Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
655 AM EST Sun Nov 05 2017

Valid 00Z Mon Nov 06 2017 - 00Z Mon Nov 13 2017

Rex block pattern with an axis well west of Hawaii north to Alaska
is forecast to propagate slowly westward through the next week,
keeping the flow pattern across Hawai'i relatively stable. Upper
ridging centered overhead is forecast by all guidance to slowly
weaken through the week, although, weakly positive height
anomalies are forecast by the ECMWF ensemble mean to remain in
place across the Islands - likely an effect of the upstream area
of strong negative height anomalies near 160-170E. At the surface
a weakening high initially centered well northeast of Hawai'i will
result in slightly weakening easterlies as the pressure gradient
lessens, from 20 kt today to 10-15 kt by the middle of next week.
This flow pattern will keep relatively low precipitable water
values in place as guidance shows very dry air (PWs near or even
less than 1 inch) originating in the northeastern Pacific
advecting across Hawai'i. Therefore, expect showers to be
generally focused along windward terrain, becoming a bit more
sparse through the week. A trough forecast to amplify across the
northeastern Pacific by early-mid next week will force the tail
end of a cold front southward toward the Islands, although the
model consensus is that the front should remain well north of the
Islands through next weekend as it washes out.

Ryan