Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
809 AM EDT Sun Jun 02 2019

Valid 00Z Mon Jun 03 2019 - 00Z Mon Jun 10 2019

Most guidance shows reasonable continuity and agreement with the
expectation of a trade wind pattern of varying strength and
periods of primarily (but not exclusively) windward-focused
rainfall during the next week. 

Progression of mid-latitude surface highs will lead to modest
weakening of trades at the start of the week, some strengthening
into midweek, and then a weaker trend late week when high pressure
settles over the eastern Pacific and a front approaches/stalls to
the northwest of the main islands.  The surface ridge may build
back to the southwest during the weekend to strengthen trades
again in that time frame.  From Friday through the weekend the one
model difference of note is that the 00Z GFS brings the front
closer to the state than other guidance as supporting upper
troughing becomes more amplified than consensus--resulting in
weaker trades.  The 06Z GFS is more comparable to favored
consensus that includes the 00Z ECMWF and 00Z GEFS/ECMWF means.

Late Tuesday into Thursday remains the most favorable period for
some enhanced rainfall as consolidating shortwave energy
approaches and crosses the main islands.  GFS/GEFS-based guidance
shows precipitable water values a little higher than the
ECMWF/ECMWF mean but in principle they are similar in representing
the increased moisture expected with the shortwave.  Showers will
likely become lighter during the late week and weekend period as
heights aloft trend higher and precipitable water values gradually
decrease.  Next weekend guidance still disagrees over the precise
extent to which upper ridging to the west builds over the area. 
Trends from yesterday show a bit of a delay so it may be
reasonable to lean more toward the 00Z GEFS mean versus the
stronger/eastward ridge seen in the 00Z CMC/CMC mean and 06Z GFS.

Rausch