Topline:

A rare March heat wave is pushing temperatures 20 to 35 degrees above normal — from Big Sur all the way to San Diego. The National Weather Service is warning Californians to take precautions, such as avoiding strenuous activity in the hottest hours of the day, to prevent heat illness.

Graphic shows temperatures forecast for L.A., Ventura and Santa Barbara counties.

This heat wave will be with us for a while: the highest temperatures will be Tuesday through Friday.

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National Weather Service

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Why now: The heat wave is here, and the hottest weather is forecast for Tuesday through Friday. At the beaches, temperatures will approach or exceed 90 degrees, according to the latest National Weather Service. Inland, expect high 90s or even low 100s.

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Heat warnings and advisories

Heat warnings and advisories will be in effect at least through Friday for much of California.

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National Weather Service

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Orange and San Diego counties are under heat advisories or extreme heat watches through Friday.

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National Weather Service

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Why it matters: Extreme temperatures can cause heat exhaustion and heat stroke, which can be deadly. If a person becomes confused, dizzy or loses consciousness, it’s time to call 911. This rare March heat event could also break temperature records.

What to do: Stay as cool as you can — seek out air conditioning, wear loose-fitting clothing and avoid strenuous activity in the heat of the day. Stay hydrated, as well: drink lots of water, and avoid caffeine and alcohol. You can find cooling centers run by L.A. County and the city of Los Angeles online.

A graphic shows the symptoms of heat exhaustion and heat illness, including dizziness, sweating, nausea, confusion and losing consciousness.

Make plans now to prevent heat illness.

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National Weather Service

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What’s next: We’ll have to wait for the weekend for relief. Expect slight cooling Saturday, and then noticeably cooler weather on Sunday.