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Hawaii Extended Forecast Discussion
(Latest Discussion - Issued 1230Z Aug 18, 2017)
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Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
830 AM EDT Fri Aug 18 2017

Valid 00Z Sat Aug 19 2017 - 00Z Sat Aug 26 2017

Models highlight an inverted upper trough slowly sliding toward
the west although the core of the positive vorticity advection
should stay north of the Hawai`ian island chain. This feature
should continue to push toward the International Dateline while an
expansive 594-dm mid-level ridge sets up across the mid-latitudes.
To the south of Hawai`i, the Central Pacific Hurricane Center has
continued to monitor an area of disturbed weather approximately
600 miles southeast of Hilo. Based on this forecast, it appears
conditions remain unfavorable for any further development while
also remaining well south of the region. At the surface,
persistent ridging to the north will keep the usual trade wind
regime in place with winds generally in the 10 to 15 knot range.
By Tuesday, a strengthening of the parent anticyclone will lead to
an uptick in the low-level winds, likely up to 20 knots or so. It
appears this increase in the trades should remain a fixture in the
forecast throughout much of next week.

Considering the precipitation forecast, windward showers will be
the norm early on with a likely increase in coverage and intensity
expected by late Sunday/early Monday as precipitable water values
rise above 1.50 inches. This moister regime should continue
through mid-week before drier air infiltrates the region. During
the period of increasing tropospheric moisture, models do show an
increase in forecast rainfall amounts, particularly across the Big
Island as well as over Kauai.