Yes, clearly substandard care. Police are investigating it as a criminal matter. Death toll is now up to 8: Eight Dead After Florida Nursing Home Goes Without Air Conditioning After Irma

Note that the nursing home is right across the street from a major hospital (not affiliated). Fortunately, after several emergency patients came in from the nursing home, hospital staff checked for themselves. What they found was a classic MCI (Mass Casualty Incident).
Quote:
The first evacuee was rushed into Memorial Regional Hospital’s emergency room around 3 a.m. on Wednesday, escaping a nursing home that had lost air conditioning in the muggy days after Hurricane Irma splintered power lines across the state. Another arrived at 4 a.m. After a third rescue call, at 5 a.m., hospital staff were concerned enough to walk down the street to see the facility for themselves. What they found was an oven. The Rehabilitation Center at Hollywood Hills needed to be evacuated immediately. Fire and rescue units were hurrying the nursing home’s more than 100 residents out. Dozens of hospital staff converged on the area, establishing a command center outside, where workers set up equipment designed for a multi-casualty incident like a bus crash. Red wristbands went to patients with life-threatening conditions, yellow and green for those in better shape.
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The police and state authorities were conducting a criminal investigation into the deaths, according to Chief Sanchez and the governor’s office. Witness accounts suggested that the heat had caused problems inside the nursing home at least since Tuesday afternoon. When Eli Pina went to visit her mother, Mirelle Pina, 96, on Tuesday at noon, it was sweltering inside, she said.
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"Toto, I've a feeling we're not in Kansas any more."
-Dorothy, in The Wizard of Oz