September Arrives With Cool, Overcast Conditions : Weather: It is a marked departure from the hot, humid month of August. But forecasters say that summer isn’t over yet.

September signaled its arrival with cool temperatures and cloudy skies Tuesday, a distinct contrast to the hot and humid August that plagued the region.

The average daily high temperature this August was 87.2, three degrees above normal, in Santa Ana, and the humidity averaged 82.7% over the month. The El Nino weather system brought warmer water to the California coast, which in turn brought more swimmers into the ocean, area lifeguards said.

“It was a nice, beautiful month, warmer than last August, and certainly a busy August compared to other Augusts in the past,� said Lt. John Blauer of Newport Beach. “The sun was out early in the morning, which induced people to consider the beach as an option for the day.�

The hottest part of the month was the middle, when the mercury topped 90 for seven days running. Record-breaking temperatures came in Santa Ana on Aug. 15, when the thermometer read 94, and two days later, when the high was 96. In between, the temperature tied the record of 94 degrees set in 1983.

Daily low temperatures were also abnormally high, with the average low of 66.9, more than four degrees above normal. The mercury did not dip below 60 until the end of the month--that low came on Aug. 31--and there were 21 days when the temperature never fell below 65.

This was the hottest August in the last five years, according to Tom Handzus, a geological technician at Cal State Fullerton, where temperatures averaged a daily high of 89.3 and a daily low of 69.6.

Handzus attributed August’s heat and humidity to a series of tropical storms, about a dozen in all, that have come up the coast since summer began. In addition, he and meteorologist Dean Jones of WeatherData said the El Nino pattern, an oscillation in the tropics that stirs about once every decade, was partly responsible for the warmer weather.

Lifeguards around the county reported bigger beach attendance figures for the month of August, and said that unusually high water temperatures of about 75 degrees throughout the month meant many more beach-goers actually went in the water this season.

More than 1.6 million people went to Huntington City Beach during August, a jump of 37% from the average of 1,184,856 over the past five Augusts. In Newport, lifeguards recorded attendance of 2,289,000 over the month, up 27% from the previous five Augusts’ average. And in San Clemente, the number of beach-goers rose more than 15,000 to 325,700 this August.

“We’ve had warm water, warm weather, some surf, it gives the lifeguards something to do,� said Mike Dwinell, marine safety manager at Laguna Beach, where about 430,000 people visited this month. “It’s been a good summer, one of the better ones we’ve had as far as weather goes.�

As if in synch with the calendar, this week marked an end to August’s dog days, with clouds along the coast and mild temperatures overall for a high of 79 degrees Tuesday, according to WeatherData, which provides forecasts for The Times. Meteorologist Jones said the temperatures would remain in the 70s with high clouds for the next few days, providing fair, mild weather for the beginning of September.

But residents should not be fooled by the cool weather. August and September are the hottest months of the year.