Autumn heat wave headed our way

A fall heat wave will begin this weekend and strengthen into the middle of next week, though forecasters differ on just how hot it could get.

The National Weather Service predicts daytime temperatures will jump into the 90s countywide. John Lindsey, who has more than two decades of local forecasting experience, says only the North County will reach into the 90s.

The National Weather Service says building high pressure off the California coastline is scrubbing out any fog and low clouds and making for warm, sunny conditions.

This weekend, the weather service says highs along the coast will be in the 70s. San Luis Obispo will see highs today and Sunday around 80 degrees, while Paso Robles will be in the mid-80s.

Starting Tuesday, high temperatures will start climbing even more. Tuesday’s high in San Luis Obispo is forecast to be 86; on Wednesday, the thermometer will rise to 92, and then peak at 93 on Thursday, the weather service said.

By Friday, cooling will start and the high will fall back to 78 degrees in San Luis Obispo.

Paso Robles will also peak in the low 90s next Wednesday and Thursday. That is not unusual — the North County city routinely reaches 100 degrees during the summer.

But Pismo Beach will also have its high near 90 on Wednesday and Thursday, the NWS said. That’s a big departure from typical coastal highs in the 60s and 70s.

The reason for that is offshore winds that will blow from the interior and out to sea. As the winds blow down the mountains toward the coast, air gets compressed and heats up, creating warmer temperatures in coastal cities.

Lindsey predicts slightly cooler temperatures than the weather service. “By Thursday, beach temperatures will be in the 70s with a few 80s and the coastal valleys (San Luis Obispo) will reach the mid-80s. Temperatures across the North County will range between high 80s and low 90s.”