SYDNEY—Australia’s trade surplus unexpectedly grew to a record in August as strength in liquefied natural gas and coal exports more than offset a pullback in iron ore prices, a windfall to mining profits and tax receipts. Figures from the Australian Bureau of Statistics out on Tuesday showed the surplus on international trade jumped to A$15.1 billion ($11.0 billion) in August, from A$12.7 billion the month before. That was the highest on record and confounded analysts’ forecasts of a drop to A$10.3 billion. Exports climbed 4.1 percent in the month to A$48.5 billion led by LNG, hard coking coal, and thermal coal, courtesy of strong energy demand in Asia. Both prices and volumes were higher, eclipsing a sharp fall in prices for iron ore, Australia’s number one export earner. Demand for energy in Asia has only got hotter as shortages of electricity in China led to blackouts and countries compete for …