Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
722 AM EST Fri Dec 23 2016

Valid 00Z Sat Dec 24 2016 - 00Z Sat Dec 31 2016

The presence of a stout 588-dm ridge will dominate the islands
throughout much of the period. The attendant surface anticyclone
north and east of Hawai`i should lead to an uptick in the trade
winds with models suggesting 20 to 30 knots expected by late in
the weekend. This feature should gradually migrate eastward in
response to lowering heights across the mid-latitudes by the
middle of next week. In the wake of this next system, an even
stronger surface ridge is being forecast to cross the
International Dateline around 40N latitude with an increase in
east-northeasterly winds over the northern most islands. Toward
the end of the work week, the influence of the Central Pacific
system to the north will carry a possibly shearing frontal zone
through the region, particularly in the 06Z GFS run. In terms of
guidance, the most outlying solution remains the 00Z CMC which is
much more progressive, including relative to its own ensemble
mean. Recent ensemble means all show indications of this split in
the mid-latitude flow taking shape, especially the 06Z GEFS/00Z
CMC ensemble means.

Looking at the precipitation threat, the usual trade wind driven
activity should be the norm with emphasis across areas of
orographic ascent and along any mesoscale boundaries. However, the
guidance does show a decrease in precipitable waters from the 1 to
1.25 inch range to 0.75 inches by late in the weekend into early
next week. This should be a mitigating factor in more widespread
activity across the region. With the possible frontal passage
toward the end of next week, there is a brief increase in
moisture, but the better forcing should remain up in the
mid-latitudes.


Rubin-Oster