IRI Climate Digest August 2001
August - October 2001 Seasonal Forecasts
Date and Period of Forecast
In July 2001, the IRI prepared a Climate Outlook
for August 2001 - January 2002. Here we provide a subset of the July Net Assessment
Forecast. The entire IRI July Net assessment forecast for the period
August 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 periods August-September-October,
September-October-November, October-November-December, and November- December-January
can 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.
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.
August-October 2001 Precipitation Probabilities for North America
September-November 2001 Precipitation Probabilities for Africa
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 http://iri.columbia.edu/climate/forecast/net_asmt/
for the probabilities of each tercile class.
August-October 2001 Temperature Probabilities.
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 are near their long-term average
(SSTs)
, although slightly lower than average SSTs have developed along the
immediate western coast of South America and warmer than average SSTs
persist in the extreme western part of the basin. Near neutral
equatorial Pacific SST conditions are in effect for the first three periods of
the forecast,
August-September-October 2001,
September-October-November 2001,
October-November-December 2001,
while during the last period,
November-December 2001-January 2002,
they are expected to be slightly above average. 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 south Atlantic Ocean is
expected to persist through at least the first half of 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.
Additional sources of information include ACMAD, COLA, CPTEC, CPC/NOAA,
CMC, Department of Natural Resources (Queensland, Australia), NIWA, ECMWF,
Indian Meteorological Department, PAGASA, Bureau of Meteorology, and the
South African Weather Service. |
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