Although large numbers of vacationers start returning as early as mid-April, most officially recognize Memorial Day weekend as the first weekend in the summer season.
Just like most locations at the Jersey Shore (and most swimming pools across the USA), Memorial Day is typically celebrated as the beginning of summer. As such, there are rarely any vacancies in Sea Isle on this weekend. From Memorial Day through Labor Day, weekends in Sea Isle are bustling. However, in June you can usually find lodging during the work week (unlike July and August which are the most busy months of the year).
To beat the crowds, you should consider coming in early to mid May. That’s the best time of year to get great beach weather without the large crowds, especially if you come during the week. Since most colleges and universities finish their semesters by the first week in May, it is not uncommon for college students and professors to celebrate by visiting the Jersey Shore in mid-May.