IRI Climate Information Digest - December 1998
Issued 15 January 1999, Next
Issue 15 February 1999
NOAA NCEP EMC CMB GLOBAL
monthly Sea Surface Temperature Anomaly |
Highlights
La Niña Matures
The area extent of relatively cold equatorial waters has expanded over
the past several months. By December 1998 the magnitude and extent
of the La Niña
were becoming comparable to the 1988 cold episode. The strongest
negative sea surface temperature departures extend from the dateline eastwards
to the central eastern Pacific. An area of above average sea surface temperature
that lies to the south of the equator in the eastern Pacific is not of
sufficient magnitude nor in an optimal position to significantly influence
the atmosphere. Recent numerical and statistical forecasts suggest
this cold episode will slowly decrease in magnitude over the next several
months.
Precipitation Patterns
Many of the typical La Niña
rainfall patterns are now evident. These include enhanced rainfall
in the far west Pacific, northern Australia, and southern Africa and drier
conditions in central equatorial Pacific, eastern Equatorial Africa and
southeastern South America. La
Niña related spatial contrast in dry-wet rainfall
patterns are particularly strong in the central (dry) to western (wet)
Pacific and in Africa. Extremely dry conditions characterize the
area from northern Mozambique northward through Ethiopia in strong contrast
to heavy rainfall to the south through much of South Africa. Rainfall
patterns not directly related to the La Niña
include a continuation of dry conditions in the Iberian Peninsula and Morocco,
an excess rainfall in an area surrounding the Adriatic, and dry conditions
in the far eastern Mediterranean and Near East including parts of Iran,
Iraq, and Saudi Arabia. Slight variations of this dry-wet-dry pattern have
characterized these areas for the past several months. Dry conditions continued
to effect the east coast of North America.
Global Temperatures
The December global mean temperatures were above the long term average,
completing a year of above average temperatures and contributing to the
warmest year in the instrumental record (see the Nov 1998 Climate Information
Digest). Average December temperature departures for continental
areas were positive except for South America which experienced average
to colder than average in most areas.
Forecasts - Seasonal Temperature and Precipitation
Impacts - On Fisheries, Agriculture, Health and Hazards.
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