Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 817 AM EDT Sat Nov 03 2018 Valid 00Z Sun Nov 04 2018 - 00Z Sun Nov 11 2018 Eastern Pacific high pressure will promote at least moderate trades over the main islands through this weekend into early next week, supporting a general windward focus for rainfall during that time frame. Meanwhile a compact upper low approaching from the northeast will reach near the Big Island shortly and may lead to areas of heavy rainfall/thunderstorms especially over the eastern islands. Some activity could stray over to leeward locales at times. Expect rainfall to trend lighter by Monday-Tuesday as the upper low lifts northward. From Wednesday onward the current array of guidance continues to suggest greater than average uncertainty in pattern evolution at the surface and aloft along with associated sensible weather. There is the general theme that weak shortwave energy crossing the western Pacific will amplify into an upper trough to the north and west of the region. This will lead to some degree of surface frontal/inverted trough enhancement that would disrupt the trades. However solutions diverge regarding the character of embedded upper trough energy. The 00Z ECMWF is on the more extreme side of the full ensemble spread in separating the southwestern part of the trough into an upper low west of 170W longitude, ultimately leading to less trade disruption and keeping the greatest deep moisture west of the main islands. The 00Z ECMWF ensemble mean keeps the upper trough somewhat west of remaining guidance but its open character does allow moisture to reach farther eastward than the operational model run. On the other side of the spectrum the 00Z FV3 GFS/00Z CMC may become a tad on the progressive side with the upper trough and surface reflection. Therefore would ultimately recommend a compromise among the 00Z/06Z GFS and 00Z GEFS/ECMWF ensemble means in principle. This scenario would yield a meaningful increase of moisture and rainfall potential over the area, especially the eastern half of the main islands, during next Friday-Saturday. Rausch