Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
759 AM EDT Sat Apr 14 2018

Valid 00Z Sun Apr 15 2018 - 00Z Sun Apr 22 2018

The model guidance is in good agreement closing off an upper low
just west of the state today and drifting it slowly westward
through the end of the weekend, reaching around 170W by 12Z
Tuesday.  Southeasterly low-level flow is bringing in plenty of
moisture and combined with a fair amount of instability, expect
widespread showers and isolated thundershowers through the weekend
and into Monday, with locally heavy rainfall amounts.  The
greatest instability appears to be focused over the northern
islands, so expect activity to be more organized in this region.

The majority of the guidance continues to retrograde the upper low
westward toward the dateline and slowly dissipate it during the
middle to latter part of next week, and consequently show drier
air moving in from the north and northeast.  The GFS, however,
rotates some energy around the upper low and then strengthens it
into a relatively well-defined shear axis which moves eastward
across the state mid-late next week.  This solution maintains
deeper moisture and the threat for organized trade wind showers,
especially over the southern islands.  The ECMWF hints at a
similar solution, but is notably weaker and keeps the
precipitation/moisture suppressed farther to the south than the
GFS, while the UKMET/Canadian are both much drier across the
island chain.  Tend to think the GFS is too strong with this
feature (perhaps suffering some convective feedback) and therefore
favor drier conditions with moderate trades mid-late next week.

Klein