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. Ryan