Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
820 AM EDT Fri Oct 25 2019

Valid 00Z Sat Oct 26 2019 - 00Z Sat Nov 02 2019


Over the weekend, a trough and trailing sfc boundary will fill and
lift northward, with a low level ridge building in from the
northeast. This allows a returning the state to a more normal
trade wind regime, with showers mostly confined along
windward/mountain locations.

During early next week, a trough aloft will develop near the
islands and move slowly. There's uncertainty regarding the
amplitude of the trough as the ECMWF is not as amplified as the
GFS, with the ECMWF more amplified than the 00z operational ECMWF.

The main impact of the differences will be on the strength of the
trades, with periods when the weakness aloft leads to surface
winds becoming lighter than usual.

Later next week, slight retrogression of the mid level waves
allows the low level flow to have a bit more southerly component,
with both the 06z GFS and 00z ECMWF advecting higher precipitable
water values into the big island.  This leads the 00z ECMWF to
indicate higher rainfall amounts later next week in upslope areas
of the big island.

Petersen