Federal Reserve officials trying to decide when to raiseinterest rates for the first time in a decade may want to avoidwaiting until December to make their move.

The reason: Treasury-market liquidity has a clear pattern ofthinning out at year-end, potentially exacerbating volatility inreaction to an increase in the Fed's benchmark rate. A sharp risein yields could hurt the economy and complicate liftoff.

These concerns won't be a deal-breaker if economic data supporta rate rise in December and not sooner, economists say. Still, theycould make officials look more favorably upon a September orOctober start. Fed Chair Janet Yellen has said liftoff will beappropriate this year if the economy evolves as expected.