The rain could cause areas of flooding in Philadelphia, New York and Boston, while winds may be strong enough to topple trees and cause power outages in eastern New England.
This particular storm will begin to take shape Monday evening when a zone of low pressure over the Ohio Valley, the same one that triggered damaging tornadoes in Missouri and Illinois on Sunday, begins to transfer its energy to a new low pressure center developing east of North Carolina. By Tuesday morning, it will be rapidly gaining strength and unleashing heavy rain from the eastern Delmarva Peninsula to New York City.
It’s forecast to peak in intensity Tuesday afternoon and evening, when it’s east of Long Island and dumping wind-swept rain from central New Jersey to southeast Maine.
Tuesday night into Wednesday, while the storm starts to weaken, its forward progress is forecast to slow as it meanders off the Northeast coast, prolonging its assault. The rain and wind could linger from the Delmarva north to New York City through Wednesday morning and into the afternoon and evening in eastern New England. The storm should finally move away from the coast Wednesday night.
Two to four inches of rain could fall from Philadelphia to New York. Boston and Providence may see three to five inches of rain, with locally higher amounts.
“Heavy rainfall may cause flooding of roads and pounding of water in low lying areas,” wrote the National Weather Service in Taunton, Mass. “The Tuesday evening commute may be particularly impacted.”
Flash flood and flood watches are in effect in many of the same areas that were deluged by the devastating rains from Hurricane Ida’s remnants, including much of eastern Pennsylvania, New Jersey and New York. While drenching rain is predicted from this event, it will be far less intense than Ida’s rain. Peak rainfall rates for this storm are expected to be around one inch per hour compared with more than three inches per hour in Ida.
Exact rainfall totals will depend on the specifics of the storm track. If the storm jogs to the east of current forecasts, rainfall will end up at the lower end of projections but a nudge to the west could bring high-end totals.
While the cold front energizing the storm will generate showers and storms for Washington and Baltimore on Monday evening, those cities will mostly miss the slug of rain from the storm itself as it passes too far to their north and east. These circumstances occasionally play out with winter storms in which the corridor from Philadelphia to Boston is walloped with heavy snow while population centers in the Mid-Atlantic see little.
As the storm cranks up Tuesday, winds will howl from the Mid-Atlantic northward and turn hazardous in some areas. The gusts will be strongest in eastern New England, especially in eastern Long Island and eastern Massachusetts, where gusts could reach 50 to 70 mph.
“Wind damage may overachieve given trees remain fully leaved,” wrote the Weather Service office serving Boston. “Hence, power outages are possible.”
Boston is under a high wind warning for gusts up to 60 mph between Tuesday afternoon and Wednesday morning.
Winds won’t be quite as strong for areas farther inland and to the south, but gusts to 40 mph are still possible in Philadelphia and New York, and maybe as far south as Washington.
While the storm will generate big waves and pounding surf along the coast, severe shoreline flooding is not expected because of lower-than-average astronomical tides (tied to the phase of the moon). Still, minor coastal flooding is predicted in eastern New England for water levels up to one foot above normal Wednesday.
The storm’s rate of intensification, as measured by its drop in pressure, is forecast to be impressive.
Between Monday and Tuesday afternoon, the storm’s pressure is forecast to plummet from around 1,000 millibars to 974 millibars. Such a 26-millibar drop in pressure meets the criteria for the storm to be considered a “bomb cyclone” or one whose pressure drops at least 24 millibars in 24 hours. The lower the pressure, the stronger the storm.
A storm with a pressure of 974 millibars is unusually strong for October along the East Coast and on par with a typical Category 2 hurricane.
Interestingly, the storm has its origins from the first of two bomb cyclones that formed offshore the Pacific Northwest since late last week. That cyclone drove a disturbance into California on Thursday and Friday that has since tracked across the country toward the Ohio Valley. Now it is initiating this East Coast storm.
The storm will also become a classic nor’easter, as it gains strength over the Atlantic Ocean and generates strong winds from the northeast as it charges up the East Coast.