Indonesia's trade surplus rose to a three-month high in August, topping forecasts, as exports grew much faster than expected, official data showed on Tuesday. The August trade data is among economic indicators the central bank will analyse during its two-day policy meeting starting on Tuesday. Economists polled by Reuters ahead of the trade data expected Bank Indonesia (BI) to leave rates unchanged. The world's top exporter of thermal coal, palm oil and nickel metals reported a surplus of $2.89 billion last month, compared with $1.96 billion expected in a Reuters poll. The surplus was the biggest since May.