The National Weather Service issued this summer’s first heat advisory for the Baton Rouge area Sunday as highs climbed from 95 to 100 across the Gulf Coast.

The heat index, which is a combination of the temperature and the relative humidity, was expected to reach between 105 and 112 degrees, said Tim Destri, a meteorologist with the National Weather Service based in Slidell.

Multiple heat advisories usually arrive every summer in southeast Louisiana — but this summer the first did not arrive until late August, Destri said.

Unusually cool temperatures throughout the summer, driven in part by three cold fronts in July and one in August, were behind the delay, said Fred Zeigler, also a National Weather Service meteorologist based in Slidell.

Causing the heat advisory Sunday was a large area of high pressure that settled over the Gulf states, suppressing cloudiness and rainfall, which limited the typical relief from daytime heat, the National Weather Service said.

Several other parishes in the area also were affected, including West Baton Rouge, East and West Feliciana, Ascension, Assumption, Livingston, Iberia, Pointe Coupee and St. James, according to the National Weather Service.

The Weather Service issued advisories across a broad stretch of the country, including the Florida Panhandle, Missouri, Tennessee and even Illinois just shy of Chicago, Zeigler said.

Residents during a heat advisory are advised to stay out of the sun, and those who have to work outdoors should take frequent breaks, drink plenty of water and avoid areas like blacktop, Destri said.

The advisory ended at midnight Sunday as a weather system moving in from the East promised to bring down temperatures and increase chances of rain, he said.