RIO DE JANEIRO — The number of fires in the Amazon rainforest dropped significantly in September, a month when fires typically increase, Brazil’s satellite research agency reported.

The number of fires since the beginning of the year continued to outpace 2018, according to data watched closely by scientists and activists.

Around 20,000 fires burned in the Brazilian portion of the Amazon during September, Brazil’s National Institute for Space Research reported. That was a 35 percent drop from August, when roughly 31,000 fires burned — a nine-year high. It was nearly a 20 percent drop from September 2018, when 24,500 burned.

The plunge — which followed a summer of international attention on the fires, and the Brazilian government’s response to them — caught Amazon watchers by surprise.

Since measuring began two decades ago, September, the peak of dry season, has almost always been more flammable than August. That history fueled expectations that the problem would only worsen as the dry season deepened.