Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
717 AM EDT Thu Jun 23 2016

Valid 00Z Fri Jun 24 2016 - 00Z Fri Jul 01 2016

The Subtropical Ridge covering the majority of the eastern Pacific
will reach its weakest point along 150W --- in the 26/12Z-27/00Z
time frame --- per the (23/00Z cycle) deterministic GFS/ECMWF.
This should dampen the intensity of the Trades over the weekend.

The reason---a vertically-stacked low in the Gulf of Alaska and
its associated surface trough are expected across the northeast
Pacific. The low is expected to weaken and fill --- with the
23/00Z GFS/ECMWF both in good agreement.

However, 
the 23/00Z ECMWF threw a new wrinkle into the forecast the middle
of next week by allowing secondary shortwave energy originating
east of Kamchatka to reinforce the trough invof 150W-155W by day
5. The 23/00Z GFS is significantly slower (a full day to 1 1/2
days slower) with this feature --- which allows the Subtropical
Ridge to slowly rebuild north of Hawai'i next Tuesday and
Wednesday (days 5 and 6).

The 23/00Z ECENS/GEFS means actually support the ECMWF here. Using
a 50/50 blend of these means on/after 29/00Z (mid-point day5) may
be the better way to go. That is --- until the mid-latitude north
Pacific settles down with the solutions regarding this secondary
shortwave energy transfer from the southern Bering Sea to the Gulf
of Alaska.

The 22/00Z cycle guidance (yesterday's solutions) found more of a
middle ground with this secondary shortwave. But as the 23/00Z
cycle illustrates --- the details of the shortwave's influence
downstream are yet-to-be determined and do have a temporary but
subtle impact on the Subtropical Pacific.

Vojtesak