Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
823 AM EDT Sun Oct 04 2015

Valid 00Z Mon Oct 05 2015 - 00Z Mon Oct 12 2015

The 4/00Z deterministic GFS/ECMWF and their means are in very good
agreement with the pattern across the eastern half of the Pacific
Basin until the end of day 4 (9/00Z).

Both deterministic solutions identify the key synoptic-scale
features responsible for the movement and track of the current
tropical systems near the Hawai'i forecast area. The closed low
invof 41N 151W migrates northward---anchoring in the far northwest
Gulf of Alaska. And the secondary mid-level trough and low-level
front---located west of 160W along 30N---remains 'on-track' to
reach the Islands on Tuesday.

Please refer to the Central Pacific Hurricane Center (CPHC), for
the latest information regarding sensible weather impact for
Hawai'i---with respect to 'Oho' and 'Eight-C'.   

---Days 5-7---
Downstream of the closed low and secondary mid-level trough, an
expansive mid-level ridge---centered invof 29N 128W--- will
gradually retrograde southwestward. This ridge looks to bring back
more of a 'normal' tradewind regime. The 4/00Z ECENS/GEFS differ
on the impact of this ridge as a 'blocking' feature in the east
Pac---an amplified projection of the longer-term flow pattern. For
now, would lean towards the ECENS solution for a day 6-8
transition to the 'more-amplified' pattern in the east Pac.

Of note,
The deterministic guidance continues its struggles beyond the day
3 time frame---with the moisture/energy transfers between Tropics
and mid latitudes. The 4/00z forecast cycle is no exception...with
the ECMWF a good day faster than the GFS with the ejection and
infusion of energy (from 'Oho') into the downstream mid-latitude
westerlies. These timing differences primarily impact the
Mainland---but is the primary reason--- to suggest using an
ensemble mean approach beyond day 4.  

Vojtesak