Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
349 AM EDT Mon Apr 08 2024

Valid 00Z Tue Apr 09 2024 - 00Z Tue Apr 16 2024

The forecast continues to show light to moderate windward-focused
showers early this week as trades trend gradually weaker, with a
weakness aloft over/north of the islands into early Tuesday likely
offsetting slightly below normal values of precipitable water. 
Over the past day the guidance has maintained good continuity with
a deep upper low closing off to the northwest of the state by
Wednesday-Thursday.  The upper low should drift northward
thereafter while energy dropping into the base of the overall
trough should ultimately lead to some eastward progression of this
trough by Sunday-Monday.  A surface low corresponding to the upper
system should extend a front/convergence axis southward to just
west of the islands during the latter half of the week into the
weekend, helping to focus bands of heavy rainfall as precipitable
water values increase to 1.5 inches or more across the state from
late week onward. Most dynamical and machine learning guidance
currently suggests that Kauai and Niihau will be on the eastern
side of the enhanced rainfall, with slight changes in longitude
producing significantly drier or wetter conditions.  Low
predictability for such minor differences a few days out in time
keeps confidence in specifics low within the agreeable larger
scale evolution.  Meanwhile expect winds over the state to turn
southeasterly by Wednesday and persist into the weekend.  There is
reasonable agreement that the axis of enhanced rain should start
to advance eastward ahead of the lingering upper trough by
Sunday-Monday.  Latest GFS runs by Monday show a little more
southeastward amplitude of the upper trough versus other guidance,
but for now this does not seem to lead to pronounced differences
with the eastward progress of the surface reflection and
associated rainfall.

Rausch