IRI Climate Digest
July 2000
July-September Seasonal Forecasts
Date and Period of Forecast
In June 2000, the IRI Experimental Forecast Division prepared a Climate Outlook
for July-September 2000. Here we provide a subset of the June Net Assessment Forecast.
The complete forecast, which includes long-lead global forecasts for October-December 2000,
can be found 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 July-September 2000 can also be found at
http://iri.columbia.edu/climate/forecast/net_asmt/.
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.
Areas marked "D" (dark grey) experience a pronounced dry season during
the forecast period, typically receiving less than 15% of their annual
precipitation or less than 5 cm total during this three-month period.
Boundaries
between sub-regions should be considered transition zones, and their location
considered to be only qualitatively correct.
July-September 2000 Precipitation Probabilities
Temperature Outlook
The Outlook for July-September 2000 can also be found at
http://iri.columbia.edu/climate/forecast/net_asmt/.
The temperature map shows expected probabilities that the seasonal temperatures
will fall into the warmest third
of the years (top number), the middle third of the years, or the coldest
third of the years (bottom number).
A qualitative 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.
July-September 2000 Temperature Probabilities
Ocean Conditions
Of relevance in the preparation of this Outlook has been the weakening
remains of the 1998-2000
La Niņa conditions
(lower than average sea-surface temperatures (SSTs) in the central equatorial
Pacific Ocean). Thus, near neutral but slightly below-average
equatorial Pacific SST conditions are in effect for the first season of
the forecast,
July-August-September 2000, and
near-normal conditions are expected for the second forecast season,
October-November-December 2000. The SSTs of
the tropical Indian Ocean were assumed to remain near-normal. Tropical
Atlantic SSTs were not expected to change
significantly.
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.
Sources of information include ACMAD,
COLA, CPTEC, CPC/NOAA, CMC, Department of Natural Resources (Queensland,
Australia), NIWA, ECMWF, Indian Meteorological Department,
PAGASA, Bureau of Meterology, and the South African Weather Service. |
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