Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
801 AM EDT Mon Sep 18 2017

Valid 00Z Tue Sep 19 2017 - 00Z Tue Sep 26 2017

Large scale flow over the central Pacific remains in good ensemble
agreement for the next seven days. Strong upper/sfc high to the
NNE of the region will slide eastward and weaken by the weekend
which will allow a weakness aloft to move westward and then
northwestward around the high's circulation to the northeast of
the area. By next Monday, the ensembles showt this weakness
extending back to the island chain -- 06Z GEFS show the
probability of 500mb heights below -1 standard deviation rises to
about 40% by late Sunday. Trades will be higher than average for
most of the week due to the strong pressure gradient but relax by
the weekend as the 1031-33 mb sfc high moves east of 140W by
Saturday. Hawai'i should remain in between the axis of moisture
well to the northwest of the area (associated with a strong north
central Pacific system) and the ITCZ, but the possibility remains
of increased moisture (temporarily) to at least the Big Island
mid/late week. Generally, windward/mauka showers are expected
(though some leeward as well given breezy trades) with generally
light accumulations but some higher amounts may be possible on the
Big Island.


Fracasso