* WHAT. High temperatures in the 90s to 102 expected. Low temperatures in the mid 60s to lower 70s. * WHERE. San Diego County Mountains. * WHEN. From 10 AM this morning to 8 PM PDT Thursday. * IMPACTS. Hot temperatures may cause heat illnesses.

* WHAT. High temperatures for the inland valleys in the upper 90s to 106 expected. Low temperatures in the upper 60s to mid 70s for the far inland valleys near the foothills of the mountains. * WHERE. San Diego County Valleys. * WHEN. From 10 AM this morning to 8 PM PDT Thursday. * IMPACTS. Heat related illnesses increase significantly during extreme heat events.

* WHAT. Dangerously hot conditions with temperatures from 108 to 115 expected. Low temperatures in the mid 70s to around 90 expected. * WHERE. Coachella Valley and San Diego County Deserts. * WHEN. From 10 AM this morning to 8 PM PDT Thursday. * IMPACTS. Heat related illnesses increase significantly during extreme heat events.

Patchy dense fog with visibility of 1 nautical mile or less are expected this morning. Fog will lift and visibility will improve after 9 AM. Mariners should be prepared for sudden changes in visibility. Reduce speeds and be on the lookout for other vessels. Use radar or GPS navigation if available, and consider remaining in harbor if such equipment is unavailable.