* Manny Fontenla-Novoa steps down as CEO with immediate effect
* Sam Weihagen is interim CEO
* Q3 operating profit down 22 pct to 20.1 mln stg
* Still sees FY underlying operating profit about 320 mln stg
* Shares rise more than 5 percent (Adds details, background, analyst comments; updates shares)
By Adveith Nair
LONDON, Aug 3 (Reuters) - British travel firm Thomas Cook said Chief Executive Manny Fontenla-Novoa is to step down with immediate effect, following a spate of profit warnings and a steep drop in the company's share price since the start of the year.
Fontenla-Novoa was criticised by analysts and investors after the group issued a profit warning in July, its third in 12 months, as tough conditions in Britain and unrest in the Middle East and North Africa (MENA) hit trading.
The value of Thomas Cook shares has dropped by two-thirds since January, but Fontenla-Novoa, who has been Chief Executive since 2007, told Reuters only last month his own position was not under pressure.
Numis analyst Wyn Ellis said the CEO's departure was expected after the company's latest profit warning.
"It was inevitable that the CEO had to go," the analyst said. "It is fair to say Thomas Cook has disappointed under his regime, but it is never good for a company when a CEO leaves under such circumstances," Ellis added.
Sam Weihagen, deputy to the chief executive, will take on the role of interim CEO of the 170-year-old firm and the hunt for a permanent successor was already underway.
Shares in Thomas Cook, Europe's second-biggest travel firm, rose more than 5 percent to 63.9 pence on Wednesday following Fontenla-Novoa's departure. Rival TUI Travel's shares were up 0.33 percent
Separately, Thomas Cook said underlying operating profit for the third quarter fell 22 percent to 20.1 million pounds ($32.76 million). The company said the impact of unrest in the MENA region for the quarter was estimated at 25 million pounds and it expects a similar effect in the fourth quarter.
Peel Hunt analyst Nick Batram said although the company's trading position was no worse than the most recent profit warning, today's news "will not encourage many buyers", despite Fontenla-Novoa's departure.
In July, Thomas Cook said the MENA impact had been heavier than anticipated, with its French business seeing reduced demand and lower margins during the peak season for key destinations in Egypt, Morocco and Tunisia.
On Wednesday, it confirmed full-year profit would be lower than it previously expected at 320 million pounds. It also reiterated plans for a strategic review of its UK business and an asset disposal programme to raise up to 200 million pounds.
Thomas Cook, which has about 750 travel shops in the UK, has said around two thirds of the full-year profit shortfall was because of a continued squeeze on disposable incomes in Britain.
British consumer sentiment fell in July towards the two-year low seen earlier this year, fuelling concerns that consumers will continue to cut spending and hamper the fragile economic recovery.