1. WEATHER SUMMARY FOR DECEMBER 1998
1.1 Rainfall Summary.
Most stations in the country recorded rainfall far below their long term means for the month of December. The frequency of rainfall over Southeastern districts significantly reduced after the first week of the month. However, occasional rainfall covering few places continued being received up to the end of the month. The highlands east of the rift valley and Nairobi area received rainfall over few places mainly in the first half the month. The rainfall performance over the western sector of the country was generally poor throughout the month. The highest rainfall total of 81.8 mm was recorded over Kisii which was just 56.5% of the total expected rainfall in the month.
1.2 SYNOPTIC SITUATION DURING DECEMBER 1998
The Southwestern Indian Ocean Anticyclone was generally weak during the month, however, it occasionally slightly strengthened leading to a little northward movement of the Inter-tropical convergence zone (ITCZ). The high pressure systems over southern Atlantic Ocean and those over the Mediterranean region were generally weak for most of the month. Pressures over Arabian peninsular gradually built up, however, the persistent warm sea surface temperatures (SSTs) associated with the ENSO effects over the Arabian sea and the Indian Ocean led to Arabian ridge being slightly weaker than normal. This led to poor performance of rainfall over most parts of the eastern sector of the country. The zonal (East-West) arm of the Inter Tropical Convergence Zone (ITCZ) was located over southern most parts of our country in the first one week, but thereafter it migrated to Tanzania and northern Malagasy for the remainder of the month. The meridional (North-South) arm of the ITCZ was located over Central Africa, Uganda and occasionally over some parts of the western sector of our country.
2. DAIRY FARMING WEATHER CONDITIONS DURING DECEMBER 1998.
Throughout the month of December, very little rainfall was received in central rift vaalley except in Kitale where a total of 9.93mm of rainfall was recorded. In Nakuru and the sorrounding areas, generally dry conditions were experienced with temperatures ranging between 8 and 26 degrees celsius. During this period there was still adequate dry fodder and pasuture to sustain dairy production in most areas of rift valley. Relatively high temperatures were recorded over Eldoret and Kitale of 24 and 27 degress celsius respectively.
3. EXPECTED SYNOPTIC SITUATION DURING JANUARY 1999.
The high pressure systems over southern Atlantic Ocean and southwestern Indian Ocean will be relatively weak, but the southern Atlantic ocean pressures will achieve near normal intensities towards the end of the month. The high pressure systems over the Mediterranean and and Azores regions will remain relatively weak, though a slow build up of pressures is expected to commence by the end of the month. The pressure patterns over the Arabian region are expected to remain relatively strong though the Arabian ridge will assume a continental axis for most of the month. As a result the zonal arm of the ITCZ will be located far to the south covering south African countries and Malagasy areas. The meridional (North-South) arm of the ITCZ will overly Central Africa and Uganda but will periodically shift eastwards to cover parts of western sector of Kenya. Occasional formation of tropical cyclones (or deep lows) over the southwestern Indian Ocean will reduce the moisture influx into the eastern parts of the country.
4.EXPECTED WEATHER IMPACTS OF DAIRY PRODUCTION DURING THE MONTH OF JANUARY 1999.
4.1 Lake Victoria Basin, Highlands West of the Rift Valley and Central Rift Valley:
Occasional Afternoon showers and thunderstorms spread over few places increasing to several places as the period progresses. These conditions will enhance regeneration of vegetation in a few areas although the milk production is expected to be lower as the dry spell conditions sets in.
4.2 Northwestern.
Mainly dry conditions will prevail. Destocking is expected by the pastoralists as lack of water may contribute to loss of animals as well as the production quality and quantity.
4.3 Southeastern, highlands east of the Rift valley and Nairobi area.
Mainly long sunny periods will prevail with a chance of occasional afternoon showers over few places. Areas sorrounding Mt. Kenya are expected to maintain high amounts of pasture but the quality is expected to be poor by the end of January 1999.
4.4 Northeastern districts.
Mainly dry conditions will prevail, however, areas to the south will receive occasional morning rains and afternoon showers over few places. Similar dairy conditions like those of north western are expected to dorminate.
4.5 Coast.
Occasional morning showers spread over few places will occur.
KEY OF SCIENTIFIC WORDS USED
INTER-TROPICAL CONVERGENCE ZONE (ITCZ): An extensive area of seasonal low pressure caused by the seasonal migration of the sun and associated with heavy rainfall, lightning and thunder.
HIGH PRESSURE SYSTEM: An area associated with clear skies or fine weather clouds.
RIDGE: Asymptote of high pressure from which winds flow outward.
TROUGH: Asymptote of low pressure towards which winds flow and meet.
MOST PLACES: Between 66% and 100%.
SEVERAL PLACES: Between 33% and 66%
FEW PLACES: Between 0 and 33%