March travel presents very different scenarios depending on Carnival and Easter. If either one of those holidays is in March, travelers will be faced with multi-day package reservations for both. If neither of them is in March, many hotels in the top touristic destinations will be charging high season rates, but dispensing guests from the need to book several stays at once.
That allows March travelers the chance to hop more frequently from one destination to the other throughout the month.
Though some colleges only start the year in March, most kids up to high school have been back to school for over a month. It's still summer until the third week of the month (and by all means still rainy season in a great part of the country); however, the chance of having a whole beach all to yourself greatly increases at this time of the year, especially on weekdays.
Locals will still be seeking the last of summer heat on weekends, so check with hotels about higher rates from Thursday or Friday to Sunday, a practice which may be applicable in other seasons as well.
The Extraordinary activity brought on by El Niño and global climate change on the side, March weather in Brazil has always carried the possibility of summer storms and a high rainfall index along with hot weather. For at-a-glance rainfall index average/temperature graphs for Brazil capitals through the year, see CPTEC weather maps.
Roughly speaking, beachgoers seeking the least chance of rain should concentrate on the stretch of coast between Búzios and Southern Bahia.
If you check the CPTEC maps for Brazil's Northeastern coastal capitals such as Natal or Fortaleza, you'll see how they still show high-temperature averages but have already entered their rainier season in March.
If Carnival or Easter are not in March, the month is marked by local rather than national holidays. Rio de Janeiro, for example, commemorates the city's foundation on March 1 (the city was founded in 1565).
The abrupt drop in number of tourists right after Carnival motivated Salvador to create a late summer festival called Espicha Verão ("Summer Stretcher"), also known as Praia 24 Horas ("24-Hour Beach"). Maybe other cities in Brazil will follow suit.