The weather generally starts cooling down in late September to October, with the astronomical start of autumn being September 22. However, in many regions such as West Central and Southwest Florida, significant cooling usually does not happen until November, with the first brief cooler spells sometimes occurring in mid-October. In the northern and central United States, autumn- like weather often arrives in late September or early October, marked by cooler temperatures brought by cold fronts moving south from Canada. This cool down tends to linger longer than earlier brief cool spells that sometimes occur in mid-September. The cooler temperatures in early to mid-September in some northern areas can be a preview but are not always sustained.
In summary:
- Astronomical autumn begins around September 22.
- Early cooling can start in mid to late September especially in northern U.S. regions.
- Significant, consistent cooling generally occurs through October and into November in many areas.
- Coastal areas tend to cool down more slowly due to moderating effects of water.
- Some brief cooler spells may occur before sustained cooler weather sets in.
