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WEEKLY NEWSLETTER
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Sudan
Index
Although Sudan lies within the tropics, the climate ranges
from arid in the north to tropical wet-and-dry in the far
southwest. Temperatures do not vary greatly with the season at
any location; the most significant climatic variables are
rainfall and the length of the dry season. Variations in the
length of the dry season depend on which of two air flows
predominates, dry northeasterly winds from the Arabian Peninsula
or moist southwesterly winds from the Congo River basin.
From January to March, the country is under the influence of
the dry northeasterlies. There is practically no rainfall
countrywide except for a small area in northwestern Sudan in
where the winds have passed over the Mediterranean bringing
occasional light rains. By early April, the moist southwesterlies
have reached southern Sudan, bringing heavy rains and
thunderstorms. By July the moist air has reached Khartoum, and in
August it extends to its usual northern limits around Abu Hamad,
although in some years the humid air may even reach the Egyptian
border. The flow becomes weaker as it spreads north. In September
the dry northeasterlies begin to strengthen and to push south and
by the end of December they cover the entire country. Yambio,
close to the border with Zaire, has a nine-month rainy season
(April-December) and receives an average of 1,142 millimeters of
rain each year; Khartoum has a three-month rainy season (JulySeptember ) with an annual average rainfall of 161 millimeters;
Atbarah receives showers in August that produce an annual average
of only 74 millimeters.
In some years, the arrival of the southwesterlies and their
rain in central Sudan can be delayed, or they may not come at
all. If that happens, drought and famine follow. The decades of
the 1970s and 1980s saw the southwesterlies frequently fail, with
disastrous results for the Sudanese people and economy.
Temperatures are highest at the end of the dry season when
cloudless skies and dry air allow them to soar. The far south,
however, with only a short dry season, has uniformly high
temperatures throughout the year. In Khartoum, the warmest months
are May and June, when average highs are 41° C and temperatures
can reach 48° C. Northern Sudan, with its short rainy season,
has
hot daytime temperatures year round, except for winter months in
the northwest where there is precipitation from the Mediterranean
in January and February. Conditions in highland areas are
generally cooler, and the hot daytime temperatures during the dry
season throughout central and northern Sudan fall rapidly after
sunset. Lows in Khartoum average 15° C in January and have
dropped
as low as 6° C after the passing of a cool front in winter.
The haboob, a violent dust storm, can occur in central Sudan
when the moist southwesterly flow first arrives (May through
July). The moist, unstable air forms thunderstorms in the heat of
the afternoon. The initial downflow of air from an approaching
storm produces a huge yellow wall of sand and clay that can
temporarily reduce visibility to zero.
Data as of June 1991
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