Pat Shingleton for Sept. 20, 2012

During the middle of the 18th century, seafarers believed a major storm would occur around the end of summer, closer to the autumnal equinox. As noted in a previous column, sailors would refer to these systems in September and October as a “line storm.” When the sun crossed the equator, its rays also would move in a line across the equator. The sun’s rays caused thermal contrasts. The cool air from the north colliding with super-warm, southerly air activated more tropical storm activity. The results are contrasting air masses that produce drastic fronts and winter-type storms in temperate regions. The traditional period for the peak threat of storm activity is the 60-day interval centered on Sept. 10. The Caribbean becomes active and New England also becomes vulnerable.

Fastcast: Chilly morning.