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Hawaii Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1222Z Oct 17, 2014)
 
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Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
822 AM EDT Fri Oct 17 2014

Valid 00Z Sat Oct 18 2014 - 00Z Sat Oct 25 2014

... 'Ana' to create sensible weather impacts for Hawai'i this
weekend ...

The 17/00Z ECENS/GEFS formed a general consensus approach---though
their deterministic runs anticipated different outcomes for track
and forward speed of 'Ana' for days 3-7. Please refer to the CPHC
for the latest forecasts and most current information concerning
'Ana'.

The shorter-term guidance---with 'Ana' passing south of the
state---was well within the guidance envelope---supporting the
official CPHC track, and would continue to suggest that 'Ana' will
generate substantial periods of very heavy rainfall and strong,
gusty winds on Saturday and Sunday. The sensible weather impacts
shift westward on Monday and Tuesday---focusing on Kauai and
points northwestward.

Medium Range (beyond day 3)...
A large portion of the evolving medium range storm track---will
'key off of' the next 48 hours and where 'Ana' tracks invof the
Hawai'ian Island chain.

The 17/00Z ECENS has trended noticeably westward of its previous 2
cycles (16/00Z & 16/12Z) with its 500mb and surface circulations.
The 17/00Z GEFS/GFS maintains a similar approach to its 16/00Z
cycle---producing a northward re-curvature between day 3-4 (20/12z
to 21/00Z). In very broad terms, the EC and GFS solutions
'book-end' the entire realm of possibilities. A similar disparity
between ECENS/GEFS solutions were observed in the Gulf of
Alaska---with the 17/00Z GEFS/GFS 500mb forecasts maintaining a
faster shortwave solution from the easternmost Aleutians
southeastward into the eastern Pacific---along 145W at mid-point
day 5 (22/12z).

In either case, this mid-latitude shortwave will not completely
incorporate 'Ana' and send its remnants (in entirety) eastward
towards the Mainland. The idea of leaving 'Ana' behind to wobble
along invof 24N-25N and 164W-165W heading into day 6-7 seems more
than plausible---at this point in time.

For days 5-7, continue to recommend using a blend of the 17/00Z
GEFS/ECENS means to cover the general northwestward drift of this
disturbance.

Vojtesak