Q.when to plant drought tolerant shrubs – specifically potentilla
I live in ZIP code 97301 which plant map shows as 8a. The exposure I want to place the shrub is full west sun. When specifically could I plant a shrub? I’m thinking in terms of this year being a heavy rain season because of the talk of the oncoming El Nino concern. Can I plant in the fall and will the new shrub last through heavy rain?

Potentilla may not be a good choice for a drought tolerant garden. They prefer a evenly moist soil.
I'm listing a few links for you that may give you more help in selecting plant species.
I always encourage you to visit local garden centers to look around and find plants that are good cultivators for you growing zone.
Fall is generally a very good time to get new planting is the ground. Follow the planting directions for each species and make sure they receive adequate water, daily for the first 2 weeks and then you can cut back.
Heavy rain can be stressful and cause the death of any plant material. Mother Nature is impossible to control. Remember that most reputable garden centers guarantee their plants for 1 year.
https://www.gardeningknowhow.com/special/xeriscape/drought-resistant-shrubs.htm
https://www.gardeningknowhow.com/special/xeriscape/drought-tolerant-plants-for-nearly-any-landscape.htm
https://www.gardeningknowhow.com/special/xeriscape/drought-tolerant-gardening-the-cheaper-landscape-alternative.htm
https://www.gardeningknowhow.com/ornamental/shrubs/potentilla/growing-potentilla-shrubs.htm