Last summers heat wave
 

During last summers heat wave we all suffered terribly. We all suffered terribly during last summers heat wave.

All the machine translations wanted to make "last years" plural.

Durante la última ola de calor de los veranos todos sufrieron terriblemente. Todos sufrieron terriblemente durante la última ola de calor de los veranos.

Should it be more like:
Durante la ola de calor del verano pasado....

It seems so simple until you really think aboit it. Thanks, Bob

Including proper punctuation will make for a better translation. ;)

... last summer's heat wave ...

Thanks Rusty. That changed the machine translation to exactly what I had. Computers are dumb. They only know what you tell them, not what you meant to tell them.