Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 727 AM EST Thu Dec 01 2016 Valid 00Z Fri Dec 02 2016 - 00Z Fri Dec 09 2016 ...Heavy Rainfall Pattern for Hawai'i... ...Guidance and Uncertainty Assessment... Very active pattern will remain for the 50th state over the next week. An upper low currently to the southwest of the Big Island will drift northwestward and weaken over the next couple of days. Ensembles generally agree on the longwave pattern across the central Pacific this weekend into next week. This supports another upper low dropping down from the mid-latitudes to near 25N/165W early Sunday before lifting out to the northeast and then another low around next Wednesday but farther west (around 170W). For the lead upper low this weekend, the 00Z-06Z GFS runs represent reasonable solutions in between the quicker/weaker 00Z UKMET and the stronger/slower 00Z ECMWF/Canadian. Only about 20% of the ECMWF ensembles were slower/deeper than the deterministic ECMWF. By next week, much more spread among the deterministic runs was seen with the next digging trough and perhaps closed low. The 00Z-06Z GFS runs appear too quick to bring lower heights eastward (among the quickest 10% of all GFS/Canadian/ECMWF ensembles) while the 00Z ECMWF lies just slower than the GEFS/EC-ens mean consensus, which is reasonable. ...Weather Highlights/Threats... Tightened pressure gradients underneath high pressure centered to the northeast of the state will favor moderate to brisk trades over the next couple of days. Rainfall associated with the current upper low may be very heavy over the Big Island over the next two days -- both the ARW/NMMB hi-res windows show in excess of five inches over the eastern portions of the Big Island and Maui, but more uncertainty lies farther northwest over Oahu and Kauai. Next week, inverted troughing will act to pull/pool deep layered ITCZ-based moisture over the state to fuel a widespread excessive rainfall and runoff threat as precipitable water values rise to near or above 2" early next week. ECMWF ensembles were generally wetter than the GEFS ensembles by about two or even three times, which is not unreasonable. Fracasso