Alberto was moving north at 9 miles per hour and will continue to weaken as it moves north into Alabama then into the Tennessee Valley, where it's expected to pour heavy rain across that area throughout the rest of week.
The Florida Panhandle is forecast to receive 4 to 8 inches of rain through Tuesday.
AccuWeather said Alberto is becoming more organized as it hovers in the eastern Gulf of Mexico and is gaining strength. As the center of the storm approaches land, a dome of high pressure over the upper Midwest will slow it down.
Subtropical Storm Alberto bearing down on Florida's coastline Sunday.
Strong storms possible Thursday and Friday: As Alberto moves away, a different type of summertime weather pattern kicks in; that could deliver some intense summertime storms on Thursday and Friday.
In Taylor County, there are voluntary evacuations for those in coastal zones and beach communities, mobile homes, RV parks and low-lying areas.
Nearly 140 damaging storm reports, including eight tornadoes, were made Sunday from the Midwest into the Rockies, where damage was reported to homes in Wyoming.
Subtropical Storm Alberto is pictured nearing the Florida Panhandle in this May 27, 2018 NASA handout photo.
The storm system could move slowly through Upstate; if so, that would increase the chances of heavy rain.
Mark Bowen, the Bay County emergency management director, suggested people stay safe - preferably indoors. The highest winds are also now away from the center.
View Slideshow A satellite image shows Alberto as it nears landfall on the Florida Panhandle and the Gulf Coast on Monday. NOAA STAR
Even hotter temperatures are forecast for some areas Monday - with more records possible.
"My boyfriend and I usually try to go to the store and stock up on lots of bottled water, and get like canned goods and things that won't go bad if our power goes out", she said. Some of those storms could be severe, he said.
Alberto is not considered a pure tropical system, but will have the same impacts as a tropical storm, which includes tropical storm-force winds of 39-65mph, a storm surge potential, heavy rain and the potential for isolated tornadoes. "So how often can you say you rode a storm out?"
Maximum sustained winds were clocked at 65 miles per hour (100 kph).
Meteorologists expect a turn toward the north-northwest at a slower speed into Sunday.
But most other energy companies are leaving offshore crews in place while they watch 2018's first Atlantic storm. Alberto will continue to bring a flood threat to the Southeast United States as it spreads moisture across the region into the middle of the week.
Winds from the storm are forecast to hit Florida's Panhandle on Sunday night.
Over 350mm of rain is possible along the coast, which in the long term will be beneficial, given the dry conditions which have prevailed in recent weeks.
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