Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
818 AM EDT Sat Apr 07 2018

Valid 00Z Sun Apr 08 2018 - 00Z Sun Apr 15 2018

The forecast pattern this weekend continues to favor a heavy
rainfall threat over the state as an approaching shortwave aloft
interacts with a pronounced southwest-northeast band of deep
moisture (precipitable water values in the 1.75-2.00 inch or so
range) associated with a stalled front.  Models/means still
suggest that the dynamics aloft will likely generate some enhanced
surface troughing over the eastern half of the islands by Sunday
to provide an added focus for rainfall.  The shortwave aloft will
push just south of the islands by early next week, leading to a
drying trend over northwestern/central areas, but expect some
degree of enhanced moisture to linger over/near the Big Island
into the middle of next week.

Guidance is consistent with the idea of high pressure building
eastward along 30-35N latitude through midweek.  This high will
support a trend toward brisk trades, perhaps slackening a bit by
Thursday-Friday as the high moves eastward, but a trailing high
passing to the north by Saturday should keep trades on the
stronger half of the spectrum.  Therefore expect showers to favor
windward terrain but with activity occasionally reaching windward
locales.  As ridging aloft builds over/north of the area by
mid-late week in addition to the surface highs tracking north of
30N, the aforementioned moisture lingering near the Big Island
should begin to dissipate and move westward by the latter half of
the week.  Overall rainfall will likely trend lighter for the late
week/weekend time frame.

Rausch