Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
403 AM EDT Tue Mar 17 2020

Valid 00Z Wed Mar 18 2020 - 00Z Wed Mar 25 2020

...Heavy rainfall threat extending at least into midweek...

Latest guidance agrees that the strong Kona low currently west of
the main islands will wobble in place through Wednesday and then
open up/lift northward ahead of a trough/upper low approaching
from the west.  Models and means continue to show that the
southerly/southeasterly flow around this system will bring
considerable moisture into the state and greatest heavy rain
potential--with some strong thunderstorms possible--during the
next couple days over the western half of the islands.  There is
still some debate over how far eastward the heaviest rain will
extend.  The fact that most guidance shows the axis of highest
precipitable water values drifting west to east from Tuesday into
Wednesday supports the potential for some of the enhanced rainfall
to extend into the central islands for a time.  The moisture axis
should retreat somewhat westward after early Wednesday but
lingering shortwave energy south of the departing Kona low could
maintain some threat for locally heavy rainfall over the western
islands into late week. 

From the weekend into next week expect the pattern to transition
to a more typical trade regime with mostly light windward/mountain
shower focus.  By next Monday or Tuesday the easterly winds may be
on the brisk side as high pressure over east-central portions of
the Pacific drops southward.  One model difference of note arises
during the weekend, involving the 00Z ECMWF pulling upstream
shortwave energy farther southeast toward/across the state versus
nearly all other guidance.  This evolution leads to the lingering
north-south moisture axis being held farther east than the
majority cluster that includes the 00Z GFS/GEFS mean and 12Z/16
ECMWF mean.  Thus the preference leans away from the 00Z ECMWF for
that aspect of the forecast.  

Rausch