Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
815 AM EDT Sun Apr 08 2018

Valid 00Z Mon Apr 09 2018 - 00Z Mon Apr 16 2018

Today's guidance shows decent agreement and continuity with most
aspects of the forecast during the next seven days.  In the
immediate short term, the interaction of shortwave energy aloft
and a lingering northeast-southwest axis of deep moisture
associated with a weakening cold front will promote areas of
rainfall that could be heavy over some locations.  By
Monday-Tuesday the shortwave aloft and moisture axis will sag
southeastward.  This will lead to a drier trend over the
northwestern islands but enough moisture will persist over/near
the Big Island to offer the possibility of locally moderate-heavy
pockets of rainfall extending into the early week time frame.

High pressure building eastward to the north of the state
Monday-Wednesday will bring a return to northeasterly/easterly
trades, which may become rather brisk by midweek.  Continuing
eastward progression of the high should relax the pressure
gradient a bit by Thursday-Friday.  Then models/ensemble means
advertise another surface high passing by to the north during the
weekend supporting another period of fairly strong winds.  Expect
the best focus for shower activity to be over windward locations
with the lingering pocket of higher precipitable water values near
the Big Island early in the week tending to return westward and
become more diffuse under the influence of easterly winds at low
levels--as well as aloft by Tuesday-Wednesday as an upper ridge
briefly builds/passes by to the north.

There are a couple guidance differences that may be worth
monitoring by late week/weekend.  One is the 06z GFS and to some
extent 00z GFS/GEFS showing a little more amplitude than other
solutions for an upper trough passing by to the north around
Friday (with at most peripheral effect on the islands).  The other
involves ECMWF-based guidance bringing more moisture into the
region from the east-southeast than GFS/GEFS solutions.  This
relative difference has existed over the past couple days with
little clear trend one way or the other so far.

Rausch