Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 814 AM EDT Tue Oct 16 2018 Valid 00Z Wed Oct 17 2018 - 00Z Wed Oct 24 2018 Most guidance shows similar ideas for the pattern evolution over the next seven days. At the start of the period surface high pressure north of the state will support moderate trades from the east/northeast. Then an upper trough consisting of two individual shortwaves will amplify toward/into the islands, likely reaching its greatest amplitude around Friday/Friday night. 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 a bit for a day or so late in the week, 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. However there is a fair degree of spread in how far southeastward the best moisture (as denoted by 1.50"+ precipitable water values) is pushed, with 00Z/06Z GFS runs farther southeast than other guidance. Then from late weekend into early next week the 00Z GEFS mean brings back more moisture over the area than other solutions--possibly due in part to being on the weak side of the envelope with the upper ridge. From the weekend into next week anticipate mostly light shower activity but with some uncertainty for intensity given the guidance spread for moisture. Rausch