Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Sun Apr 19 2020

Valid 00Z Mon Apr 20 2020 - 00Z Mon Apr 27 2020

Guidance maintains good continuity in showing a pattern evolution
that supports fairly light rainfall during the period. 
Models/ensembles are similar through about Thursday and then
diverge for details of shortwave energy aloft that may push a
front toward/into the state, with at most a modest signal for a
little more rainfall by the weekend.

As best defined high pressure settles into the eastern Pacific, a
weak surface ridge will settle over the area into the start of the
week.  The Big Island may see some lingering trade flow while the
rest of the state should see lighter winds that would promote more
land/sea breeze focus for any light showers that occur.  Then the
eastern Pacific high will strengthen with flow around its
periphery tending to support easterly to southeasterly winds
through midweek.  A front stalled to the northwest of the main
islands through midweek will likely advance eastward late in the
week and weekend due to progression of an upper trough.  As
model/ensemble spread widens for what happens with the southern
part of the upper trough, the latest GFS/CMC runs are within the
full ensemble envelope but perhaps become a bit deep relative to
other models and means.  With the 00Z ECMWF not yet available, a
compromise among the 12Z/18 ECMWF and 00Z GEFS/12Z ECMWF means may
be the best option for a specific solution.  Regardless of the
exact scenario, guidance expects precipitable water values along
the front to decrease as the boundary approaches the islands thus
tempering the potential increase in rainfall.  Faster trend with
the portion of the front north of the islands and trailing high
pressure offers potential for a quicker return to more typical
trades by next weekend. 

Rausch