October had a split personality in New York City this year. It started off unseasonably warm, but then temperatures plunged dramatically in the middle of the month and remained mostly below average until Halloween. Highs ranged from a balmy 80°F to a brisk 50°F. But in the end, these extremes balanced each other out. The city’s mean temperature for the month was 57.7°F, which is only 0.8°F above average.
In terms of precipitation, the city was fairly dry. Overall, 3.59 inches of rain was measured in Central Park. Of this total, 35% fell in single day during the first nor’easter of the season. On average, the Big Apple gets 4.40 inches of rain for month. This October also marked first month since June that the city received below average rainfall.
Autumn is a season known for colorful leaves and falling temperatures. Every once in a while, however, summer warmth makes a resurgence. When this happens, it is often dubbed “Indian Summer”.
This weather phenomenon, according to the NWS glossary, is defined as “an unseasonably warm period near the middle of autumn, usually following a substantial period of cool weather.” In the northeastern US, it is generally associated with an area of high pressure to the south that ushers warm air northward.
In popular use since the 18th century, the exact origins of the term are a bit foggy. One of the more reasonable explanations behind this unique phrase suggests a connection to when Native Americans began their hunting season, but no one knows for sure.
In other parts of the world, this summer-like weather goes by a variety of different names. In Europe, a number of countries associate the unusual warmth with the nearest saint’s day. It is known as “St. Luke’s Little Summer” if it develops in October or a “St. Martin’s Summer” if it occurs in November. In temperate parts of South America, it is simply known as “Veranico” (little summer).
The timing and intensity of these autumn warm spells vary from year to year. Nevertheless, when they do occur, they usually only last a few days. So, as we inevitably move toward winter, enjoy them while you can.
The first nor’easter of the season slammed the northeastern United States on Saturday. Heavy precipitation, strong winds, and coastal flooding were reported across the region.
Here in New York City, the storm dumped 1.34 inches of rain in Central Park. Its powerful winds knocked down trees and caused power outages around the city’s five boroughs. The storm also caused significant travel delays, including shutting down part of the FDR Drive because of flooding.
While nor’easters are not uncommon at this time of year, this one was interesting because it started off as a hurricane in the eastern Pacific. Hurricane Willa made landfall near Mazatlan, Mexico on Tuesday night and then moved inland toward Texas. From there, the storm’s remnants merged with a cold front and became re-energized. Traveling in the jet stream, it worked its way up the eastern seaboard and became a nor’easter.
First nor’easter of the season downed trees and branches in Queens. Credit: D. Herrick
According to the NWS, the temperature in Central Park only made it to 55°F on Saturday and 58°F on Sunday. The overnight lows were also rather chilly in the mid-40s. This was the coldest weather the city has seen since last spring. Its rather sudden arrival was a bit a jolt for many New Yorkers who had to scramble to find their jackets and sweaters that had been tucked away for months.
The average high and low for NYC at this time of year is 65°F and 51°F, respectively.
The calendar says October, but it still feels like summer in New York City.
The temperature in Central Park soared to an unusually balmy 80°F on Wednesday. While this did not break any records, the overnight low did. The mercury only dropped to 71°F, setting a new record warm minimum temperature for the date. The previous record of 69°F had been in place since 1949.
It is also interesting to note that Wednesday’s low was warmer than the date’s normal high. The city’s average high and low temperatures for this time of year are 66°F and 52°F, respectively.
New record warm low temperature set in NYC. Credit: The Weather Gamut
September 2018 was another temperature roller coaster in New York City. Highs ranged from an unseasonably cool 62°F to a sizzling 93°F. However, with fifteen days posting above average temperatures, including three with readings in the 90s, the heat won out in the end. This warm finish was also aided by the unusually balmy overnight lows that were seen throughout most of the month. In fact, on September 5, the low only dropped to 77°F. That tied the record high minimum temperature for the date, which was set in 1985. In the end, the city’s mean temperature for the month was 70.7F°, which is 2.7°F above average.
In terms of precipitation, September was a soggy month in the Big Apple. In all, 6.19 inches of rain was measured in Central Park. Of this impressive total, 51% fell on just two days, each of which saw flash flooding around the five-boros. The city, on average, gets 4.28 inches of rain for the entire month.
Today is the Autumnal Equinox, the first day of fall in the northern hemisphere. The new season officially begins at 9:54 PM Eastern Daylight Time.
The astronomical seasons, as opposed to the meteorological seasons, are a product of Earth’s axial tilt – a 23.5° angle – and the movement of the planet around the sun. During the autumn months, the Earth’s axis is tilted neither toward nor away from the sun. This position distributes the sun’s energy equally between the northern and southern hemispheres.
Since the summer solstice in June, the arc of the sun’s apparent daily passage across the sky has been sinking and daylight hours have been decreasing. Today, the sun appears directly overhead at the equator and we have approximately equal hours of day and night. The word “equinox” is derived from Latin and means “equal night”.
Transitioning from summer to winter, autumn is also a season of falling temperatures. According to NOAA, the average high temperature in most US cities drops about 10°F between September and October.
Earth’s solstices and equinoxes. Image Credit: NASA
The Santa Ana winds are notorious for exacerbating wildfires in southern California.
These strong winds blow warm, dry air across the region at different times of the year, but mainly occur in the late autumn. They form when a large pressure difference builds up between the Great Basin – a desert that covers most of Nevada and parts of Utah – and the coastal region around LA. This pressure gradient funnels air downhill and through the passes of the San Gabriel and San Bernardino mountains toward the Pacific. According to the NWS, the Santa Ana winds can easily exceed 40 mph.
Originating in the high desert, the air starts off cool and dry. But as it travels downslope, the air compresses and warms. In fact, it warms about 5°F for every 1000 feet it descends. This dries out the region’s vegetation, leaving it susceptible to any type of spark. The fast-moving winds then fan the flames of any wildfires that ignite.
The Santa Ana winds are named for Santa Ana Canyon in Orange County, CA.
The winter solstice is still a few weeks away, but meteorological Fall (September, October, and November) has officially ended and it was the fourth warmest on record in New York City.
The season, a transitional period between summer and winter, can often feel like a temperature roller coaster. This year, highs ranged from 91°F to 38°F. In the end, though, the warmth came out on top. The city’s average temperature for the three months was 60.4°F, which is 2.9°F above normal.
This autumn was dominated by a pattern of warm spells separated by a few short-lived blasts of cold air. It was largely driven by the jet stream staying well to the north for most of the season with just a few dips southward.
The city’s warmest autumn on record, according to the NWS, occurred in 2015, which tied 1931 with an average temperature 61.8°F. The coldest was 1871 when the three-month average was only 51.7°F. Central Park weather records date back to 1869.
September 2017 felt like a temperature roller coaster in New York City. Highs ranged from an unseasonably cool 66°F to a record warm 91°F. But with eighteen of the month’s thirty days posting above average readings, the heat won out in the end. The city’s mean temperature for September was 70.5°F, which 2.5°F above average.
In terms of precipitation, the month was mostly dry. Only 2.0 inches of rain was measured in Central Park, marking the third month in a row to deliver below average rainfall. The city usually gets 4.28 inches of rain in September.