Monsoonal flow and residual tropical moisture will arrive from the south tonight through Sunday morning. This will bring a slight chance of a few thunderstorms over the local water. The chances are currently less than 20 percent at any one location. The most likely timing of this activity will be late tonight through Sunday morning. Any thunderstorms that develop would be capable of producing dangerous cloud-to-water lightning, gusty winds, small hail, and brief heavy rain. Mariners are encouraged to closely monitor the situation and consider making alternative plans if the chances for thunderstorms were to increase.

* WHAT. Temperatures 90 to 98 degrees. * WHERE. For elevations below 5000 ft in the Riverside County Mountains, San Bernardino County Mountains, and San Diego County Mountains. * WHEN. Until 8 PM PDT this evening. * IMPACTS. Hot temperatures may cause heat illnesses.

* WHAT. Temperatures 95 to 100 degrees today and 95 to 98 degrees Sunday. * WHERE. San Diego County Valleys. * WHEN. Until 8 PM PDT Sunday. * IMPACTS. Hot temperatures may cause heat illnesses.

* WHAT. Dangerously hot conditions with temperatures 110 to 114 degrees. * WHERE. San Diego County Deserts. * WHEN. Until 8 PM PDT Thursday. * IMPACTS. Heat related illnesses increase significantly during extreme heat events. * ADDITIONAL DETAILS. High temperatures will fall a few degrees Sunday, but increase again through the middle of next week.