The heat and humidity peak today with highs around 90 degrees. But it will really feel like 95-100 when you factor in the humidity. Why? The more moisture there is in the air, the harder it is for your body to sweat and the warmer you feel.
Afternoon thunderstorms are possible with plenty of instability and shear (wind direction changing with height). But the atmosphere is also "capped". So a trigger mechanism is needed for storms to develop. Sometimes differences in terrain is all it will take to break through the cap on a hot and humid day like today. But for this reason I think storms will be hit or miss and not widespread. Any storms that develop have the potential to be strong or severe with damaging winds, and even small hail possible.
Tomorrow will remain very warm with high temperatures in the mid to upper 80s. More numerous storms are possible with a cold frontal passage. Relief in the form of less humid, cooler air arrives Thursday and Friday.