Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 305 AM EST Fri Jan 22 2021 Valid 00Z Sat Jan 23 2021 - 00Z Sat Jan 30 2021 Latest guidance shows fairly good agreement for the overall pattern evolution through the period. During the weekend into early next week expect winds to strengthen and turn somewhat southeasterly as strong high pressure builds over the eastern Pacific and an upper ridge meanders northeast of the state. The combination of this deep-layer ridge and an upper trough/low plus surface reflection developing just west of 170W will likely draw up an area of enhanced moisture northwestward across the main islands during the first half of next week. Then a westward repositioning of the surface/upper ridge should bring drier air in from the northeast while trades return to a more easterly orientation. Anticipate moderate shower activity through the weekend though one or more upper level impulses over the area may enhance amounts somewhat. With the early-mid week moisture surge the GFS/ECMWF and their means are fairly similar with the timing but the GFS/GEFS indicate heavier rainfall reaching the islands in contrast to the ECMWF/ECMWF mean whose axis is generally a little farther south. Interestingly the 00Z GEFS/12Z ECMWF means both show precipitable water values peaking at a little over 2.0 standard deviations above normal (around Tuesday) while the 00Z ECMWF peaks at plus 2.5-3.0 standard deviations. The 00Z GFS is the extreme, reaching above plus 3.0 for a time. The 00Z GFS did trend somewhat southwest of the 18Z run with its axis of heaviest rain, adding support for an intermediate solution that could be somewhat heavier than the ECMWF given the latter's available moisture. The most agreeable part of this time frame is the eastern/southeastern windward focus of rainfall on the Big Island. There is good agreement in a drier trend during the latter half of the week as near or slightly below normal precipitable water values approach/reach the area. Rausch