Tracking weak regional markets, the Sensex at the Bombay Stock Exchange opened 44 points lower, at 19,936, on Friday morning. But it later rebounded, to stand 55 points, or 0.3 per cent in the green, at 20,038, in afternoon trade, a short while ago. Stock markets in Japan, China, Hong Kong, South Korea, and Taiwan fell by between 0.2 percent and 0.7 percent.