Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
338 AM EDT Tue Sep 28 2021

Valid 00Z Wed Sep 29 2021 - 00Z Wed Oct 06 2021

Another day of breezy easterly trade winds is likely as a surface
high pressure system drifts to the north of Hawaii and an
upper-level ridge persists to the northwest of the state. Other
than some shower activity over windward and mauka areas, generally
dry conditions are expected. Trade winds may lessen to moderate
levels on Wednesday as the high shifts eastward, until additional
high pressure tracks north of the state around Thursday and winds
pick back up. Around Thursday or Friday, some increase in
available moisture is forecast per the global model guidance. This
should initially be the case for the Big Island, but the enhanced
moisture could track farther west as well by the weekend, which
particularly the GFS model continues to show. Increasing showers
especially in windward areas are possible given the higher
moisture, though the amount of moisture at the surface will also
be a factor. Then, by early next week, mid/upper-level troughing
may spread southward into the state and push a surface front
closer to (but not through) Hawaii, which could draw moisture
northward and possibly enhance rainfall chances. This will
continue to be monitored in the days ahead.

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