Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
352 AM EDT Mon Sep 27 2021

Valid 00Z Tue Sep 28 2021 - 00Z Tue Oct 05 2021

Over the next couple of days, a surface high pressure system
drifting eastward to the north of Hawaii and an upper-level ridge
to the northwest of the state will continue to cause breezy
easterly trade winds. Other than some shower activity over
windward and mauka areas, generally dry conditions are expected.
By around midweek, a weakness in the upper-level flow should lead
to trade winds lessening to light or moderate. Then, some increase
in available moisture is possible by around Thursday/Friday.
Though most guidance has some increase, deterministic GFS runs
remain the most aggressive with the magnitude and westward spread
of the anomalously high moisture compared to the GEFS and EC means
and the deterministic ECMWF. Additionally, though overall moisture
(precipitable water) increases, there is some question as far as
how much available moisture there will be at the surface itself.
So these differences will continue to be monitored, but the
pattern overall suggests that increasing shower activity is
possible by later in the workweek.

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