Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
716 AM EST Thu Nov 23 2017

Valid 00Z Fri Nov 24 2017 - 00Z Fri Dec 01 2017

The persistent positive height anomalies to the northwest of
Hawai'i will weaken and be replaced by an upper low near the
Aleutians and Bering Sea next week as elongated SW-NE troughing
remains over the 50th state. 00Z GEFS/ECMWF ensembles show this
evolution rather nicely with expected detail differences. A blend
of the 00Z guidance should suffice this period.

The 1034mb sfc high to the northwest of the region will be
reinforced this weekend and slide southeastward then eastward
along 33N next week which will maintain breezy/windy trades into
next week. Light to scattered windward/mauka showers are expected
with only some spillover to leeward areas possible as the overall
airmass remains dry. By about next, ensembles show an increase in
column moisture as a remnant boundary lifts back to the northwest
from near the ITCZ. Troughing or even a weakly closed low may
retrograde to just west of the area midweek next week, which could
act to increase rain coverage from southeast to northwest. The
GFS/ECMWF have wavered on how much to increase precipitable water
values and the latest 00Z ECMWF was more aggressive than the GFS
and also a bit more aggressive than the ensemble means. A blended
solution may still be appropriate since the pattern suggests the
potential for at least some modest to locally heavy rain next
week. This may persist through the end of the week as the
ensembles maintain higher than average PW values into December,
especially over the Big Island/Maui.


Fracasso