SenseHAT cyclic data behavior?

[nikertneca]

I'm using my SenseHAT to stream sensor data every minute, and I'm seeing things that I need help understanding so I can fix them. All of the readings (temp, humidity, and pressure) seem to vary cyclically:

20180626_215201.jpg (144.88 KiB) Viewed 5910 times

Why would this be happening, and how can I fix it? I'm not altering the reading other than to convert it from C to F (yes, we Americans are funny that way). Nothing about that multiplication seems like it would explain this behavior.

Thanks for any ideas!