Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
811 AM EDT Thu Apr 19 2018

Valid 00Z Fri Apr 20 2018 - 00Z Fri Apr 27 2018

High PWs (1.60-1.80 inches) across the Hawaiian Islands initially
along with an upper-level shortwave passing just north of the
state will produce scattered, locally heavy showers through
Friday. Low-level easterlies averaging 10-20 kt will favor the
heaviest rains falling across windward areas. As the shortwave
moves east by Saturday, heights will quickly rise across Hawai'i
as an upper ridge expands west of the state. This will allow much
drier air (PWs near or below 1 inch) to spread across the state,
which will significantly reduce the coverage of any windward
showers. Low-level easterlies should also increase into the 20-30
kt range by mid-week as the surface pressure gradient tightens a
bit. Models/ensemble show general agreement that this drier
pattern should persist into late next week, before a northern
stream Pacific trough amplifies well northwest of the state. At
this time, any influence from this late week trough across Hawai'i
seems very limited, with the deepest moisture remaining well south
of the state through next Thu night.

Ryan