São Paulo, Brazil's largest city, is living through its rainiest September since weather records began in 1943. By 9 a.m. on Monday, September 14, the station of the National Institute of Meteorology (Inmet) at Mirante de Santana, in the city's north zone, had collected 253.8 millimeters of rain in the month, roughly 10 inches, according to agency data published by the state news service Agência SP. That is three times the climate average for all of September, 83.3 millimeters.
The total has passed the previous September record of 1983, when the same station measured 243.1 millimeters. Next in the ranking come 1993, with 206.7 millimeters, 2015, with 201.7, and 1957, with 197.2. The record fell quickly: at 9 a.m. on Saturday, September 12, the month stood at 198.2 millimeters, and another 55.6 millimeters fell on the station in the following 48 hours. Between Friday and Saturday, the site registered 75.4 millimeters in 24 hours, the largest volume recorded anywhere in Brazil in that period, according to Inmet data reported by G1. September is now the second rainiest month of 2026 at the station, behind only January, which accumulated 256.4 millimeters.
The record extends across the state
The high totals are not confined to the capital. Between September 1 and 13, Campinas accumulated 257.2 millimeters, 3.1 times its monthly average of 83.7 millimeters and its largest September since the local series began in 1961, beating the 1976 mark of 183.3 millimeters. In Registro, a town in the Vale do Ribeira valley in southern São Paulo state, the 185.3 millimeters through the 13th make this the third rainiest September in a series that also dates from 1961. In São José dos Campos (161 millimeters), the Baixada Santista coastal region around the port of Santos (232.7 millimeters) and Bauru (118.8 millimeters), volumes are also well above the climate averages, according to Agência SP. In the capital, the storms flooded streets and left people missing, G1 reported; across the state there have been river floods, urban flooding and landslides, with deaths recorded, according to InfoMoney. Families in the Vale do Ribeira and around Itapeva have already received state aid because of the rains.
The role of El Niño
The state Civil Defense attributes the heavy rain to El Niño, a natural phenomenon linked to abnormal warming of Pacific waters along the Equator that changes atmospheric circulation and redistributes moisture and temperature across the planet. Climatologist José Antônio Marengo of Brazil's National Center for Monitoring and Early Warning of Natural Disasters (Cemaden) says the phenomenon is established and still strengthening. In his view, a strong El Niño does not by itself guarantee a summer with more severe storms: heavy rain, damaging winds and tornadoes can happen with or without it.
"In the equatorial Pacific region where it forms, the warming has already passed 1.8 degrees Celsius of anomaly, and when it reaches 2, that would mean a very strong El Niño, which is forecast for the end of this year and the start of the next," Marengo said.
What is being done
Since Friday, September 11, a crisis cabinet has been working in person at state Civil Defense headquarters, bringing together representatives of the state government, the power, water and gas utilities, the highway department (DER), state regulators (Arsesp, SP Águas and Artesp), the Fire Department and the state Highway Police. The agency is tracking conditions with radar and satellites, with teams mobilized across the state, and residents can receive free SMS alerts by texting their postcode, called CEP in Brazil, to 40199; in emergencies the numbers are 193 and 199. "Numbers like these show why monitoring cannot stop. Information and risk awareness are what allow people to protect themselves in this period. Prevention is what saves lives," said Colonel Araújo Monteiro, the state coordinator of civil defense. Ahead of the storm season's peak, the state has also advanced the delivery of emergency response kits and training for municipal teams, including sessions of the Operação Chuvas de Verão, the summer rains operation, held in Piracicaba, according to the local outlet Piranot.
Forecaster Climatempo expects the rain to start easing on Tuesday, September 15, with clouds thinning only on Thursday the 17th. State Civil Defense meteorologist William Minhoto warns that the record may still grow: "Since September is still under way and more rain is forecast in the coming days, the monthly total may increase until the end of the period, extending the current record," he said. Even as the weather system moves away from Wednesday the 16th, saturated soil keeps the risk of flooding, flash floods and landslides, mainly in vulnerable areas, and the arrival of polar air should hold temperatures below 20 degrees Celsius in the capital this week.