This topic might help you.
Sunny suggests clicking API at the top of this page to goto the Tempest help about the API. from there you should be able to experiment with http calls to the API for your device. Not the station, but your Tempest device id. And depending on the time period you request the data is returned in different detail with 24 hour period returning 1min data. Larger time periods summerise the results into larger chunks. I am not at my computer atm to experiment for you which is why I pointed you to that topic. There are other topics which also discuss it but I found experimenting with the API link above was the best help.
Your project sounds great I would love to see a screen capture, and hear how you tackled it.
Cheers Ian 