There is some rounding going on, but @sunny is correct in general: The daily probability will almost always be higher than the hourly probability, but it is also not as simple as a textbook probability equation. The details are complicated (and some of them are part of our secret sauce), but we’ve posted an FAQ with a little more detail here:
This is likely the case of a very low hourly probability (1% or 2%) rounding to zero, while the daily probability value rounds to 10%.