Generally when you see a surge in the mempool size, and therefore the average fee, it is usually around 13:00 - 23:00 UTC, which corresponds to day time in most of Europe, and initially the east coast and then all of the Americas. Conversely, the mempool is usually fairly empty, with fees around 1-2 sat/byte, around 01:00 - 06:00 UTC, when the aforementioned continents are generally sleeping and Australia and eastern Asia are awake.
Perfect! It means most of bitcoin transactions have been made in America and European continents and locals there tend to use higher fees (likely), whilst the Asia and Australia continents tend to make less numbers of transactions as well as they likely are ready to move their coins with lower fees.