LISBON, Sept 30 (Reuters) - Lingering uncertainty about rising inflation requires close monitoring by the European Central Bank, which sees it as a temporary trend, but it must be prepared to act flexibly, ECB Governing Council member Mario Centeno said on Thursday. "Concerning the monetary policy the best answer to uncertainty is to keep close monitoring, a steady hand and stand ready to act flexibly," he told an online conference in Lisbon, adding that the bank had tools to respond "with agility and effectiveness". He said growth in the euro area was expected to continue to grow rapidly, exceeding its pre-crisis level in the fourth quarter, and while inflation continued to exceed projections, "this spike is still regarded as temporary".