The ringgit shed as much as 1.0 percent to 3.2300 per dollar, its weakest since June 25, as some offshore hedge funds sold the Malaysian currency, traders said.
Economists are evenly split over whether Malaysia's central bank will raise its policy interest rate again later this week, a Reuters poll showed.
Investors also rushed to cover short positions in the dollar ahead of a local holiday on Tuesday as the greenback hovered a near 14-month high.
The Indonesian rupiah weakened to its weakest in more than two months as long-term government bond prices fell.
South Korea's won hit a near five-month low as offshore funds sold the currency, but then some of the losses were pared on demand from exporters for settlements.
As markets prepare for the meeting, giving the dollar a firm bias, one-month implied volatility in most emerging Asian currencies rose from historic lows.