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SAN DIEGO (CNS) – High pressure was forecast to strengthen and expand over the Desert Southwest Saturday through the middle of next week, bringing a heat wave to much of the region, the National Weather Service said.

A sea breeze and shallow marine layer was expected to keep temperatures moderated in the coastal areas, along with some patchy night and morning low clouds and fog at times, according to the NWS.

High temperatures in coastal areas Saturday were expected to be 69-74 degrees with overnight lows of 55-60, the NWS said. Western valley highs will be 79-84 and 86-91 in the foothills with overnight lows of 55-60.

Mountain highs were expected to be 85-95 with overnight lows of 55-65. Highs in the deserts will be 106-111 with overnight lows of 70-78.

Increasing temperatures and relative humidity of 10-15% were predicted to result in elevated fire weather conditions in the afternoons and evenings.

Northwest winds in the outer waters with a few gusts exceeding 20 knots were expected to continue each afternoon and evening Saturday through Monday.

An excessive heat warning was issued by the NWS from 10 a.m. Monday to 9 p.m. Friday for San Diego County deserts.

An excessive heat watch was issued from Tuesday morning through Friday evening for San Diego County mountains.

An excessive heat watch was also issued from Tuesday morning through Thursday evening for San Diego County valleys.

The ridge over the Southwest was expected to slowly weaken late next week, with gradual cooling spreading slowly inland next weekend.

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