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Hawaii Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 1216Z Apr 18, 2015)
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Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
816 AM EDT Sat Apr 18 2015

Valid 00Z Sun Apr 19 2015 - 00Z Sun Apr 26 2015

From this weekend into early next week expect trades to be on the
moderate to strong side as eastern Pacific high pressure is
replaced by another surface high tracking eastward across the
mid-latitude Pacific.  By the middle of next week winds should
become more southeasterly.  Generally windward focused showers
should be fairly light given precipitable water values around or
below an inch into Mon and presence of a ridge aloft over or just
north of the islands.

Over the past couple days guidance has become increasingly
divergent and inconsistent with respect to the handling of a
central Pacific upper low and the corresponding surface front. 
One note of interest is that even with the varied eastward extent,
multiple solutions suggest the upper low will extend far enough
south to yield 500mb height anomalies reaching as low as 4-5
standard deviations below normal.  Latest trends of the
ECMWF/ECMWF mean to the western side of the guidance spread
occupied by GEFS means from 24 hours ago, plus the tendency for
closed lows to have timing in the slower half of the envelope,
seem to favor moderately slow timing.  The 00z GEFS/ECMWF means
best represent this idea as the 00z ECMWF is farthest west at some
forecast hours.  This preferred scenario would keep the surface
front well west of the islands through the forecast period with
southeasterly trades persisting over the state though with a
gradual weakening trend.  Farther eastward progression of this
system would lead to a more enhanced band of rainfall reaching the
area, a scenario that still requires monitoring even if given
somewhat less probability than the preferred one.