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Hawaii Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1213Z Jan 29, 2015)
 
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Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
713 AM EST Thu Jan 29 2015

Valid 00Z Fri Jan 30 2015 - 00Z Fri Feb 06 2015

Unsettled weather is expected across the Islands this weekend with
below normal night time low temperature readings.

The 29/00Z ECENS/GEFS and deterministic runs signal persistent
surface troughing and persistent 'cold advection' through day 5.
Cold advection being a relative term at Subtropical
latitudes---but nonetheless. The ECMWF...GFS and Canadian
deterministic runs indicated---above normal baroclinicity surging
along/south of 30N latitude, and mid-level shortwave energy
producing sub-synoptic scale warm advection with distinct wind
shifts---more characteristic of mid-latitude migratory weather
systems.

The 29/00Z GFS/ECMWF are equally-aggressive solutions with the
arrival of the initial cold front---moving west to east---on
Friday. The 28/00Z GFS migrates the front southward to near 20N
over the weekend---making a full journey across the entire state.
The ECMWF stalls the front over Kauai---allowing it to settle no
further eastward than Oahu. The Canadian, an even weaker solution.

As was the case yesterday when the 28/00Z ECMWF first considered
secondary wave energy development invof 160W---the 29/00Z forecast
cycle guidance seem to be in somewhat better agreement (in
principle); with developing a surface reflection and low-level
wave invof 30N 165W on/around 2/12Z. In turn, the low-level flow
attempts to set up a more distinct south to southwest wind---in
true mid-latitude warm advection fashion. This flow pattern
disrupting the trades, and encouraging a relatively-wet flow
"setup" for the state for next week.

There are indications that a pattern transition is going to take
place in the central Pacific---during the day 4-6 period. This was
noted yesterday in the north Pacific along 35-45N 160W (see PMDAK
discussion) as the upper-level cyclone and long wave shifts
east-southeastward and away from the Aleutians.

Recommend a blend of the 29/00Z GEFS/ECENS for days 5-7.
Meanwhile, the deterministic GFS (29/00Z) seemed reasonable
through day 3, if a more pessimistic approach/preference was in
order.     

Vojtesak