IRI NET ASSESSMENT FORECAST
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Date and Period of Forecast
In October 1999, the IRI
Experimental Forecast Division prepared a Climate Outlook for October-December
1999. Here we provide a subset of the October Net Assessment Forecast.
The complete forecast, which includes additional regional forecasts for
October-December 1999 and a global forecast for January-March 2000,
can be found at http://iri.columbia.edu/climate/forecast/net_asmt/.
Uncertainties
This Climate Outlook is dependent on the quality of the 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.
October-December 1999 Precipitation probabilities |
Precipitation Outlook
The Outlook for October-December 1999 can also be found at http://iri.columbia.edu/climate/forecast/net_asmt/.
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Maps are given showing 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).
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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.
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Areas marked "D" (dark grey) experience a pronounced
dry season during the forecast period, typically receiving less than 15%
of their annual precipitation total during this three-month period.
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Boundaries between sub-regions should be considered transition
zones, and their location considered to be only qualitatively correct.
Temperature Outlook
The Outlook for October-December 1999 can also be found at http://iri.columbia.edu/climate/forecast/net_asmt/.
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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).
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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.
Ocean Conditions
Of relevance in the preparation of this Outlook has been the current weak
La Niña conditions (lower than average sea-surface temperatures
(SSTs) in the central equatorial Pacific Ocean) that are expected to amplify
slightly throught the end of 1999. The persistence of slightly warmer than
average conditions in the western Pacific has been assumed also. The
SSTs of the tropical Indian Ocean were assumed to return to near-normal
conditions with the period October-December 1999. The forecast of tropical
South Atlantic SSTs suggests a warming trend through December 1999.
October-December 1999 Temperature Probabilities |
Methods The following
procedures and information were used to prepare this Climate Outlook:
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Coupled ocean-atmosphere model predictions of tropical Pacific SST. Particularly
heavy weighting has been given to the NOAA /NCEP, Climate Modeling Branch
coupled model.
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Statistical forecasts of Indian Ocean and Atlantic Ocean sea surface temperature.
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Atmospheric global circulation model (GCM) predictions response to the
present and predicted SST patterns.
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Statistical analyses.
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Appropriate Regional Climate Outlook Forum consensus guidance.
Sources of information
include ACMAD, Caribbean Meteorological Institute, CPTEC, CPC/NOAA, Department
of Natural Resources (Queensland, Australia), ECMWF, Indian Meteorological
Department and the South African Weather Service. |
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