At 1516 GMT, the rand was at 19.0475 to the dollar, about 0.44% weaker than its closing level on Friday.
Analysts said the risks were for the rand to fall further, owing to weak economic data out of China, higher-than-expected core producer inflation in the U.S. and increased bets on another Federal Reserve rate hike in September.
"Concerns over the global economic outlook... negatively affect the rand, as does higher levels of risk aversion in global financial markets," said Investec analyst Annabel Bishop.
Bishop said the weakness in the rand can also be attributed to market players taking fewer risks in northern hemisphere summer vacation months, when trading volumes tend to be thinner.
"This causes increased volatility, as market reactions to events tend to be more pronounced," she added.
ETM Analytics played down the market-moving potential of this week's South African data releases, which include second-quarter unemployment data on Tuesday and June retail sales on Wednesday.
"South Africa's economy remains under considerable pressure... As U.S. bond yields rise, the rand will remain vulnerable," it said in a research note, adding that this week's U.S. releases, including Federal Reserve minutes, were likely to be more market-moving.
Shares on the Johannesburg Stock Exchange fell, with the blue-chip Top-40 index closing down over 1.1%.
South Africa's benchmark 2030 government bond slumped, the yield up 16.5 basis points to 10.330%.
(Reporting by Alexander Winning, Tannur Anders and Bhargav Acharya; Editing by Sonali Paul and Sharon Singleton)
