Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
352 AM EDT Tue Apr 18 2023

Valid 00Z Wed Apr 19 2023 - 00Z Wed Apr 26 2023

Early in the period, an energetic front anchored by a system
tracking well north-northwest of the state will push eastward
across the islands, producing strong southerly winds and heavy
rainfall with possible thunderstorms.  Recent guidance runs have
been consistent in showing an associated band of tropical moisture
(precipitable water values reaching 3+ standard deviations above
normal) with this front as it brings the heaviest rainfall to
western areas on Tuesday and central locations on Wednesday.  Some
heavy rain may extend into the Big Island by Thursday as the front
reaches the eastern half of the islands, though with totals or
coverage that may be a little lower than over areas farther west. 
Expect the front to weaken by Friday with the lingering moisture
band returning back to the northwest from Friday into the weekend
as easterly to southeasterly trades likely develop.  By early next
week, some guidance has changed significantly for the details of
an upper low forecast to track northwest-north of the state as
well as the surrounding upper trough, with impacts on the surface
pattern.  While latest GFS runs still track the upper low closer
to the main islands than other guidance, other solutions have
adjusted the overall trough more toward the GFS scenario.  As a
result there is now better than average agreement that the
associated front should track into the state early next week.  The
front may provide some rainfall focus but with much lighter totals
than with the first front, as models/means show precipitable water
values holding steady or slowly declining by next Monday-Tuesday.

Rausch