Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
341 AM EDT Sat Aug 20 2022

Valid 00Z Sun Aug 21 2022 - 00Z Sun Aug 28 2022

Latest guidance is fairly agreeable and consistent with the
forecast through at least the middle of next week.  From late this
week through the weekend expect fairly light and primarily
windward-focused showers as a surface ridge to the north supports
moderate trades and precipitable water values stay below
climatology.  Upper ridging will prevail as well.  Monday will
serve as a transition into a brief period of lighter winds
Tuesday-Wednesday as upper troughing and a surface front north of
the state erode the surface ridge.  In addition consensus still
shows a band of moisture crossing the area in this time frame, so
expect showers to produce somewhat higher totals and with some
sea/land breeze influence.

Some guidance differences and continuity adjustments arise later
in the week.  There is still a general theme that eastern Pacific
high pressure should build westward somewhat, helping to support a
rebound in trades and a return to more windward focus for showers.
 However with models/ensembles diverging for specifics aloft over
the central-eastern Pacific, consensus is ultimately somewhat
weaker with the surface gradient over the islands compared to
yesterday's forecast.  By Friday-Saturday the 00Z ECMWF is in the
minority in a couple respects.  One is with another area of
enhanced moisture passing over the area.  The 12Z ECMWF mean hints
at this but with noticeably lower precipitable water values, while
the GFS/GEFS keep moisture values fairly low.  The other issue is
that the ECMWF deposits a closed upper low well north of the
state, which promotes a break in the surface ridge along 30-40N
latitude.  Consensus has no more than weak upper troughing and
depicts a more coherent surface ridge.  Thus trades in the ECMWF
may become too light late in the period. 

Rausch