Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
241 AM EST Thu Nov 21 2019

Valid 00Z Fri Nov 22 2019 - 00Z Fri Nov 29 2019

Increasing trades through late this week into the weekend (20-30
kt by Sat-Sun), the result of surface high pressure well north of
Hawaii, should keep a showery pattern in place through at least
early next week. Models continue to show amplification of the
higher latitude flow well northwest of Hawaii by early next week,
with an upper low forecast by all guidance to develop by Mon
night/Tue morning somewhere in the vicinity of 30N/175W. A cold
front should move southeastward toward Hawaii ahead of the
trough/upper low, but should remain at least a few hundred miles
west of Kauai through the middle of next week per the latest
model/ensemble consensus. The ECMWF has backed off the solution it
showed this time last night (which had little ensemble support),
depicting a potential heavy rain event across Hawaii, the result
of another weak upper low arriving from the east and deep moisture
transport ahead of the large scale upper low farther west. The
GFS/ECMWF now agree that the deepest low-level southerly flow and
associated moisture transport may remain mostly west of Hawaii
through the middle of next week (albeit inching rather close ahead
of the aforementioned cold front). In this scenario, the western
islands could see some possible threat of heavy rain by the middle
of next week, but ensemble QPF probabilities continue to keep the
greatest threat of heavy rain west of Hawaii through next Wed.

Ryan