I received my Tempest yesterday, and spent much of the evening trying to get it to pair, unsuccessfully.
When I turned it on, the green LED would flash quickly for a couple of seconds, and then turn purple, and then turn off. The app could not locate it.
There were some misleading comments in the app about checking the batteries, which turned out to be incorrect and irrelevant.
Eventually, I found a hint on another thread, and held down the green LED button for ten seconds, which apparently reset the device. It resulted in the green LED blinking slowly, and then it paired.
Hopefully this helps anyone else stuck in this position, and I’d kindly suggest that Weatherflow update the pairing part of the app with clearer instructions.