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Hawaii Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 1212Z Feb 17, 2018)
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Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
712 AM EST Sat Feb 17 2018

Valid 00Z Sun Feb 18 2018 - 00Z Sun Feb 25 2018

Models/ensemble suggest a blocky pattern developing across the
north/central Pacific over the next several days, with an ridge
amplifying south of Alaska and persistent negative height
anomalies in the vicinity of Hawai'i. Early in the period, through
Sunday, a weakening surface boundary (evident on current satellite
imagery) is forecast to slowly drift westward across the eastern
Hawai'ian Islands. An upper low is forecast by all guidance to
close off in the vicinity of Hawai'i by late Sun, with the low
weakening and a second upper low closing off west of the Islands
by Wed-Thu. Low-level southerly flow will continue to transport
deep moisture northward across Hawai'i, with Pwats of 1.50-2.0
inches through early next week, especially across the eastern
Islands. As the second upper low develops west of Hawai'i by
midweek, a broader region of southerly flow will spread deeper
moisture across the entire state. The ECMWF has backed off the
solution it showed yesterday in which a surface low tracked across
Hawai'i during the period. Both the ECMWF and the GFS now show
similar solutions in terms of the upper low west of the state by
midweek, and broad southerly flow spreading deep moisture north
across Hawai'i. Thus, expect precipitation to initially be most
widespread and heaviest across the eastern islands through Tue-Wed
(in the vicinity of the surface boundary), before gradually
expanding westward by later in the week, with even the western
islands seeing notable increases in precip chances. In terms of
surface winds, flow will generally be east-southeasterly through
much of the next week, gradually increasing into early next week.