Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
813 AM EDT Tue May 15 2018

Valid 00Z Wed May 16 2018 - 00Z Wed May 23 2018

The majority of model/ensemble guidance show Hawaii remaining in a
relatively benign weather pattern over the next week, with
gradually rising heights and increasing trades later in the week
as the subtropical ridge takes hold north of the state. A trough
is expected to pass well north of Hawaii Tue night into Wed, with
the associated surface cold front likely washing out well before
it reaches Hawaii. At this time, models show no major differences
with the handling of these features, with respect to any affects
on Hawaii. As the trough moves east, upper-level ridging is
expected to expand across the central Pacific, with a surface high
strengthening approximately 600 miles north of the state by Thu
night-Fri. Models continue to diverge in their solutions after
Sun. The GFS/GEFS continue to be the most aggressive solutions
with amplifying another trough north of Hawaii. The ECMWF now
shows a trough developing as well, although not as amplified as
the GFS, while the CMC maintains a strong ridge in place north of
Hawaii. At this point, a solution along the lines of the ECMWF or
ECENS mean seems like the best compromise with respect to trough
evolution across the north central Pacific next week.

In terms of sensible weather, trades will initially be relatively
weak through mid-week as the pressure gradient remains weak and a
surface trough sets in the vicinity of Hawaii. By later in the
week as the subtropical ridge expands to the north, easterlies
should increase into the 15-25 kt range, and continuing into early
next week. Moisture will be rather limited in this pattern, and
would expect only isolated to scattered windward showers


Ryan