Increasing southerly winds will build seas to 4 feet and slightly higher by Tuesday afternoon, especially on the South Shore, the National Weather Service said in its marine report.
Morning wave heights on the ocean were at 2 feet or slightly lower but were expected to climb by the evening hours, the service's Upton office said.
Winds should build to 5 to 10 knots with some gusts to 20 knots.
Mostly, Long Island waters should be reasonably calm from Wednesday through Saturday because of a relaxed low pressure gradient that sets up over the region.
For beachgoers, water temperatures range from 72 degrees at Bergen Point to about 68 degrees at Kings Point and Montauk.
Inland conditions across Nassau and Suffolk counties on Tuesday are warm and humid with daily highs in the low 80s and a chance of showers and thunderstorms after noon.