Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 730 AM EDT Thu Sep 08 2016 Valid 00Z Fri Sep 09 2016 - 00Z Fri Sep 16 2016 Persistent trade wind flow continues into this weekend with high pressure remaining to the northeast of the islands, continuing to favor a windward focus for shower activity. Overall expect amounts to be light and typical of a tradewind flow regime. the pattern changes late in the weekend to early next week as a tropical wave approaches and then passes through the islands. A few models even develop surface low pressure along the wave axis. The tropical wave advects copious amounts of moisture across the islands. Areas where enhanced convergence occurs with the tropical wave will be prone to periods of heavy showers. the gfs precipitable water anomalies early to mid next week are 3-4 standard deviations above normal. The GFS and ECMWF show 2 inches of available precipitable water. the ECMWF QPF shows doses of moderate to heavy rain each day the beginning to middle portion of next week. There is better than average agreement in the large scale 500 mb pattern among the gfs/ecmwf and their respective ensemble means, so a consensus based approach could mitigate detail differences. Petersen