Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
253 AM EST Mon Nov 27 2023

Valid 00Z Tue Nov 28 2023 - 00Z Tue Dec 05 2023

...Heavy Rain and Flash Flooding possible this week across much of
Hawaii...

General trade wind weather in place across Hawaii today will be
disrupted Tuesday and beyond as a Kona low sets up west of Hawaii
and lingers through about Saturday. There continues to be
increasing concern for widespread heavy rainfall and thunderstorms
across all of the Hawaii islands this week with a threat for flash
flooding as precipitable water values surge up to two or more
standard deviations above normal. While the guidance shows
excellent agreement on the large scale pattern, there remains
quite a bit of uncertainty in the details including total rainfall
amounts. The latest run of the GFS continues to suggest the
heaviest rains may remain to the northeast of the islands, which
the CMC and ECMWF do suggest some relatively significant rainfall
totals across at least some of the islands. A general model blend,
along with the ensemble means, should provide a good starting
point for the forecast with time to iron out the details still. By
the weekend, the guidance shows this low weakening and slowing
drifting eastward over the islands with rainfall trending lighter
with time and easterly trades beginning to build back in.

Santorelli