Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
403 AM EDT Sat Mar 14 2020

Valid 00Z Sun Mar 15 2020 - 00Z Sun Mar 22 2020

...Heavy rainfall threat next week...

Latest guidance is fairly consistent with the general pattern
through the period.  During the weekend a surface trough drifting
westward across the main islands will provide some focus for
rainfall.  Areas where winds are sufficiently light will see a
land/sea breeze influence on shower activity.  Then most guidance
is well-clustered for the Kona low that is likely to close off to
the west of the main islands by Sunday night-Monday.  This feature
should linger to the west-northwest of the state into Wednesday
night-early Thursday and then open up/lift northward in response
to an approaching upstream trough aloft.  Adding some confidence
to the general forecast is the recent trend of the GEFS/ECMWF
ensemble means toward the average of operational model solutions
from the past day.  Models/ensembles continue to show that the
southerly flow of moisture will likely bring precipitable water
values at least as high three standard deviations above normal
over some locations--and an axis of multi-inch rainfall over parts
of the western/central islands during the first half of the week,
bringing a potential for flash flood issues.  Among 00Z models
there is sufficient agreement to recommend an average of their
solutions for the upper low position.  Locating the axis of
highest rainfall is still a lower-confidence endeavor and will
likely take into the short range time frame to resolve better. 
Currently the 00Z GFS/GEFS mean depict this axis somewhat eastward
of most other solutions but not to such an extreme degree to
exclude it from a multi-model compromise.  Expect rainfall focus
to become steadily more diffuse later in the week as the upper low
opens up and lifts northward.  Note that by late Fri-Sat the past
couple GFS runs keep lower heights aloft over/west of the western
islands, so preference for specifics would transition to the ECMWF
and the GEFS/ECMWF means.  At the surface there will be a fairly
tight gradient over the main islands early/mid-week, between low
pressure to the west and a ridge to the east, leading to brisk or
strong southeasterly winds.  Persistence of eastern Pacific high
pressure while low pressure to the west weakens/lifts northward
will promote more moderate winds from the east or southeast late
week into the weekend.

Rausch