Rain fell heavily in places throughout Southwest Florida last week, but often just a mile away, the spotty showers left plants barely wet and little to no change for ground parched by six months of drought.
Grass untouched by rainfall for so long, in a state as hot as Florida can get, disappears within weeks. What appeared to be dark and rich soil underneath, once the moisture evaporates, turns back into what it is without watering, fertilizer, and attention: sandy loam.
What the rain that did fall do is knock back the risk of wildfire for a few days.
The Keetch-Byram Drought Index, a widely used metric that can help determine the general risk of wildfire, calculates the threat by measuring the lack of moisture in the soil — zero indicates saturated soil; 800 equates with a desert.
Before the spotty rains last week, the index in Lee, Collier, and DeSoto counties averaged about 675; after, the indexes in the three counties dropped to an average of roughly 500. In the week without rainfall, the numbers are back up to the mid-500s.
That amount of volatility with the moisture content of the soil, day-to-day or week-to-week, is not particularly dangerous to people. Nor does it threaten the tourism industry or farming operations.
Then, meteorologists said a high-pressure system would fix a heat dome in place over the Sunshine State.
North Carolina State University geographer Ronald Leeper realized that meant a powerful heat wave was going to slide over Florida's Peninsula, then linger over the worst drought in the state in 25 years.
Unlike the mild variation in moisture levels a few days earlier, Leeper knows the combination of a deep-south drought and an exceptional heat wave can bring longer-lasting heat to Southwest Florida.
Heat waves beget heat waves?
Leeper knows drought.
He specializes in weather and forecasting at the Cooperative Institute for Satellite Earth System Studies in Asheville.
Just three weeks ago, Leeper and six colleagues published an article about how heat waves and droughts interact in the American Meteorological Society's peer-reviewed Journal of Applied Meteorology and Climatology.
In the introduction to "The Influence of Drought on Heat Wave Intensity, Duration, and Exposure," the authors referenced findings by other researchers that made Leeper believe that when a heat wave rolls into a drought-stricken area, air temperatures would soar even higher. But the results were more nuanced, and the findings perhaps more important for everyday Floridians.
Leeper expected to find that when heat waves and drought combined, the air temperature would rise considerably -- but that was not always the case.
"Some heat waves and droughts were really, really hot, kind of like I expected, and then other ones weren't so hot," Leeper said. "But it does stretch out the period of dangerous heat, keeping temperatures elevated into the night."
For certain seniors and others who struggle with it being warm outside, that information could be lifesaving.
"This shift doesn't necessarily make the hottest part of the day hotter," Leeper said. "That tells me there are some droughts where the connection between heat and heat waves is, you know, magnified, and then other ones where it's not."
He said the real surprise came from the soil: as drought dries out the ground, the soil's ability to store and conduct heat changes. Instead of immediately releasing heat to the air, the parched earth holds onto it longer, releasing it later in the day and slowing the rate at which temperatures cool in the afternoon and evening.
That led to the finding that droughts lengthen the duration of heat waves, by 13% to 50% on average, resulting in more hours of extreme heat exposure.
"While droughts tended to lower humidity and thus the 'feels-like' temperature in some regions," Leeper said, "the extended heat exposure poses greater health risks, as bodies and infrastructure have less time to recover."
Knowing when a heat wave and drought are happening, that it may be warmer for longer, public safety officials can open cooling centers with extended hours to stay cool and prevent heat-related illness or death.
Rain eventually
Irene Sans, a meteorologist with the Florida Public Radio Emergency Network, said the drought and heat wave will stay with us for at least another week or two.
"This heat wave started this week. We have experienced temperatures between the mid-to-upper 90s, and these are potentially record temperatures across parts of Southwest Florida, and we will continue with this trend through the rest of the week," she said. "This high-pressure system will break eventually. These highs in the middle of the upper levels of the atmosphere tend to take a little longer to break because they're part of the blocking pattern in the atmosphere, and they tend to sit in the same place for several days. In our region, it'll be this whole week, so temperatures will continue to be warm."
Sans said early next week she expects a round of showers and storms, which will change wind patterns and start to mix things up. Soon after, the drought may break as we get into a more typical summertime pattern.
"That's going to take the temperatures closer to normal temperatures, or to average temperatures for this time of year," Sans said. "And that will be for Memorial Day on Monday, where we can expect temperatures to be into the low 90s."
Before we get to that point, Sans reminds everyone we are still in a drought with a high threat of wildfire.
"When there is an active drought in play, everybody has to remain extra careful," Sans said. "Wildfire season is year-round in Florida: May, June, is the peak of the season," she said. "So don't let your guard down with that, because with this amount of drought and with this heat anything could happen.
"Just be on the lookout for that, and make sure to avoid any burns outdoors, even if it's humid, because there's a lot a lot of dry vegetation," she said. "So keep that in mind."
Environmental reporting for WGCU is funded in part by Volo Foundation, a non-profit with a mission to accelerate change and global impact by supporting science-based climate solutions, enhancing education, and improving health.
Sign up for WGCU's monthly environmental newsletter, the Green Flash, today. WGCU is your trusted source for news and information in Southwest Florida.
Copyright 2025 WGCU
