Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 825 AM EDT Sat Sep 29 2018 Valid 00Z Sun Sep 30 2018 - 00Z Sun Oct 07 2018 Expect a trend toward drier conditions with moderate trades from later this weekend into early next week. Separate areas of enhanced moisture over and near the Big Island and northwestern main islands will progress westward as high pressure initially northwest of the state drifts eastward and helps to re-establish trade flow. Winds will become southeasterly next week as stronger high pressure sets up farther northeast over the eastern Pacific. The forecast from about Wednesday onward still has its complexities and significant uncertainty, but on the positive side there is a somewhat more common theme in today's guidance with respect to sensible weather effects over the state. Leading up to that time, one feature of interest will be the disturbance currently well south of the islands (Invest 97C) and likely to develop into a tropical cyclone and track to the west and then north--reaching a position within a few degrees of 20N 170W by 12Z Wednesday. The other will be an upper trough amplifying to the northwest of the region and forecast to close off an upper low in the vicinity of 30N 170W by early Tuesday. Solutions remain quite varied on how these two features will interact, and differences persist for degree of progression of the upper trough. However today there is a greater proportion of guidance that holds the trough fairly far westward. The 00Z ECMWF and FV3 GFS show greater progression than the majority (though within the full ensemble spread)--but are strong enough with downstream ridging aloft that the main islands remain in the southeasterly low level flow around the periphery of the East Pacific surface high. The average of today's guidance would suggest that the interaction of the two main features will produce an axis of very high precipitable water values/heavy rainfall to the west of the main islands. Note that the 00Z GEFS mean is on the eastern side of the guidance with this moisture. Overall a compromise between the 00Z-06Z GFS and farther westward 00Z ECMWF mean (the latter somewhat closer to the average of guidance than the operational run) appear to be the best starting point for the overall forecast at this time. Rausch