Warmer weather will not affect your basal body temperature as your body is very good at maintaining itself at its optimal temperature. Meaning that you can still keep measuring as always even if the temperature increases/decreases due to seasonal changes. However, remember that our best advice is to always mark the temperature as deviating if you feel any need to be concerned about the accuracy of it.
In the case of a bad sunburn, we do advise that you mark your temperature as deviating as a precaution.
If you're experiencing a big, sudden, increase in outdoor temperatures, such as in the event of a heat wave or when traveling to a very different climate than your home country, we recommend that you continue measuring to keep up the habit but mark the temperature as deviating the very first morning if you're feeling warmer. After the first morning, you can continue adding your temperature as 'Normal'.
When traveling to a new country and/or starting to use air conditioning during the night, we recommend that you continue measuring to keep up the habit but mark the temperature as deviating the first morning as the cooler air may very well be cooler than at your home and normal environment.