New York City, New York — Summer may not be ready to disappear just yet, with temperatures expected to surge across parts of the eastern United States during the first week of October before cooler fall conditions return.
The shift comes as a rapidly strengthening El Niño climate pattern begins influencing weather across the Lower 48. The biggest effects are expected to include more frequent storms and above-average rainfall from the Gulf Coast through parts of the Southeast, Mid-Atlantic, Ohio Valley and Northeast.
At the same time, the Northwest, Rockies and Upper Midwest could remain noticeably drier and warmer than average during October.
Summer Heat Could Return in Early October
The first week of October could feel more like late summer than the middle of fall for millions of Americans. Beginning Wednesday, temperatures are expected to climb 10 to 15 degrees above average across portions of the Mid-South, Mid-Atlantic and Northeast.
Record-breaking heat is not expected, but temperatures could still become unusually warm for October. Parts of the Southeast could reach the low 90s Wednesday, while New York City could approach the mid-80s by Friday.
The warmth is not expected to last throughout the month. Cooler fall temperatures are forecast to spread across much of the country by the end of the weekend.
Another Surge of Tropical Moisture Is Coming
While the early October warmth grabs attention, rainfall could become the bigger story across the Southeast.
Another surge of tropical moisture from the Gulf of Mexico is expected to move across the Southeast this weekend. The setup follows a moisture-fueled flood threat that brought significant rainfall to parts of the Central United States this week.
Additional moisture could produce periods of heavy rain and thunderstorms, particularly where storms repeatedly move over the same areas.
The combination of warm temperatures, abundant moisture and developing storm systems could make for an unsettled start to October across portions of the South and East.
El Niño Could Shape October Weather
The broader weather pattern is being influenced by El Niño, one of the three phases of the El Niño-Southern Oscillation, or ENSO.
El Niño occurs when ocean temperatures become unusually warm across parts of the central Pacific. Those changes can alter atmospheric circulation and influence weather patterns across large portions of the world.
Some of the most noticeable effects across the Lower 48 begin emerging during the fall.
As El Niño strengthens, the Pacific jet stream can intensify and shift farther south, changing the typical path taken by storms across the United States.
The jet stream acts like an atmospheric conveyor belt, guiding storm systems from the Pacific toward the West Coast and eventually across the southern and eastern United States.
Gulf Coast and East Could Turn Wetter
That changing jet stream pattern is expected to help establish a persistent wet pattern from the Gulf Coast and Southeast toward the Mid-Atlantic, Ohio Valley and Northeast.
Those areas could experience above-average rainfall during October, creating repeated opportunities for heavy rain and potentially localized flooding.
The Southeast and Gulf Coast may remain closer to seasonal temperature averages despite the broader warm pattern because frequent clouds and rainfall can limit daytime heating.
For communities that have already experienced significant rainfall, additional storms could create concerns if the ground remains saturated.
Northwest and Upper Midwest Could Stay Dry
While the East and South turn wetter, the weather pattern is expected to look very different across the northern and western United States.
A ridge of high pressure is expected to settle across the Northwest, helping suppress storm activity and keeping parts of the region relatively dry.
The pattern could extend into the Rockies and Upper Midwest, where October is expected to bring warmer-than-average conditions in addition to below-average precipitation.
The Northern Plains and Rockies are among the areas with the greatest potential for unseasonable warmth during the month.
Most of the Country Could Stay Mild
Despite the expected regional differences, much of the United States is projected to experience mild to warmer-than-average conditions during October.
The biggest contrast could be between the wetter East and South and the drier northern and western regions.
For now, the first week of October appears likely to deliver one more taste of summer across portions of the East before cooler air returns. But as the month progresses, El Niño could increasingly shape where storms develop, where rain falls and which parts of the country remain unusually warm.
Forecasters said the overall pattern favors a mild and warm October for much of the country, while rainfall becomes more concentrated across the Gulf Coast, Southeast and eastern states.
What kind of October weather are you expecting in your area—one more round of summer heat or an early arrival of fall? Share your city and state in the comments and let us know what you’re seeing.
