Heavy rain, thunderstorm, tornado risk: What Beryl remnants could mean for Rochester

The Rochester area could see some wet and windy conditions on Wednesday, with the remnants of post-tropical cyclone Beryl entering early in the morning. Those remnants will bring a slight risk of flash flooding, damaging winds and tornadoes to much of upstate New York and across the New England region, according to the National Weather Service.

Rainfall totals for the storm are expected to be in the 1-2 inch range through Thursday. 

The main hazards of the storm system are damaging winds, though the possibility of a tornado “cannot be ruled out,” according to the National Weather Service in Buffalo.

What is a slight risk of thunderstorms?

What a “slight” risk means varies based on what outlook is being considered, though all are the chances of the event occurring within 25 miles of any given point.

For instance, there is a slight chance of excessive rainfall in the Rochester area on Wednesday, which means there’s at least a 15% chance of rainfall exceeding flash flood guidance. “Slight” is the second lowest risk identified by the NOAA’s Weather Prediction Center and Storm Prediction Center; the lowest is “marginal” and the most severe are “moderate” and “high,” respectively. 

There is also a slight risk for severe thunderstorms in central and southern New York, with Rochester right at the edge of the area between slight and marginal risk. Rochester is similarly on the edge of the tornado risk map between the 2% and 5% bands; and on the edge of the 5% and 15% risk of damaging thunderstorm winds or wind gusts of 50 knots (roughly 58 mph) or greater.

The risk of tornado formation in upstate is a result of triple point — where the cold, warm and occluded fronts meet — being located over southwestern New York and the Finger Lakes area. An occluded front is created when a cold front overtakes a warm front, creating a composite front.

Hazardous weather outlook

The National Weather Service in Buffalo has issued a hazardous weather outlook for western and north central New York due to the Beryl remnants. While a soaking rainfall of 1-2 inches will come to most locations, the outlook said, some localized areas could receive heavier rainfall capable of causing flooding. Where those areas will be remains uncertain. 

Radar: Weather in Rochester and surrounding areas

Beryl earliest major hurricane in history

Beryl was the first hurricane of the Atlantic season and the first Category 4 hurricane to form in June.

The rapid increase in intensity of the storm, which went from a tropical depression to a hurricane in just 24 hours, is something seen more often in recent years, and is expected to become more frequent due to human-caused climate change, according to NOAA. 

Beryl became the earliest Category Five hurricane to form in the Atlantic and just the second in July, beating the previous mark set by Hurricane Emily in 2005. 

This is incredibly early for such strong storms, as major hurricanes (Category 3 and stronger) have an average formation date of Sept. 1, according to the National Hurricane Center. The average formation date for the first hurricane in the Atlantic is typically Aug. 11, based on data from 1991 to 2020. 

Those actual dates vary season to season, but Beryl was formed far earlier than the typical marks.