Angola + 3 more

Southern African Regional Rainfall Outlook Seasonal Update No. 2

December 2000-January-February 2001 (DJF) forecast summary
Normal to above normal rainfall is expected over much of the sub-region, for the period December 2000 to February 2001 (DJF). There is, however, an exception in northern Tanzania and parts of South Africa, western Namibia and southern Botswana where normal to below normal rainfall is likely to occur.

Sea surface temperature anomalies and Southern Oscillation Index

The sea surface temperature (SST) anomalies for the equatorial Eastern Pacific continue to be near the average category and are expected to remain so until March 2001 when they should rise above zero. The state of the SST anomalies (NINO=5F3=5F4=5F00) by the end of October were still negative but slightly higher than last year (NINO=5F3=5F4=5F1999), Figure1(a.). This signifies a weakening La Niña.

Meantime, the Southern oscillation index (SOI) has been showing an upward trend since June 2000, to positive1.0 as from September 2000, Figure 1 (b). A positive SOI is favourable for good rains in most parts of southern Africa, the exception being the north easternmost. Normal to above normal rainfall was received in most areas across the region during the 1999/2000 season.

Figure 1(a) SST anomalies for NINO3=5F4 for 1999 and 2000

Figure 1(b) SOI anomalies for NINO3=5F4 for 1999 and 2000

Significant weather systems

From October 2000 the middle level subtropical high pressure systems have significantly weakened, thereby allowing the monsoon trough over southern Africa to be established better. This resulted in moisture influx over the bulk of the subcontinent. The conditions also became favourable for precipitation over parts of the western Indian Ocean, including Mauritius and Seychelles.

During the remainder of the rainy season, frequent incursions of the westerly troughs over the sub-region should be maintained. At the same time, the ITCZ will be well established over the southern half of the region. This should allow for more moisture to spread into the southern half of the sub-region.

October and November rainfall summary

The bulk of the region received generally low rainfall during the month of October. Over most countries, the total cumulative rainfall amounts for October were less than 30 mm. As an exception the DRC, northern Mozambique, Swaziland, Lesotho and the eastern part of South Africa received rainfall amounts exceeding 60 mm. The highest rainfall (greater than 150 mm) was received over the DRC. Figure 2 (a) shows the cumulative rainfall for the month of October across the region. For most parts of the region the registered rainfall amounts represented 65 % or less of the long-term average for the month. However, for the DRC, Malawi, northwest Angola, southern Tanzania, central Mozambique, Mauritius, the eastern part of South Africa, Lesotho and Swaziland the rainfall amounts recorded constituted between 75% and 125% of the long-term average for October. The percent rainfall departure from normal is illustrated on Figure 2(b).

Figure 2(a) Total rainfall for October 2000, Figure 2(b) Percentage of normal rainfall for October 2000