Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 AM EST Sat Nov 30 2019

Valid 00Z Sun Dec 01 2019 - 00Z Sun Dec 08 2019

Guidance still agrees that high pressure over the mid-latitude
Pacific will produce strong trade winds through the weekend into
the start of next week.  After early Monday this high will give
way to another high approaching from the west, continuing brisk
trades into at least Thursday though likely a little weaker than
expected during the weekend.  After Thursday guidance diverges for
the timing and shape of the high, with the latest GFS runs and 00Z
GEFS mean/12Z ECMWF mean providing the best overall cluster.  The
00Z ECMWF becomes much slower.

Typically windward/mountain-focused showers may occasionally stray
to some leeward locations.  A band of moisture associated with an
old front should produce a brief enhancement to rainfall as it
drops southward over the state during the weekend.  After a brief
drier trend early in the week, guidance continues to suggest an
increase of precipitable water values mid-late week.  At least
into early Friday there are some differences as to the magnitude
of this increase but there is better agreement than seen
yesterday.  By Friday-Saturday, in varying ways operational models
are bringing some shortwave energy from the west toward/across the
main islands with a general signal for higher rainfall totals. 
Among latest guidance the ECMWF runs are by far the most
enthusiastic with heavy rainfall potential--brushing the
northwestern islands in the 12Z/29 run and crossing the Big Island
in the 00Z/30 run.  The full array of guidance currently suggests
low confidence in any individual model solution but recommends
monitoring the potential for increasing rainfall during that time
frame.

Rausch