Astronomical fall arrives on Tuesday at 8:05 p.m. with the autumnal equinox — and Mother Nature is leaning right into the prompt.
As we lose about three minutes of daylight each day, New England temperatures are taking a noticeable dive. School bus mornings will feature crisp starts in the 40s in many suburbs in the coming days. Daytime highs will struggle to climb past the low 60s. That’s roughly 10 degrees below our late-September average.
While most of mid-week remains quiet and mainly dry, all eyes are turned toward the water, as a high-impact coastal marine storm is brewing for the end of the week.
Predicted radar showing the coastal storm for Friday, Sept. 25 at 2 p.m. (Danielle Noyes/1DegreeOutside)
Mid-week overview
For Tuesday through Thursday, the main weather story on land will be plenty of clouds, a few breaks of sun and cool, jacket-worthy air.
High pressure over eastern Canada and developing low pressure to the south will squeeze the atmosphere over New England, creating a tight pressure gradient that funnels a persistent, chilly wind right off the Atlantic Ocean.
- Tuesday and Wednesday: Highs stay stuck in the low 60s. Expect a persistent northeast wind gusting 20 to 30 mph along the coastline on Wednesday.
- Thursday: Still mainly dry, though we can’t rule out a stray shower for the Cape, Islands and South Coast. Persistent northeast winds continue with higher gusts of 30 to 40 mph possible from the immediate coast of the South Shore down to Cape Cod.
Friday’s coastal storm
By Friday, an upper-level low diving to our south will attempt to capture ocean moisture and pinwheel a full-fledged nor’easter back toward southern New England.
Because the storm’s exact track determines where the heaviest rain band lands, some areas may stay largely dry while far southeastern Massachusetts has the highest probability of rain at this point.
Chance of precipitation for Friday, Sept. 25, 2026. (Danielle Noyes/1DegreeOutside)
Fifteen-foot seas and coastal flooding
While the rain footprint remains a question mark, the coastal marine impacts are a lock. Those near the shore should prepare for a significant deterioration in conditions late this week:
- Building seas: Wave heights will ramp up quickly, from 4–5 feet near Boston and the outer Cape on Tuesday, up to 9–16 feet offshore on Thursday, and a staggering 14–17+ feet by Friday.
- High astronomical tides: The full harvest moon is Saturday, elevating astronomical tide levels along our coastline.
- Pounding surf and erosion: Expect pounding surf, minor coastal flooding and localized beach erosion in vulnerable east and northeast-facing spots, particularly around the Friday high tide windows.
Predicted wave height for Friday, Sept. 25 at noon.(Danielle Noyes/1DegreeOutside)
The bottom line
Break out the light layers for the kids at the bus stop this week, and secure any loose outdoor items or boats along the coast before the wind and waves peak on Thursday and Friday.
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