Monsoon moisture was returning to southern California from the southeast, and isolated showers or thunderstorms could develop over the mountains Sunday afternoon, National Weather Service forecasters said.

Increased humidity and clouds on Monday and Tuesday could ease the heat but bring better chances of showers and more widespread thunderstorms, the NWS said. Some drying out was possible after Tuesday, but small chances of mountain and desert thunderstorms could continue through the end of the week.

Thunderstorms began to appear in the Riverside Mountains early Sunday evening, bringing the possibility of heavy rain, lightning, gusty winds and localized flooding in that area, NWS tweeted.

The shallow marine layer was expected to persist along the coast. Expected a limited amount of low cloud formations overnight.

High temperatures along the coast on Sunday are forecast to be 76 to 81 degrees with overnight lows of 64 to 69. Highs in the western valleys are forecast to be 88 to 93 and 94 to 99 near the foothills with lows nightly highs of 66 to 71. Highs in the mountains were expected to be 91 to 98 with overnight lows of 67 to 73, and highs in the deserts were expected to be 109 to 114 with overnight lows of 81 to 87.

Increased humidity is good, right? Maybe not. NBC 7’s Joe Little has the answers.

Northwesterly winds gusting to about 20 knots may occur over portions of outer coastal waters between 30 and 60 nautical miles offshore later Sunday afternoon and early evening.