The IRI has prepared this experimental Climate Outlook for South America for August 2001 - January 2002. 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, August-September-October 2001, September-October-November 2001, October-November-December 2001, while during the second season, November-December 2001-January 2002, 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 August 2001 - January 2002 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 in global SST predictions is a source of uncertainty in the Outlook provided here. 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 season 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 four seasons: August-September-October 2001, September-October-November 2001, October-November-December 2001 and November-December 2001-January 2002. 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 5cm of precipitation typically occurs over the season. Otherwise, for example, in the case of August-September-October 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 in part of eastern and northeastern Brazil.

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.

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

August-September-October 2001:

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

Slightly enhanced probabilities for above normal precipitation (30%-30%-40%) are forecast for north-central Argentina.

Slightly enhanced probabilities for above normal precipitation (25%-35%-40%) are forecast for eastern Venezuela and northern Guyana.

Slightly enhanced probabilities for below normal precipitation (40%-35%-25%) are forecast for N Colombia and northeastern Venezuela.

Slightly enhanced probabilities for below normal precipitation (40%-35%-25%) are forecast for central Chile and part of western Argentina.

A greatly enhanced probability for below normal precipitation (55%-30%-15 and 50%-30%-20%) is forecast for central and part of northeastern Brazil. Weaker probabilities for below normal precipitation (45%-35%-20%, 45%-30%-25%, 40%-35%-25% and 40%-30%-30%) surround this region, including eastern Bolivia, part of southern Brazil, and the southern tips of Guyana, Suriname and French Guiana.

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

Slightly enhanced probabilities for near normal temperature (35%-40%-25% and 25%-40%-35%) are forecast for the central coast of Brazil.

Slightly enhanced probabilities for near normal temperature (25%-40%-35%) are forecast for French Guiana, Suriname, Guyana, northwestern Brazil, southern Venezuela, parts of Columbia, small parts of Ecuador, and northern Peru.

An enhanced probability for above normal temperature (20%-35%-45%) is forecast for west-central Argentina and central Chile. Weaker probabilities for above normal temperature (25%-35%-40%) surround this region, including additional portions of Argentina and central Chile.

Slightly enhanced probabilities for below normal temperature (40%-35%-25%) are forecast for south-central/southeastern Brazil.

A greatly enhanced probability for above normal temperature (15%-30%-55% and 20%-30%-50%) is forecast for part of northern and northeastern Brazil. Weaker probabilities for above normal temperature (20%-35%-45%, 25%-35%-40%) surround this region, including additional areas in Brazil, northeastern Bolivia and extreme southern French Guiana.

Slightly enhanced probabilities for near normal and above normal temperature (20%-40%-40%) are forecast for northern Columbia, extending northward into Central America.

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

A greatly enhanced probability for below normal temperature (50%-30%-20%) is forecast for South Georgia Island (of the UK).

Slightly enhanced probabilities for above normal temperature (25%-35%-40%) are forecast for southern Brazil.

September-October-November 2001:

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

Slightly enhanced probabilities for near normal precipitation (30%-40%-30%) are forecast for extreme western Colombia and northern Ecuador.

Slightly enhanced probabilities for near normal precipitation (25%-40%-35%) are forecast for Guyana, Surinam, French Guyana and part of northern Brazil.

Slightly enhanced probabilities for above normal precipitation (25%-35%-40%) are forecast for French Guyana and adjacent northern Brazil. An isolated small region to the east of this region, over northeastern Brazil, also has these forecast probabilities.

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

Slightly enhanced probabilities for above normal precipitation (25%-35%-40%) are forecast for part of north-central Chile and northern Argentina.

Slightly enhanced probabilities for below normal precipitation (40%-30%-30%) are forecast for northern Argentina and part of southern Paraguay.

Slightly enhanced probabilities for below normal precipitation (40%-30%-30%) are forecast for central Chile and adjacent Argentina.

Slightly enhanced probabilities for below normal precipitation (40%-35%-25%) are forecast for part of southern Brazil and adjacent eastern Bolivia.

An enhanced probability for below normal precipitation (45%-35%-20%) is forecast for northern Colombia and northwestern Venezuela. Weaker probabilities for below normal precipitation (40%-35%-25%) surround this region to the south and west, penetrating farther into these two countries.

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

Slightly enhanced probabilities for near normal temperature (30%-40%-30% and 25%-40%-35%) are forecast for much of southeastern and east-central Brazil.

Slightly enhanced probabilities for near normal temperature (30%-40%-30%) are forecast for east-central Argentina and southern Uruguay.

Slightly enhanced probabilities for near normal temperature (25%-40%-35%) are forecast for northern Venezuela.

Slightly enhanced probabilities for near normal temperature (25%-40%-35%) are forecast for northeastern Brazil.

An enhanced probability for above normal temperature (20%-35%-45%) is forecast for part of Colombia and Venezuela. Weaker probabilities for above normal temperature (25%-35%-40%) surround this region, including more of Colombia and Venezuela, much of Ecuador, and northwestern coastal Peru.

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

A greatly enhanced probability for above normal temperature (20%-30%-50%) is forecast for west-central Brazil, as well as a separate but associated region in northeast Brazil (20%-30%-50%). Weaker probabilities for above normal temperature (20%-35%-45%, 25%-35%-40%, and 20%-40%-40%) surround and connect these two regions, including additional large portions of Brazil, eastern French Guiana and northern and northeastern Bolivia.

