NEW YORK (TheStreet) -- The economy may not be growing as fast as everyone hoped, but consumers are spending more -- and that may prompt the Federal Reserve to start raising interest rates in September, one economist says. 

The government reported Friday that gross domestic product, the primary measure of economic growth, rose 2.2% in the fourth quarter, short of the 2.4% expected. But inflation-adjusted consumer expenditures jumped 4.2%, up from 3.2% in the third quarter.

"If you dig down into the details, the GDP wasn't that bad," said Emanuella Enenajor, U.S. economist at Bank of America Merrill Lynch. "You had upward revisions to consumption, domestic demand and downward revisions to inventories, so this sets up Q1 up for a bit of a stronger pace."

But weakness in February durable goods orders, reported earlier this week, fueled concern that consumer spending may have softened. That is likely to show up in the first-quarter GDP reports, released at the end of April. 

Enenajor still expects the Fed to tighten in September, but urges investors to keep an eye out for the dollar's continuing strength, especially as it relates to inflation.

"We think a 20% appreciation in the dollar could weigh on inflation by about five-tenths of a percentage point over the next four quarters," she added. "The dollar is something the Fed will be putting more attention on, given how weak inflation is already. It's like kicking inflation when it's already down."

The Fed is well aware of the dollar's momentum, as central bank intervention across the world, notably in Europe, weakens currencies overseas. In a speech at The Economic Club of New York, Fed Vice Chairman Stanley Fischer maintained the central bank's vague stance on a rate-hike timeline, saying one "likely will be warranted before the end of the year."  

Going forward, Enenajor is monitoring jobs data: Continued strength in the labor market would make the Fed more comfortable about raising rates in 2015, even though inflation remains tepid.  The jobs report for March is slated to be released next Friday by the Bureau of Labor Statistics.