Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
812 AM EDT Thu Apr 13 2017

Valid 00Z Fri Apr 14 2017 - 00Z Fri Apr 21 2017

Expect potential for some locally moderate to heavy shower
activity during the next couple days as a shortwave trough aloft
moves over the state.  Trades should be moderate to light with a
hint of surface troughing over the islands, so land and sea breeze
boundaries may provide a greater than average focus for rainfall. 
From Sunday into Tuesday trades will strengthen as high pressure
building into the central Pacific reaches north of the islands by
early Tuesday.  In previous days there was a wide timing spread
for this high but faster guidance trends toward the ECMWF/ECMWF
mean have yielded better consensus today.  The stronger trades
will support greater windward focus for showers.  By
Tuesday-Thursday models/ensembles have been trending southward
with a central Pacific storm whose cold front may approach the
state from the northwest toward the end of the period.  The 00z
CMC is not too far off but the 00z/06z GFS and 00z GEFS mean are
on the faster side of the envelope with the front due to a more
amplified trough aloft/farther south upper low.  The 00z GFS
evolution yielded a pocket of 500mb heights reaching 5+ standard
deviations below normal while the 00z ECMWF has more plausible
lowest standardized anomalies in the -3 to -3.5 range.  Also the
ECMWF-based guidance has had a more stable handling of this system
in recent days, with less pronounced run to run changes, so at
this time would lean more toward the ECMWF/ECMWF mean.

Rausch