Complex sentence: On June 18, shortly after the formation of Tropical Depression One-E, a broad area of disturbed weather persisted off the southern coast of Mexico, generating shower and thunderstorm activity; the National Hurricane Center remarked upon the possibility for tropical cyclone formation.
Split into simpler sentences: On June 18, shortly after the formation of Tropical Depression One-E, a broad area of disturbed weather persisted off the southern coast of Mexico, generating shower and thunderstorm activity. At this time, the National Hurricane Center remarked upon the possibility for tropical cyclone formation.