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Africa: Drought and floods hazards assessment: 2 Oct 2003

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CCA Guidance for Southern Africa Rainfall in Oct-Dec 2003 at One Month Lead

Southern Africa is defined here as the region between 5°S and 35°S; 10-50°E. The prediction for Oct-Dec 2003 southern Africa rainfall at one month lead (safond1.gif) is weak and calls for climatology across much of southern Africa. Slightly higher than climatological probabilities for below normal rainfall are predicted for the areas of northern Mozambique, southeastern Madagascar and southwestern South Africa. Slightly higher than climatological probabilities for above normal rainfall are predicted over areas in central and eastern South Africa, southern and central Mozambique, and south central Angola. The neutral state of ENSO and weak sea surface temperature anomalies across the Atlantic and the Indian Ocean suggest uncertainty in the forecasts for the next few months.

The diagnostic data produced by CCA indicate that Oct-Dec Southern African rainfall has a modest predictability at 1 month lead.

With respect to the general weather over Africa, heavy rainfall continued over portions of southern Senegal, northern portions of Guinea, and Guinea Bissau during the previous week with rainfall amounts exceeding 75 mm in some areas. Daily rain showers continued over northern Ghana, Togo, and Benin. Many of these areas have reported flooding over the past several weeks. Heavy rain also continued along the Cameroon-Nigerian border where a flooding region was present during the past several hazard periods. Elsewhere, isolated storms brought rainfall totals that were greater than 50 mm along the Ethiopia-Sudan border. Portions of southern Sudan and Chad, Central African Republic and northern Democratic Republic of the Congo also had heavier amounts as tropical waves continue to move across the central portions of the continent with some heavier rains extending into northern and central Angola. In southern Africa, rainfall amounts were around 10 mm over most of Angola, Namibia, South Africa, and Lesotho.

NOAA/CPC USGS



WEEKLY AFRICAN WEATHER HAZARDS ASSESSMENT STATEMENT OCTOBER 1, 2003

DISCUSSION:

1) Tropical Cyclone 01S (Abaimba) developed in the South Indian Ocean on September 29, and is the first classified storm of the 2003-04 season. At the time of writing, TC 01S was several days from land. It is drifting westward, and there is only a slight possibility that it will impact northern Madagascar or the east coast of Africa by the end of the period. See cyclone bulletins for the latest track, intensity and forecast information.

2) Recent heavy rains have resulted in elevated antecedent moisture levels across southeastern Nigeria, southwestern Cameroon, northern CAR and parts of western Ethiopia. It is possible that many of these locations will receive significant amounts of additional rainfall during the period. As a result, the potential for flooding exists. In mountainous areas, the potential for landslides also exists. The rains in western Ethiopia have likely raised water levels along the Blue Nile as it flows into eastern Sudan, therefore the potential for flooding exists along the upper portions of the Blue Nile.

3) Much below normal rainfall three years in a row has resulted in long term drought across southern Sanaag and northern Sool regions in Somalia. Long term drought has degraded pastures and reduced water supplies across the area. Showers across the southern portion of the region during the last week of September resulted in little relief. Scattered showers during the period may result in some relief, however substantial rains are needed to ease impacts. The area's minor rainy season occurs during mid and late September. More substantial rains typically occur during the major wet season in May and June.

4) Rainfall across the southernmost portions of the Ethiopian highlands was below normal and erratic during the Meher season. This may negatively impact local agriculture and water supplies. Because of the high amount of variability and complexity of terrain across this region, some locations may have experienced good seasonal rains while others may not have. As a result, not all areas included in the shaded region were affected. Likewise, it is possible that some locations near, but not within, the shaded region were affected by dryness and the erratic Meher rains.

5) Wetter than normal conditions were observed across southwestern Kenya and adjacent parts of Uganda during August and early September. In recent weeks, rainfall has tapered off, easing excessive wetness. However, the potential for scattered thunderstorms exists during the period. As a result, the risk of isolated flooding continues. Widespread flooding is not expected. In areas where significant rainfall occurs, harvest activities may be hampered.

6) Rainfall totals for the 2002-03 rainy season were between 40 and 65% of normal across northeastern South Africa, southern Mozambique, and much of Swaziland. Seasonal rainfall deficits range from 150 to 400 mm across the region. This has resulted in a hydrologic drought across the region, reducing water supplies for wells, reservoirs and watersheds. Conditions are expected to be dry until late in the period when showers are expected. The best chance for rain will be in southern and eastern parts of the area..

7) Winter precipitation has been lighter than normal across Lesotho and adjacent portions of South Africa. This has reduced top soil moisture and snow water reserves for spring runoff from the mountains. The cool season dryness has negatively impacted winter agriculture in the area. Light showers are possible during the period.

8) Recent rains have eased short term dryness and favored second season agriculture across southwestern Ghana and southeastern Cote D'Ivoire. However, large long term deficits remain as a result of the early withdrawal of the first season rains. Additional rains are expected during the period, which will continue to favor second season crops while slowly reducing long term moisture deficits.

AUTHOR: Chester V. Schmitt