In which range of july dew points do most thunderstorms take place?

Thunderstorms are the smallest storms, that can range from several km to over 50 km diameter. They can exist in isolation or as organized clusters often associated with mid-lat cyclones and hurricanes.
Thunderstorms take place in high dew points, associated with maritime tropical air masses, provide favorable conditions for the formation of thunderstorms.

Water flows along the east coast and across the western tropical pacific towards south america, while they both are directed towards that way,  el niño does not directly affect the southern flow of water along the coast.