Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 829 AM EDT Thu Oct 11 2018 Valid 00Z Fri Oct 12 2018 - 00Z Fri Oct 19 2018 ...Some heavy rains expected this weekend... As one upper low drifts farther away from the Hawaiian islands, another band of heights are expected to slowly push through the region on Saturday. Attendant to this axis of positive vorticity advection will be a modest wave of low pressure which should be a focus for heavy rainfall. Overall wind fields should be quite weak given a general lack of substantial pressure gradients. The southern extension of the cold front is expected to reach the Big Island by 14/1200Z with post-frontal winds shifting back to the northeast by early next week. At this point, the pattern aloft begins to favor a positive height anomaly across the central Pacific with lower heights remaining up in the active mid-latitude flow. A dome of high pressure building to the north of Hawai`i will afford an increase in the east-northeasterly trades from Tuesday onward. This will drive scattered shower activity although it should not be terribly focused given the lower precipitable water environment. The main event during the period will be over the weekend with the 00Z ECMWF particularly heavy over Maui and the Big Island with 6-hour rainfall amounts up to or even exceeding an inch. However, the signal is not nearly as strong in other models. Beyond that period, the global models seem to be aligned with the return of a trade wind regime next week. Rubin-Oster