Simplify the following text for a Grade 11 native English-speaking person.
Original: When the wave approached the Leeward Islands on July 28 , the National Hurricane Center monitored the system closely for any possible development , which did not occur at that time .
Simplified: When the wave came across the Leeward Islands on July 28 , the National Hurricane Center began to watch the system closely for any possible strengthening , which did not happen at that time .