Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
810 AM EDT Fri Oct 20 2017

Valid 00Z Sat Oct 21 2017 - 00Z Sat Oct 28 2017

...Heavy rain threat for next week...

Breezy trades will slowly subside over the next few days with
generally light windward/mauka showers expected. Next week, a
trough is forecast to dig along/past 165W north of 35N (Mon 12Z)
and likely form a closed low near 30N/160W per the latest
deterministic guidance, which cluster closely together through
early Tuesday. Though there is now consensus on that even
happening, there remains disagreement on how this upper low
meanders for the rest of the week just north of the area. The GEFS
members were closer to the GFS/ECMWF/Canadian which linger the
upper low between 152-162W next Wed-Fri while the ECMWF ensemble
members mostly allow it to lift northeastward. Strong
deterministic consensus and likely strong downstream ridging
suggest that the slower cluster of solutions may be more correct.

As the upper low dives southward and lower level flow veers to
southeasterly, an increase in moisture is expected over the region
next week. Deep ITCZ moisture may get pulled northward ahead of
the front, which may push through the whole island chain. Should
the front actually make it east of the area, then the NW flow
behind it should lessen the heavy rain threat. However, given the
spread in the ensembles (including some members farther west than
the 00Z GFS/Canadian), the moisture axis could remain over at
least part of the Hawai'i later next week.


Fracasso