Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 307 AM EST Tue Dec 22 2020 Valid 00Z Wed Dec 23 2020 - 00Z Wed Dec 30 2020 Today's guidance continues to show enough progression of features to promote periodic changes in the pattern, while a couple points of difference among some guidance persist as well. Heading into midweek expect relatively dry conditions, with light winds over the islands between eastern Pacific high pressure and a front approaching from the northwest while an east-west ridge builds overhead. Showers that do occur may have some land/sea breeze influence. Expect rainfall to increase later in the week as the aforementioned front arrives. Trailing high pressure building north of the state late this week into the weekend will promote trades that will reach brisk to strong levels, returning precipitation to a primarily windward/mountain focus. Rainfall should trend somewhat lighter with time as the greatest deep moisture pushes southward. Continued progression of the surface high along with the approach of another front should bring wind speeds back down early next week. As the front arrives by Friday/Christmas Day and the southern fringe of an upper shortwave approaches, there is a continued dramatic difference in how much moisture may reach into the area from the southeast. The 00Z GFS brings precipitable water values up to 1.50-2.00 inches over the southeastern half of the main islands while the more suppressed 00Z ECMWF and 12Z ECMWF mean keep the southeastern moisture source well suppressed leading to PWATs around 1.25 inches or lower over the southeastern islands. The only trend of note since yesterday is the GEFS mean nudging closer to the GFS scenario. Persistence of the two extremes and the overall evolution possibly supporting an evolution somewhere between the two would recommend an intermediate solution at this time. Meanwhile the GFS/ECMWF/CMC and their means maintain a majority cluster that has any shortwave amplification during the weekend into early next week occurring well east of the state. The UKMET continues to be on its own among operational models, now bringing an upper/surface low to just north of the state. Individual ensemble members still show the idea of a farther west upper trough versus the majority as possible but with fairly low probability. For the front approaching the area near the end of the period next Tuesday, most model/ensemble guidance suggests that supporting dynamics aloft should be somewhat faster than in recent GFS runs--pushing the front a little farther east/southeast versus that model. Rausch