June 5 (Reuters) - Average sales growth at nine U.S. retailers, including Costco Wholesale Corp and Rite Aid Corp, topped expectations in May for a second month in a row as shoppers headed to malls in droves around the Memorial Day weekend, according Thomson Reuters data.
Sales at established stores on average rose 4.3 percent in May, higher than the 3.9 percent increase analysts had estimated, according to the Thomson Reuters' same-store sales index.
The results exclude Gap Inc, one of the index's 10 components. It will release its May sales later Thursday. Gap was included in the 3.9 percent average estimate.
The May increase followed a growth spurt in April, when same-store sales for the group rose 6.4 percent, buoyed by the release of pent-up demand after a harsh winter that had kept many consumers home.
Most of the retail group, which excludes giants such as Walmart Stores Inc, Target Corp and Best Buy Co, exceeded or equaled sales growth in May 2013.
"It's not just warm weather," said Michael Niemira, chief economist at the International Council of Shopping Centers. "In comparison, temperatures were nearly identical to last year. Presumably 1/8the change 3/8 is more fundamental."
Costco reported a 6 percent increase, stronger than the 4.8 percent that analysts had expected, and its shares rose nearly 1 percent in late morning trading.
Drugstore operators Rite Aid and Walgreen Co posted an average sales increase of 4.1 percent, slightly lower than analysts' estimates, but higher than the average 2.8 percent growth they had recorded in May 2013.
While apparel retailers inched ahead of May forecasts, their sales growth slowed after strong April buying.
L Brands Inc, which owns brands such as Victoria's Secret, managed a 3 percent comparable sales increase after 8 percent growth in April.
Gap Inc faces the weakest May estimate at 0.2 percent, compared with 7 percent growth recorded last year. The company will release its results at 4 p.m. EDT (2000 GMT) Thursday.
(Editing by Frank McGurty; and Peter Galloway)