Officials warn the storms could cause flash flooding and the temperatures may be harmful to those at risk during heat waves.
Here's a breakdown of what to expect.
Temperatures will rise into the 90s and 100s through the weekend, along with a major rise in humidity.
"The combination of high temperatures and increasing humidity may cause some areas to approach excessive heat levels, especially Thursday and Friday. During this time, people at risk of heat-related illness should be extremely cautious and seek shelter in air conditioning if possible," the National Weather Service said in a bulletin.
The thunderstorms are most likely to develop in mountain, inland valley and desert areas, but coastal areas might see them as well, according to the NWS.
"Any storms that develop by Thursday will be capable of producing heavy downpours, dangerous cloud-to-ground lightning, strong gusty winds and flash flooding," the NWS said.
The heat and humidity place frail people at risk, especially during the peak days of Thursday and Friday.
"During this time, people at risk of heat-related illness should be extremely cautious and seek shelter in air conditioning if possible," the NWS says.