Hot and muggy conditions are expected in most parts of San Diego County Tuesday and thunderstorms will be possible in the mountains and deserts.

A high-pressure system lingering over southern California will create a chance of thunderstorms in those two areas each afternoon through Thursday, according to the National Weather Service office in San Diego.

The chance of measurable precipitation is 40 percent in the mountains and 20 percent in the deserts.

Monsoonal moisture will remain in the region until Friday, when the high pressure system is expected to weaken and temperatures will drop through the weekend, forecasters said.