Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 AM EST Sun Nov 14 2021

Valid 00Z Mon Nov 15 2021 - 00Z Mon Nov 22 2021

...Locally Heavy Rainfall to Extend into Sunday Night/Early
Monday...

In the very short term, guidance continues to refine what has been
a fairly consistent forecast in principle.  Consensus still shows
decent potential for locally heavy rainfall and possibly isolated
thunderstorms--favoring the central/northwestern islands--as an
approaching shortwave aloft and southerly flow of moisture
interact with a stalled front that should weaken to a trough but
persist into the first part of the week.  Rain will trend lighter
on Monday as the shortwave tracks over/northeast of the state.  On
the other hand models continue to oscillate for specifics around
Tuesday as another shortwave approaches late Monday/early Tuesday.
 The latest clustering has trended more shallow with this
shortwave.  As a result precipitable water values show only a
modest rebound and with highest values tending to stay near the
Big Island, with Tuesday rainfall now expected to be somewhat
lighter than the guidance average from 24 hours ago.  

After midweek, continuity is good with the idea of light to
moderate easterly/southeasterly trades becoming established around
the southwest periphery of eastern Pacific high pressure while
moisture gradually declines.  Thus expect a combination of
windward and land/sea breeze focus for rainfall with a gradual
decrease in amounts.  By next weekend solutions diverge for a cold
front that may at least approach the northwestern islands.  At the
moment the 00Z ECMWF is on the extreme side, actually bringing the
front into the islands.  The 00Z CMC gets close to the
northwestern islands.  Other models and the 00Z GEFS-CMC/12Z ECMWF
means support keeping the front farther northwest to varying
degrees.   

Rausch