The weakness in the U.S. economy shows no signs of immediate abatement, and significant challenges may last well into 2009, according to a new report.

The Manufacturers Alliance/MAPI Quarterly Economic Forecast predicts that inflation-adjusted gross domestic product (GDP) growth will slow to 1.6% in 2008 and decelerate to 1.3% in 2009. The 2009 GDP forecast is down from 1.9% growth projected in MAPI’s May report.

The Internal Revenue Service accelerated the payment of tax rebates this year under the economic stimulus plan, getting cash in consumers’hands earlier than expected,”said Daniel J. Meckstroth, Manufacturers Alliance/MAPI chief economist. “The cash windfall is only temporary, and we expect a corresponding decline in spending in fourth quarter 2008 and into …