Cumulus clouds building in San Diego County Sunday morning. Photo via @NWSSanDiego

Another hot day Sunday was forecast for inland San Diego County, and increasing monsoon moisture is expected to create more humid conditions and a chance for showers and thunderstorms each day through Wednesday, the National Weather Service said.

A heat advisory was issued until 9 p.m. Sunday for San Diego County mountains and valleys and an excessive heat warning was issued until 9 p.m. Sunday for county deserts.

High heat and low relative humidity were expected to create elevated fire weather conditions through Sunday, especially north of San Diego County, forecasters said. The main threat is for plume-dominated fires. Gusty winds along the sea breeze front and near desert passes will also be a concern Sunday afternoon, the NWS said.

High temperatures along the coast Sunday are predicted to reach 80 degrees, 87 inland, 91 in the western valleys, 100 near the foothills, 98 in the mountains and 112 in the deserts, according to the weather service.

Storms over the lower deserts and mountains were expected Sunday afternoon and there could even be a few stray showers tumbling into the foothills west of the peninsular ranges of San Diego County, forecasters said.

Minimum relative humidity of near 20% will trend upward into Monday due to the monsoon flow.

Cooler weather was forecast to spread farther inland after Sunday, as the marine layer rebuilds with periods of night and morning low clouds and fog.

For Tuesday, flow turns more southerly, and instability aloft was expected to increase over the entire area as another surge of subtropical moisture pushes northward.

Southwest flow should dry San Diego skies later this week, and rebuilding high pressure will bring warming into the Labor Day Weekend, the NWS said.

City News Service contributed to this article.

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