Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
723 AM EST Sat Dec 24 2016

Valid 00Z Sun Dec 25 2016 - 00Z Sun Jan 01 2017

Much of the first half of the forecast period will feature a
persistence of ridging aloft. This will gradually break down in
response to a lowering of heights to the north of the islands
across the mid-latitudes. All model solutions agree on a split
occurring with a closed low sinking southward reaching the
vicinity of 35N/145W by Thursday afternoon. Like yesterday, the
06Z GFS/GEFS mean are to the southwest of the consensus while now
being supported by the 00Z CMC. Unlike the system a couple weeks
back, this closed low should remain north of the Hawai`ian
islands, at least through the remainder of the year based on
examination of the ensemble spaghetti plots.

At the surface, an uptick in the intensity of the trade winds is
likely later into the weekend as well as early next week given a
strengthening of the ridge to the northeast. Generally speaking,
the consensus suggests easterly flow picking up to around 25 to 30
knots across the region before shifting to more northeasterly as
an even stronger anticyclone (1042-mb plus) builds just east of
the International Dateline by mid-week. Depending on the position
of the mid-latitude closed low, a cold frontal passage is likely
on Thursday before the boundary begins to shear or become less
defined. Looking at the threat for precipitation, in spite of
periods of enhanced trades, there is a decrease in tropospheric
moisture as sub 0.75 inch precipitable water air infiltrates the
region. In spite of the diminishing supply of moisture, expect the
usual trade driven activity with perhaps a brief increase in
coverage along the frontal zone late next week.


Rubin-Oster