Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
719 AM EST Sun Nov 26 2017

Valid 00Z Mon Nov 27 2017 - 00Z Mon Dec 04 2017

...Heavy rain likely this week...

Surface high to the north of the region will slide eastward which
will maintain breezy/windy trades for the next few days. Light to
scattered windward/mauka showers are expected today. Deep moisture
from the ITCZ will surge northward starting later today into the
Big Island and Maui which will increase rain coverage from
southeast to northwest.

An approaching trough from northwest Wed/Thu is forecast to dip
southward but the models split on how much troughing to carry
eastward vs drop southward. The GFS has mostly maintained the
northern portion at the expense of the southern while the
ECMWF/Canadian were opposite. Ensembles still suggest something
like the ECMWF/Canadian which then ties into how a surface low
lifts out of the ITCZ late Thursday into Friday. ECMWF ensemble
mean and GEFS mean have trended more defined with the ECMWF-like
scenario and still prefer this to the GFS solution (which at least
showed a sfc low in recent runs but either weaker and to the west
(00Z) or farther east (06Z)). Ensemble precipitable water plumes
show the GFS among the lowest 10 percent of ECMWF/GEFS members
while the ECMWF wavered in between the middle to highest 10
percent.

00Z GEFS M-Climate QPF percentiles remain at or above the 99th
percentile (some MAX values as well) from about Thursday 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 and assuming a surface low lifts
northward to the west of the region.


Fracasso