Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 719 AM EST Thu Dec 14 2017 Valid 00Z Fri Dec 15 2017 - 00Z Fri Dec 22 2017 ...Heavy rain threat next week... An upper low will east of the islands will slowly drift west-northwestward tomorrow into Saturday, passing just north of Oahu. By Sunday the upper low is forecast to lift northward and become absorbed into the flow ahead of an approaching trough from the northwest. That trough may close off one or two upper lows early next week - one to the north of the region around 35N/160W and perhaps another to the northwest of the Kauai. GFS/UKMET were quicker with the trough than the ECMWF/Canadian but given the uncertainty in evolution prefer a consensus position between the two camps which is a bit slower than the ensemble means. Ensembles and most deterministic solutions then show reinforcing troughing from the northwest next Wed/Thu with perhaps yet another upper low just to the north of the region. Breezy northeast may exceed 30 kts with higher gusts into tomorrow morning before the closed low approaches from the east. Moisture will wrap back around the surface low from the north but the heaviest rain on the east side of the upper low will remain displaced to the northeast of the region over the next several days. The next upper trough or weak upper low next week will likely draw deep tropical moisture from the ITCZ and has the potential for much more precipitation given its location. Deterministic models still show several inches of rain over some of the islands next Tue-Thu ahead of the front well to the northwest. 00Z ECMWF ensembles and 06Z GEFS ensembles now show a probability of at least an inch of precipitation exceeding 60-80% in the 72 hrs ending 00Z/22 over the Big Island and Maui. This was a big increase from just 24 hrs ago. Fracasso