1.1 WEATHER SUMMARY FOR MAY 1999
. During May as reflected in the amounts accumulated up to 29 May 1999, the highlands West of the Rift Valley, Central Rift Valley, Lake Basin, Nairobi area, parts of central districts and coastal areas, received amounts of rainfall generally near their respective long term means (LTM). The other parts of the country received amounts below their respective LTMs. The highest amounts of rainfall for the month were reported over Kericho, Malindi, Mtwapa and Kisumu, which received 259.6 mm, 257.2 mm, 245.6 mm and 169.3 mm respectively (see attached table). The rainfall was characterized by large spatial and temporal variations.
1.2 SYNOPTIC SITUATION DURING MAY 1999
During this period, the high-pressure systems around Spain (the Azores region) and North Africa remained fairly strong. The monsoonal low-pressure system established itself over India and extended to the region of Arabia, completely replacing the Arabian high-pressure ridge. The high pressure system over Southwest Indian Ocean strengthened significantly during the month and the Eastern African high pressure ridge was well established, though with weaker than normal intensity. The coastal low-pressure trough was active throughout the month. The Atlantic Ocean high-pressure system was frequently weakened by transient frontal low-pressure systems during the month. The La Nina conditions continued to exist over the Pacific Ocean and positive SSTA's (Sea Surface Temperature Anomalies) continued to be observed over Southern Atlantic and Southwestern Indian Oceans. The Northern Atlantic Ocean reported negative SSTA's. There was moderate cooling over the Northern Indian Ocean.
2. DAIRY FARMING WEATHER CONDITIONS DURING MAY 1999.
Throughout the month of May 1999, the rainfall performance in Central and North Rift Valley was generally poor, both in amounts and distribution. In Nakuru, 49.2mm compared to a LTM of 122.7mm was recorded, Eldoret56.5mm compared to a LTM of 116.1mm and in Kitale 93.6mm compared to a LTM of 175.7 was recorded.
Temperatures during the day over central rift valley remained relatively high but the nights were fairly cooler over the north rift recording aas below as 10 degrees celsius. However, no major animal stress was expected and production on both milk and meat was expected to be above normal following the April rains which were generally good for pasture growth.
3. EXPECTED SYNOPTIC SITUATION DURING JUNE 1999.
The high-pressure systems over the Mediterranean region and North Africa will remain relatively strong during the period, and will retreat further north. The Southern Atlantic Ocean high-pressure system will be relatively weak due to the warm SSTs over the region. The Southwestern Indian Ocean high pressure system will intensify as the month progresses. However the warm SSTs to the south of the tip of Southern Africa will cause the East African high-pressure ridge to be relatively weaker than usual leading to reduced injection of cold airmass from the south and convergence along the coast. The meridional (North-South) arm of the ITCZ will overlie central Africa, Uganda and western sector of our country. The zonal arm of the ITCZ will be located over the southern parts of Ethiopia and Sudan. The cooling over the Northern Atlantic and parts of the Southern Atlantic, and warming over the Southwestern Indian Ocean will assist in marked and frequent eastward displacement of the north-south (meridional) arm of the ITCZ to affect the lake basin, highlands west of the Rift Valley, Central Rift Valley, and occasionally parts of central districts and Nairobi. The La Nina conditions will persist though weakening.
From these developments, it is expected that the rainfall performance
in June will be normal to above normal in the western and normal to below
normal along the coastal areas of the country. The highlands East of the
Rift Valley and Nairobi area are expected to experience cool cloudy morning
with occasional light rains. However the temperatures are likely to be
generally mild due to the warm Southern Indian Ocean SSTs. Occasionally,
cold temperatures are likely to be experienced.
4. EXPECTED WEATHER IMPACTS OF DAIRY PRODUCTION DURING THE MONTH OF JUNE 1999.
From the foregoing, it is expected that the Lake Victoria basin, highlands West of the Rift Valley, Northwestern districts, central Rift Valley including Narok`, will receive normal to above normal rainfall in June.
It is therefore anticipated that, the level of milk production will continue to increase as a result of regenerated pasture in these areas.
The highlands East of the Rift Valley, Nairobi area will be mainly dry with cool cloudy mornings with occasional light rains. The temperatures will be mild due to the warmer than average SST's over the Indian Ocean and reduced injection of moist cold air from the south.
As a result of favorable temperatures during the period, animal production is expected to be on the increase
Northeastern and the southeastern districts will be mainly sunny and dry.
The coastal region will experience normal to below normal rainfall in June.
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%