Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
754 AM EDT Thu Oct 24 2019

Valid 00Z Fri Oct 25 2019 - 00Z Fri Nov 01 2019

A relatively strong upper trough moving through the polar
westerlies north of the islands will maintain lighter than average
trades through Friday.  As a result, showers will tend to focus on
sea/land breeze boundaries, though conditions overall are fairly
dry, so rainfall should be mostly scattered.  The guidance
indicates an area of deeper tropical moisture sliding westward
across the Big Island later Friday and Friday night, which may
support slightly higher rainfall rates in any shower activity.  

Over the weekend, this trough will fill and lift northward,
returning the state to a more normal trade wind regime, with
showers mostly confined along windward/mountain locations. During
early next week, an amplified trough will push across the central
Pacific and push a cold front southward toward the northwest
islands.  There's more uncertainty during this period as
differences exist among the guidance with respect to how much
energy drops southeastward over the state associated with energy
along the southern end of the trough.  The ECMWF remains the most
aggressive, closing off a low and inducing a frontal wave just
north of the state. The main impact of the differences will be on
the strength of the trades, with the ECMWF weakening them more
than the Canadian/GFS and the majority of ensemble members (there
is pretty good agreement that the front itself will remain north
of the islands).  Generally think the ECWMF is a bit too strong,
but believe that some short wave troughing will set up/move across
the state, which should reduce the trades to slightly below normal
during the early-mid part of next week.

Klein