Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
717 AM EST Sun Dec 28 2014

Valid 00Z Mon Dec 29 2014 - 00Z Mon Jan 05 2015

For Hawai'i and much of the Pacific, the 28/00Z ECENS/ECMWF is the
preferred solution. Its deterministic output could be utilized
into day 6 (3/12z) and has been a consistent choice with respect
to the expected flow pattern in the Subtropical and Mid-latitude
Pacific. For day 6 and beyond, the 28/00Z is a solid choice across
the entire Pacific.

The primary feature of the flow this period will be the
progression of migratory systems across the central
Pacific---originating along a resurgent western Pacific jet axis
emerging off the east central Asia. 

The trough that has been on track to pass across Hawai'i in the
31/00z to 1/00Z time frame will be 'followed up' by another
mid-latitude trough in the 2/12z to 3/12z time frame.

Both frontal passages appear to be related to the same complex
long wave trough/ridge interactions occurring over the
high-latitude western hemisphere. In particular, the retrogression
of the pattern over Alaska and the Bering Sea is allowing a
progressive west-to-east pattern along 45N-50N to 'undercut' the
high latitude ridge..

In this medium range forecast period (2/12z to 4/12Z)---a broad
trough and cyclonic flow aloft invof the Kamchatka Peninsula will
be the anchor point for an active westerly Pacific flow and
cyclogenesis near the Dateline. It's the character of the central
Pacific 'wave train' (in my opinion) that favored the 28/00z ECENS
solution longer term versus the 28/00Z GEFS.

Thought the amplitude of the upper-level ridge and the
retrogression of the flow over the Gulf of Alaska---in the GEFS
solution---relies too much on the formation and then incorporation
of a 500mb cutoff low into the mid-latitude flow. Its northward
migration along 155W in the day 5-6 period looks out of place.
Other factors---over the Yukon and west central Canada---appear to
me--to be 'driving things' in the northeast Pacific with respect
to the retrograding ridge.

It will be worth watching...but felt the 28/00Z GEFS/GFS was
'okay' guidance for Hawai'i until 2/00Z. But then, it begins to
influence the mid-latitude flow and the eastern Aleutians-western
gulf of Alaska with erroneous mid-level energy transfer.

Vojtesak