Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
811 AM EDT Tue Aug 26 2014

Valid 00Z Wed Aug 27 2014 - 00Z Wed Sep 03 2014

Aloft, 26/00Z ECENS/GEFS cycle and their deterministic runs
remained in very good agreement concerning the movements of a
broad upper-level ridge in the north central and eastern Pacific
heading into day 6 (1/12Z).

At the surface, the 26/00Z GFS MOS data (extended version)
indicated a slackening of the current trade wind intensity for a
slightly longer period of time (Friday through Sunday) versus the
ECMWF solution.  

After day 6, the 26/00z GEFS/ECENS part ways at 500 millibars
along the Dateline---with the deterministic ECMWF containing a
flatter flow over the mid-latitude Pacific and stronger
Subtropical Ridge solution vs the GFS and its cutoff 500mb low
solution. The GFS carries a well-defined low invof 39N 175W (@
2/12Z) and a weaker downstream Subtropical Ridge axis between
California and Hawai'i.

In turn, these differences translate to widening model/ensemble
spread with respect to latitude--and where tropical moisture
associated with 'Marie' and the remnants of 'Lowell' is displaced
across the southeast Pacific. Both runs displace the moisture and
vorticity along a westward path but do not agree with the
latitude. The GFS suggests the moisture and vorticity reach 30N
150W while the ECMWF suggests more organization of the moisture
westward to ~ 25N 155W.

Recommend a blend of the GFS/ECMWF deterministic runs and their
means through day 5, then reverting to the means and a straight
GEFS/ECENS blend for day 6-7 to mitigate the changes emerging
along the Dateline--and to dampen the sensible weather impacts of
any 'tropicals'--ie 'Marie' and 'Lowell'.

Vojtesak