Last weekend of August will be hot, muggy but clear across greater San Diego

The last weekend of August will be warm and mellow at the coast but stifling hot everywhere east of Interstate 15, particularly in the deserts, where the temperature could reach 117 degrees on Saturday and 112 on Sunday.

The National Weather Service also says that the monsoon will return to the region on Sunday, possibly producing thunderstorms and the sort of dry lightning that can spark wildfires in the eastern half of the county.

An excessive heat warning will be in effect for desert areas through 9 p.m. on Sunday.

The temperatures will ease some on Sunday. But forecasters say the monsoon will increase the humidity into Monday, and greater San Diego could get moisture from Tropical Storm Nora on Tuesday or Wednesday.

Nora is churning off the west coast of Mexico, below Baja California, and is expected to become a hurricane on Saturday. It does not appear that the storm will send large waves to Southern California.

Forecasters say the day time high will be in the upper 70s on Saturday and Sunday in San Diego and in the 80s just a few miles to the east. The heat could reach 100 Saturday in areas like Ramona, El Cajon and Alpine.

The marine layer will be thin and should burn off early. Forecasters say the surf will only reach 2 to 3 feet and that sea surface temperatures remain unusually low, reaching only the mid-to-upper 60s. Upwelling is responsible for the cool water temperatures.