Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 AM EST Sun Nov 27 2022

Valid 00Z Mon Nov 28 2022 - 00Z Mon Dec 05 2022

Today's models and ensembles remain stable for the forecast during
the first half of the week, with a pronounced northward surge of
tropical moisture and shortwave energy aloft into the state
bringing a period of enhanced rainfall.  Consensus still shows
precipitable water values reaching at least 2.0 inches at some
locations, corresponding to standardized anomalies of 3 or
greater.  Enough southeasterly background flow may exist at low
levels to promote rainfall focus over favored terrain on the Big
Island, while other areas could also see episodes of moderate to
heavy rainfall depending on how any individual bands set up.

After early Wednesday and through next weekend the guidance
continues to go astray with respect to important upper level
details that will determine how much moisture lingers over the
state and what the low level wind regime will be.  In a persistent
theme from recent days, the 00Z GFS/GEFS mean are farthest east
with the overall upper pattern with a trough approaching from the
west and the downstream ridge heading to the east of the state. 
This scenario results in the greatest persistence of moisture and
makes it difficult for trades to get established.  In contrast,
the 12Z ECMWF mean and 00Z CMC mean actually have the upper ridge
axis west of the main islands into Friday and passing over the
region Saturday--leading to a significant drying trend and enough
of a surface gradient to promote resumption of light to moderate
trades late week into the weekend.  The 00Z ECMWF still leans
toward a drier trend but does not decrease precipitable water
values as dramatically as the 12Z ECMWF mean.  The operational 00Z
ECMWF/CMC runs both support somewhat more trade flow than the GFS.
 Thus for the late week into weekend time frame, preference would
side with the moderate majority of guidance showing a decrease of
moisture/rainfall and the return of trade flow to some degree.

Rausch