A cloudy, warm and humid Tuesday will be giving way to unstable weather for the next two days, forecasters said.

Thunderstorm activity was causing arrival delays late Tuesday afternoon of more than three hours on average at Kennedy Airport, and nearly two hours at LaGuardia, according to the Federal Aviation Administration website. Some departures from those airports, as well as Long Island MacArthur Airport, were also delayed, and the FAA advised travelers to check with their airlines.

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The National Weather Service said there's a 30 percent chance of showers and thunderstorms for most of Long Island for Tuesday evening.

Then, Wednesday brings a 50 percent chance of showers and thunderstorms, the National Weather Service said, with the possibility of heavy rain.

The service issued a warning that in Nassau County, storms Wednesday afternoon and evening "could produce locally heavy rainfall with a low probability of flash flooding." Around half an inch of rain was forecast for Nassau, possibly higher locally, with amounts diminishing farther east, according to the weather service.

A hazardous weather outlook was also issued at 8 p.m. Tuesday for Suffolk County, warning of possible "widespread heavy rainfall" and thunderstorms Thursday and Thursday evening.