The Kenya Meteorological Department has issued a fresh update on the onset of the March-April-May (MAM) 2026 long rains.
In an update on Tuesday, February 24, Kenya Met noted that several parts of the country have already met the rainfall onset criteria, while others are expected to experience delayed onset.
The department noted that the March to May period remains the major rainfall season over most parts of Kenya and much of equatorial East Africa.
“The March to May period is the major rainfall season (Long Rains) over most parts of Kenya and much of equatorial East Africa. The highest seasonal rainfall amounts (greater than 300mm) are normally received over the Lake Victoria Basin, the Highlands West of the Rift Valley, the Central and South Rift Valley, the Highlands East of the Rift Valley (including Nairobi County) and the Coastal Strip (Fig. 1),” the statement read.
Under the updated MAM 2026 rainfall onset dates, the department explained that the rainfall currently being experienced is likely to continue into early March and is expected to meet the onset criteria in several regions.
It further clarified the scientific benchmark used to determine onset.
“The onset criteria is defined as the receipt of at least 20 mm of rainfall within three consecutive days, with no dry spell exceeding seven (7) days thereafter,” the statement added.
According to the update, the MAM 2026 long rains onset has already been realized from mid-February over western, central and highland regions, including Nairobi.
Counties in the Highlands West of the Rift Valley, Lake Victoria Basin, Central and South Rift Valley, as well as the Highlands East of the Rift Valley, met the onset criteria in mid-February.
The Southeastern Lowlands, including Kajiado, Kitui, Makueni, Machakos, Tana River and Taita Taveta, met the onset criteria in the fourth week of February.
However, the department warned that rainfall performance may fluctuate in the coming weeks.
“Indications suggest that the Madden–Julian Oscillation (MJO) is likely to transition to less favourable phases from mid-March, which may result in a reduction in rainfall amounts and an increased likelihood of dry spells, as the convective environment becomes suppressed over some regions,” the statement continued.
For the North Coast counties of Lamu, Malindi, coastal parts of Tana River and Kilifi, onset is expected between late March and early April, despite intermittent rainfall experienced earlier.
Similarly, the Northwestern region, including Turkana and Samburu, and the Northeastern counties of Wajir, Isiolo, Garissa, Mandera and Marsabit, are projected to experience onset between the first and second week of April.
The department attributed the early seasonal rainfall to favourable atmospheric systems.
“The forecasted early season rainfall is associated with the presence of favourable mesoscale and large-scale atmospheric systems, including the enhanced convective activity linked to the Madden-Julian Oscillation (MJO). These systems are expected to temporarily enhance moisture convergence and rainfall amounts over several parts of the country during the late February to early March period,” the statement noted.
Farmers and other stakeholders have been advised to rely on continuous updates and expert guidance when making decisions during the season.
“This outlook should be used together with the 24-hour, 5-day, 7-day, monthly and special forecasts, as well as regular updates and advisories issued by this Department, in addition to the Weekly and Monthly County forecasts developed and disseminated by the County Meteorological Offices. Farmers are advised to consult Agricultural Extension Officers for further guidance and decision-making,” the statement concluded.
