DUBAI, May 22 (Reuters) - Stock markets in the Gulf may trade with a weak bias on Sunday as short-term traders book profits because of a lack of strong positive catalysts.

Oil prices slipped on Friday as a stronger U.S. dollar encouraged investors to sell, with Brent crude settling down 9 cents at $48.72 a barrel.

"Stock markets in the Gulf are now in an adjustment phase and I believe investors will book profits if there is a lack of other positive stimulus in the market," said Mohammad al- Shammasi, chief executive of Riyadh-based Derayah Financial.

Dubai's index, last at 3,230 points, fell on Thursday below technical support on the late March and early May lows of 3,248-3,256 points. A second straight close below that area would confirm a break, triggering a bearish head & shoulders pattern formed by the highs and lows since March and pointing down to the 2,800-point area.

But while bourses in the United Arab Emirates were laggards in the region last week, relatively attractive valuations may limit losses; indexes in Abu Dhabi and Dubai are trading at about 10.0 and 8.0 times trailing earnings, compared to Riyadh's 12.3 times, and also offer investors strong dividend yields.

(Reporting by Celine Aswad; Editing by Andrew Torchia)