Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 718 AM EST Tue Dec 12 2017 Valid 00Z Wed Dec 13 2017 - 00Z Wed Dec 20 2017 Cold front will move across Hawai'i today as an upper trough amplifies north/northeast of the islands. An upper low will form just to the east of Hawai'i Wed night/Thu and then slowly drift west-northwestward into the weekend. By Sun-Mon the upper low should lift northward and become absorbed into a positively tilted trough axis extending from just northwest of Hawai'i to the Gulf of Alaska. That may again close off an upper low on its southwest tail to the north of the region next Tuesday. A blend of the recent 06Z GFS and 00Z ECMWF (both near their ensemble means) offers a reasonable starting solution. Scattered showers and perhaps even a few localized areas of heavy rainfall will accompany the front today into tomorrow. Behind the front, breezy northwest winds will bring in drier and cooler air and veer to the north and northeast tomorrow into Thursday when winds may exceed 30 kts. Trend has been to keep most but not all of the moderate/heavy rain associated with the upper low this weekend just north of the area as the main moisture axis to the east wraps around from the north into the islands. 00Z ECMWF ensemble probabilities of exceeding 1 inch QPF in a given 72 hour period was no larger than about 15-20% anywhere over the islands. As the next upper trough amplifies northwest of Hawai'i by early next week, additional rain will be probable given the location of the upper low or sharp trough to the west of the region. Fracasso