Astronomical fall begins today, when Florida with get cooler weather

Today’s midday sun will shine squarely on the equator as summer says goodbye and the Northern Hemisphere begins its first tentative tilt into autumn.

The fall equinox, the astronomical end of the hottest, longest days of the year, happens tomorrow. At the moment of equinox, the Earth’s axis leans neither toward or away from the sun — a parity that produces a nearly equal day and night.

It’s a cosmic promise that the unbroken hum of air conditioning will soon quiet, that a bite of air as crisp as an apple is within reach.

Related: Who’s to blame for Daylight Saving time? It’s not who you were taught

But while the universe says it’s autumn, South Florida is on a slightly different timeline.

“We see summer linger a little longer here,” said Larry Kelly, a meteorologist with the National Weather Service in Miami. “It’s September, but it’s still hot. We’re still seeing afternoon thunderstorms.”

Earth on the fall equinox, courtesy NASA Earth Observatory.

Adding to the seasonal uncertainty in South Florida, is that astronomical seasons don’t correspond with meteorological seasons, which are grouped neatly by months. Summer, on meteorological terms, ended Sept. 1. Then there’s Daylight Saving time. This year, most of America will turn clocks back one hour on Nov. 5.

Check The Palm Beach Post radar map.

“If you live in the Northern Hemisphere, you can easily notice the later dawns and earlier sunset,” said Deborah Byrd, editor-in-chief for the online magazine Earth and Sky, about the fall equinox. “Also notice the arc of the sun across the sky each day. You’ll find it’s shifting toward the south.”

In West Palm Beach, the normal daytime temperature remains in the high 80s into mid-October, with overnights cooling to 70 at about the same time. The first nighttime temperature below 70 doesn’t happen until nearly Halloween.

It will be Thanksgiving before days top out at 80-degrees and night dip into the mid-60s.

“We don’t really get fall-like weather until late October,” Kelly said.

And even then, the difference between the warmest and coldest periods of the year in South Florida can be just 25 degrees, according to the book Florida Weather, which was co-authored by Florida Climatologist David Zierden.

“A source of frequent complaint among northern migrants to Florida is its lack of distinct seasons,” the book notes.

In Chicago, Cleveland, and New York City, there is a difference of approximately 70 degrees between the average maximum temperature and the average minimum temperature.

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The more subtle shift in seasons doesn’t mean South Florida won’t feel the change.

While daytime temperatures this weekend will reach near 90 degrees with a 40 to 50 percent chance of rain today and Saturday, drier air may filter in Sunday.

Hurricane Maria, which is expected to remain a hurricane for at least the next five days, is on a northerly path east of the Bahamas. It parallels Florida until late in the weekend when a shift will take it away from the U.S. coastline.

That move will allow a high pressure area to move into the state, bringing clear skies and drier air.

But Kelly cautioned that it may not be the best beach weekend. Tropical Storm Jose, which sat stationary off the coast of Nantucket on Thursday, has been sending higher ocean swells toward Florida. Hurricane Maria’s passing will do the same.

“The ocean is going to be pretty hazardous,” Kelly said. “That’s the main affects we’ll see from Maria, hazardous marine conditions, a high risk of rip currents and bigger waves.”

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