Rainfall Scenarios of March-April-May 2023

1.??Introduction

The MAM 2023 season in Kenya is normally referred to as the long-rains season. It begins about the 3rd or 4th week of March (onset) and runs all the way to the 2nd /3rd week of May (cessation). It has a peak in the 4th week of April and 1st week of May. Sometimes the season may extend to the month of June in areas around the coast and western parts of Kenya.

Our forecasts and climate predictions are based on astronomical observations and predictions of key phases of the planets of the solar system and do not factor in the common climate drivers, e.g. MJO, ENSO and IOD. An astronomical-based forecast was issued for the season and was set on a week by week basis. This forecast is based on Astronomical cycles of Jupiter, Saturn, Mercury and Venus. Normally, the forecasting process involves analogue years associated with Jupiter, Saturn, Mercury, Venus, Mars and the Moon on experimental basis. The cycles are referenced on key phases of the planets, e.g. Conjunctions and oppositions of the planets as well as the Moon's Apogee-Perigee and Full Moon-New Moon phases. A summary of this planets and their associated phases are given in Table 1.

A pool of analogue years are selected by use of these cycles and it is from these years that a careful analysis of the rainfall events is done. The forecast, given in section 2, was developed and is based on this analysis. The country is divided into 8 regions. The regions are areas of homogenous rainfall and are the traditional areas used in seasonal forecasting in the country (with minor adjustments). Figure 1 shows a map of Kenya with the 8 regions used. The regions are Highlands East of the Rift Valley; the Rift Valley; Highlands West of the Rift Valley; South East low lands; North West lowlands; North East lowlands;?Eastern lowlands and the coast.

2.????Forecast Summary

The season is likely to have largely DRY conditions in the whole country. Generally, the rainfall may come in 4 events between February 2023 and June 2023. Most of the rainfall will be received in the 2nd or 3rd week of February, 3rd or 4th week of March, the period between the 3rd week of April to the 2nd week of May and the month of June. The onset and cessation dates for most regions are not possible to determine due to the highly erratic nature of the rains. In some regions, where possible, there is likelihood of a very short rains season and a failed rains season in other regions (for a summary of the forecast see Table 2).

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3.??Forecast per Region

?1)?????South East: Most areas of will be generally dry most of the period but may experience some grass rains for some days in the 2nd or 3rd week of February and 4th week of March which may be characterized by a few isolated storms. The main rainfall season is not a good one as rain my only be realized in the 4th week of May and may extend for some days as light rains into June in some places. The onset and cessation dates are not possible to determine.

2)?????Highlands East of the Rift valley: Most areas of will be generally dry the whole period but may experience some grass rains for a few days in the 2nd or 3rd week of February and to some extent a day in the 2nd week of March which may be characterized by a few isolated storms. The main rainfall season will be erratic and may be experienced in the 2nd / 3rd week of April and 3rd / 4th week of May but will maintain dry conditions during the period. The onset and cessation dates are not definite.

3)?????Coast: The region may have isolated cases of rainfall in a few days in the beginning of February and the beginning of March. The main season may begin in the 3rd week of April and end in the 2nd week of May. We may also have rains from the 2nd week of June. While the main rainfall season normally falls mainly in the period April to June, there may be a long dry spell between 2nd week of May and 2nd week of June splitting the short rain season into two.

4)?????North Western: The region will be mainly dry with sporadic rains in the 2nd week of February and 2nd or 3rd week of March. The main rainfall season will be experienced from the 2nd or 3rd week of April to the 2nd week of May but will generally remain dry during the whole period.

5)?????North Eastern: The region will be dry the whole period. ?Long dry spells will be common but may be interrupted by a sporadic event in the 4th week of February and rains may be experienced from time to time between 2nd week of April and 3rd week of May. There is a likelihood of light rains from the 2nd week of June.

6)?????Eastern: The region will be dry the whole period.?Long dry spells will be common but may be interrupted by a sporadic event in the 4th week of February, 4th week of March and 3rd week of April. There is a likelihood of light rains from the 2nd week of June. This is a characteristic feature of dry conditions in the region.

7)?????Highlands West of the Rift valley: The region may have a general dry condition from February to the 2nd week of April but may have rainfall incursions from the west from time to time especially in the 2nd or 3rd week of February and the 3rd week of March. Significant rainfall may be experienced from the 3rd week of April to the 1st week of May and then some rains may be sporadic in some areas between 3rd week of May and 2nd week of June. This is a characteristic feature of a very short period of rains in some areas and a failed rains season in other areas.

8)?????Central / South Rift Valley: The region will be dry the whole period.?Long dry spells will be common but may be interrupted by a sporadic event in the 2nd or 3rd week of February, 3th week of March and 3rd / 4th week of April. There is a likelihood of significant rains from the 4th week of May to 1st week of June. This is a characteristic feature of a very short rains season in some areas and a failed rains season in others.

4.??Disclaimer

The forecasted conditions may deviate due to influences of other non-astronomical factors, e.g. ENSO, IOD and MJO. In the past, the forecasts issued have been found to deviate from the intended conditions due to influences these climate drivers. While the first two are fairly stable, MJO is highly unstable and unreliable in seasonal forecasting. The MJO is associated with weekly to monthly periods of enhanced and suppressed rainfall in many parts of the tropical world that includes Kenya. Past experiences have shown that the MJO is a significant causative factor in variations of short-term climate conditions in Kenya. Its evolution is highly erratic and therefore its prediction skill is fairly low even within 14 days and the skill is almost negligible beyond two weeks.?In the past, MJO has been found to alter or shift the periods of forecasted rainfall by as much as 1 week in some instances, however, most of the key conditions forecasted remained as projected.??The forecast can, therefore, be followed with all this effects in mind and that minor variances are possible from time to time.