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 the demise of slightly cool but near-average conditions during the first forecast season with the development of weak, slightly above-average temperatures during the second season.  The forecast for slightly above average conditions is consistent with most other numerical and statistical forecasts of central and eastern Pacific SSTs.

B) Forecasts of the tropical Atlantic and the Indian ocean using statistical models developed by the CPTEC and IRI, respectively.

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 Center for Ocean-Land-Atmosphere Studies; Goddard Space Flight Center .

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 April - September 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 Atlantic ocean has been an important influence on the forecasts over South America. 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: April - June 2001 and July - September 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). 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 region II in April - June 2001 (Map A), there is a 40% 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 25% 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. (Sometimes this map may be blank, due to no expected extremes.) 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.

April - June 2001:

PRECIPITATION

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

Region II) slightly enhanced probabilities of above-normal precipitation across northern Brazil, primarily north of the Amazon River;

Region III) slightly enhanced probabilities of near-normal to below-normal precipitation across northeastern Brazil;

Region IV) slightly enhanced probabilities of below-normal precipitation across central Chile and Argentina.

TEMPERATURE

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

Region V) slightly enhanced probabilities of below-normal temperatures over most of Venezuela and northeastern Colombia.

Region VI) slightly enhanced probabilities of above-normal temperatures over eastern Brazil.

July - September 2001:

PRECIPITATION

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

Region IV) slightly enhanced probabilities of below-normal precipitation over Costa Rica and Panama and northwest Colombia extending northward into Mexico;

Region V) enhanced probabilities of above-normal precipitation over Guyana, Suriname, French Guiana and northern Brazil north and west of the Amazon delta.

Region VI) slightly enhanced probabilities of below-normal precipitation over eastern coastal regions of northeast Brazil;

Region VII) slightly enhanced probability of below-normal precipitation over much of southern Brazil and a small portion of adjacent Argentina.

TEMPERATURE

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

Region III)  enhanced probabilities of above-normal temperatures over southwest Colombia, Ecuador and northwest Peru;

Region IV) slightly enhanced probabilities of near-normal to above-normal temperatures over a broad area including much of the northern half of Brazil excluding northeastern areas, Guyana, Suriname and French Guiana;

Region V)  Slightly enhanced probabilities of above-normal temperatures over northeast Brazil.