves that rotate around the feature could
enhance rainfall a bit at times.

As for notable guidance comparisons, one item of note is that the
00Z ECMWF has its upper low drifting west of other models/means by
Sunday-Monday.  Also from the weekend into next week the latest
GFS runs become out of phase with many aspects of the pattern over
the Pacific.  This results in the GFS disrupting the surface high
north of the state late in the period and possibly ejecting the
nearby upper trough/low prematurely.  The GEFS mean is closer to
the remaining solutions.  These considerations lead to favoring
the non-GFS consensus for high pressure late in the period and the
CMC/CMC-GEFS-ECMWF means for the upper feature northeast of the
state once solutions diverge.

Rausch