What does 'above-average rain' in Kenya's November forecast mean, and how sure is it?

The Kenya Meteorological Service Authority (KMSA) uses the word 'expected' for its call of above-average rainfall in November, in a bulletin issued on 30 October 2026. The bulletin's appendix defines above average as more than 125% of the long-term mean (LTM) and puts 'expected' at a probability of 76% to 90%, which it labels high confidence. The appendix table is headed 'Rainfall Amount (24 hrs.)', and the bulletin does not say which period the percentage covers or which years the long-term mean spans.

The bulletin, reference KMD/FCST/04-2026/MO/11 and signed by Acting Director General Edward M. Muriuki, lists Nairobi, Mombasa, Kisumu, Nakuru, Machakos, Kajiado, Kwale and Kilifi among the counties expected to get above-average rain in November, along with much of West Pokot, Samburu and Marsabit. For parts of Turkana, West Pokot, Samburu, Baringo and Marsabit it says near-average to above-average. It makes the same above-average call for November to January and forecasts warmer-than-average temperatures nationwide for November.

The appendix defines the terms. Below average is under 75% of the long-term mean, near average is 75% to 125%, and above average is over 125%. For a place whose long-term mean is 100 mm (a hypothetical figure for illustration, not a Kenyan measurement), above average would start past 125 mm.

KMSA's bulletin gives no probability for individual counties. A regional seasonal outlook does give probabilities, for the October–December season as a whole, and its categories differ from KMSA's: 'above normal' there means the wettest third of past seasons, not more than 125% of the mean. The IGAD Climate Prediction and Applications Centre (ICPAC) released the outlook at the 74th Greater Horn of Africa Climate Outlook Forum, held in Kigali on 17 and 18 August 2026. It sorts historical rainfall totals for 1991 to 2020 into thirds: the upper third is 'above normal', the lower third 'below normal', and the middle 'normal'. With no forecast at all, each third would be equally likely.

ICPAC then gives each zone three probabilities. In Zone I, above normal is 90%, normal 5% and below normal 5%. In the most widespread shade of Zone II the figures are 65%, 25% and 10%; in Zone III, 55%, 30% and 15%. Only in Zone IV is below normal the likeliest category, at 45%. The strongest wet signal, above 90%, lies over southern Ethiopia, central to southern Somalia and north-eastern Kenya.

ICPAC linked the regional wet outlook to two oceans. El Niño, a warming of the tropical Pacific, was already established when the forum met in August. In its discussion of 8 October 2026, NOAA's Climate Prediction Center kept its El Niño Advisory in force and said most Niño indices had risen over the past month, with Niño 3.4 reaching +2.1°C. It said El Niño continued to strengthen, with a strong-to-very strong event likely through January–March 2027, a chance of more than 83%. The Indian Ocean Dipole was neutral in August and likely to turn positive, though forecast skill for it has 'historically been low'.

ICPAC's outlook is 'relevant for seasonal timescales and for relatively large geographical areas'. Local and month-to-month variations might occur, and dry spells may occur even where above-normal rain is likelier. KMSA's review of October found that most counties had below-average to near-average rain; stations including Marsabit, Garissa, Mandera, Kisii, Kisumu and Lamu passed their October long-term means, and the other stations in its chart fell below.

The October–December season supplies up to 70% of annual rainfall in parts of Ethiopia, Kenya and Somalia. KMSA's bulletin lists what extra rain can bring: waterlogging, delayed farm work and crop pests; rural access roads that may become impassable; urban drainage that may be overwhelmed; and flash floods, river floods and landslides in low-lying coastal areas, flood-prone river basins, towns with poor drainage and steep highlands. Standing water may raise the risk of malaria, and contaminated water the risk of cholera, typhoid and diarrhoeal infections. The rain is also likely to raise river flows and replenish dams, water pans and groundwater.

KMSA says the outlook should be used with its 24-hour, 5-day, 7-day and special forecasts. Its appendix grades a day's rain as heavy at 21 to 50 mm and very heavy above 50 mm. The Star reported on 4 November that the weekly forecast covers 3 to 10 November and that Muriuki said most parts of the country were expected to receive above-average rain in November and December.