Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 827 AM EDT Sun Apr 28 2019 Valid 00Z Mon Apr 29 2019 - 00Z Mon May 06 2019 Through Monday expect light winds with showers tending to focus more along sea/land breeze boundaries, as a front approaches but likely stalls out just before reaching the main islands. An approaching shortwave aloft may produce localized heavier rainfall and possibly a thunderstorm. Trade flow will return for Tuesday-Thursday with winds from the northeast as high pressure tracks north of the area. Most windward-focused rainfall should be fairly light as a ridge aloft builds toward/over the state behind the departing shortwave. A model consensus provides a reasonable starting point for the forecast through Thursday. Model and ensemble guidance is still having difficulty resolving the details of upstream central Pacific flow and effects on Hawai'i. Into late this week the overall average of guidance has trended faster with the mid-latitude trough aloft whose southern periphery drops toward the islands. This is more toward GFS runs that were on the faster side of the envelope yesterday. From about late Thursday-early Friday onward models and ensemble members again diverge dramatically. GFS runs (especially the 06Z version) are still on the faster side of the spread and maintain an open trough. This solution would lead to another approaching front (but with modest rainfall) and trailing high pressure that would bring north-northeasterly winds by next Sunday. The 00Z CMC is a little slower but with the same idea. In contrast the 00Z UKMET/ECMWF quickly drop a compact upper low west of or over the state respectively, leading to a much greater trade interruption and heavier rainfall. Looking at the 00Z ensembles valid early next Sunday, a few ECMWF members show a closed low but either farther west/northwest or north of the main islands. One CMC member has an upper trough to the northwest but all other members plus all GEFS members are flatter and faster with the upper trough. The faster trend of non-GFS guidance over the past day for forecasts valid late this week and the majority of ensemble guidance seem to favor a conservative approach given by an average of the GEFS/ECMWF ensemble means. This would provide at least some increase in rainfall chances with the approach of a front late this week into the weekend but not nearly to the extent of the wettest side of the spread that has stronger upper dynamics and inverted surface troughing. Rausch