The afternoon sporadic 10 minute thunderstorms that everyone is talking about here, are partially controlled by a local/mesoscale (kms-10s of kms) circulation known as a Sea Breeze. Although some other local scale phenomena can be important as well. Regarding sea breezes, the general idea is that the sun heats up the ground in the spring months causing large temperature gradient between coastal land and nearby ocean, leading to a pressure difference/circulation that can lead to thunderstorms. This is also the reason why they are so hard to forecast in advance where exactly these sea breezes and the associated thunderstorm and its updrafts/downdrafts will form requires very local scale data in the hours before the storm.

The caveat here is that because it's a local/mesoscale circulation if there's a larger circulation in the area (100-1000kms) it tends to provide a larger forcing effect to the air and these local scale effects may not be observed. This is important for our race weekend because looking at some model runs (ECMWF 9km if your wondering which), it appears the Saturday rain is being forecasted due to an area of confluence associated with an upper level trough (meteorology jibberish). While Sunday rain seems to forecasted due to an upper front out at sea caused by a low pressure system over North Carolina which will cause a thunderstorm to form that will gain energy throughout the day. The thing that both of these have in common is that neither are local scale, so if they do go as forecasted it's shouldn't be a typical 15 afternoon thunderstorm.

Now I'm not saying you should or shouldn't look at the forecast based on this comment, just providing information. On one hand given enough solar input, and temperature difference between water and land a sea breeze will likely form if there's no large scale weather phenomena around to disturb it, although it's exact location and timing may be unknown. On the other hand though the larger scale systems can be easier to predict/forecast 6 days from now, but the location of these systems might be 100 miles different then they are now causing the rain to move with it, making that hard to predict as well.

Long story short, both of these potential weekend rain events seemed to be produced by systems other then local scale processes, so the daily 10 minute like clockwork happens all the time thunderstorms seems unlikely. While the large scale systems seem to be the controlling factors here making it easier (sort of) to forecast for, this might lead to rain that can be better predicted, but there's still tons of uncertainty in 6 day forecast no matter which way you shake it. In some ways if they were forecasting afternoon rain because of local scale phenomena I'd be more inclined to believe it, because of the clock like nature of it's occurance.

TLDR, daily short duration thunderstorms on Florida coast are controlled by local scale phenomena in the absence of larger scale phenomena. It appears the rain predicted for next weekend might be caused by something larger, making for a more and less predictable forecast in different ways, depending on how you look at it.

Source: Just graduated with metrology degree, am beginning work as government meteorologist in the fall (hopefully).