Philly has an excessive heat warning until 8 p.m., but a cooldown is coming

An excessive-heat warning is in effect until 8 p.m. Wednesday for heat indexes as high as 105 in the Philly region, and all pumpkin-spice concoctions and Halloween displays notwithstanding, evidently August isn’t quite over.

But in a month that hasn’t exactly been a bright shining moment for the science of long-range weather prediction, the first hot spell in three weeks is going to be short-lived, and forecasters say the majority of the Labor Day weekend should be decent.

After reaching an official high of 90 degrees Tuesday, it didn’t get an lower than 73 overnight, and temperatures are due to reach the mid-90s Wednesday. More than 60 Philadelphia schools that do not have air-conditioning are to dismiss early, as they did on Tuesday.

“Code orange” air-quality alerts are up for ground-level ozone for the entire region from 11 a.m. to 11 p.m. on Wednesday. In code-orange conditions, people with respiratory or heart conditions are urged to exercise caution outdoors.

» READ MORE: More than 60 Philly public schools don't have air-conditioning

Strong, scattered thunderstorms are expected to pop Wednesday afternoon, and the government’s Storm Prediction Center sees a 40% chance that some of those storms could be severe. That could be an issue for the Phillies game, scheduled to start at 4:05 p.m.

Then a cool-down is expected to quickly take hold, with highs perhaps not reaching 80 degrees Thursday and Friday. Shower chances are likely to persist into the weekend, said Amanda Lee, meteorologist with the National Weather Service in Mount Holly.

The best chances for showers would be Saturday, she added, the last day of what has been a surprising month of August in the weather world.

» READ MORE: Dozens of Philly schools are dismissing early Tuesday and Wednesday

After a June 1-July 31 period that was among the five warmest on record in Philadelphia, the National Oceanic and Atmospheric Administration’s Climate Prediction Center said the odds strongly favored above-normal temperatures again in August.

That outlook looked golden at the start of the month as it hit 97 on Aug. 1 and went above 90 on five of the first six days.

But Aug. 6 marked what had been the last 90-degree reading of the month. And based on the forecasts, the August average temperature is going to finish shockingly close to normal.

» READ MORE: Forecasters had expected a hot August. It hasn't turned out that way

What happened? The sun- and warm-wind encouraging high pressure that had dominated lost its mojo, said Scott Homan, meteorologist with AccuWeather Inc.

It yielded to a succession of upper-air low pressure systems that imported cool air from the north and touched off showers.

More than five inches of rain has been measured officially in Philly this month, about 1.5 inches above long-term averages.

Speaking of rain, you may be wondering what happened to all the hurricanes that were expected during what was shaping up to be a record season in the Atlantic hurricane basin, where the waters have been simmering.

A whole lot of meteorologists are wondering the same thing in a season with the conditions in the tropical Pacific and in the Atlantic hurricane basin, which includes the Gulf of Mexico and the Caribbean Sea appeared to align perfectly for a season of mayhem on the Gulf and Atlantic coasts.

With nothing on the horizon, this would mark the first time in 27 years that no named storms have formed in the basin between Aug. 21 and Sept. 2, said Philip Klotzbach, tropical-storm specialist at Colorado State University.

» READ MORE: The hurricane outlooks were frightening, but August is ending with a surprising lull

The last named storm, Ernesto, which contributed to significant rains in the Philly region, dissipated on Aug. 20.

Klotzbach believes the lull is related to the behavior of the African monsoon, an important component in the development of hurricanes that originate off the African west coast.

That lull isn’t expected to last, but it is safe to say that anyone heading to the Shore or the Outer Banks or Cape Cod won’t have to fret about tropical storms on the unofficial last weekend of summer.

In the immediate Philly region, showers are possible Saturday, but Sunday and Monday are looking glorious in the city and at the Shore, with sun and highs in the 80s.