Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
402 AM EDT Thu Mar 19 2020

Valid 00Z Fri Mar 20 2020 - 00Z Fri Mar 27 2020

...Heavy rainfall threat to decrease by late in the week...

The consensus of latest guidance shows the Kona low to the west of
the main islands opening up as it lifts northward over the next
day.  As this occurs expect the potential for some bands of heavy
rain/thunderstorms to continue into late Thursday/Thursday night
until the remaining shortwave that extends southeast from the
original upper low center crosses the state Thursday night/very
early Friday.  Flow around a separate upper low farther northwest
could still keep a moisture axis fairly close to the northwestern
islands into the weekend but any associated rainfall should be
much lighter than in the activity forecast through Thursday.  From
late week into the weekend the flow around the southwest periphery
of a surface ridge will support low level winds ranging from
east-southeast near the Big Island to more southerly over the
western islands.  Then expect brisk trades early-mid week as the
southward drift of Pacific high pressure strengthens the gradient
over the state.  Drier air moving in from the east will bring
precipitable water values down to a range between 0.75 inch and
near or slightly over an inch so expect windward/mountain-focused
showers to be fairly light.  Trades could trend a little lighter
by next Thursday as the surface high well north-northeast of the
state weakens in favor of a another high to its northwest.  Also
rainfall may increase slightly as models/ensemble means agree upon
a decrease in heights aloft as the upper ridge to the north of the
state rapidly collapses.

Rausch