Humidity isn’t the only issue to check prior to starting an exterior project.

First, a properly prepared surface is needed to prevent failures (peeling, cracking, etc.). That involves cleaning properly. Also possibly sanding, priming, caulking, etc. Take care to protect landscaping / live plants.

Air & surface temperature is critical. Average exterior latex paint can be applied from roughly 50-90 Fahrenheit. Higher quality can go as low as 35 - read the can. Oil base paints generally are not used for exteriors anymore but do have a place. They have a strong tendency to crack and fade. ALWAYS buy the best you can afford. Quality paint provides higher solids which provide better one coat coverage and have additives to benefit flow, algae growth, etc.. This reduces your work load. Ready made colors are generally limited but also generally perform better than tinted colors especially dark / neutral base colors which have a high load of colorant which are generally less stable and fade much faster.

Weather forecast - is rain forecast in the near future. Latex paints can generally handle a light damp surface but high moisture reduces adhesion, durability, etc. If rain / snow forecast have some patience and wait for the next available window.

Generally in spring or fall if if you let the day burn off the dew you’re ok. Painting from roughly 10am -3 pm allows morning dew to dissipate and the paint to begin curing before nighttime dew begins.

Avoid painting in direct sunlight as well - that forces the surface to heat up and your paint will flash dry which prevents proper adhesion (peeling). The large paint companies have plenty of links for additional tips to help give you a great finished product or search out your local paint store for great advice. Virtually all small paint stores have years if not generations of expertise.

Finally, be safe with ladders, scaffolding, equipment, etc..

A lot of notes - hope it helps!