Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
751 AM EDT Mon Apr 22 2019

Valid 00Z Tue Apr 23 2019 - 00Z Tue Apr 30 2019

Model and ensemble guidance seem well clustered into Friday,
bolstering forecast confidence. A favored composite shows that
surface high pressure bridging to the north and northeast of the
state is supportive of seasonal to breezy island trades under a
mean upper level ridge. This stable pattern offers passing rounds
of enhanced moisture and windward terrain focusing showers and
some upper trough energy will temporarily dent the upper ridge
Tuesday/Wednesday.

Amplification by next weekend as shown in most guidance is
expected to lead into a transition to a pattern with more
sustained moisture influx to fuel potential for widespread and
heavier rainfall statewide this weekend into early next week. This
would occur as a deep layered closed upper low develops to the
northwest of the state and with approach of a low trailing cold
front and disruption of trades. There is more ample forecast
spread with the aspects of upstream closed low development that
effect the progression of the front underneath. The 00 UTC
ECMWF/UKMET are less amplified with the flow as the 06 UTC GFS or
00 UTC Canadian with the closed low southward digging/settling.
Prefer a solution on the more amplified side of this forecast
envelope considering favorable upstream ridge building and stream
separation. This solution is also supported by GEFS/NAEFS and a
reasonable number of ECMWF ensemble members, albeit in less
certain flow.

Schichtel