Southern California is bracing for a hot and muggy week ahead, with heat watches in place and a chance of thunderstorms across the mountains and desert regions.

Temperatures are expected to increase each day into midweek, prompting officials to extend a heat advisory until 10 a.m. Tuesday, when it will transition to an extreme heat watch for even warmer conditions through Thursday evening.

Temperatures are expected to peak on Wednesday, with many locations topping 100 degrees and some reaching 110, according to the National Weather Service.

“Monsoonal moisture moving over the area will add to the discomfort, also bringing the potential for showers and thunderstorms each day,” the Weather Service said.

Those thunderstorms are most likely to occur over the mountain and desert areas as subtropical moisture is drawn into the region by a strong ridge of high pressure.

Temperatures along the coast may even reach the 90s by midweek, with very warm temperatures continuing through the night.

“Given the extreme heat and humidity, it’s highly recommended to complete outdoor activities as early as possible,” the Weather Service said.

The high pressure is expected to slowly weaken Thursday, bringing afternoon highs to within a few degrees of normal in most areas by Friday.