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Hawaii Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1211Z Feb 13, 2018)
 
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Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
711 AM EST Tue Feb 13 2018

Valid 00Z Wed Feb 14 2018 - 00Z Wed Feb 21 2018

Today's guidance continues to suggest that mean troughing aloft
will support a lengthy period of unsettled weather, along with a
persistent north-south trough axis at the surface preventing any
semblance of trade flow.

Within the overall mean trough aloft the first feature of interest
will be a deep upper low northwest of the state.  Guidance
consensus shows this upper low tracking southeast to position
north of Kauai by Thursday followed by a rapid turn to the north
in response to upstream flow.  Exact details vary by model but in
principle there is decent agreement that this evolution will
likely generate enhanced focus of deep moisture with an axis of
heavy rainfall potential drifting from west to east across the
islands during Wednesday to Thursday night.

With the northward departure of the upper low, the axis of
greatest deep moisture may stall near the Big Island into the late
week/weekend time frame.  Thus the Big Island may continue to see
some rainfall while western islands see a period of relatively
drier weather.  Then over the weekend upstream energy reloading
the mean upper trough may pull some moisture back to the west
leading to another period of enhanced rainfall potential.  There
is somewhat more spread for the precise evolution during this part
of the forecast versus the prior episode though.  By next Monday
most guidance indicates that the trough energy will close off
another upper low near the islands.  The 00z CMC track ends up
south of most other solutions while the 00z/06z GFS are deeper
than other models/means.  Looking at the ensembles, as might be
expected 00z GEFS members offer more support for the GFS depth (on
a percentage basis) than do ECMWF members.  This feature will
likely keep the area fairly unstable but at least push the axis of
high precipitable water values farther to the east away from the
state.

Rausch