Maximum lossless compression ratio for floating point time series

There is a very battle-tested library for this called fpzip, which has both lossless and lossy compression. There's a paper by the authors about their approach (here's a link without a paywall too). If you look at table 1 in their paper, they get compression ratios on the order of 100 for some simulation outputs, but as low as ~1.3 on others. Clearly the results depend very strongly on the nature of the data you're compressing. For some fields, like the velocity in a fluid mechanics simulation, nearby values tend to have similar magnitudes, which makes it possible to compress the exponents of those nearby floating-point values. I haven't used fpzip personally, but since your time series is relatively smooth I think you'd get good results.