Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Tue Dec 03 2019

Valid 00Z Wed Dec 04 2019 - 00Z Wed Dec 11 2019

Trades should be fairly persistent and moderate in strength
through Thursday and possibly into Friday as a central Pacific
surface high tracks toward a position well north of the islands by
early Friday.  Expect trade flow to become noticeably lighter
during the weekend as the high moves quickly east-southeast and a
front approaches from the northwest.  Although there are
differences in precise amplitude of supporting flow aloft
(consensus less amplified than the 00Z GFS) and the degree to
which the upper ridge west of the state builds eastward (consensus
including the 00Z GEFS mean suggesting more than latest GFS runs),
most guidance is similar in showing a southward trend for the
front--bringing it into the main islands by Monday versus keeping
it just north.  A weak surface high behind the front may freshen
the trades a bit during the first part of next week.

Showers will tend to favor windward/mountain areas through
Thursday given the moderate trades in place.  Guidance continues
to show shortwave energy passing over the area around Friday with
a corresponding increase in moisture and potential for a brief
period of enhanced rainfall.  While it is hard to have much
confidence in specific amounts/locations of highest rainfall
totals generated by the operational models, it is noteworthy that
the GFS/ECMWF are hinting at higher potential totals than
yesterday (though a couple ECMWF runs in the distant past were
quite heavy before backing away).  The weekend will see a drier
trend with any shower activity possibly exhibiting land/sea breeze
influence.  The front reaching the area around the start of next
week may provide a modest increase of rainfall at that time. 
Showers would regain some windward focus early next week based on
the current forecast of trades returning to some degree.

Rausch