seasonal
adjective
uk/ˈsiːzənəl/ usrelating to, available, or happening during a particular period of the year:
a seasonal employee/worker
a seasonal business/job
seasonal demand/employment/work
seasonal crops/fruit/products
Chefs are recruited on a seasonal basis.
seasonal adjustment/change/variation
ECONOMICS
a change made to figures or other data in order to remove the effect of things that only happen at particular times of year:
Construction employment, which had been surprisingly strong since the beginning of the year, fell by 65,000 after seasonal adjustment.
The figures are adjusted for seasonal changes.