It’s that time of year again when we usher in a new change of seasons – and the autumnal equinox – which marks the beginning of astronomical autumn in the Northern Hemisphere. This important threshold was reached at 8:44 a.m. on Sunday.

Of course, we often associate changing weather with the transition of seasons, and New England already has quite a temperature change from June to August (what is known as meteorological summer) in September – a significant cooling down and cool but pleasant weather for sleeping.

And now our days will also see a change, from the warm, summery temperatures we’ve enjoyed over the past few weeks to more seasonal temperatures around 15 degrees. You’ll notice the chill in the air that will linger through at least the weekend. This is due in part to the Earth’s position in relation to the Sun at this time of year. During the autumn equinox, the Earth’s axis is aligned so that the Sun is directly over the Equator and day and night are the same length at all latitudes. After the Sun crosses the Equator, it continues its journey south.

From this point on, our days become even shorter. As a result, daytime temperatures begin to cool as the hours of daylight increase. passes and shortens even more rapidly until October. In September, daylight hours in New England shorten by 1 hour and 22 minutes – or about 20 minutes per week.

In October we lose even more hours of sunshine until the winter solstice on December 21st, after which the days become longer again. In other words: the autumn equinox marks the midpoint between the longest day of summer and the shortest day of winter.

Remember, the start of astronomical autumn doesn’t mean we change our clocks. That doesn’t happen until November 3, when daylight saving time ends and we set our clocks back an hour and lose an hour of daylight.

From warm and humid to pleasantly cool

The most striking thing in recent weeks has been the transition from the well-above-average night temperatures of the meteorological summer months – those warm and humid evenings – to the cool night temperatures we have recorded so far in September.

The reason? In September there were high pressure areas with very low humidity, which could keep the heat on the surface, as was the case in summer.

The map below shows that nighttime low temperatures during the summer were 1 to 4 degrees above average throughout New England.

And so far, September has seen a massive drop in temperatures, with temperatures 1 to 5 degrees below average. Cooler air cannot hold much moisture, and when strong high pressure systems are present, the sun’s surface heat can escape unhindered through the atmosphere.

Temperature fluctuations of five to six degrees from average were measured at measuring stations near Providence and Springfield, which can be felt if you pack a light jacket when you go out at night or early in the morning.

That’s a tough change in such a short period of time and it will be interesting to see what the next few weeks bring. Currently, our general configuration will favor high pressure systems more often, leading to warm afternoons and likely cooler temperatures at night – at least for the next few weeks. After a brief cooldown this weekend due to more clouds and a northerly flow, things are looking set to warm up in late September.

Temperatures have been above average in seven of the last ten fall seasons, and temperatures in Boston and much of New England are currently right around average.

Is there a concern about drought?

Our parched lawns and suffering plants and vegetation may look different, but the Boston area has not officially entered drought territory with this 29-day dry spell we are finally leaving behind today. Rain is expected in the city and across southeastern Massachusetts from today through Friday, but it will only provide temporary relief to the region. Boston is nearly 2 inches below average for the month, and virtually all of New England is below that in September, raising concerns about drought in October.

According to the latest Drought Monitor report released Thursday, parts of New England are experiencing “abnormally dry” conditions, including the Boston area, Cape Cod, south-central New Hampshire and parts of Maine. If conditions worsen, they would fall into the “moderate drought” category.

Autumn also brings more hurricanes

Yes, fall is known for its shorter days and cooler weather, but it also produces some powerful hurricanes. And while this disappointing Atlantic season hasn’t yet lived up to meteorologists’ predictions of a hyperactive season, there’s still a long way to go—hurricane season ends on November 30.

NOAA’s updated August outlook predicts 17 to 24 named storms and eight to 13 hurricanes in the Atlantic. The scoreboard currently shows seven named storms and four hurricanes.

Remember, all it takes is one tropical system to create a season to remember. Fortunately, New England has escaped relatively unscathed, except for two residual storms that devastated some areas with extensive flooding.

Reach Ken Mahan at [email protected]. Follow him on Instagram @kenmahantheweatherman.