“Allergies and sinus problems are common during the warmer seasons. A reason for this is that plants release pollen in the spring, summer, and fall. People allergic to pollen may experience symptoms similar to a cold during these seasons. However, a cold or flu will usually not last longer than 2 weeks, while allergies can last 6 weeks or longer — depending on the cause of your allergic reaction.

Depending on where you live, another cause of summer sinus problems is the hot and dry air, which can irritate your sinuses and lead to a sinus infection — or sinusitis.”

Medicine Net (Can Hot Weather Cause Sinus Problems?)