Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
354 AM EDT Tue May 16 2023

Valid 00Z Wed May 17 2023 - 00Z Wed May 24 2023

For Tuesday into Wednesday, easterly trade winds look to average
around moderate levels, with a relatively dry airmass in place.
But the pattern should start to change late Wednesday into the
latter half of the week as an upper trough sets up west of the
state and slowly moves eastward. Winds turning more southerly
ahead of the upper trough will help draw in anomalously high
tropical moisture (likely above the 95th percentile for
precipitable water). Enhanced rainfall totals are likely to start
across the western islands on Thursday as showers increase in
coverage and intensity. The upper trough moving in could lessen or
eliminate the typical inversion, providing instability for some
possible thunderstorms. There remains some uncertainty for if/when
heavy rainfall makes it all the way to the eastern islands and
when the threat for heavy rainfall ends. The GFS suite of models
maintains the upper trough longer and presses it across Hawaii
Friday-Saturday, while other guidance generally has the trough
tracking east and weakening more quickly. While ample moisture
looks to stay in place, depending on how the upper and lower level
dynamical features evolve, there may be less support for heavy
rain into the weekend and beyond, though likely some showers would
continue regardless. By early next week a more typical trade wind
pattern looks to return, with slowly decreasing moisture levels.

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