Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
728 AM EST Mon Feb 20 2017

Valid 00Z Tue Feb 21 2017 - 00Z Tue Feb 28 2017

Gusty winds from the north and northeast will linger for the next
few days as a lead and subsequent 1030mb surface high slides
eastward along 30N. Another shortwave will dig and deepen to the
north and then northeast of the state midweek, closing off about
900 miles to the NNE. This upper low is forecast to sink southward
to near 32N but then pull eastward which should keep the tropical
moisture plume (mostly associated with the leftover front in the
near term) to the southeast of the area. However, the upper
pattern remains rather complicated by another upper low off
British Columbia that may (per the ECMWF) or may not (per the
other models) slide westward along 40N.

Regardless, the ensembles show yet another shortwave to drop
southward from the mid-latitudes on Friday into Saturday around
160W which looks to sink southward toward 30N. The deterministic
00Z ECMWF was farther north (around 34N) than the GFS/Canadian
(near or just south of 30N), likely affected by the prior British
Columbian upper low. The ensembles generally clustered around
their parent model. Uncertainty is high with the evolution of
these closed features.

Moisture associated with the next systems to the northwest may
still stay to the northwest by next Sunday/Monday per even the
more southerly GFS but tropical moisture from the lower latitudes
is forecast to slowly lift northward toward the Big Island. This
could leave Hawai'i in between the two in a drier pattern but that
window appears to be closing next week.


Fracasso