Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
827 AM EDT Sun Oct 14 2018

Valid 00Z Mon Oct 15 2018 - 00Z Mon Oct 22 2018

Through much of the next week Hawaii will be situated near the
interface between a tropical/subtropical ridging and higher
latitude westerlies attempting, often unfruitfully, to dig
southward across the central Pacific. An upper-level low initially
centered about 900 miles north-northeast of the state is forecast
by all guidance to move eastward over the next few days, sweeping
a weak cold front across the state and taking the plume of deeper
tropical moisture (and more widespread showers) with it. From
early to mid week, Hawaii will be located in a relative weakness
between to subtropical ridge centers, with drier air gradually
working into the state, and relatively weak (10-15 kt) trades. A
series of amplifying upper shortwaves across the north central
Pacific later in the week will not likely dig far enough southward
to have significant effects on Hawaii, with the associated surface
cold fronts likely remaining north of the state. This will serve,
however, to keep trades across Hawaii relatively weak due to the
lack of strong surface high pressure north of the state. Light
trades and a relatively dry air mass by later this week will serve
to inhibit shower activity, with the Big Island seeing the best
chance of showers in closest proximity to more abundant moisture.
Ensemble means show general agreement that upper ridging may
strengthen across the central Pacific by next weekend, with
heights gradually rising across Hawaii, perhaps setting up a more
typical trade regime.

Ryan