Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 AM EST Sun Jan 24 2021

Valid 00Z Mon Jan 25 2021 - 00Z Mon Feb 01 2021

Periodic reinforcement of strong high pressure to the north of the
state will likely support brisk to strong trades through next
weekend along with a windward/mountain focus for rainfall.  The
overall forecast is still on track for the episode of heavier
rainfall expected during the first half of the week, as
southeasterly flow between deep-layer ridging north-northeast of
the state and a system evolving near 170-175W longitude pulls an
area of enhanced moisture over the area.  Latest GEFS/ECMWF means
have stabilized in showing precipitable water values reaching 2.5
or so standard deviations above normal for a time with GFS/ECMWF
runs reaching plus 3.0 or so.  The GFS had been on the extreme
side of guidance in the amount of heavy rainfall reaching the
northwestern islands but has finally trended its heavy rain axis
somewhat westward toward the remaining guidance.  However after
early Tuesday the consensus still suggests the GFS may be weak
with the southern periphery of the upper ridge to the north and
overdone with low pressure that tracks west of the main islands. 
There continues to be good agreement for a period of heavier
rainfall over the Big Island.  Rainfall will trend lighter after
midweek through next weekend as the upper ridge drops
south/southwest closer to the state.  Precipitable water values
should be near to slightly below normal in that time frame.

Rausch