Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 820 AM EDT Tue Apr 03 2018 Valid 00Z Wed Apr 04 2018 - 00Z Wed Apr 11 2018 Expect a threat for periods of heavy rainfall in association with a wavy front to be the continuing focus of the forecast. As for specifics, guidance is fairly agreeable through at least Thursday. A leading weak surface feature and diffuse shortwave energy will depart to the northeast of the state today (Tuesday). Developing west-southwesterly flow aloft ahead of an upstream front will quickly bring another surge of moisture across the area, with precipitable water values reaching or exceeding 2.00 inches at some locations in GFS/ECMWF runs. There is reasonable agreement that mid-latitude dynamics passing by Thursday-Friday will bring the front into the state by Friday. By Friday-Saturday guidance essentially splits into two clusters, leading to differences in timing and location of heaviest rainfall potential. The 00z-06z GFS and 00z GEFS/CMC means are slower than the 00z ECMWF/ECMWF mean/CMC with a lower latitude shortwave, which results in the former cluster holding back the wavy front and axis of highest rainfall over the northwestern part of the state for a time in contrast to the ECMWF cluster that quickly shifts rainfall emphasis toward the Big Island. The 06z GFS run seems to represent a gentle nudge forward from the 00z GFS/GEFS scenario so a solution at least as fast as a GFS/ECMWF compromise looks reasonable. Regardless of exactly what transpires in the Friday-Sunday time frame, guidance actually suggests somewhat better confidence that passage/departure of another mid-latitude system will be followed by high pressure building eastward along 30N latitude--helping to establish northeasterly to easterly trades with rainfall focus over windward terrain. By next Tuesday the 06z GFS holds the axis of highest PWATs a little farther northwest but otherwise the majority of model/ensemble guidance shows the axis of greatest deep moisture lingering near the Big Island. Rausch