Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 820 AM EDT Sun Sep 30 2018 Valid 00Z Mon Oct 01 2018 - 00Z Mon Oct 08 2018 Through about the first half of the week expect fairly light shower activity with precipitable water likely declining to below normal values over the coming day and remaining near those levels over the area into Wednesday. Low level winds will become southeasterly as weak high pressure initially north of the islands shifts northeastward and stronger high pressure farther northeast becomes dominant. Wind speeds should generally be light to moderate, with episodes of lighter winds allowing for some land/sea breeze influence. Guidance is steadily improving its clustering with respect to evolution west of the main islands. The Central Pacific Hurricane Center is currently issuing advisories on Tropical Storm Walaka which is well to the southwest. Walaka is most likely to start tracking northward as it nears 170W longitude as an amplifying upper trough to its north closes off a low. Around Wednesday-Thursday most guidance shows some degree of interaction between the upper low and Walaka, and then northeastward ejection ahead of mid-latitude Pacific troughing. Overall there is a good consensus that in the wake of these features there will be a north-south axis of enhanced moisture/rainfall. The primary forecast concern is the exact longitude of this axis. The 00Z GFS/GEFS mean are farthest east with the moisture axis, bringing some associated rainfall into Ni'ihau and Kauai, due to being weakest with the upper ridge over/north-northeast of the state. With remaining guidance stronger with the ridge aloft--plus the 06Z GFS/00Z ECMWF each nudging the moisture axis a little westward versus their previous runs, would favor a starting point closest to the 06Z GFS/00Z ECMWF. Farther eastward anticipate a gradual increase in moisture that may lead to somewhat higher rainfall totals in late week/weekend showers versus earlier in the week. Rausch