Aug. 21 (Bloomberg) -- Cotton tumbled, capping the biggest three-day slump since November 2011, as dry weather forecast for the Southeast aided crop prospects in the U.S., the worldΆs top exporter.

Southeast cotton-growing areas will be drier Aug. 27 to Aug. 31 after wet conditions this week, particularly in Georgia and South Carolina, Commodity Weather Group LLC in Bethesda, Maryland, said in a report. About 46 percent of the U.S. crop was rated good to excellent as of Aug. 18, up from 41 percent a year earlier, the government said on Aug. 19.

“TheyΆve been getting way too much water, so any drying in the Southeast could be extremely bearish,” Michael Smith, the president of T&K Futures & Options in Port St Lucie., Florida, said in a telephone interview.

Cotton for December delivery tumbled 5.2 percent to settle at 84.24 cents a pound at 2:38 p.m. on ICE Futures U.S. in New York, the biggest drop for a most-active contract since June 21, 2012. In three days, the fiber plunged 9.7 percent, the most since Nov. 21, 2011.

Today, the price touched 84 cents, the lowest since July 18. Losses accelerated after cotton fell below 86.5 cents, Sharon Johnson, a senior market specialist at KCG Futures in Roswell, Georgia, said in an e-mail.

On Aug. 16, the fiber reached 93.72 cents, a five-month high.