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Heavy rainfall alert: Where it will flood this short rains season
Residents of Sigiri wade through flood waters in Budalangi on May 7, 2024. The floods were caused by an overflow from Lake Victoria due to ongoing heavy rains in the Nyanza region.
The Kenya Meteorological Department has issued a heavy rainfall warning in 39 counties, including Nairobi, warning of potential flooding, as the October-November-December short rains season continues.
The advisory warned that "rainfall currently affecting parts of the Lake Victoria Basin, the Rift Valley and Highlands West of Rift Valley is expected to intensify to more than 30mm in 24hrs and spread to the Highlands East of Rift Valley including Nairobi and parts of Southeastern lowlands on Thursday."
Already, Budalangi in Busia County is flooding, as heavy rains continue across western Kenya.
When the weatherman posted the alert on its social media pages, Kenyans were quick to point out the contradiction of heavy rains, yet the weatherman's own forecast had predicted depressed rains for the season.
The Kenya Meteorological Department's seasonal outlook, issued in September, had already painted a picture of disappointment for most regions. In the forecast, the department stated: "Most of the Northeast, Southeastern lowlands and Coastal region are expected to receive below average rainfall, while the Highlands West of the Rift Valley and parts of Northwestern are likely to receive near to above average rainfall."
Residents of Magongo in Mombasa block the road following flooding in their houses, May 31, 2015. They were demanding an immediate solution to the problem.
The reason for this uneven distribution traces to oceanic patterns far away. According to the forecast, "the main driver of this outlook is the developing negative Indian Ocean Dipole (IOD), which is expected to persist from September to November 2025 before returning to neutral conditions in December.
A negative IOD typically brings drier than normal conditions over East Africa, potentially suppressing rainfall during the short rains."
The IOD is a natural climate pattern where warm and cold ocean temperatures shift between the eastern and western sides of the Indian Ocean, affecting rainfall patterns across the region.
Even more concerning for long-term water security, meteorologists warned that drought conditions are increasingly likely. Using a tool called the Standardised Precipitation Index (SPI), which measures how wet or dry a period is compared to what normally happens, forecasters projected a 55 to 90 per cent chance of mild drought across much of Kenya, compared to the normal 46 per cent likelihood. The risk is highest in the eastern and central regions.
A woman carried across a flooded section of Mau Mau market in Budalang'i in Busia County on May 15, 2021.
In Budalangi, the flood-prone constituency of Busia County in western Kenya, excessive rainfall is already proving catastrophic, even as the broader forecast predicted near-average to below-average conditions for much of the Lake Victoria Basin.
Budalangi experiences rainfall in October and December during the short rains season, with the area receiving a minimum and maximum mean monthly rainfall of between 20 and 200 millimetres. But when the rains come hard, the Nzoia River often cannot contain them. In recent major floods, at least 20,000 people were forced to leave their homes in Budalangi, with the river bursting its banks.
The heavy rainfall advisory issued on Wednesday, October 22, flagged these risks, noting that "residents in all the mentioned areas are advised to be on the lookout for potential floods. Flood waters may appear in places where it has not rained heavily especially downstream."
This paradox, flooding in western Kenya even as much of the nation faces drought, highlights the complicated reality of climate forecasting and seasonal rainfall patterns.
The Met Department emphasised that "the OND 2025 rainfall is expected to be poorly distributed, both in time and space over several parts of the country. The western sector is expected to have a fair to good distribution while the central sector is expected to have a poor to fair distribution."
With about a 55 per cent chance of La Niña developing during September through November 2025, rising to 60 per cent in October through December, the department said it would continue monitoring oceanic conditions closely.
La Niña is a climate pattern where cooler-than-normal ocean temperatures in the Pacific Ocean change global weather patterns, often bringing drier conditions to East Africa.
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