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Africa: Drought and floods hazards assessment: 16 Oct 2003

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EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION

Equatorial surface and subsurface temperatures were slightly warmer than average throughout most of the Pacific during September. Equatorial SST anomalies greater than +0.5°C (~1°F) persisted in the region west of the date line during September, and developed over most of the region between the date line and 120°W during the last half of the month. Generally, atmospheric conditions in the tropical Pacific have been near average in recent months, with no significant trends that would support large-scale anomalous warming or cooling of SSTs in that region. Thus, slightly warmer-than-average conditions are likely to persist for the next several months.

A majority of the statistical and coupled model forecasts indicate near neutral conditions (Niño 3.4 SST anomalies between -0.5°C and +0.5°C) for the remainder of 2003 and early 2004. However, over the past few months there has been a trend in the suite of forecasts towards somewhat warmer conditions, consistent with observations. Thus, it is likely that slightly warmer-than-average conditions will persist in the equatorial Pacific through the Northern Hemisphere winter of 2003-04.

This discussion is a consolidated effort of NOAA and its funded institutions.

With respect to the general weather over Africa, as last week, locally heavy rainfall fell over the region from western Guinea eastward to western Ethiopia with rainfall amounts exceeding 75 mm in some areas. This rainfall covered much of Cameroon, the Central African Republic, and southern Sudan. The heavy rain along the Cameroon-Nigerian border continues in the flooding region depicted during the past several hazard periods.

In southern Africa, local rainfall amounts up to 75 mm were observed over northern Angola. Lesser amounts of up to about 10 mm were observed over central and southern Namibia. A storm system did come through South Africa on October 13th and the weekly rainfall in southern South Africa and Lesotho totaled about 30 mm with up to about 50 mm along the southeast coast.

Finally, in northern Africa, rains up to about 20-30 mm fell in Morocco and Algeria with lesser amounts in Tunisia.

NOAA/CPC USGS



Africa Weather Hazards Assessment Text Explanation October 16-22, 2003

1) Rainfall decreased during the last week in parts of southern Nigeria and western Cameroon, though soil moisture remains high throughout the area. Weekly precipitation totals were generally less than 75 mm in the region from October 8-14, but the previous week saw totals closer to 150-200 mm locally. Latest meteorological forecast models indicate a good chance for rainfall totals up to and exceeding 150 mm locally during the next period, and thus local flooding concerns remain.

2) Drought continues in parts of north central Somalia due to seasonal rainfall deficits during each of the past three years. Some precipitation fell over the area during the last week, though accumulations were generally light with totals not exceeding 15 mm and common amounts closer to 5 mm. Forecast rainfall totals of similar magnitude are expected during the next week and would slightly help to ease dryness if this holds true.

3) The region in southern Ethiopia that has been experiencing seasonal dryness in 2003 received healthy rainfall during the past week, as widespread totals topped 15 mm and local amounts reached 50 mm. This is complicated by the fact that the current season is already late to start by a week or two. The previous 2003 season was a few weeks late and once rains arrived, they were erratic and lighter than normal. Indications are beginning to show dryness extending to the east and southward into north central Kenya as well. Healthy rains are again expected in the hazard region throughout the next week.

4) Local flooding remains a concern in parts of western Kenya bordering Lake Victoria due to heavier than normal rainfall since September. October 1-12 rainfall has already reached around two-thirds of the climatologically normal October total, and additional rains, though somewhat lighter, are possible through the next week. If rainfall subsides during the next period, this hazard area may be removed from weekly assessments but will continue to be monitored for further problems.

5) Dryness is again becoming a concern in the region extending southward from Mombassa, Kenya to Dar es Salaam, Tanzania. March-June 2003 rainfall in this area ranged from 10-60 percent of normal and September rains were virtually non-existent in the region. October precipitation totals should normally range from 75-150 mm, though no rainfall was recorded through the first 12 days of the month. This situation should be closely monitored for dryness/drought.

6) Long term drought continues in parts of eastern South Africa and southern Mozambique due to poor performing rains during the 2002-2003 monsoon. Normal September rainfall totals of 25-50 mm were nearly equalled in 2003. October rains should reach 25-150 mm with the heaviest amounts west and south of Swaziland, and accumulations so far have ranged from 10-50 mm. Although this is slightly drier than normal, a more active weather pattern is emerging and additional rainfall is expected during the next week.

7) Winter moisture conditions in and around Lesotho have been drier than normal, though temperatures have remained near normal. Past weekly rainfall ranged from 10-30 mm and similar amounts are expected for the next week. This area may be susceptible from the slightly slow-to-start rainy season in southern Africa.

8) A cold front, similar to that which pushed through eastern South Africa during last week may push through and east of the area from October 18-22. The system has the potential to affect a region from east of Lesotho to north of Maputo, Mozambique with heavy rains, strong winds, and possibly large hail. Environmental conditions which were evident during last week would be again favorable for severe weather in the area if the cold front maintains its forecast intensity.

Timothy Love