NAIROBI, Kenya — Rainfall is expected in parts of 32 Kenyan counties between September 29 and October 5, as meteorologists monitor ocean conditions that could influence the October-December rainy season.
The Kenya Meteorological Department’s latest weekly forecast indicates that several parts of the country could receive rainfall during the seven-day period, including areas along the Coast, in eastern and central Kenya, Nairobi, the western region, the Rift Valley and parts of northern Kenya.
The counties named in the forecast are Lamu, Kwale, Kilifi, Mombasa, Tana River, Taita Taveta, Mandera, Marsabit, Meru, Embu, Garissa, Kiambu, Kirinyaga, Kisumu, Kitui, Laikipia, Machakos, Makueni, Murang’a, Nairobi, Nakuru, Nyandarua, Nyeri, Tharaka-Nithi, Trans Nzoia, Bungoma, Elgeyo Marakwet, Bomet, Kericho, Kisii, Nyamira and Wajir.
The forecast follows rainfall recorded in several parts of the country between September 21 and 27, with stations in western Kenya and the Lake Victoria basin among those recording significant amounts.
The Kibabii University rainfall station in Bungoma recorded 125.1mm over the seven-day period, the highest total reported during the week.
The Miyare rainfall station in Migori recorded 61.2mm within 24 hours on September 21, the highest daily rainfall total during the period.
Recent daily forecasts have also pointed to rainfall and thunderstorms affecting parts of western Kenya, the Lake Victoria basin and the Coast, indicating an increasingly active rainfall pattern as the country moves towards October.
El Niño alone does not determine Kenya’s rainfall
The latest forecast comes amid growing attention to the October-December rainfall season and the possible influence of El Niño and the Indian Ocean Dipole (IOD).
Jemima Gacheru, a principal meteorologist at the Kenya Meteorological Service Authority, said El Niño should not be treated as a guarantee of heavy rainfall across Kenya.
“So this is just to demystify that notion that El Niño is always equal to rainfall. That is not always the case,” Gacheru said during a webinar hosted by the authority.
She said conditions in the Indian Ocean were also important in determining the distribution and intensity of rainfall over East Africa.
The Indian Ocean Dipole measures the difference in sea-surface temperatures between the western Indian Ocean, near East Africa, and the eastern part of the basin near Indonesia. A positive IOD is generally associated with warmer-than-normal waters in the western Indian Ocean and cooler conditions in the eastern basin.
According to Gacheru, the IOD index was at about +0.7°C and was expected to rise towards +1.0°C in October.
However, the Australian Bureau of Meteorology has cautioned against treating a single elevated weekly reading as proof that a positive IOD event has been established.
The bureau reported an IOD index of +0.65°C for the week ending September 13, but classified the IOD as neutral, noting that one observation above the +0.4°C threshold does not establish a positive event. Sustained values above the threshold are required.
That distinction is important as forecasters assess how the competing climate signals will affect Kenya during the coming rainy season.
Why the Indian Ocean matters
Gacheru said the strength of the IOD could help determine whether Kenya experiences widespread heavy rainfall or a more mixed pattern, with some areas receiving more rain than others.
She pointed to 1997 as an example of what can happen when strong El Niño conditions coincide with a strong positive IOD. That year was associated with exceptionally heavy rainfall across large parts of Kenya.
The situation was different in 2015, when strong El Niño conditions occurred alongside a weaker IOD signal. Gacheru said the result was a more mixed rainfall pattern, with some areas recording above-normal rainfall while others experienced near-normal or below-normal conditions.
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The examples highlight why forecasters assess several climate indicators rather than relying on El Niño alone.
Most areas expected to receive above-normal rainfall
Gacheru said the broader outlook points to above-normal rainfall in most parts of Kenya during the coming season, although this does not mean all areas will receive the same amount of rain.
She said rainfall distribution was also expected to be relatively favourable in many areas, with fewer prolonged dry spells.
“Most areas are expected to have fair to good distribution, meaning the dry spells will not be as many,” she said.
The seasonal outlook comes after the Kenya Meteorological Department previously indicated that wetter conditions were expected to increase from October and continue into November across much of the country.
For farmers, county governments and emergency-response agencies, the forecast provides an early indication of where rainfall is likely to occur, while the intensity and distribution of the rains will continue to be monitored through updated weather advisories.
The Kenya Meteorological Department maintains county-level forecasts to provide more localised information for planning agriculture, disaster response and other activities affected by weather conditions.
