Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
816 AM EDT Sun May 13 2018

Valid 00Z Mon May 14 2018 - 00Z Mon May 21 2018

Trades will gradually trend lighter during the first half of the
week as high pressure initially to the north of the state weakens
while tracking to the northeast.  Lightest winds will likely be
around Wednesday when upper troughing briefly dips toward the
region and potentially supports a weak surface trough over the
area.  Sea/land breezes may be possible at that time.  High
pressure rapidly building eastward behind a cold front that passes
by to the north will bring a return of moderate to brisk trades
later in the week.  By next weekend guidance diverges on details
of mid-latitude Pacific flow and effects on the east-west surface
ridge.  The 06z GFS/00z GEFS mean are in the minority with more
upper troughing, a weaker surface ridge, and thus weaker trades
over Hawai'i.  The 00z GFS/ECMWF/ECMWF mean/CMC/CMC mean are more
agreeable in maintaining trade strength through Sunday though they
still differ on some details over the mid-latitudes.

Expect mostly light and windward-focused showers during the period
except perhaps around midweek when trades will be lightest. 
Precipitable water values should settle at slightly below normal
values for the time of year until late week when a pocket of
somewhat higher moisture passes through from the east/southeast. 
The ECMWF continues to be faster than GFS/GEFS mean runs with a
compromise preferred until any notable trends become apparent. 
Deep moisture will likely return to near or slightly below normal
values next weekend.

Rausch