Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
232 AM EDT Fri May 08 2020

Valid 00Z Sat May 09 2020 - 00Z Sat May 16 2020

Surface high pressure is expected to persist north of Hawaii
through the middle of next week, before perhaps spreading
southward closer to the state. This setup will allow light to
moderate trades to persist, with relatively sparse moisture
supporting scattered windward and mauka showers. As high pressure
weakens and spreads more across Hawaii by the middle to latter
portion of next week, trades should weaken a bit. There is some
disagreement among ensemble guidance as to the large scale flow
across the north central Pacific by later next week. The ECENS
keeps a stronger ridge in place, while the GEFS weakens the ridge
a bit more by that time, developing a broad area of modestly
cyclonic flow and lower heights just north of Hawaii. These
differences may manifest in the potential (or lack thereof) for a
cold front to approach the state toward the end of the extended
forecast period and beyond. At this point confidence is low given
the ensemble spread. The Rex Block from the North Pacific to the
Arctic Ocean is forecast to persist, with the arctic ridge perhaps
becoming the dominant anomaly center. This would favor somewhat
more progressive flow farther south, perhaps limiting the degree
of height falls toward Hawaii (more like the ECENS scenario).
Future ensemble runs will likely shed additional light on the
setup for late next week.

Ryan