The Suffolk County Health Department has issued an advisory against swimming at 22 beaches, while Nassau County has closed 13.
Officials say runoff from the storms could push bacterial levels in the water beyond healthy limits.
The department recommends that bathing and other water contact be suspended in affected areas until the waters have been flushed by two successive tidal cycles (at least a 24-hour period) after the cessation of rainfall.
Unless sampling done by the department finds elevated bacterial numbers persisting beyond the 24-hour period, this advisory will be rescinded at 8 p.m. Friday.
Steers Beach in Northport and Valley Grove Beach in Eatons Neck are still closed to bathing, as results of recent samples are elevated in relation to standard criteria.
For the latest information on affected beaches, call the Bathing Beach hotline at (631) 852-5822, contact the Department's Office of Ecology at 852-5760 during normal business hours, or visit SuffolkCountyNY.gov/health and click on "Beach Advisories and Closures" in the "Popular Links" section.
The Nassau County beaches that are closed are: