Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
820 AM EDT Sun Oct 29 2017

Valid 00Z Mon Oct 30 2017 - 00Z Mon Nov 06 2017

An amplified, blocky pattern is evident in the upcoming days
across the central Pacific. Initially, an elongated upper trough
will continue to drift away from the Hawai`ian island chain with
the resultant closed low spinning within the mid-latitudes just
east of 150W. Looking upstream, pronounced height falls approach
from east of the International Dateline with a closed upper low
developing around 30N/170W by Tuesday. A gradual northward shift
is noted while a broad upper high strengthens over the islands. By
late Thursday, a general consensus is noted supporting a broad
588-dm ridge settling over the region. This should continue to be
the case into next weekend as the flow across the Pacific remains
very amplified.

At the surface, a weak convergence zone is noted in the local wind
fields which will foster the develop of scattered shower activity.
A gradual shift in the flow takes place into early next week as a
warm advection regime ensues. By Monday night into Wednesday,
south-southeasterly flow strengthens up to around 15 knots which
spreads higher precipitable water values poleward. This should
expand the coverage of showers with frontal activity moving very
close to Kauai by the Wednesday/Thursday timeframe. This is
particularly noted in the 06Z GFS and 00Z CMC/UKMET solutions.
Beyond this period, a strong surface ridge sinks down from the
Aleutians with a 1036-dm high anchoring the northeastern Pacific
by Friday evening into next weekend. The resultant surface
gradients leads to a return to moderate to occasionally stronger
trade winds over the region. Models show broad 20 to 25 knot winds
to overspread the islands although this appears to be accompanied
by a decrease in tropospheric moisture. However, windward showers
will remain likely given the return to a more climatological trade
wind pattern.


Rubin-Oster