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If the temperature is above 90 degrees and you do not have a heat resistant tomato it won't produce many flowers in the heat and if it does, the flowers are likely to drop off without setting. As long as the tomatoes are healthy they will start producing again when the temperatures are milder.
There are some varieties of tomatoes that will set fruit in the heat. Most are Florida cultivars like sunmaster, solar fire, and heatmaster. Some of these varieties will continue to set if they get enough water well into the 90's.
Heatwave II, Creole, Sioux, Phoenix, Super Sioux, Summer Set, and Kewalo are others. Pink Brandywine, Cherokee Purple, and Pruden's Purple are Heirlooms with good heat tolerance but don't expect them to produce near the century mark, but they will produce longer than most.
Cherry tomatoes have better heat tolerance than beefsteaks and most will perform fairly well. Husky, sungold, sunsugar, sweet 100, black cherry (not very productive, but it is tasty), red currants do much better in the heat.
Other than that there are early, mid and late season varieties. Most gardeners with short seasons can only plant early varieties (55 days) . Those of us who live near the equator usually grow mid and late season varieties that take 80 days or more to mature. Where I am I can grow both, but early usually means cold tolerant. Cold tolerant means no tomatoes in summer and often it cannot take the heat. The tradeoff is that I can grow tomatoes nearly year round as long as I grow heat and disease tolerant ones.