I’ve had a few people message me mentioning that they went out in the rain shortly after a spray tan, and it appeared that the rain was instantly affecting their tan. First of all, your tan is probably fine, so don’t stress about that.
What is actually happening probably, is that the guide color that is in most spray tans (which is essentially like makeup) is washing off unevenly as the rain is hitting it, making it look like your tan is getting messed up. However I can almost guarantee you if you go home and shower, your skin color will probably even out and you’ll likely notice that your tan is just fine.
Many self-tans that you get online also have guide color (I don’t personally prefer these) which can help people that are new to the craft apply their tan more evenly because you can actually see where it is going on your skin, and assure that it is being applied evenly.
Additional to that, I did a test once and if you’ve ever had a splash of tan on you, you will know that a dot of tan once developed can be an inch wide. So whilst rain washes off bronzer, unless it was a rainstorm and you got soaked it wouldn’t really affect it much at all as tan in the nearby non-rained in areas would spread. So once washed off should be fine however it’s very common to have a couple of white patches on deltoid area from dry skin and anywhere else with dry bits, and those are usually able to be blended with a bit of exfoliation after a couple days so can do the same if needed. Can also use a cotton bud to put gradual tan or tan solution on those bits to match up too.