The IRI has prepared this experimental Climate Outlook for Africa for July 2001 - December 2001. Of relevance in the preparation of this outlook is the prediction of near-average to slightly warmer than average conditions in the eastern equatorial Pacific for the next 6 to 9 months. Currently the sea surface temperatures (SSTs) across much of the eastern and central equatorial are near their long-term average (SSTs), although slightly lower than average SSTs have developed along the immediate western coast of South America and warmer than average SSTs persist in the extreme western part of the basin. Near neutral equatorial Pacific SST conditions are in effect for the first season of the forecast, July-August-September 2001, while during the second season, October-November-December 2001, they are expected to be slightly above average. The warmer than average SSTs that continue to dominate much of the Indian Ocean are expected to decrease slowly through the forecast period. The area of above-average temperature in the tropical south Atlantic Ocean is expected to persist through at least the first half of the forecast period.

METHODS -

This Outlook was prepared using the following procedures and information:

A) Coupled ocean-atmosphere model predictions of tropical Pacific SST covering the forecast period. Particularly heavy weighting has been given to predictions from the coupled model operated by the NOAA National Centers for Environmental Prediction, Climate Modeling Branch. This model suggests a continuation of near-average conditions during the first forecast season. The forecast for near-neutral conditions is consistent with some, but not all, numerical and statistical forecasts of central and eastern Pacific SSTs.

B) Forecasts of the tropical Indian ocean using a statistical model developed by the IRI.

C) Global atmospheric general circulation model (GCM) predictions of the atmospheric response to the present and predicted sea-surface temperature patterns.

D) Other sources of information include NASA's Seasonal to Interannual Prediction Project (GSFC-NASA).

The procedures, models, and data used to derive this Climate Outlook may be somewhat different from those used by the national meteorological services in the region. Thus, this product may differ from the official forecasts issued in those areas. The Climate Outlook for July - December 2001 is dependent on the accuracy of the SST predictions. For the tropical Pacific, these predictions can be expected to provide useful information, but there is some uncertainty concerning the evolution of SSTs. Spread (variation) in global SST predictions is a source of uncertainty in the Outlook provided here. In particular, the forecasts for the tropical Indian and Atlantic oceans have been an important influence on the forecasts over Africa. Note that even if perfectly accurate SST forecasts were possible, there would still be uncertainty in the climate forecast due to chaotic internal variability of the atmosphere. These uncertainties are reflected in the probabilities given in the forecast.

It is stressed that the current status of seasonal-to-interannual climate forecasting allows prediction of spatial and temporal averages, and does not fully account for all factors that influence regional and national climate variability. This Outlook is relevant only to seasonal time scales and relatively large areas; local variations should be expected, and variations within the 3-month period should also be expected. For further information concerning this and other guidance products, users are strongly advised to contact their National Meteorological Services.

OUTLOOK -

This Outlook covers two seasons: July - September 2001 and October - December 2001. Maps are given showing tercile probabilities of precipitation and temperature. The maps for precipitation indicate the probabilities that the seasonal precipitation will fall into the wettest third of the years (top number), the middle third of the years (middle number), or the driest third of the years (bottom number). The color shading indicates the probability of the most dominant tercile -- that is, the tercile having the highest forecast probability. The color bar alongside the map defines these dominant tercile probability levels. The upper side of the color bar shows the colors used for increasingly strong probabilities when the dominant tercile is the above-normal tercile, while the lower side shows likewise for the below-normal tercile. The gray color indicates an enhanced probability for the near-normal tercile (nearly always limited to 40%). As before, numbers and their associated histograms show the probabilities of the three terciles. In areas with lots of spatial detail, there may not be sufficient room on the map, to allow histograms for each region. In those cases, some idea of the probabilities may be gained from the color alone. A qualitative outlook of climatology ("C") indicates that there is no basis for favoring any particular category. Areas that are marked by "D" represent regions experiencing their dry season (less than 15% of annual precipitation) and for which less than 5 cm of precipitation typically occurs over the season. Otherwise, for example, in the case of Somalia in July - September 2001 (Map A), there is a 25% probability that the precipitation will be in the wettest third of the years, a 35% chance it will be in the near-normal third of the years, and a 40% chance that the precipitation will be in the driest third of the years.

Maps of temperature show expected probabilities that the seasonal temperatures will fall into the warmest third of the years, the middle third of the years, or the coldest third of the years (Map A) . The numbers for each region on the temperature maps indicate the probabilities of temperatures to fall in each of the three categories, above-, near-, and below-normal.

