Tonight you'll stay mostly dry in Sarasota, though there's a small chance (28%) of an isolated shower or light rain as leftover moisture and convection work through the area. By Wednesday, that moisture deepens as it pushes inland, and you'll see scattered showers and thunderstorms develop mainly in the afternoon and evening, with about a 44% shot at rain. Wednesday night into Thursday is when things get more active. A cold front approaches from the north, and the atmosphere fills with deeper tropical moisture (what forecasters call precipitable water, basically the total amount of water vapor in a column of air above you). By Thursday, that front combines with the moisture to trigger more substantial storm chances, around 73%, so rain becomes likely that day.
Here's what's driving the pattern: An upper-level trough (a dip in the jet stream, that river of fast air around 30,000 feet) has been keeping things relatively dry and cool. But Wednesday that trough gets cut off from the main flow, and a high-pressure system starts moving back in from the Atlantic. That high-pressure dome steers southeast winds that tap into tropical moisture, setting up our typical summertime sea-breeze storms. By Thursday and Friday, high pressure over the Atlantic takes over completely, which sounds like it'd be clear weather, but instead it channels moisture-laden winds from the southeast right across central Florida and into our area. The combination of that flow pattern and the approaching front creates a more favorable setup for organized storm development.
Looking ahead, this wet pattern sticks around through the weekend. Moisture stays abundant and showers will likely be slow-moving, which means some spots could pick up decent rainfall totals. By early next week, the high-pressure ridge shifts more into the Gulf, which should ease things down slightly. So if you're planning outdoor activities, plan around afternoon and evening storms for the next several days, especially Thursday onward when rain becomes more certain.