Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 829 AM EDT Tue Apr 17 2018 Valid 00Z Wed Apr 18 2018 - 00Z Wed Apr 25 2018 A series of high pressure cells bridging to the north of the state over the next week will act to periodically reinforce trade flow across moderate to brisk levels into the islands. Drier air as a lead surface high slides eastward between 30-35N will retreat over the next few days as guidance shows a surge in precipitable water values by Thursday as a weakness moves eastward over and to the north of the region. This along with old front approach should act to increase showers and local downpours. Expect some decrease in PW values again by the weekend in the wake of the front. A preffered composite of reasonably well clustered model and ensemble guidance shows increasing heights to the northwest of Hawaii as an upper ridge/closed high strengthens near the Dateline with heights about +1.5 standard deviations above the mean, and the downstream pattern will continue to favor some windward terrain trade showers. Schichtel