An additional precipitation map is provided for the first season indicating probabilities for extreme precipitation anomalies. Extremes are defined as anomalies that fall within the top and bottom 15th percentile of the observed records. A priori, there is a 15% probability of being within the extremely wet category, and a 15% probability of being within the extremely dry category, leaving a 70% probability that the precipitation will not be extreme. The maps indicate areas of increased risk of extreme precipitation totals. Three levels of increased risk are defined: slightly enhanced risk, enhanced risk, and greatly enhanced risk. For slightly enhanced risk, there is a 25-40% probability that precipitation will be within the indicated extreme, i.e. wet or dry. This represents an approximate doubling of the climatological risk. For enhanced risk, there is a 40-50% probability that precipitation will be within the indicated extreme. This represents an approximate tripling of the climatological risk. For greatly enhanced risk, the probability that precipitation will be within the indicated extreme exceeds 50%, i.e. the indicated extreme is the most likely outcome. A similar map is provided in the first season indicating probabilities of extreme temperature anomalies.

Boundaries between sub-regions should be considered as transition zones, and their location considered to be only qualitatively correct.

July - September 2001:

PRECIPITATION

The following regions of enhanced probabilities of precipitation anomalies are indicated:

Slightly enhanced probabilities for below normal precipitation (40%-30%-30%) are forecast for a small portion of northern Algeria, with a separate region of in eastern Algeria, eastern Tunisia, western Libya, northern and most of eastern Egypt, Jordan, Israel, and most of Saudi Arabia.

Slightly enhanced probabilities for below normal precipitation (40%-35%-25%) are forecast for northern Senegal, much of southern Mauritania, central and eastern Mali, most of Niger, northern Chad, and central and northern Sudan.

A greatly enhanced probability for above normal rainfall (20%-30%-50%) is forecast for part of the Guinea Coast of Africa, including southeastern Liberia, and the central and southern portions of Cote D'Ivoire, Ghana, and Togo. Weaker probabilities for above normal precipitation (25%-30%-45% and 25%-35%-40%) surround this region, including Guinea-Bissau, Guinea, the southernmost portion of Mali, most of Burkina Faso, the northern portions of Cote D'Ivoire, Ghana and Togo, Benin, extreme southern Niger, and northern and western Nigeria.

Slightly enhanced probabilities for below normal precipitation (40%-35%-25%) are forecast for the immediate coast of Cameroon, Equatorial Guinea, most of Gabon, and the immediate coast of the Republic of the Congo.

Slightly enhanced probabilities for near normal precipitation (30%-40%-30%) are forecast for southern Ethiopia, southern Somalia and northeastern Kenya.

Slightly enhanced probabilities for above normal precipitation (30%-30%-40%) are forecast for northeastern Zimbabwe, central and southern Mozambique, southern Malawi and parts of Madagascar, and the Mascarene Islands.

Slightly enhanced probabilities for near normal precipitation (30%-40%-30%) are forecast for portions of southeastern South Africa.

Slightly enhanced probabilities for below normal precipitation (40%-30%-30%) are forecast for a very small portion of the immediate coast of southwestern South Africa.

The following regions of enhanced probabilities of temperature anomalies are indicated:

Slightly enhanced probabilities for near normal temperature (mainly 35%-40%-25%, but also 30%-40%-30% on northeast side) are forecast for parts of northern Africa, including the Canary Islands, parts of coastal Western Sahara, most of Morocco, mainly northern and eastern Algeria, most of Tunisia and Libya, small northern portions of Niger, Chad and Sudan, and western Egypt.

A greatly enhanced probability for above normal temperature (10%-35%-55% at maximum, 15%-35%-50% elsewhere) is forecast for a significant region along the Guinea coast and central Africa, including southeastern Liberia, and the central and southern portions of Cote D'Ivoire, Ghana, Togo, Benin, Nigeria, much of Cameroon, Equatorial Guinea, northern Gabon, western Central African Republic and southern Chad. Weaker probabilities for above normal temperature (20%-35%-45% and 25%-35%-40%) surround this region, including southern Gabon, Republic of the Congo, northern Angola, most of Democratic Republic of the Congo, Rwanda, Burundi, extreme northwestern Tanzania, southern and central Sudan, northern Ethiopia, southern Saudi Arabia, part of Chad, part of Niger, southern Mali, Burkina Faso, most of Guinea, Sierra Leone, and the northern portions of Liberia, Cote D'Ivoire, Ghana, Togo and Benin. There is a slightly enhanced risk of extreme above normal seasonal temperatures along the coasts of Cote D'Ivoire, Ghana, Togo, Benin, andsouthwestern Nigeria.

