IRI NET ASSESSMENT FORECAST
DISCUSSION
In April 1999, the IRI Experimental
Forecast Division prepared a Climate Outlook for July-September 1999.
The Precipitation and Temperature Probabilities presented in this Outlook
are based on predictions of the continuation of cooler than average conditions
in the eastern and central equatorial Pacific Ocean (La Niña),
and the persistence of warmer than average conditions in the western equatorial
Pacific. The sea surface temperatures of the western Indian
Ocean are above average. It has been assumed that the northern and
tropical Atlantic Ocean will remain warmer than average, and that sea surface
temperatures in the South Atlantic will increase during the forecast period.
PRECIPITATION OUTLOOK
The Outlook for July-September 1999 can also be found at http://iri.ucsd.edu/forecast/net_asmt.
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). An
outlook of climatology "C" indicates equal probabilities in each class
i.e.; there is no basis for favoring the forecast of any particular category.
Areas marked "D" experience a pronounced dry season during the forecast
period, typically receiving less than 15% of their annual precipitation
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 1999 Precipitation Probabilities |
METHODS The
following procedures and information were used to prepare this Climate
Outlook: 1) Coupled ocean-atmosphere model predictions of tropical Pacific
SST Particularly heavy weighting has been given to the NOAA /NCEP, Climate
Modeling Branch coupled model which suggests continued development of moderate
La Niña conditions, with the persistence of strong positive sea-surface
temperature anomalies near Indonesia, 2) statistical forecasts of Indian
Ocean and Atlantic Ocean sea surface temperature, 3) Atmospheric global
circulation model (GCM) predictions response to the present and predicted
SST patterns, 4) Statistical analyses, 5) Appropriate Regional Climate
Outlook Forum consensus guidance.
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. This Outlook has been prepared in the time available,
using all information that was reasonably accessible. Inclusion of other
climate information and guidance requires further arrangements. The IRI
is engaged in establishing collaborative arrangements with the goal of
improving its capability to provide the best and most complete global climate
guidance.
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.
For further information concerning this and other guidance products, users
are strongly advised to contact their National Meteorological Services.
July-September 1999 Temperature Probabilities |
TEMPERATURE OUTLOOK
The Outlook for July-September 1999 can also be found at http://iri.ldeo.columbia.edu/climate/forecast/net_asmt/.
The temperature map show 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" 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.
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 Bureau. |
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