Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 829 AM EDT Fri Nov 02 2018 Valid 00Z Sat Nov 03 2018 - 00Z Sat Nov 10 2018 Guidance agrees that a compact upper low northeast of the state will track southwestward and reach a position close to the Big Island by Saturday. Arrival of this feature will bring added moisture/instability and potential for some heavy rainfall/thunderstorms through the weekend. By early next week the upper low will likely lift far enough northeastward to allow for at least a brief drier trend. Greater uncertainty in the forecast arises by midweek as guidance diverges regarding upstream trough amplification, which will likely lead to some inverted troughing at the surface and weakening of the trades. The question will be the longitude at which troughing at the surface and aloft will set up. Currently there appears to be no overwhelming signal for one side of the solution envelope, with at least a small number of 00Z GEFS members going along more with the 00Z ECMWF/ECMWF mean idea of a farther westward trough than operational 00Z/06Z GFS runs--and at the same time some ECMWF ensemble members offering the possibility of troughing closer the GFS scenario. In addition there may be some influence of very weak small-scale upstream energy that could affect the evolution closer to the state and such energy typically has low predictability. Given this and the mixed array of model/ensemble guidance, would recommend a solution halfway between the ECMWF and GFS clusters for position of the developing trough and corresponding weakening of trades/increase of deep moisture. Before this uncertain portion of the forecast mid-late next week, eastern Pacific high pressure will support moderate to brisk trades into the weekend with some gradual weakening during the first part of next week. Rausch