Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
816 AM EDT Fri Apr 26 2019

Valid 00Z Sat Apr 27 2019 - 00Z Sat May 04 2019

Today's guidance agrees fairly well with the forecast through the
middle of next week.  Trades will become light through the weekend
as high pressure continues into the eastern Pacific and a front
stalls to the north/northwest of the main islands.  Thus expect
showers to have more land/sea breeze focus.  During Sunday-Monday
an upper shortwave approaching and crossing the region will
increase the potential for locally heavy rainfall and possibly
thunderstorms.  By Tuesday-Wednesday expect moderate trades to
become established with rainfall trending lighter, as surface high
pressure builds north of the state and heights aloft rise behind
the departing shortwave.

After Wednesday the models and ensembles increasingly diverge for
an upstream trough which would increase rainfall potential if it
were to be sufficiently amplified and extend far enough
east/southeast.  Among operational models the 00-06Z GFS/06Z FV3
GFS show the greatest height falls reaching the main islands.  The
full ensemble spread is quite broad by Thursday-Friday,
encompassing the GFS solutions as well as the much slower/closed
00Z ECMWF.  The ECMWF mean supports fairly slow timing but the old
12Z ECMWF looked more like a slower version of the latest GFS runs
versus the deep/closed 00Z ECMWF.  Based on the entire array of
guidance and ECMWF continuity, would recommend a compromise
between the 00Z GEFS/ECMWF ensemble means as the best option for a
single deterministic forecast at this time.

Rausch