The world's biggest retailer, Wal-Mart Stores Inc, on Wednesday posted a 4.6 per cent rise in April same-store sales but said it expects that figure to drop to between one and three per cent for this month. The Arkansas-based retail goliath cited unseasonal weather for its failure to hit its comparable sales growth target for last month and added total sales for the four-week period jumped 12.2 per cent to $18.56bn from $16.54bn in the year-ago period.