First understand why sinusitis occurs it occurs either due to dryness of nose or pharynx or due to increased susptibility to infections in summer there is reduced susceptibility to infections of nose or pharynx and in winter there is high susceptibility so u get it often in winter not in summer
Next Steps
in winter or rainy season u should take steam alternate day in morning ani have something warm for the pharynx like green tea
Health Tips
Just dont go anywhere where u experience very high temperature changes