WASHINGTON — The U.S. economy has resembled an especially dizzying roller-coaster ride this year, with a hurtling dive followed by a steep climb leading to yet another slide.

Today, when the government issues its first of three estimates of growth in the July-September quarter, it’s expected to show an economy slumping — but poised to rise again.

Economists’ consensus forecast is the economy eked out just a 1.7 percent annual growth rate last quarter, a subpar pace by any standard.

“We got a lot of weakness during the summer from a widening of the trade deficit and a drawdown of inventories,” said Mark Zandi, chief economist at Moody’s Analytics.