Hundreds of people may have died from heat in one Arizona county

(CNN) 鈥� Hundreds of people may have died from heat in Arizona鈥檚 Maricopa County amid another record-breaking summer in the state.

Heat has killed 27 people in the county, which is home to Phoenix, and is suspected as the cause of at least 396 other deaths so far this year, .

A total of 645 people died last year during the deadliest year for heat in the county since it started tracking the deaths in 2006. Nearly half of last year鈥檚 deaths came during a stretch of the most intense heat from July 10 to July 25. Fewer deaths were under investigation during that time span than the 396 currently under investigation.

It typically takes two-to-three months to complete a heat death investigation and 75% of deaths under investigation last year were confirmed as heat related, Jeff Johnston, Maricopa County鈥檚 chief medical examiner, told CNN.

Suspected heat deaths have soared in recent weeks alongside temperatures. About 100 of the suspected heat deaths this year happened from July 7 to 13, when high temperatures in Phoenix hit 118 degrees 鈥� exactly the kind of dangerous conditions scientists expect in a world warming due to fossil fuel pollution with more frequent, intense and long-lasting heat waves.

鈥淲e certainly know that when we have higher temperatures that we see more heat-related illness, and in those who are at highest risk, there are more heat related deaths,鈥� Nick Staab, Maricopa County public health鈥檚 assistant medical director, told CNN. 鈥淭hat correlation between the temperature and the number of deaths has been shown over time.鈥�

Phoenix is currently experiencing its hottest start to summer on record. This June was hotter than last June, and this July has been nearly as warm as last July, which was .

Maricopa County said it is working to mitigate heat deaths by increasing the amount of cooling centers across the county, and lengthening operating hours for unsheltered individuals, the county鈥檚 most vulnerable group to heat.

Heat is the聽聽in the US, killing more than twice as many people each year on average as hurricanes and tornadoes combined.

But heat deaths are still often undercounted, and there are many places that fail to report them accurately or regularly. A聽found heat-related deaths were being underestimated in 297 of the country鈥檚 most populous counties. Researchers said mortality records tend to neglect other potentially heat-related causes of death, like heart attacks.

Maricopa County changed the way it tracks heat-related deaths last year to account for聽how the death occurred and the factors that led up to it. The previous tracking method only tracked death certificates that specified heat as the cause of death, and 鈥減roduced undercounts,鈥� according to Johnston.

Summer and heat in Arizona are far from over. Even though heat peaks in July in Phoenix, average high temperatures don鈥檛 drop below 100 degrees until mid-September.

So, with suspected heat-related deaths already so high, the coming months will prove even more deadly.

The-CNN-Wire