Slightly enhanced probabilities for above normal temperature (25%-35%-40%) are forecast for central Chile and parts of central and southern Argentina.

Slightly enhanced probabilities for above normal temperature (25%-35%-40%) are forecast for coastal portions of southern Brazil.

Slightly enhanced probabilities for below normal temperature (40%-35%-25%) are forecast for a tiny portion of central coastal Peru.

Slightly enhanced probabilities for below normal temperature (40%-30%-30%) are forecast for the Falkland Islands.

A greatly enhanced probability for below normal temperature (55%-30%-15%) is forecast for South Georgia Island (of the UK).

October-November-December 2001:

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

Slightly enhanced probabilities for above normal precipitation (30%-30%-40%) are forecast for east-central Brazil.

Slightly enhanced probabilities for above normal precipitation (25%-35%-40%) are forecast for an area near and along the northern coast of Brazil.

Slightly enhanced probabilities for above normal precipitation (25%-35%-40%) are forecast for the Galapagos Islands

Slightly enhanced probabilities for above normal precipitation (25%-35%-40%) are forecast for a small part of northern Chile, and southern Bolivia.

Slightly enhanced probabilities for below normal precipitation (40 30 30) are forecast for part of east-central coastal Argentina.

An enhanced probability for below normal precipitation (45%-35%-20%) is forecast for northern Colombia and northwestern Venezuela. Weaker probabilities for below normal precipitation (40%-35%-25%-25%) surround this region, including additional parts of Colombia and Venezuela, and small parts of northern Brazil and Panama.

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

Slightly enhanced probabilities for near normal temperature (35%-40%-25%) are forecast for part of southeastern Brazil.

Slightly enhanced probabilities for near normal temperature (25%-40%-35%) are forecast for west-central Brazil, near the border of Bolivia.

Slightly enhanced probabilities for above normal temperature (30%-30%-40% and 25%-35%-40%) are forecast for central Chile, central Argentina, small portions of Uruguay, and southern Brazil.

Slightly enhanced probabilities for above normal temperature (25%-35%-40%) are forecast for west central Brazil, northern Bolivia and part of southern Peru.

Slightly enhanced probabilities for near normal and above normal temperature (20%-40%-40%) are forecast for southwestern Colombia, Ecuador and much of Peru.

Slightly enhanced probabilities for near normal and above normal temperature (20%-40%-40%) are forecast for extreme northern Chile, part of Bolivia, parts of central and northeast Brazil.

Slightly enhanced probabilities for above normal temperature (25%-35%-40%) are forecast for much of Colombia, northwestern Venezuela, and a small portion of northwestern Brazil.

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

Slightly enhanced probabilities for above normal temperature (25 35 40) are forecast for west-central Brazil, northern Bolivia and southern Peru.

Slightly enhanced probabilities for below normal temperature (40%-35%-25%) are forecast for Guyana, Surinam, French Guiana and small portions of northern Brazil.

November-December 2001-January 2002:

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

Slightly enhanced probabilities for near normal precipitation (30%-40%-30%, 35%-40%-25% and 25%-40%-35%) are forecast for northern Brazil and southern Guyana and Surinam.

Slightly enhanced probabilities for above normal precipitation (25%-35%-40%) are forecast for the coast of Ecuador.

An enhanced probability for above normal precipitation (20%-35%-45%) is forecast for northeastern Brazil. Weaker probabilities for above normal precipitation (25%-35%-40%) surround this region, including more of northeastern and northern Brazil.

A greatly enhanced probability for above normal precipitation (15%-30%-55%) is forecast for the Galapagos Islands.

Slightly enhanced probabilities for below normal precipitation (40%-35%-25%) are forecast for northern Colombia, most of Venezuela, a small portion of northern Brazil, and northern Guyana. This region extends northwestward into Central America.

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

Slightly enhanced probabilities for near normal temperature (25%-40%-35%) are forecast for northern Venezuela.

An enhanced probability for above normal temperature (20%-35%-45%) is forecast for coastal Ecuador and extreme nortern coastal Peru. Weaker probabilities for above normal temperature (25%-35%-40%) flank this region, including more of Ecuador and Peru.

Slightly enhanced probabilities for above normal temperature (25%-35%-40%) are forecast for northern Colombia and northwest Venezuela.

A greatly enhanced probability for above normal temperature (20%-30%-50%) is forecast for the Galapagos Islands.

An enhanced probability for below normal temperature (45%-35%-20%) is forecast for French Guiana and the adjacent portion of northern Brazil. Weaker probabilities for below normal temperature (40%-35%-25%) surround this region, including more of nothern Brazil, Suriname, and Guyana.

Slightly enhanced probabilities for below normal and near normal temperature (40%-40%-20%) are forecast for the Lesser Antilles and northeastern Venezuela.

An enhanced probability for above normal temperature (20%-35%-45%) is forecast for a portion of the coast of southern Brazil. Weaker probabilities for above normal temperature (25%-35%-40%) surround this region, including southern Brazil, southern Paraguay and northeastern Uruguay.

Slightly enhanced probabilities for below normal and near normal temperature (40%-40%-20%) are forecast for southeastern Brazil.

OBSERVED CLIMATOLOGY DATA for Aug-Sep-Oct, Sep-Oct-Nov, Oct-Nov-Dec and Nov-Dec-Jan

CLIMATOLOGICAL AVERAGE: Temperature Precipitation

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

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

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