Blistering temperatures rising to 40°C and above will now be branded “cruelly hot” or “kokusho-bi” in Japan, the weather agency said Friday, as heat wave days become increasingly frequent in the region.
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For other Americans, 40C is 104F.
When I have to convert C to F in my head, I start with 10C = 50F, and then every additional 5C is 9F. So 40 is 30 more than 10, 30/5 is 6, 6*9 is 54, and 50 + 54 is 104. This is easier than multiplying by 1.8 and adding 32.