Relative humidity is usually high near the coast, but can be quite low along the foothills. During periods of high temperatures, relative humidity is usually higher in the morning when the air temperature is colder, and lower in the afternoon when the air temperature is higher. On Monday, temperatures hit triple digits in Los Angeles County, as a high-pressure ridge kept the heat a little above normal for much of the week. This could be hotter than it is, as the lunar humidity of Mexico could produce showers and thunderstorms on Monday, even in the Antelope Valley.
Temperatures will remain roughly the same on Sunday in Los Angeles. When it's hot, it's more difficult to maintain an objective pace, use more power to climb and cycle further. In an area with a lot of traffic or coal trucks, the sane cyclist will not drive until the fog clears or will leave the road every time a vehicle approaches. Your body uses energy to cool itself down when it's hot, so you can't ride as fast, for a long time, or as hard.
If you're not used to riding in humid conditions, you can be very affected when you go to other places for attractions and excursions. If you live in an area where summer isn't hot, but you're going to travel to a hot place to cycle, you can acclimate yourself by pedaling with enough clothes to sweat a lot. You might be tempted to spend most of your time in an air-conditioned environment and just cycle for a few straight hours in the heat. However, this can be dangerous as humidity peaks in the morning; therefore, you can avoid a little heat by pedaling early, but you pay the price of pedaling in even more oppressive humid conditions. In general, assuming that the dew point or absolute humidity does not change, values of 2 inches in summer indicate a very high moisture content in the atmosphere, typical of a tropical air mass.
The higher the heat index, the more difficult it will be to cycle. While weather conditions affect people differently, surface dew point temperatures in the 50 degrees are usually comfortable for most people, in the 60s they are somewhat uncomfortable (humid) and in the 70's they are quite uncomfortable (very humid). You can adapt to riding in a humid area by acclimating yourself in the same way you would to ride in a less humid but hot environment. The heat doesn't bother me as much as walking around in wet clothes and knowing that sweat corrodes my bike. So if the dew points are in the 30 degrees, you will be cold regardless of the relative humidity; however if they are in the 60's, you will be warm even if the temperature is only in the 60 degrees. When cycling during hot and humid weather conditions it is important to take into account both temperature and humidity.
High temperatures combined with high humidity can make cycling more difficult and uncomfortable. To make sure your ride is safe and enjoyable it is important to acclimate yourself to riding in humid conditions by wearing enough clothes to sweat and pedaling early when humidity peaks. It is also important to take into account dew point temperatures as they can indicate how comfortable or uncomfortable cycling will be.
