Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 821 AM EDT Fri Oct 12 2018 Valid 00Z Sat Oct 13 2018 - 00Z Sat Oct 20 2018 ...Some heavy rains expected this weekend... Early morning Himawari satellite imagery showed a broad mid-latitude trough well to the north of Hawai`i while a separate shortwave was approaching the island of Kauai. Showers and thunderstorms will continue to ignite along the southern extension of a baroclinic zone where a wave of low pressure should gradually press southeastward. The latest blended-TPW product shows much higher precipitable water air intruding from the west with numbers likely to exceed 2 inches within in the next 12 hours. Model guidance supports locally heavy rainfall as this occurs, particularly across Maui and the Big Island with the 00Z ECMWF being wetter than other solutions. Much of the activity will wind down beyond Saturday night as the boundary sinks south of the region. From Sunday into early next week, building heights aloft will be commonplace while the Hawaiian islands generally sit within a break in the 588-dm mid-level ridge. The active mid-latitude flow should remain well to the north as shown by recent operational/ensemble guidance. Some amplification is possible just beyond Day 7/October 19 but the details remain nebulous at best given notable ensemble spread. At the surface, cold advection behind the shearing frontal zone will support a period of modest north-northeasterly flow on Sunday with wind fields continuing to veer in time. With transient domes of high pressure sweeping to the north, a return to east-northeasterly trades are anticipated for much of next week, generally in the 10 to 15 knot range. This should support periods of trade driven showers throughout the week. Overall model guidance seem to be in decent agreement with the mentioned pattern. Rubin-Oster