The National Weather Service has issued a warning to winter-weary Mainers: Wednesday may feel like a beach day, but don’t go jumping in the ocean.

Wednesday is anticipated to be the warmest day so far this spring, with temperatures predicted to reach 80 degrees in parts of the state. Ocean water temperatures, however, are still in the middle to upper 40s.

People eager to get out on the water in their canoes, kayaks and paddle boards may want to take some extra precautions. The risk of cold-water shock is high for swimmers and paddlers who hit the water at those temperatures, according to the weather service. Hypothermia can set in quickly for people in the water.

“Without cold water protective gear, these temperatures will incapacitate even a good swimmer in minutes,” the weather service said in an advisory issued Tuesday.

As part of its “Beach Hazards” warning, the weather service urged boaters to wear life jackets, but also to be aware that they will not protect against the cold water.

On the bright side, the warm air and bright sun will help bring coastal waters up to the somewhat-tolerable summerlike temperatures that Mainers are anxious for.

“Temperatures headed for the 80s tomorrow and it has been a while,” the weather service said Tuesday in a post on its Facebook page.

According to the weather service, more than seven months have passed since Portland reached temperatures exceeding 80 degrees. Portland reported a high temperature of 84 degrees on Sept. 27.

In addition to the hidden dangers associated with exposure to extremely cold ocean temperatures, the weather service on Tuesday also urged Mainers to be mindful of the threats posed by thunderstorms and poor air quality.

“Warm weather is on the way this week, but it will also bring the threat of thunderstorms,” the weather service said on Facebook. “Identify where the nearest shelter is located, and if the skies turn threatening, seek shelter immediately.”

As if thunderstorms and dangerously cold ocean water temperatures were not enough to worry about, the Maine Department of Environmental Protection issued an air quality alert for Wednesday. The air quality alert will remain in effect from 11 a.m. through 11 p.m. Wednesday.

“Ground level ozone concentrations will be climbing in Maine on Wednesday and are expected to reach unhealthy levels,” the DEP said in a statement. “Much of the state is expected to reach higher ozone levels due to a combination of transport, extremely warm temperatures, along with little vegetation growth to absorb ozone.”

The DEP said that very young children, the elderly, and people with pre-existing respiratory conditions such as asthma, or heart disease, should limit strenuous outdoor activity on Wednesday to reduce the risk of adverse health effects. Symptoms could include shortness of breath, coughing or throat irritation.

James Brown, a meteorologist with the weather service, said temperatures in Portland on Wednesday should soar into the 80s, but he does not expect the city to break the heat record of 91 degrees that was set on May 1, 2001.