* Aug sales +6 pct vs consensus +11 pct
* Aug comparable sales -4 pct vs consensus +1 pct
* June-Aug sales 28.8 bln SEK vs consensus 29.5 bln
* Analyst says H&M probably lost market share (Adds analyst, share price)
By Anna Ringstrom and Veronica Ek
STOCKHOLM, Sept 17 (Reuters) - Hennes & Mauritz, the world's second largest fashion retailer, said unusually warm weather in Europe dented demand for autumn clothes and led to an unexpected drop in sales in August.
Shares in the Swedish budget apparel firm, which trails Zara owner Inditex by value and turnover, as well as by the number of markets and stores, fell more than 2 percent, lagging the STOXX Europe 600 retail index. Sales at stores open a year or more shrank 4 percent in local currencies in August, well below a Reuters poll forecast for 1 percent growth.
"It was primarily the extreme heat wave in a number of European markets in August that affected sales negatively," H&M said in a statement.
DNB Markets analyst Haakon Aschehoug, who rates the stock a "hold", said the figures probably meant H&M, which has the bulk of business in Europe, lost market share after outperforming it in recent months.
"We already know the (apparel sales) numbers from Sweden and Germany, and the U.S retail sales. This represents, in our view, an underperformance on the key markets of about 4 percent."
Societe Generale analyst Anne Critchlow said the figures meant flat like-for-like sales overall in the third quarter.
"This does suggest a small amount of downward pressure on consensus estimates for both Q3 and the full year," she said.
H&M said that, in its full third quarter, a strong appreciation of the Swedish crown, mainly against the euro, led to large negative currency translation effects.
Critchlow also noted that currencies had become an issue for H&M again as they purchased in relatively strong U.S. dollars, sold mainly in weak euros and then had to convert back to Swedish crowns, which have surged this year.
"(This is) the worst possible situation for the company and a repeat of what we saw in 2011, when EBIT fell 17 percent year-on-year, of which 10 percent was due to currency problems," she said.
H&M has more than 2,600 stores in 44 markets across Europe, Asia and North America. In Germany, H&M's biggest single market, apparel sales dropped 2 percent in August, industry data show.
H&M said total sales in August, the last month of the fast-expanding firm's fiscal third quarter, were up 6 percent from a year earlier, lagging the mean forecast of an 11 percent rise.
Turnover in the June-August quarter grew 7 percent from a year earlier to 28.8 billion crowns ($4.4 billion), undershooting expectations for a 9 percent rise to 29.5 billion.
H&M's regular quarterly earnings report is scheduled for Sept. 27. In the second quarter, H&M grew profits more than expected due to its low-price focus, easing input prices and a broadening geographic footprint. ($1 = 6.5419 Swedish crowns) (Reporting by Stockholm Newsroom; Editing by Louise Heavens)