LONDON (Reuters Breakingviews) - GREY SKIES. Tui’s holiday forecast looks increasingly cloudy. Shares in the 5 billion euro package tour operator fell 6% on Friday after it announced plans to issue a 350 million euro convertible bond. The company’s opportunism in cashing in on sun-starved investor optimism is understandable: Tui shares are up by around a third this year due to the increasing pace of vaccination rollouts. Still, the deal only buys Chief Executive Friedrich Joussen around a month of extra flying time, giving him enough cash to last eight months including existing resources. That’s according to Breakingviews calculations based on the current rate of cash burn and zero revenue. The fact he is having to pay handsomely for the modest extension – the bonds offer a chunky coupon of up to 5% – indicates worries about a shrinking season for the key summer period. Even after Friday’s drop, the company is valued at 8 times 2022 EBITDA including debt – well above a pre-pandemic historical average of about 5 times. Shareholders hoping for sun should bundle up instead. (By Christopher Thompson)