Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
346 AM EDT Sun Sep 26 2021

Valid 00Z Mon Sep 27 2021 - 00Z Mon Oct 04 2021

Continued showery weather is forecast for the southern islands of
Hawaii through Sunday night, as a surface trough just to the south
of the state enhances moisture. Windward areas of the Big Island
can once again expect the most coverage of showers. After that,
much of the workweek will see quiet weather. Breezy easterly trade
winds are expected especially early this week, due to a surface
high pressure system and upper-level ridging to the north of the
state. By around Friday into the weekend, moisture may increase
once again given a weakness in the upper-level pattern. There are
some differences in the model guidance with this--the 00Z GFS has
moisture arriving a bit more quickly into the southern islands by
Thursday night, with the 00Z ECMWF waiting until Friday. The ECMWF
and the 00Z GEFS and 12Z EC means have increased moisture mainly
affecting the Big Island, but it is worth noting that the GFS
spreads anomalously high moisture westward as far as Oahu. So
these differences will continue to be monitored, but the pattern
overall suggests that increasing shower activity is likely by the
late week/weekend.

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