* 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.

Tropical moisture will move through the region through Monday, and enough moisture and instability could be in place for isolated thunderstorms over the coastal waters mainly Sunday afternoon. The chances are currently 10 percent or less at any one location. Any thunderstorms that develop will be capable of producing dangerous cloud-to-water lightning and gusty winds. Mariners should seek safe harbor if threatening weather occurs.

* WHAT. Dangerously hot conditions with temperatures up to 112. * WHERE. San Diego County Deserts. * WHEN. Until 8 PM PDT Thursday. * IMPACTS. Heat related illnesses increase significantly during extreme heat events.

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

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.