January 8, 2003
The Intertropical Convergence Zone (ITCZ), also known as the Intertropical Front (ITF) or the Intertropical Discontinuity (ITD), represents the boundary between dry, hot air to the north and warm, humid air to the south. The ITCZ reaches its northernmost position near the 19th parallel around mid-August, when Sahel rainfall peaks. After August, the ITCZ typically retreats rapidly southward. The ITCZ location during June to September is closely related to both cumulative rainfall and crop production in the Sahel countries and West Africa. Drought years are associated with the ITCZ being south of its normal position, while wet years are associated with the ITCZ north of normal. While we have, in the past, monitored the position of the ITCZ from April-October, in response to requests from our user-community we have extended the ITCZ dekadal analysis into December as it has migrated to southern Africa. We have now reached the point, however, when the ITCZ has become less-well defined and the location errors are quite large. Therefore, we are discontinuing the dekadal ITCZ analysis and will resume in April. With respect to the weather in Africa, the remains of Cyclone Delfina continued to bring heavy rains and the potential for flooding to northeastern Mozambique during the past week. Satellite-estimated rainfall totals topped 300 mm in Nampula Province for the 7 days ending January 5. Nearly the entire northern third of the country saw over 100 mm during this period. The cyclone, which made landfall on December 31 in northeastern Mozambique, also brought heavy rains to southern Tanzania, where totals exceeded 200 mm locally. The moisture benefited dry areas in southern Malawi and north-central Mozambique, with totals exceeding 75 mm. In contrast, only scattered showers fell south of the Zambezi River, resulting in continued drought development across much of central and southern Mozambique and eastern Zimbabwe. Unfavorably dry weather also covered the remainder of Zimbabwe, most of Botswana, northern South Africa, and Swaziland. Heavy rains ranging from 100 to 200 mm for the week covered central and northern Madagascar, while unusually light amounts (less than 25 mm) fell in the extreme south.
WEEKLY AFRICAN WEATHER HAZARDS ASSESSMENT STATEMENT
JANUARY 9, 2003 DISCUSSION:
1) Moisture deficits continue across much of southern Mauritania, which has resulted in poor pasture conditions. Significant rains are not expected until the next growing season.
2) Dryness throughout recent years has resulted in poor pasture conditions and low water supplies across central Ethiopia, and adjacent portions of Eritrea and Djibouti. Isolated showers in the southwestern portions of the area may result in limited improvement.
3) Below normal rainfall totals in Guinea has resulted in low reservoir levels, which aid in the generation of hydro-electric power. Improvement is not expected until April or the start of the next rainy season in the region.
4) Persistent dryness over southern Mozambique and northeastern South Africa continue to threaten the maize crop as it enters a critical growing period. This area has slowly been expanding westward and now covers much of central and southern Zimbabwe and into extreme eastern portions of Botswana. Also, a new area across southern Zambia should be included as December totals are around 150 mm below normal, which is compounded by a late start to the rainy season. Most of these areas should have some relief as widespread showers move into the area by 10/01 and 11/01 bringing significant rainfall totals. Local areas could see as much as 300 mm over the next week.
5) Saturated conditions in southern Malawi, north-central Mozambique, and the Lake Victoria basin could lead to isolated areas of flooding as rains continue over the next week. Flood prone areas should be monitored closely as some convective showers could bring over 200 mm of rain over the next seven days.
Author: Kevin B Laws