Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
803 AM EDT Mon Oct 22 2018

Valid 00Z Tue Oct 23 2018 - 00Z Tue Oct 30 2018

Dry air at the mid-levels has overspread Hawaii as evident on
latest water vapor satellite imagery early this morning. A plume
of deeper moisture is noted several hundred miles east of the Big
Island, associated with an easterly wave. Farther north, an active
mid-latitude flow regime is also evident on satellite well north
of Hawaii. Moderate trades are expected to increase a bit (into
the 20-30 kt range) by Tue-Wed as the easterly wave passes south
of Hawaii. On the eastern side of the wave, deeper moisture will
once again begin to spread north across portions of Hawaii by mid
to late week. The deepest moisture associated with the wave will
affect the Big Island, where PWs may rise to near 2.00 inches late
Wed as the wave passes. ECENS probabilities suggest the best
chance for locally heavy rains across the Big Island will be
Wed/Wed night, while GEFS probabilities indicate that the
potential for locally heavy rains could persist into Thu-Fri.

Models show relatively good consensus by late in the week with a
trough of moderate amplitude developing across the north central
Pacific by Fri-Sat, and the associated cold front nearing (but
perhaps remaining just north of) Hawaii. As the mid-latitude flow
becomes more progressive, ensembles show general agreement that a
second, similar trough will amplify across the north central
Pacific by Sun-Mon. There is some consensus that this second
trough may be quite a bit more amplified than the late week one,
with the potential for more significant impacts on Hawaii, just
beyond the end of the forecast period.

Ryan