The IRI has prepared this experimental Climate Outlook for South America 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 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 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 5cm of precipitation typically occurs over the season. Otherwise, for example, in the case of 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 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.

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 above normal rainfall (25%-35%-40% and 30%-30%-40%) are forecast over portions of northern South America, including southern and eastern Colombia, most of Venezuela, part of Guyana, and a large part of northwestern Brazil stretching from the extreme northern coast to near the border of Bolivia.

Slightly enhanced probabilities for near normal and above normal rainfall (20%-20%-40%) are forecast over part of Suriname, all of French Guiana and a small portion of the northeast coast of Brazil to the north and northwest of the Amazon.

An enhanced probability for below normal rainfall (45%-30%-25%) is forecast for the Galapagos and the central Ecuador coast. Weaker probabilities for below normal rainfall (40%-30%-30%) surround this region in a narrow inland band including part of interior Ecuador, extreme southwestern Colombia and extreme northwestern coastal Peru.

Slightly enhanced probabilities for near normal rainfall (35%-40%-25%) are forecast for a portion of western Colombia.

Slightly enhanced probabilities for below normal rainfall (40%-35%-25%) are forecast for the coastal portions of northeast and central Brazil.

Slightly enhanced probabilities for near normal precipitation (35%-40%-25%) are forecast for central Chile and the adjacent portion of western Argentina.

TEMPERATURE

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

Slightly enhanced probabilities for near normal temperature (25%-40%-35% or 35%-40%-25%) are forecast for Ecuador, the Galapagos Islands, western and northern Colombia, and northwestern Venezuela.

An enhanced probability for below normal temperature (45%-30%-25%) is forecast for central and northeastern Venezuela, Guyana, Suriname, French Guiana, and part of northern Brazil. Weaker probabilities for below normal temperature (40%-35%-25%) surround this region, including much of the remainder of Venezuela, eastern Colombia, and separate portions of northwestern Brazil and northern Brazil, respectively.

Slightly enhanced probabilities for below normal temperature (40%-30%-30%) are forecast for part of central and western Peru.

An enhanced probability for above normal temperature (20%-35%-45%) is forecast for western Brazil, eastern Bolivia, and much of Paraguay, as well as a separate but associated region along the central and southeastern coast of eastern Brazil (20%-35%-45%), and another separate but associated region in the central portion of Chile (25%-30%-45%). Weaker probabilities for above normal temperature (25%-35%-40%) surround and connect these three regions, including portions of central and western Brazil, Bolivia, southeastern Peru, northwestern and southern Paraguay, portions of southern and eastern Brazil, northern Argentina, and northern and central Chile.

Slightly enhanced probabilities for below normal temperature (40%-30%-30%) are forecast for a small portion of south-central Brazil.

Slightly enhanced probabilities for below normal temperature (40%-30%-30%) are forecast for the extreme southern portions of Chile and Argentina, as well as the Falkland islands.

October - December 2001:

PRECIPITATION

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

lightly enhanced probabilities for above normal rainfall (25%-35%-40%) are forecast for a large portion of eastern, northeastern and northern Brazil, as well as Guyana, Suriname and French Guiana.

Slightly enhanced probabilities for below normal rainfall (40%-35%-25%) are forecast for southwestern Ecuador and northwestern Peru.

Slightly enhanced probabilities for below normal precipitation (40%-35%-25%) are forecast for southern Paraguay, southern Brazil, most of Uruguay and part of northeastern Argentina.

Slightly enhanced probabilities for near normal precipitation (25%-40%-35%) are forecast for a portion of eastern Argentina.

TEMPERATURE

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

Slightly enhanced probabilities for near normal temperature (25%-40%-35%) are forecast for a portion of Colombia, Ecuador, the Galapagos Islands, northern Peru, and a very small portion of adjacent northwestern Brazil. A separate area (35%-40%-25%) is found in northern Venezuela and northern Guyana.

Slightly enhanced probabilities for near normal and above normal temperature (20%-40%-40%) are forecast for part of western, central and southern Columbia, extending northward into Latin America.

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

A greatly enhanced probability for below normal temperature (50%-30%-20%) is forecast for eastern Brazil, mainly inland from the coastline. Weaker probabilities for below normal temperature (45%-35%-20% and 40%-35%-25%) surround this region, including additional parts of central, northeastern and northern Brazil, as well as French Guiana, Suriname, and northeastern Venezuela.

Slightly enhanced probabilities for above normal temperature (25%-35%-40%) are forecast for Paraguay, southern and eastern Bolivia, and a minor portion of southwestern Brazil. These conditions are also forecast in another small nearby region in western Brazil, just north of the Paraguay border.

Slightly enhanced probabilities for near normal temperature (25%-40%-35%) are forecast for a small region in the extreme northeast tip of Brazil.

Slightly enhanced probabilities for near normal temperature (35%-40%-25%) are forecast for a small portion of southwestern-central Brazil.

Slightly enhanced probabilities for near normal temperature (35%-40%-25%) are forecast for a small region in southern Uruguay and the adjacent portion of eastern Argentina.

Slightly enhanced probabilities for near normal temperature (25%-40%-35%) are forecast for mainly the coastal portion of northern and central Chile.

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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