STORY HIGHLIGHTS
Four deaths in Missouri are suspected to be heat related
Heat index soaring across much of the South
A man in Alabama dies from heat exposure
(CNN) -- Forecasters have issued advisories for at least 18 states Thursday as dangerous heat continues to scorch parts of the South, Midwest and the North.
A combination of sweltering temperatures and high humidity could cause heat-related illnesses, the National Weather Service said.
The number of suspected heat-related deaths reported by health officials across the South and Midwest in the past week reached at least nine Wednesday as temperatures continued to hit triple digits.
The health department of Kansas City, Missouri, said Wednesday that the Jackson County Medical Examiner was investigating the city's fourth suspected heat-related death since Friday.
In Tennessee, Shelby County Medical Examiner Karen E. Chancellor said a 77-year-old man was found dead Tuesday evening in his Memphis home. His death was from natural causes, but heat was a contributing factor.
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In Bartlett, Tennessee, a 67-year-old man collapsed in his yard Friday while mowing the lawn, Chancellor said. He died from chronic illnesses but heat exposure was ruled to be a contributing factor.
In Mississippi, a 48-year-old Gulfport man died of heat exposure Monday, according to the county coroner.
The man was working on road construction and "had cramped in the upper extremities," said Jackson County, Mississippi, Coroner Vicki Broadus. "It was his first day on the job as a concrete smoother."
And an 81-year-old Monroe County, Mississippi, woman also died of heat stroke on Saturday, said county Coroner Alan Gurley.
The Alabama Department of Health said one man died of heat exposure last week. No other information was available.
The heat index -- what the temperature feels like when combined with the humidity -- is soaring across much of the South.
Those at greater risk include infants and young children, people 65 or older and those who are already ill, especially with heart disease or high blood pressure.
The Jackson County, Missouri, website offered tips for cooling off
-- Avoid liquids containing alcohol or caffeine.
-- Schedule outdoor activities before noon or in the evening.
-- When temperatures reach the 90s, a cool shower can help more than a fan.
-- Wear lightweight, light-colored, loose-fitting clothing, wide-brimmed hats and sunscreen.
-- If you must work in the heat, monitor the condition of co-workers and ask them to do the same for you.