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Hawaii Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 1212Z Nov 19, 2014)
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Abbreviations and acronyms used in this product

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
712 AM EST Wed Nov 19 2014

Valid 00Z Thu Nov 20 2014 - 00Z Thu Nov 27 2014

For Hawai'i, the 19/00Z guidance maintained good continuity with
the migration of a mid-latitude upper-level trough and attendant
cold front across Hawai'i---24/12Z to 26/12Z.

The 19/00Z deterministic ECMWF, GFS-Parallel and Canadian attempt
to close off a 500mb low just north of the state around the
25/00Z-25/12Z, then migrate the system slowly northeastward during
the latter portion of the medium range forecast period---days 6-7.
The 19/00Z and 19/06Z GFS are more progressive with the front and
delay the formation of the cutoff feature until it is downstream
of the Islands. The presence of a 500mb cutoff---or lack
thereof---will likely make for a challenging precipitation
forecast between Monday and Tuesday.

At this point, the deterministic guidance is unsure when--and
actually where--this cutoff will develop---with its formation,
depth and forward momentum directly tied to an Aleutian Low's
progression across the Gulf of Alaska. Using a blend of the 19/00Z
ECENS/GEFS will preserve and maintain height falls and support the
timing of the surface front (with upper-level support) from Sunday
into Tuesday afternoon. In the coming days, the forecast may then
require some alterations---with the possible cutoff generating
some additional 'shear-line' clouds and showers in the wake of the
surface frontal passage.

But at this point in time---and 6-7 days out---the depth and
overall size of the cutoff is far from clear---with respect to the
sensible weather impacts it may generate upon Hawai'i.