Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Fri Feb 17 2023

Valid 00Z Sat Feb 18 2023 - 00Z Sat Feb 25 2023

...Heavy rainfall/flooding threat especially during Friday-Sunday
within a longer term wet pattern...

Model guidance is agreeable and consistent with the short-term
pattern evolution that will favor a period of heavy rainfall and
flooding potential Friday-Sunday. Models/ensembles suggest the
overall pattern may support a continued threat for heavy rainfall
well into next week but with enough spread and run-to-run
variability on the exact position of a supporting
southeast-northwest moisture band to temper confidence in
specifics from Monday onward.

Expect the upper low initially just west of the state as of Friday
to drift south-southeast thereafter and eventually shear out by
the beginning of next week. The deep-layer southeasterly flow
between the upper low and ridge off to the northeast will continue
to bring up abundant moisture into the islands, with models
highlighting Friday as the most likely day when extremely heavy
rain may fall over southeastward-facing terrain of the Big Island.
The heavy rainfall may continue into Saturday before the guidance
agrees that rain totals will decrease significantly by
Sunday/Monday. 

From Monday through next Friday, models and ensembles maintain a
decent signal for shortwave energy approaching from the west to
form another trough/upper low, which combined with the persistent
upper ridge northeast of the state, would maintain the
southeasterly flow and southeast-northwest oriented axis of
enhanced moisture.  The GFS is an outlier in shifting this
moisture band back over the islands following a brief reprieve on
Monday, as opposed to the axis of the band remaining to the west.
The model consensus supports a decrease in rain chances next week,
but with enough moisture still present to continue a periodic
heavy rainfall threat over some locations (especially the western
islands and Big Island).

Putnam/Rausch