Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
825 AM EDT Tue Aug 18 2015

Valid 00Z Wed Aug 19 2015 - 00Z Wed Aug 26 2015

The 18/00Z GEFS/ECENS and their deterministic runs continue to
carry the quasi-stationary TUTT cell another couple of days invof
30N 160W. This will allow a westerly component to the mid-level
level flow to enhance rainfall/convective potential for
west-facing slopes.

Not sure if the deep-layered ridge centered near 46N 146W will be
the catalyst for 'change' and shifting the TUTT cell westward. Or
will a burst of moisture and energy originating in the Tropics
(between 140W-150W) be the reason for the movement? This is the
difference---the former is the GFS deterministic solution
(mid-latitude driven change)---the latter, the deterministic ECMWF
solution. I would hedge away from the GFS/GEFS here because of the
depth/strength of the deep-layered ridge (596dm +). Empirical
observation tells me that the system in the Gulf of Alaska will
never be as deep/strong (albeit---a mid-August system) to
significantly erode and 'jostle' such a strong synoptic-scale
feature. Or to the 'perfect prog' extent---to produce an outcome
that permeates to the Tropics by day 4. In short...the GFS
solution has too much 'linkage' and 'connectivity' between 10N and
50N along the entire stretch of 150W to take as 'perfect prog' for
Hawai'i this coming weekend. .

Recommend using a blend of the 18/00Z ECENS/ECMWF to depict the
subtle changes in the flow over the central Pacific (between
30N-40N) after day 3. This implies a renewed 'burst of convection'
for Hawai'i this weekend---and locally heavy rainfall
potential---continuing into the day 6-7 forecast period (next
Mon/Tue). Mind you---not a certainty, but a potential 'for'.

Vojtesak