Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
823 AM EDT Mon Sep 17 2018

Valid 00Z Tue Sep 18 2018 - 00Z Tue Sep 25 2018

Weak upper-level ridging will be generally dominant across Hawaii
over the next week, with increasingly amplified flow setting up
farther north across the Pacific. With surface high pressure
remaining anchored north to northeast of Hawaii, low-level
easterlies will be in place through the period, with trades
varying in intensity generally in the 15 to 25 kt range. Models
still show an upper low cutting off well northwest of Hawaii by
Thu, at the same time a relatively weak easterly wave traverses
Hawaii, bringing an increased chance of showers Wed-Thu. The best
moisture and greatest coverage of shower activity looks to remain
confined to the Big Island. Locally heavy rain remains possible,
although the GFS continues to deeper moisture across the Big
Island and heavier rainfall totals relative to the ECMWF. Drier
air should quickly overspread Hawaii once again by the weekend,
however. A number of model/ensemble solutions show the potential
for continued upper-level flow amplification into early next week,
with another cutoff upper low possible northeast of Hawaii. At
this time the sensible weather implication of this second upper
low look relatively limited for Hawaii, with relatively dry air
and light to moderate trades continuing into early next week.

Ryan