Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
713 AM EST Wed Feb 13 2019

Valid 00Z Thu Feb 14 2019 - 00Z Thu Feb 21 2019

...Wet pattern for the Aloha state with locally heavy rain
possible into next week...


Rex block pattern is likely to remain in place over the central
Pacific with ridging/upper high just south of the Aleutians and an
upper low very close to Hawai'i that is forecast to retrograde
westward (and be reinforced from the north) underneath the ridge.
The 00Z/06Z guidance suite were fairly close in their evolution of
the lead upper low (currently over the region) but was shifted a
bit southward from 24 hrs ago. The upper low should lift northward
next Tue/Wed away from the area, allowing heights to rise but
perhaps dragging in a partial moisture feed from the ITCZ.

This scenario would maintain below average precipitable water
values and breezy northeasterly trades for especially the western
islands as a surface low organizes to the east of the Big Island
late Thursday into Friday. With a shift in the guidance, a track
along the north side of the island chain was the consensus which
would mean an increased chance of rain and locally heavy rain as
well. Additional weaker areas of low pressure may try to lift
along the boundary to the east of the Big Island that may drift
westward in time. This would maintain the heavy rain threat via a
southerly moisture surge just as the wrap-around moisture departs
to the northwest. Multi-day rain totals may exceed several inches
over favored terrain (northeast/north-facing slopes).
Deterministic models show the heaviest rainfall to the
north/northeast/east/southeast of the state but smaller-scale
features will modulate the daily totals.

Fracasso