Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
246 AM EST Sat Nov 13 2021

Valid 00Z Sun Nov 14 2021 - 00Z Sun Nov 21 2021

...Potential for Locally Heavy Rainfall Early Next Week...

Models and ensembles are consistent with the idea of an upper
trough amplifying northwest of the state through the weekend,
pushing a front into the main islands.  This front should then
weaken but may leave a surface trough over the state during the
first half of next week.  There is still reasonable agreement and
continuity with the potential for one episode of enhanced rainfall
around Sunday as moisture lifts northward ahead of the front and a
shortwave aloft sharpens just to the west.  Expect rain to trend
lighter on Monday as the shortwave lifts northeastward.  By
Tuesday the guidance is showing improved agreement toward another
shortwave reaching just northwest of the state but still varies
regarding how much this evolution may increase rainfall once
again.  The 00Z ECMWF has trended lighter than its prior two runs
while latest GFS runs (on the amplified side of the spread for the
upper shortwave as of 12Z Tuesday) are noticeably wetter than
yesterday's 00Z GFS.  At least there is a more common signal among
the models and ensemble means today for the rebound in
precipitable water values on Tuesday, so confidence is increasing
for higher rainfall totals but just not yet for the location and
magnitude.  Passage of the second shortwave on Wednesday and
gradually strengthening eastern Pacific surface high pressure
should promote a return to easterly or southeasterly trades along
with a gradual drier trend during the latter half of the week.

Rausch