Flat courses are supposed to be the easy sell for a marathon. Miami mostly is - except for what the air does to you along the way. Humidity, more than heat alone, is what actually slows runners down here, and it's worth understanding the difference so you're preparing for the right problem. This guide is about coping strategies rather than the numbers themselves; the climate patterns behind those numbers live in this race's companion weather guide.
Why humidity matters more than heat
Humidity limits your body's ability to cool itself through sweat evaporation, which is the main mechanism your body relies on during a hard effort. A humid, moderately warm morning can feel harder on your cardiovascular system than a drier, warmer one, because sweat sits on your skin instead of evaporating and carrying heat away. That's the core challenge on this course: even on a cooler-feeling morning, humidity near the coast can blunt the benefit of a lower temperature.
Why the early start helps, and where it stops helping
The race starts well before sunrise specifically to get as many miles as possible done before direct sun and rising humidity compound the effort. That head start matters, but it has limits: by the back half of the course, the sun is up, and the causeway sections in particular offer little to no shade. Plan for the race to get physically harder in its second half for reasons that have nothing to do with fatigue alone, and build that into your pacing plan rather than treating a slowdown as a training failure.
Hydration strategy
Aid stations are placed frequently along the course, including through the exposed causeway sections, so the practical hydration plan is straightforward: drink early and often rather than waiting until you feel thirsty, since thirst is a lagging indicator in humid conditions. Alternate water and a sports drink at stations rather than skipping every other one, and consider carrying your own fluid or electrolytes if you have a specific sensitivity to sodium loss - humidity increases sweat rate even when the temperature itself feels moderate.
Pacing and effort in humid conditions
The single biggest adjustment most runners need to make for a humid race is running by effort rather than by pace, especially through the exposed middle miles. A pace that felt sustainable in cool training conditions can quietly become too aggressive once humidity is added to the equation, because your heart rate climbs faster than your pace alone would suggest. If the morning turns out warmer and stickier than expected, adjusting your goal down slightly and finishing strong beats holding a number that isn't working and fading hard in the final miles.
Acclimating before race day
If you're traveling from a cold-weather climate, your body won't be used to humidity no matter how well-trained you are. A few practical options: run some workouts in extra layers in the weeks before the race to simulate heat stress, arrive a couple of days early if your schedule allows so your body can adjust somewhat to the climate, and avoid treating race week as the time to test new hydration or fueling strategies - stick with what's worked in training.
After the finish
Recovery matters more in humid conditions than in cool ones, since your fluid and electrolyte deficit will likely be larger than it feels in the moment. Prioritize rehydrating and eating something with sodium over rushing back to your hotel, and don't be surprised if you feel more depleted a few hours later than a similar effort would leave you in cooler, drier weather.