There are three primary seasons in the Lençóis Maranhenses:
1) Rainy Season:
The rains start between the end of January and February and generally cease in May (rainy season). This time of year is not recommended to visit given that the sky is generally overcast and the rains make for a less pleasant visit.
2) Start of Dry Season:
Immediately following the rainy season, when the rains cease, yet the lagoons remain very full from the rains. Depending on how much rain has fallen in any given year during the rainy season, this period can vary. But generally goes from June to September/October. October is the end of the mid-season and start of the hotter months, the chance of finding lagoons still with water is high. The lagoons definitely won’t be as full as they would in July of August, for example, but there should still be a good number of lagoons with water. Moreover, October is the low season in Brazil (the highest season is between July and August given school holidays in both Brazil and most countries in the northern hemisphere), thus a visit in this season would offer much more intimacy and less crowds.
3) Dry Season:
With no rains and when the lagoons have mostly all evaporated. Again, this season can vary slightly depending on the rains. For example, on my most recent visit, in late November, 2019, there was still water in some of the larger lagoons, but for the most part the lagoons were dry.
We HIGHLY recommend both sunrise and sunset tours. Independent of the lagoons, the immensity of the Lençóis Maranhenses and the beautiful colors at sunrise and sunset are well worth a visit.
The Dunes and Pools at Lençóis Maranhenses truly are a special place in Brazil!