Prognostic Meteorological Discussion
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FXHW01 KWNH 191212
PMDHI

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


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