An enhanced probability for above normal temperature (20%-35%-45%) is forecast for southern Namibia, extreme southern Botswana and northwestern South Africa. Weaker probabilities for above normal temperature (25%-35%-40%) surround this region, including the remainder of South Africa, Lesotho, Swaziland, eastern Botswana, Zimbabwe, most of Mozambique, southeastern Malawi, southern Tanzania, and Madagascar.

A greatly enhanced probability for above normal temperature (20%-30%-50%) is forecast for the Mascarene Islands, east of Madagascar.

Slightly enhanced probabilities for near normal temperature (35%-40%-25%) are forecast for a small portion of the immediate coast of southwestern South Africa.

October - December 2001:

PRECIPITATION

The following regions of enhanced probabilities of precipitation anomalies are indicated:

Slightly enhanced probabilities for above normal precipitation (30%-30%-40%) are forecast for parts of northern Saudi Arabia.

An enhanced probability for below normal precipitation (45%-35%-20%) is forecast for most of Tanzania, Burundi, Rwanda, eastern Uganda, and western Kenya. Weaker probabilities for below normal precipitation (40%-35%-25%) surround this region, including Somalia, southern Ethiopia, southeastern Sudan, the remainder of Uganda, eastern Democratic Republic of the Congo, northeastern Zambia, northern Malawi and northern Mozambique.

An enhanced probability for above normal precipitation (20%-35%-45%) is forecast for Lesotho in southern Africa. Weaker probabilities for above normal precipitation (25%-35%-40%) surround this region, including Zimbabwe, central and southern Mozambique, Swaziland, and the eastern three-quarters of South Africa.

Slightly enhanced probabilities for near normal precipitation (35%-40%-25%) are forecast for extreme northern Madagascar, extreme southern Madagascar, and for Agalega Island and Cargados Carajos Island of Mauritius.

Slightly enhanced probabilities for above normal precipitation (25%-35%-40%) are forecast for the Mascarene Islands, to the east of Madagascar.

TEMPERATURE

The following regions of enhanced probabilities of temperature anomalies are indicated:

Slightly enhanced probabilities for below normal temperature (40%-35%-25%) are forecast for the Canary Islands, coastal Western Sahara, and southern and central Morocco.

An enhanced probability for above normal temperature (20%-35%-45% and 25%-30%-45%) is forecast for much of central Africa, including part of Mali, part of Niger, part of Libya, extreme western Egypt, most of Chad and Cameroon, Equatorial Guinea, part of Gabon, most of Republic of the Congo and Democratic Republic of the Congo, Rwanda, Burundi, western Tanzania, northern Zambia, western and northern Uganda, and mainly southern Sudan. A separate but associated region includes eastern Egypt, extreme northeastern Sudan, Jordan, and small portions of western and northern Saudi Arabia. This region extends northward into Europe and Asia. Weaker probabilities for above normal temperature (25%-35%-40% and 30%-30%-40%) surround and connect these two regions, including part of Saudi Arabia, much of Egypt, much of Sudan, part of Libya, a small part of eastern Algeria, northeastern Chad, southern Niger, much of Nigeria, northern portions of Benin, Togo, Ghana, and Cote D'Ivoire, southwestern Mali, and much of Senegal.

Slightly enhanced probabilities for below normal temperatures (25%-35%-40% and 30%-30%-40%) are forecast for part of Namibia, extreme southern Angola, most of Botswana, most of Zimbabwe, the northern tip of South Africa, southern Mozambique, Madagascar and the Comoros Islands.

Slightly enhanced probabilities for above normal temperature (25%-35%-40%) are forecast for the Mascarene Islands.

Slightly enhanced probabilities for above normal temperature (25%-35%-40%) are forecast for western and southern South Africa and Lesotho.

OBSERVED CLIMATOLOGY DATA for Jul-Aug-Sep and Oct-Nov-Dec

CLIMATOLOGICAL AVERAGE: Temperature Precipitation

TERCILE THRESHOLDS (33%-ile & 67%-ile): Temperature Precipitation

EXTREME THRESHOLDS (15%-ile & 85 %-ile): Temperature Precipitation

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