Most of New Jersey will be under an extreme heat watch starting on Sunday.

An extreme heat watch means that the combination of heat and humidity could create dangerous conditions where heat illnesses are possible. People are urged to take extra precautions if they work or spend time outside.

Temperatures are expected to reach over 100 degrees by Monday or Tuesday.

The alert for Western Passaic, Eastern Passaic, Hudson, Western Bergen, Eastern Bergen, Western Essex, Eastern Essex, Western Union and Eastern Union counties is in effect until 8 p.m. Tuesday.

The alert for Sussex, Warren, Morris, Hunterdon, Somerset, Middlesex, Mercer, Gloucester, Camden, Northwestern Burlington, Western Monmouth, Ocean and Southeastern Burlington counties is in effect until 8 p.m. Wednesday.

Residents are advised to stay indoors as much as possible and avoid being out directly in the sun. Residents should also wear light and loose-fitting clothing and stay hydrated.