A fall heat wave is expected to overtake San Diego this week, sending temperatures soaring potentially into triple digits for some communities, according to forecasters. The National Weather Service issued an excessive heat warning for the deserts and inland valley communities, including El Cajon Poway Santee, La Mesa, San Marcos and Escondido from 10 a.m. Tuesday to 8 p.m. Thursday. Temperatures in those areas could be in the upper 90s to low-100s during that time, particularly near the foothills. NBC 7 Meteorologist Brooke Martell said Wednesday’s temperatures are expected to be the warmest of the week. Then a coastal eddy will develop to cool temperatures slightly. Hot temperatures and low humidity could combine to create dangerous fire conditions this week. Although, San Diego isn’t expected to be affected by Santa Ana winds, which can often worsen fire weather. Humidity is expected to be 10 to 15% through the weekend with slightly better conditions on Thursday and Friday. San Diegans can expect a warm weekend — albeit slightly cooler than the week. Temperatures will remain 5 to 10 degrees above average near the coast and 15 to 20 degrees above average for the inland valleys. Some relief could come as early as next week, although we are not likely to see fall-like weather yet.