Date and Period of Forecast

In August 2001, the IRI prepared a Climate Outlook for September 2001 - January 2002. Here we provide a subset of the August Net Assessment Forecast. The entire IRI June Net assessment forecast for the period September 2001 - January 2002 is available at http://iri.columbia.edu/climate/forecast/net_asmt/.

Uncertainties

This Climate Outlook is dependent on the quality of the sea surface temperature (SST) predictions. For the tropical Pacific, these predictions can be expected to provide useful information, but there is some uncertainty concerning the detailed evolution of SSTs. Spread in global SST predictions is a source of uncertainty in the Outlook provided here. The procedures, models, and data used to derive this Climate Outlook may be somewhat different from those used by National Meteorological Services in particular regions and may differ from the official forecasts issued in those areas.

Regional Influences

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. For further information concerning this and other guidance products, users are strongly advised to contact their National Meteorological Services.

Precipitation Outlook

The Outlook for other regions of the globe for the seasons September-October-November and October-November-December be found at Net Assessment forecasts.

Maps show expected precipitation probabilities in tercile classes. The maps indicate probabilities that seasonal precipitation will fall into the wettest third of the years (top number), the middle third of years (middle number) or the driest third of the years (bottom). An outlook of climatology "C" (light grey) indicates equal probabilities in each class; i.e., there is no basis for favoring the forecast of any particular category. Boundaries between sub-regions should be considered transition zones, and their location considered to be only qualitatively correct. Color shading indicates which tercile class has the greatest probability of occurrence with darker shading indicating greater likelihood as shown by the legend to the right of the plots.

November-January 2001/2002 Precipitation Probabilities for South America

September-December 2001 Precipitation Probabilities for North America

Temperature Outlook

This forecast consists of expected probabilities of temperature in tercile classes. The terciles refer to the seasonal temperature falling into the warmest third of the years (top tercile), the middle third of years (middle tercile) or the coldest third of the years (bottom tercile). Boundaries between sub-regions should be considered transition zones, and their location considered to be only qualitatively correct. Color shading indicates which tercile class has the greatest probability of occurrence with darker shading indicating greater likelihood as shown by the legend on the bottom of the plots. Note:
The IRI is in the process of implementing new graphics for its forecast products. Currently, global maps only indicate (by shading) the tercile class with the greatest probability of occurrence.
Please consult the regional maps at Net Assessment forecasts for the probabilities of each tercile class.

Ocean Conditions

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 Pacific are near their long-term average, with locally warm anomalies near the dateline locally warm anomalies near the dateline, although slightly lower than average SSTs exist in the far eastern equatorial Pacific and warmer than average SSTs persist in the extreme western part of the basin. Near neutral (<0.5C) equatorial Pacific SST conditions are in effect for the first half of the forecast period, September-November 2001 and October-December 2001, while during the second half, November-December 2001-January 2002, December 2001-February 2002, they are expected to be slightly above average (approximately 0.5C). 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 Atlantic Ocean has weakened over the last couple months and is predicted to weaken further through the forecast period.

Methods

The following procedures and information were used to prepare this Climate Outlook:

• Coupled ocean-atmosphere model predictions of tropical Pacific SST -- particularly heavy weighting has been given to the NOAA /NCEP, Climate Modeling Branch coupled model
• Statistical forecasts of Indian Ocean and Atlantic Ocean sea surface temperature
• The response of Atmospheric global circulation model (GCM) predictions to the present and predicted SST patterns
• Statistical analyses
• Appropriate Regional Climate Outlook Forum consensus guidance.