Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
707 AM EST Sat Nov 25 2017

Valid 00Z Sun Nov 26 2017 - 00Z Sun Dec 03 2017

...Heavy rain probable next week...

Surface high to the NNW of the region will slide southeastward
then eastward along 32-33N which will maintain breezy/windy trades
through about Tuesday. Light to scattered windward/mauka showers
are expected with only some spillover to leeward areas possible as
the overall air mass remains dry today.

From late Sunday onward, deep moisture from the ITCZ will surge
northward into the Big Island and Maui which will increase rain
coverage from southeast to northwest over the island chain.
Another approaching trough from northwest Wed/Thu is forecast to
dip southward but the models split on how far east -- the 00Z
ECMWF/Canadian were farther east than the GFS. The ensemble
systems support something in between the GFS/ECMWF on Friday but
closer to the ECMWF by next Saturday (though not as deep). Prefer
a solution in between the 00Z ECMWF and the 00Z GEFS mean. This
would not yet necessarily favor a defined surface low lifting
northward just west of the islands later next week but even the
ensembles do show an inverted trough axis bulging northward around
163W next Saturday. 00Z GEFS M-Climate QPF percentiles remain at
the 99th percentile from midweek onward so the potential remains
for modest to locally heavy rain next week, perhaps shifting from
the southeastern islands to the western islands as the pattern
evolves.


Fracasso