Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
827 AM EDT Sun Apr 22 2018

Valid 00Z Mon Apr 23 2018 - 00Z Mon Apr 30 2018

The forecast period begins with a surface high building north of
Hawai'i today and persisting through Tuesday as it tracks towards
the east near 35 degrees north, and an upper level ridge situated
over the western part of the Islands.  The high to the north will
ensue a steady east to northeast trade wind flow, and becoming
windy at times as the surface pressure gradient tightens.  By
Thursday, the guidance is indicating a change in this weather
pattern as a weakness forms within the ridge as an inverted
surface trough develops near the state.  This is in response to an
amplifying long wave trough over the north-central Pacific by the
end of the week, with the EC mean showing a more amplified
solution than the GEFS mean. 

The result in either case would be a decrease in the typical trade
winds along with southeasterly veering, with a frontal boundary
approaching the northwestern Islands by Saturday.  This will also
increase the coverage of showers and some thunderstorms as PWs
approach 2 inches owing to the moist advection from the Doldrums. 
This would especially hold true for the windward facing terrain.

D. Hamrick