In Rio's summer there are days when the heat changes your plans: the midday sun, the humidity and long walks add up quickly. City Hall has a protocol with five heat levels and publishes the current level. This guide explains where to check it and how to rearrange a vacation day without missing what matters.
At a glance
- Who issues the alerts: the Rio Operations Center (COR), using forecasts from the Alerta Rio system.
- How it's measured: five levels, NC1 to NC5, based on the heat index (which combines temperature and humidity) and how many days it lasts.
- Where to check it: on the COR ↗ website and app, and on its social media.
- From NC4: the city opens cooling centers and may reschedule outdoor events.
- Rule of thumb: outdoor activities early or late in the afternoon; midday indoors or in the shade.
The heat levels
According to the COR protocol ↗:
| Level | When it's declared | What changes |
|---|---|---|
| NC1 | No high heat index forecast | Nothing in the city's routine |
| NC2 | Heat index of 36 to 40 °C for one or two days | Information for the public |
| NC3 | 36 to 40 °C forecast to last at least three days | More communication on all channels |
| NC4 | 40 to 44 °C for at least three days | Cooling centers, more hydration points and possible rescheduling of events |
| NC5 | Above 44 °C for at least three days | Bulletins every six hours, cooling centers and suspension of outdoor activities in schools |
The heat index isn't the thermometer reading: COR calculates it by combining temperature and relative humidity, so it can feel hotter than the forecast suggests.
Where to check the day's alert
- COR website: the heat levels ↗ page explains the protocol; COR announces the current level on its channels.
- COR.Rio app: free for Android and iOS, according to COR ↗.
- COR social media: it posts real-time information on X, Instagram and Facebook.
Check it the night before, when you plan the next day, and again in the morning.
How to rearrange a hot day
- Beach early. Go first thing and head back before midday. If you stay, find shade and bring water.
- Midday indoors. It's the time for museums, the aquarium or a long lunch. Ideas in the museum guide and in Rio when it rains, which also works for hot days.
- Climbs and walks in the morning. Trails, lookouts and long walks, early.
- Short transfers. Group your plans by area so you don't spend hours outside getting from one place to another.
- Outdoors at sunset. Late in the afternoon the sun drops: a good time for the waterfront or a lookout. We help you choose in sunsets in Rio.
What City Hall recommends
On days of extreme heat, City Hall recommends avoiding direct sun exposure at the hottest times of day, according to COR ↗. If you're traveling with children, older people or someone with a health condition, ask their doctor before the trip how to handle the heat. If someone feels seriously unwell, call SAMU at 192 and notify your travel insurance.
Frequently asked questions
Which months are hottest?
Summer, from December to March, although there can be very hot days outside that period. Compare months in the climate guide.
Are events canceled at NC4 or NC5?
Medium and large events may be rescheduled and outdoor activities suspended. If you have tickets for something, follow the organizer's channels.
What should I pack for hot days?
Light clothes, a hat, sunscreen and a water bottle. There's a full list in what to pack for Rio.
Sources: COR: heat levels ↗ and COR: measures for extreme heat days ↗, accessed October 27, 2026.