"Slow down, slow down, slow down, slow down," urged Dr. John Cianca, the marathon's medical director, in a statement. "This is not the year to set a personal best. It will be more difficult than you anticipated, so make adjustments."
The race will begin under a yellow caution flag, which represents a moderate risk for runners and potentially dangerous conditions. For much of the week, temperatures have been as high as 20 degrees above average for January.
While a 70-degree day is pleasant under most circumstances, ideal long-distance running weather is around 50 degrees with low humidity. Forecasters predict the temperature at the starting gun to be in the mid-60s, with 96 percent humidity. By 2 p.m., Houston could hit 74 degrees. A 30 percent chance of rain all day looms over the event.
Race organizers urge runners to drink at each water station and slow their pace to prevent overheating, as increased water intake does not decrease the body's temperature. Runners should also watch out for symptoms of distress, including headache, fatigue, profuse sweating, nausea, clammy skin, labored breathing, confusion and gastrointestinal issues.
Last year's marathon was held on a clear day on which temperatures crept only into the high 50s. Ethiopians Gebo Burka (2:10:54) and Biruktayit Degefa (2:26:07) won the men's and women's races, respectively. But don't expect to see those times again this year.