Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
304 AM EST Tue Dec 07 2021

Valid 00Z Wed Dec 08 2021 - 00Z Wed Dec 15 2021

...Significantly heavy rainfall potentially causing catastrophic
flooding could continue through Tuesday in the western islands...

Hawaii continues to be impacted by heavy rainfall causing
flooding. A kona low located to the west of the state (with a
stacked mid-upper low and surface low) is leading to deep layer
southerly flow directing tropical moisture northward from the
ITCZ, yielding highly anomalous precipitable water values. As of
late Monday, the heavy rain has ended across the southern islands
from Molokai to the Big Island as a drier air mass has moved in,
after some southern upslope areas of the Big Island received over
a foot of rain. Across the state, there have been numerous flooded
roads and road closures, as well as downed trees and power lines,
and even landslides due to flooding. Now Oahu is experiencing
heavy rain as the moisture plume passes over them, which could
continue into Tuesday and also could impact Kauai. Catastrophic
flooding is possible for these islands.

As the kona low drifts westward, an upper high will encroach
toward Hawaii and pass to the north. This will dry out the pattern
and lead to a more typical trade wind pattern beginning Wednesday
and lasting into early next week, with breezy easterly winds and
the possibility of scattered windward showers, but no widespread
rainfall expected.

Tate