Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 828 AM EDT Wed Oct 17 2018 Valid 00Z Thu Oct 18 2018 - 00Z Thu Oct 25 2018 Model and ensemble forecasts seem reasonably well clustered at larger scales, but the smaller scale details are less certain. This suggests a composite guidance solution. It is evident that surface high pressure north of the state will support moderate trades from the east/northeast in the short term. Then an upper trough consisting of several individual shortwaves will amplify toward/into the islands, likely reaching its greatest amplitude Friday into Saturday. During the weekend the upper trough will track away from the area as a ridge aloft builds eastward over the state. Corresponding to the upper trough a front should approach the state from the northwest and serve to relax the pressure gradient, leading to slightly lighter winds. As the upper features progress eastward expect an east-west surface ridge to become established along 25-30N from the weekend into next week and support steady moderate trades. Through mid-late week the Big Island will be the most likely location for light-moderate shower activity as it will be on the northwest fringe of a band of enhanced moisture. Drier air should move into the area from the northwest by the weekend as the upper trough reaches the area and then begins to move away. Accordingly, from the weekend into next week anticipate mostly light shower activity but with some uncertainty for intensity given guidance moisture spread. Schichtel