Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
820 AM EDT Thu Oct 19 2017

Valid 00Z Fri Oct 20 2017 - 00Z Fri Oct 27 2017

...Heavy rain threat for next week...

Breezy trades will slowly subside by the weekend as a 1034mb
surface high (06Z OPC analysis) weakens and moves southeastward
and then eastward along 33N later this week. Generally light
windward/mauka showers are expected. Next week, a trough is
forecast to dig along/past 165W north of 35N (Mon 12Z) but the
ensembles (and deterministic models) continue to diverge on
whether to continue digging it to/south of 30N or begin to lift it
back eastward then northeastward (generally north of 30N). The 00Z
models have completely flipped since 24 hrs ago and now the ECMWF
was most aggressive while the GFS/Canadian and even UKMET were
quicker than the ECMWF (but at least more consistent). The 00Z
ECMWF lies on the most edge of the multi-center ensemble spread
and is not preferred at this time, given the uncertainty and
inconsistency. The 06Z GFS and 00Z Canadian align near the UKMET
trough axis and are the preferred cluster. This also lies near the
06Z GEFS mean and 00Z ECMWF ensemble mean. This would take the
associated surface front into the NW islands around next Tuesday
but it is unclear how much of a SE progression it would make.
Nevertheless, southeast flow should increase moisture into the
whole island chain which may support several days of widespread
showers and embedded heavier rain.


Fracasso