Explaining the Nor’easter storm

Commanders’ Weather, which provides specialized marine weather forecasting and routing for sailing and cruising yachts worldwide, explained Nor’easters in their Winter 2023 Newsletter on January 22:

Every fall, sailors run south to escape them while skiers trek north to find them. Nor’easters are powerful storms whose centers clip the northeastern U.S. a few times each winter, and which have significant weather ramifications from the Canadian Maritimes to the Caribbean.

While these storms can develop a few different ways, the strongest tend to spin up in the Gulf of Mexico, cross the southeastern U.S., then streak up the East Coast. Initially fueled by moisture and heat in the Gulf of Mexico, the storm then pulls in wintry cold air from the interior U.S., and the resulting sharp temperature gradient fuels fast development.

Some strengthen quickly enough to be deemed a “bomb cyclone”, when the central pressure of the system drops 24 millibars in 24 hours, taking it from a weak disturbance to a powerful storm in just a day. Snow can develop in the southern Appalachians as the center of the system tracks up the coast, then spread through the mid-Atlantic and New England. Depending on the exact speed and track of the storm, feet of snow can fall across wide swaths of the Eastern Seaboard.

Ahead of the storm center, northeast winds (for which this storm is named) tend to batter the New England and mid-Atlantic coast. Freezing ocean water can inundate exposed shorelines, including the historic North End of Boston. In the wake of the storm a strong, frigid northwest wind promotes lake- and ocean-effect snow wherever there is unfrozen water to be found.

The strong northwest wind behind the storm and its trailing cold front usually extends easily down the length of the East Coast, and can blow through the Bahamas and into the northern Caribbean (as can be observed in the satellite image above). The powerful system also creates massive waves in its vicinity, and tends to emanate an unusual northwest or north swell down into the Leeward Islands.

Last week, one such NW swell event impacted the northern Caribbean, creating high surf in usually protected ports and bays. Over the next week, a few nor’easters are expected to batter New England, and there are almost certainly more to come as the winter wears on!