An ancient post from @dsj in the earliest days of the Air+Sky said that the sensors had very limited storage (just 1-3 hours) for when they can’t reach the Hub, and the Hub had about 8 ‘days’ of storage for dealing with an Internet dropout.
Remember - if when you lost power the Hub wasn’t powered up, it doesn’t matter how much storage the Hub has. It matters how ‘little’ the sensor has to hold the actual readings until the sensor can reconnect to a Hub when power returns.
From your screen grab it looks like you lost maybe 4-5 hours of data. That’s far in excess to what the old Air+Sky could store if they couldn’t connect to the (unpowered) Hub.
Sorry - I can’t find the numbers for the current Tempest systems. The forums are rather unsearchable.
The old thread is Offline data storage during internet outages - #6 by dsj