Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
149 AM EDT Tue Jul 21 2020

Valid 00Z Wed Jul 22 2020 - 00Z Wed Jul 29 2020

A broad weakness in the upper-level ridge will traverse Hawaii
over the next couple days, resulting in a temporary weakening of
the trades, and perhaps some slight enhancement in shower activity
across the state. Later in the week, trades should pick up once
again as the upper-level weakness moves west of the state. The
most significant aspect of the forecast for Hawaii over the next
week will be the eventual track of Tropical Storm Douglas, and any
potential impacts on Hawaii. The National Hurricane Center is
forecasting the system to be near approximately 17N/147W Saturday
afternoon as a tropical storm. After that time, model/ensemble
guidance are reasonably well-clustered in bringing whatever is
left of the system near or just south of the Big Island on Sunday,
and then south of the other islands on Monday. The strength of the
system by that time is highly uncertain, with some guidance
holding onto a closed low circulation longer than others. Moisture
associated with the system may result in the potential for heavy
rains and possibly flooding across the Big Island Saturday night
into Sunday. Any eventual impacts on Hawaii from Douglas will be
highly dependent on the eventual track and intensity of the
system. If the track shifts farther south, effects on Hawaii would
be limited. Please refer to advisories from the National Hurricane
Center for the latest information on Tropical Storm Douglas.

Ryan