Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
722 AM EST Wed Dec 13 2017

Valid 00Z Thu Dec 14 2017 - 00Z Thu Dec 21 2017

A cold front is currently moving through Hawai'i and will bring
scattered showers to the region. An upper trough to the
north/northeast will form an upper low around 151W by tomorrow and
then slowly drift west-northwestward into the weekend, just to the
north of Hawai'i. By Sunday the upper low should lift northward
and become absorbed into a a trough axis to the north. That trough
may close off an upper low on its southwest tail just to the north
or northwest of the region next Tuesday. 00Z ECMWF/Canadian were
preferred with their handling of the closed low - a weaker one
near 24N/160W and a stronger one around 37N/150W by 00Z/20 rather
than just one per the 00Z-06Z GFS.

Behind the front today, breezy northwest winds will bring in drier
and cooler air and veer to the north and northeast tomorrow into
Thursday when winds may exceed 30 kts with higher gusts. As the
closed low approaches from the east, moisture will wrap back
around the surface low from the north but the heaviest rain on the
east side of the upper low will remain displaced to the northeast
of the region.

The next upper trough or upper low next week has the potential for
much more precipitation given the location to the west of the
region. 00Z ECMWF indicates the potential for several inches of
rain over some of the islands while the GFS was drier given its
lack of a defined feature. 00Z ECMWF ensembles show a probability
of at least an inch of precipitation exceeding 30% in the 72 hrs
ending 00Z/21. Again, prefer a solution near the 00Z Canadian and
ECMWF.


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