Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
828 AM EDT Sun Jul 06 2014

Valid 00Z Mon Jul 07 2014 - 00Z Mon Jul 14 2014

The 6/00Z forecast cycle did not disappoint with respect to the
overall spread of the subtropical high pressure ridge and a
dominant surface cell invof 41N 142W between day 3 (9/12Z) and
early day 5 (HST--11/12Z).

Since both deterministic runs continue to project an impressive
post-frontal strengthening of the surface high invof 41N-42N and
mid-140s W, both could be used without regret with respect to
timing the resurgence of fresh trades across the Islands on/by
Wednesday.

BUT...
Chaos 'reigns supreme' across the far northeast Pacific after day
5. And to a lesser extent, large spread continues along the ITCZ
and easterly wave energy embedded within it (along 15N).

The 6/00z ECMWF-GFS-Canadian deterministic runs and their
ensembles paint completely different pictures in the Gulf of
Alaska and mid-latitude Pacific. For the medium range Hawai'i
forecast and sensible weather outlook, the pattern is not that
complicated. But using a deterministic approach with respect to
the expanse of the Subtropical Ridge along 35N from the Mainland
to 160 E longitude looked risky.

In this day 5-7 forecast period, the outcome in the Gulf of Alaska
and amplitude of the flow becomes more-and-more an exaggerated
solution if the deterministic ECMWF is followed verbatim (for the
surface pattern). Its surface ridge breakdown looked premature (on
day 6); with emphasis on a deep surface cyclone and discernible
surface front extending southward along 150W to ~35N. On the flip
side, the deterministic GFS and Canadian maintain a flat but
substantial ridge axis along 35N with a definitive frontal wave
and PROGRESSIVE surface trough originating along 150W but not
extending equatorward of 40N until reaching 130W-135W. Therefore,
appreciable forecast challenges remain linked to energy transfer
across the mid-latitude Pacific and related to the replacement of
an exiting upper-level trough in the southeastern gulf of Alaska
with 'new' energy emerging in the southern Bering Sea and central
Aleutians.

The secondary forecast challenge lies across the tropical Pacific
on either end of the mid-level Subtropical Ridge. Along the
western fringes of the Subtropical Ridge, the Canadian, GFS and
ECMWF have generally different viewpoints with how/when to inject
tropical energy into the mid-latitude westerlies off the coast of
Japan. And along the eastern end of the Ridge, residual vorticity
from 'Douglas' and a compact disturbance moving westward between
10N and 15N generate considerable spread.

For today, recommend an equally-weighted blend of the 6/00z
NAEFS-ECENS and GEFS to account for the spread after day 5.

Vojtesak