Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
824 AM EDT Sat Apr 28 2018

Valid 00Z Sun Apr 29 2018 - 00Z Sun May 06 2018

The large scale pattern across the central and north Pacific will
remain relatively unchanged through the next week. Models/ensemble
show a strong signal for a broad area of negative height anomalies
persisting in the vicinity of 35-40N/150-170W. The persistent
large scale trough will be maintained by a series of
mid/upper-level shortwaves that traverse the northern stream flow
across the Pacific and then amplify as they encounter the existing
large scale cyclonic flow in place north of Hawai'i.

Initially, satellite imagery this morning show a relatively strong
upper-level low in place approximately 500 miles north of Hawai'i.
South of the upper low, a weakening surface front and a
pre-frontal trough are crossing Hawai'i, with deep tropical
moisture along and ahead of the front. As the initial upper low
weakens and becomes absorbed in the higher latitude westerlies,
and a second shortwave enters the large scale mean trough early
next week, models show the surface front and the associated deep
moisture gradually lifting northward across Hawai'i over the next
couple days, and lingering into next weekend as it gradually
washes out. Guidance shows low-level winds remaining relatively
light and variable in the vicinity of the surface front as it
washes out, thus the potential for sustained orographic rains
appears fairly limited, despite the deeper moisture. Nonetheless,
given the deeper moisture overspreading the state, expect the
potential for at least brief locally heavy rains through much of
the next week across the state.

Ryan