Heavy rains pounding Nairobi in the past/FILE

Rainfall is expected in parts of 32 counties between September 29 and October 5, according to the Kenya Meteorological Department's weekly forecast.

The department said rainfall is likely in parts of 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 counties.

The forecast follows rainfall recorded in several parts of the country between September 21 and 27.

During the period, rainfall was recorded in Bungoma, Busia, Migori, Siaya, Nyamira, Kakamega, Kisii, Nakuru and Kericho.

Kibabii University rainfall station in Bungoma recorded the highest seven-day rainfall total at 125.1mm.

Miyare rainfall station in Migori County recorded the highest rainfall amount within 24 hours, with 61.2mm on September 21.

The forecast comes as meteorologists continue to assess how ocean conditions will influence rainfall during the October-December period.

A principal meteorologist at the Kenya Meteorological Service Authority, Jemima Gacheru said El Niño alone cannot determine how much rain Kenya will receive.

"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 the Indian Ocean Dipole, which measures differences in sea temperatures between the western Indian Ocean near East Africa and the eastern Indian Ocean near Indonesia, was also important.

When waters near the East African coast become warmer than normal, a positive Indian Ocean Dipole can support heavier rainfall in East Africa.

Gacheru said the index was currently at 0.7 degrees Celsius and was expected to rise to about 1.0 degrees in October.

However, the Australian Bureau of Meteorology reported a weekly Indian Ocean Dipole index of +0.65°C for the week ending September 13, classifying it as neutral and noting that one observation above +0.4°C does not establish a positive event.

Gacheru said the strength of the Indian Ocean Dipole could determine whether Kenya experiences extremely heavy rainfall or a more mixed pattern.

She cited 1997, when a strong El Niño and strong positive Indian Ocean Dipole coincided with heavy rainfall across most of Kenya.

In 2015, strong El Niño conditions occurred alongside a weaker Indian Ocean Dipole of about 0.5 degrees, resulting in a mixed rainfall pattern, with some areas receiving above-normal, near-normal and below-normal rainfall.

Gacheru said the current forecast expected most counties to receive above-normal rainfall, although this would not mean the same amount of rain would fall everywhere.

"Most areas are expected to have fair to good distribution, meaning the dry spells will not be as many," she said.