Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
728 AM EST Sun Dec 25 2016

Valid 00Z Mon Dec 26 2016 - 00Z Mon Jan 02 2017

Through the middle of next week, persistent upper ridging will be
the norm before the pattern breaks down and becomes more blocked
in nature. A band of height falls crossing 40N/160W on 28/1200Z
will gradually see a shortwave pinch off from the prevailing
westerlies while sinking southward in time. All recent solutions
agree on the evolution of a strong closed low by late Wednesday
with the potential for mid-level heights to drop below 546-dm
depending on the model. The core of the circulation should
retrograde along 30N latitude thereafter and remain north of the
Hawai`ian island chain. The position of the system is generally
agreed upon except the 00Z UKMET was displaced westward while the
00Z ECMWF resided well west of its ensemble mean. Toward next
weekend, this closed low should still remain out of the picture
with residual troughing across the state to conclude the year.

Looking at the surface, a strengthening anticyclone translating
away from Hawai`i will help increase the easterly flow into early
next week with models suggesting winds into the 20 to 30 knot
range at times. By Tuesday into Wednesday, an even strong ridge,
perhaps over 1045-mb, builds east of the International Dateline
helping shift winds to the more northeasterly direction. These
stronger winds should particularly affect the northern most
islands as the baroclinic zone sweeps east of the state. Most
solutions agree on the tail end of this boundary moving through
but it appears rather sheared.

Precipitation during the period should primarily be driven by the
climatological trades although the decrease in tropospheric
moisture could somewhat hinder the overall coverage. As the
frontal zone approaches late in the period, moisture does begin to
increase back toward 1 inch plus precipitable water values. Models
seem to keep the better activity further along the front where the
stronger mid-level forcing is in place.


Rubin-Oster