Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 815 AM EDT Fri Mar 16 2018 Valid 00Z Sat Mar 17 2018 - 00Z Sat Mar 24 2018 ...The current heavy rain threat eases by Saturday... ...Another heavy rain/flash flood threat late Tuesday into Friday... Trades re-establish today as moisture slowly fades as the system responsible to the heavy rainfall yesterday lifts north and northeast of the Islands. Windward showers/thunderstorms are likely to be more active with heavier rain than typical trades due to lingering moisture and a weaker wind regime, with more typical windward showers likely Saturday into Monday or Tuesday as the trades attempt to recapture their usual vigor. The departing system digs down to the northeast of the archipelago which should keep trades in the offing for the main islands into Monday. However, a new system moves slowly in from the west/Papahanaumokuakea Marine National Monument which breaks down the trades and reintroduces heavy rain into the main Hawai'ian islands from roughly Tuesday night/Wednesday into next Friday. Precipitable water values are forecast to rise into the 1.75-2" ballpark, which even in flat/non-Hawai'ian terrain would lead to the possibility of 2.5" an hour rain rates -- any cell mergers would double the potential. The guidance is very agreeable regarding progression of the next system, though the 00z ECMWF is likely too strong/too far northwest in its surface low placement with its depiction of this system. Considering saturated conditions from recent rainfall and the rugged topography, flash flooding is a realistic hazard during this time frame. Roth