Only a Jekke must wear a jacket, since the title Jekke comes from jacket, as the Jekke would be the only person always wearing a jacket even in the blazing heat on the Tel Aviv beach in 1909 when Tel Aviv was founded.
Everone else must comply with the Chiyuv Min haToro of “v’Nishmartem Me’od leNafshoseichem” and is absolutely prohibited of entering into any situation even remotely possible of coming to heat exhaustion and hence an endangering of health.