Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
804 AM EDT Sat Sep 15 2018

Valid 00Z Sun Sep 16 2018 - 00Z Sun Sep 23 2018

Deeper moisture associated with the remnants of Olivia has moved
west of Hawaii as of early this morning. In general, surface
easterlies varying in intensity from 10 to 25 kt will prevail into
next week as Hawaii will largely be under the influence of upper
ridging. By late next week models/ensembles show general agreement
that an upper trough will begin to amplify across the north
central Pacific, with a number of solutions cutting off an upper
low by Thu or Fri. The GFS and ECMWF solutions have converged
relative to this time yesterday, now both showing a cutoff upper
low near 35N by late next week. At the same time models show a
weak easterly wave approaching Hawaii. The degree of northern
stream trough/upper low amplification north of Hawaii will likely
play a role in the amount of deep tropical moisture that is able
to stream northward into Hawaii in association with the easterly
wave and thus the coverage and intensity of any rainfall. Despite
similar solutions with respect to the upper low, the GFS is more
aggressive with northward transport of deeper tropical moisture by
late in the week, and shows somewhat more widespread/heavier
precipitation across Hawaii relative to the ECMWF. At this time
due to the varying deterministic solutions, an ensemble mean
approach is preferred by late next week; ensemble probabilities
suggest the greatest chance for any heavy rains by next weekend
would be across the Big Island.

Ryan