The detail with transitions lenses in tropical countries is the hotter the weather, the slower it activates and rarely gets really dark. It doesn't activate much either inside a car because you don't have the sun shining directly on them. I ended up splurging a bit last year and got a pair that had sun glass magnetic clip (they're not common anymore as a combo) plus the transition on my regular lens. This way when I really need protection, I clip on the darker, polarized clip and when I don't need it, my normal lens takes over.
This may vary on the type of transitions and specific manufacturer of such. I have found my transitions activate quicker in warmer climates such as that of the Caribbean and Mediterranean based nations. Cloudy weather included, and just as such within vehicles. You must remember that UV rays can penetrate cloudy skies, this is why some skin types tend to burn even when it is overcast.