Answer:
C) Incidentally
Explanation:
Personally I don't like any of these answer choices. However, this one makes the most sense in this context. The others would need a much different set-up earlier on in the passage. "Incidentally" does not require such a set up, which is why it is the only one that fits.
The weather forecast for the day, or rather what we can assume the
predicted forecast is due to the preparations the family are making,
will likely be a hot and sunny day, with a lot of humidity. We can
establish this due to the fact that sunscreen is being packed, combined
with the fact that Becca will need her inhaler.
A short story's setting is made of time and place.
Apart from plot (what is going on) and characters (who is doing what they are doing), the setting (where and when is the plot happening) is the most important element of a short story. The interpretation of a short story depends very much on how the author has described the setting. It provides a context for the events.