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Açu fire, September 2025 Açu

Out · last detection 29 Sept 2025, 16:22 UTC

The fire started on 20 September 2025 in Açu, Brazil, and satellites saw it burning for 10 days. Copernicus’s global GWIS system rebuilt a burnt perimeter of 3,201 hectares from heat detections, spread across a single municipality.

Number 661 in Brazil in 2025, of 714.

The power measured by the satellite is low (13.6 MW in the strongest hotspot), more typical of grass or stubble burning, or a slow surface fire, than of a large crown fire.

Burnt area
3,201ha
GWIS perimeter (Copernicus)
Duration
10days
20 Sept 2025 – 29 Sept 2025
Municipalities hit
1
municipalities
Started on
20 Sept
2025
Heat detections
65
in a single hotspot: 14 MW
Danger at start
47
Very high · FWI index
Energy released
470MW
sum of detected power

Where it burned

29 Sept 2025
HOTSPOTS BY DAY 20 Sept29 Sept

How it evolved, day by day

2429

Fire radiative power detected each day, in megawatts, and number of hotspots. The magenta bar marks the peak day.

The weather it burned in

36°high
50km/h · peak gust
23%lowest humidity

It had gone 12 days without rain (1 mm or more) when it started.

This area had burned before

54% of the perimeter overlaps earlier fires recorded since 2016: 1,744 ha in 2024.

What happened to each town

  1. Açu 56,496 inhabitants where it started
    3,223 ha reached on 19 Sept
    2.5 %

Burnt area inside each municipality, from crossing the GWIS perimeter with administrative boundaries. The distance is from the town centre to the nearest fire: staying a kilometre away does not mean it reached the houses.

The weather day by day

ECMWF ERA5 reanalysis at the fire location, the standard reference for past weather, and the Canadian Fire Weather Index (the same system Copernicus uses), computed by WorldFires from that data. Days after the fire run until the first rain.

Open-Meteo.com (CC BY 4.0) · Copernicus Climate Change Service (ERA5)

Day High Min. humidity Peak gust Rain Danger (FWI)
13 Sept 35.3 °C 30 % 39 km/h 0.0 mm Very high 47
14 Sept 35.5 °C 31 % 43 km/h 0.0 mm Very high 48
15 Sept 35.4 °C 31 % 46 km/h 0.0 mm Extreme 51
16 Sept 35.3 °C 30 % 45 km/h 0.0 mm Extreme 50
17 Sept 35.3 °C 29 % 44 km/h 0.0 mm Very high 48
18 Sept 35.3 °C 32 % 42 km/h 0.0 mm Extreme 50
19 Sept 36.1 °C 23 % 45 km/h 0.0 mm Extreme 54
20 Sept 34.5 °C 35 % 46 km/h 0.0 mm Extreme 50
21 Sept 35.3 °C 33 % 46 km/h 0.0 mm Extreme 52
22 Sept 35.2 °C 32 % 42 km/h 0.1 mm Extreme 50
23 Sept 36.1 °C 32 % 46 km/h 0.0 mm Extreme 53
24 Sept 34.9 °C 31 % 49 km/h 0.0 mm Extreme 53
25 Sept 35.9 °C 30 % 50 km/h 0.0 mm Extreme 53
26 Sept 34.9 °C 28 % 48 km/h 0.0 mm Extreme 52
27 Sept 35.5 °C 28 % 45 km/h 0.0 mm Extreme 53
28 Sept 35.5 °C 27 % 48 km/h 0.0 mm Extreme 52
29 Sept 35.6 °C 30 % 47 km/h 0.0 mm Extreme 53
30 Sept after 36.0 °C 32 % 48 km/h 0.0 mm Extreme 54
1 Oct after 34.2 °C 38 % 47 km/h 0.0 mm Very high 48
2 Oct after 33.1 °C 39 % 49 km/h 0.0 mm Very high 48
3 Oct after 35.3 °C 29 % 46 km/h 0.0 mm Very high 49
4 Oct after 35.0 °C 28 % 46 km/h 0.0 mm Extreme 50
5 Oct after 35.6 °C 30 % 48 km/h 0.0 mm Extreme 52
6 Oct after 35.5 °C 30 % 50 km/h 0.0 mm Extreme 54
7 Oct after 35.7 °C 32 % 43 km/h 0.0 mm Very high 50
8 Oct after 35.7 °C 33 % 44 km/h 0.0 mm Extreme 50
9 Oct after 36.5 °C 30 % 49 km/h 0.0 mm Extreme 55

Before and after, from space

Drag the line to compare the same ground before the fire and after it.

Before · 13 Sept 2025
After · 6 Oct 2025

If the day is cloudy, change the date: each satellite passes once a day. In false colour the burnt ground looks brown or red.

The smoke

CAMS · Copernicus

On 25 September 2025 the air beside the fire reached 9 µg/m³ of PM2.5, but no daily average passed the WHO guideline (15).

PM2.5 peak9 µg/m³
Days over the guideline0 days
PM1010 µg/m³
Optical depth0.36
1819202122232425262728293012
Good Fair Moderate Poor Very poor Extremely poor

Particles from the Copernicus CAMS model at the centre of the perimeter; these are not measurements in each town. The pale bar is the worst hour, the solid one the daily average.

Open-Meteo.com (CC BY 4.0) · Copernicus Atmosphere Monitoring Service (CAMS)

Detections table · 65Every satellite heat detection, one by one, with time, satellite, power and coordinates.
⬇ Download CSV Times in UTC. Each detection is a 375 m pixel: a large fire yields hundreds per pass.
Date and timeSatelliteFRP (MW)LatLon

Frequently asked questions

How long did the Açu fire last?
GWIS (Copernicus) dates it between 20 September 2025 and 29 September 2025: 10 days between the first and last heat detection of the perimeter.
How much area did it burn?
The perimeter GWIS (Copernicus) rebuilt from heat detections is 3,201 hectares (32.0 km²). It is an estimate: official national figures may differ.
Which municipalities burned?
The fire only entered Açu (3,223 ha, 2.5 %).
What was the weather like?
During the fire the temperature reached 36.1 °C, humidity dropped to 23 % and gusts hit 50 km/h. The fire danger index (FWI) reached 54, class Extreme.
Where does this data come from?
From the GWIS (Copernicus) burnt perimeter, NASA FIRMS VIIRS hotspots and the administrative boundaries of Brazil (geoBoundaries). It is not an official report.

Where to verify it

A satellite detection is not an official report. Final figures and the fire’s status are published by each country’s emergency service.

Emergency number: 193

Satellite cross-check

Does something look wrong on this page?

This page is built from satellite data and official records, and it sometimes gets things wrong: the wrong dates, the wrong town, two fires merged into one, or something that was not a wildfire at all. If you know this fire first-hand (you live nearby, saw it, fought it or reported on it), tell us what really happened and we will check it.

Report an error
What do you think is wrong?

We will only use your email to reply about this report. Privacy. This is not an emergency service: if there is a fire now, call 193.

Where this data comes from

The perimeter comes from the Copernicus Global Wildfire Information System (GWIS), which rebuilds it from MODIS and VIIRS heat detections and publishes it under CC BY 4.0. It is not measured on imagery as in Europe, so it is an estimate. Heat detections come from the VIIRS sensors aboard Suomi-NPP and NOAA-20, distributed by NASA FIRMS at 375 m resolution. Municipal boundaries come from geoBoundaries ADM2 (Creative Commons Attribution 3.0 Intergovernmental Organisations (CC BY 3.0 IGO)). The area per municipality is computed by WorldFires by crossing the perimeter with those boundaries, so it may differ from each country’s official figure.