Nairobi, Coast, Nyanza among areas set for above-average rains

NAIROBI, Kenya, Aug 26 – Kenya is headed for a wetter-than-usual October to December rainfall season, with the Kenya Meteorological Service Authority (KMSA) forecasting above-average rains across large parts of the country.

The outlook released on Wednesday indicates that most counties are likely to receive above-normal rainfall during the 2026 short-rains season, with some areas expected to experience prolonged wet spells and isolated storms.

The forecast comes as the El Niño event in the equatorial Pacific continues to strengthen, while the Indian Ocean Dipole (IOD) is expected to move into its positive phase from September.

KMSA said the strengthening El Niño and a potentially positive IOD could enhance rainfall during the season, although the timing and strength of the IOD remain uncertain.

Among the areas expected to receive above-average rainfall are Nairobi, Kiambu, Murang’a, Nyeri, Nakuru, Kericho, Bomet, Kisii, Nyamira, Kisumu, Homa Bay, Migori, Siaya, Busia, Bungoma, Kakamega, Vihiga, Nandi, Uasin Gishu, Trans Nzoia, Elgeyo Marakwet, Baringo and Narok.

The forecast also places much of the Coast, eastern and northeastern regions in the above-average rainfall category, including Mombasa, Kilifi, Kwale, Lamu, Tana River, Garissa, Wajir, Mandera, Isiolo, Meru, Embu, Tharaka-Nithi, Kitui, Makueni and Machakos.

Turkana and parts of West Pokot, Samburu and Marsabit are expected to record rainfall ranging from near average to above average.

KMSA said rainfall distribution is expected to be fairly to well spread across much of the country, although Turkana and Samburu could experience poorer distribution.

The season is also expected to be characterised by prolonged wet periods punctuated by isolated storms.

Rainfall to extend into January

The timing of the rains will vary across the country.In western Kenya, including Nandi, Kakamega, Vihiga, Bungoma, Siaya, Busia, Kisumu, Homa Bay, Migori, Kisii, Nyamira, Kericho and Bomet, rainfall is expected to continue from September and extend into January.

In Nairobi, Kiambu, Murang’a, Nyeri, Nyandarua, Laikipia, Kirinyaga, Meru, Embu and Tharaka-Nithi, the rains are expected to begin between the second and third weeks of October and continue into January.

Machakos, Kitui, Makueni, Kajiado, Taita-Taveta and inland parts of Tana River are expected to receive the rains between the third and fourth weeks of October, with rainfall continuing into January.

The Coast is expected to have a shorter rainfall window, with Mombasa, Kwale, Lamu, Kilifi and the Tana Delta likely to experience onset between the second and third weeks of October before the rains ease between the first and second weeks of December.

In Marsabit, Mandera, Wajir, Garissa and Isiolo, the onset is expected during the second and third weeks of October, with the season likely to end between the first and second weeks of December.

Turkana and Samburu are expected to receive the rains from the third to fourth week of October, with cessation projected for the first week of December.

El Niño intensifies

The meteorological authority said the El Niño event has continued to gain strength, with the Niño 3.4 index showing a sustained rise.

The seasonal average for May to July stood at 1.51 degrees Celsius above normal, while the July monthly figure reached 2.03 degrees Celsius.

The weekly index centred on August 12 rose further to 2.7 degrees Celsius, indicating that the event is developing into a very strong El Niño.

The IOD, meanwhile, remains neutral but is expected to strengthen in the coming weeks.

As of August 23, the weekly IOD index stood at plus 0.17 degrees Celsius, below the plus 0.4 threshold required for a positive IOD event.

KMSA expects the index to cross that threshold from September, although there is still uncertainty over how quickly and how strongly the shift will occur.

The authority projects a peak IOD value of about plus 0.7 during the season.

Low drought risk

Despite concerns over extreme weather, the rainfall outlook points to a low probability of drought across most parts of Kenya.

KMSA’s Standardised Precipitation Index forecast shows a low likelihood of mild, moderate or severe drought during the October-December period.

Turkana is the main exception, with the county facing a 15 to 20 per cent probability of experiencing mild drought conditions.

The authority has, however, cautioned that rainfall patterns could change during the season because of shorter-term weather systems, including tropical cyclones in the Southwest Indian Ocean and the Madden-Julian Oscillation.

Temperatures expected to rise

The wetter season is also expected to be warmer than average in several parts of the country.

KMSA forecasts the highest likelihood of above-normal temperatures in Mombasa, Kwale, Kilifi and Lamu, as well as parts of Tana River, Taita-Taveta and Garissa.

Temperatures during the October-December period normally range from about 17 degrees Celsius in cooler highland areas such as Kericho and Uasin Gishu to more than 30 degrees Celsius in parts of Turkana.

The expected above-average rainfall could have both positive and negative consequences for different sectors, with the specific impacts to be assessed by relevant sector agencies.

KMSA has urged Kenyans and institutions to keep monitoring subsequent forecasts, noting that the national outlook will be supplemented by 24-hour, five-day and seven-day forecasts, monthly updates and county-specific advisories.

The authority said regular updates would be issued as the season approaches to provide more precise information on rainfall onset, distribution and cessation.