It is the HUMIDITY!!! No matter what the temperature, it is the increased Humidity that causes the increased swelling and pain, the sausage fingers and toes.
Evidenced by those who have been to drier climates. I personally discovered this several years ago, while in Florida to visit parents at their condo. It was warm, then it rained a couple days, suddenly my hands were swollen and achey. The humidity was up in the 90%s, that is why so many arthritics choose to move to the drier USA climates, like Arizona and California!
The humidity causes terrible, penetrating pain in the joints, the only relief is to stay in the air-conditioned rooms, which are also dehumidified.
The heat is a relief for the arthritis as long as it is not accompanied by increased humidity!!
But, try to enjoy the summer anyways, just watch the weather reports that give the humidity level, and avoid being out in it if it increases. Cheers, Loret xx