Watching new Atlantic disturbance and southeast US waters this week

Models suggest development of another tropical wave set to roll off Africa and possible subtropical development off the southeast US by this weekend

As we frequently discuss in this newsletter, hurricane season activity is misaligned with the calendar. While the calendar says we’re halfway through the 6-month hurricane season on September 1st, history tells us we still have another 70% of storm activity left at the start of September.

But in September, Mother Nature quickly catches up to the calendar, as we’re currently witnessing, with three Atlantic hurricanes forming in a span of only a few weeks. This week, historical storm activity finally caught up to the calendar – both telling us we’re 60% through the season – and by the end of the month, we’ll be down 80% of seasonal activity. But don’t overlook October, South Florida’s most likely month for a hurricane encounter.

Possible development close to home by late week

A cold front that’s brought the first taste of fall to much of the southeast U.S. as far south as north Florida will stall across the South Florida peninsula this week.

Along this stalled frontal boundary, an area of low pressure is forecast to form near the Bahamas by late week. Models indicate some development potential as this low-pressure system lifts northward toward the Carolinas and mid-Atlantic for the weekend.

Whatever forms will do so from the top-down rather than the bottom-up as tropical systems do, so the low-pressure area will be non-tropical to start. Eventually, it may acquire tropical characteristics as thunderstorms organize.

Though the system will be moving away from South Florida, it will contribute to our unsettled and active weather pattern this week, and the cold pocket aloft from its parent upper-level low could increase our severe weather chances by late week.

Regardless of development, the main impacts this week from the system will be gusty onshore winds along the southeast by late week into the weekend, which could produce rough surf and the potential for coastal flooding depending on the strength of the low. Interests along the southeast coast from Florida’s Space Coast northward to the Carolinas should monitor the forecasts this week.

Nigel now a hurricane, set to rapidly strengthen, but no threat to land

Overnight, Nigel became the 6th hurricane of a busy Atlantic hurricane season over the open central Atlantic. For context, the 6th Atlantic hurricane typically doesn’t form until the middle of October.

Nigel is forecast to rapidly strengthen into a Category 3 hurricane this week, making it the 4th major (Category 3 or stronger) hurricane of the season. Thankfully, the hurricane will make a sharp right into the North Atlantic well east of Bermuda and poses no threat to land.

New Atlantic disturbance likely to form west of Africa later this week

Another vigorous tropical wave is set to roll off Africa by mid-week. As we discussed in Friday’s newsletter, conditions appear favorable for development and NHC raised formation odds to high Monday morning for a new tropical depression or storm (either Ophelia or Philippe) by the end of the week.

The system will take a westward trajectory and not immediately turn out as it strengthens into next week so we’ll need to follow. Thankfully, it has a long ways to go before it becomes a concern, if at all.

Low-pressure tracks through Saturday morning, September 23, 2023, from the European ensemble modeling system. Models show slow development by late week into the weekend as the system moves toward the west-northwest. Credit:

Lee no longer

Lee – the once powerful Category 5 hurricane whose journey we chronicled for over two weeks – blew into southeastern Canada and northeastern Maine over the weekend, downing trees and knocking out power to more than 200,000 people across Maine, Nova Scotia and New Brunswick.

While the hurricane transitioned to an extratropical cyclone only 12 hours before crossing into Canada, it remained a large and powerful storm. Winds gusted as high as 83 mph in far eastern Maine and as high as 56 mph at Bangor International Airport. Maximum rainfall totals in Maine were generally around 4 to 6 inches Downeast.

Although storm surge was a minor issue for Maine’s rocky coastline, splashover and runup from large and battering waves flooded coastal roads through parts of Maritime Canada. The low-pressure system is accelerating through the North Atlantic today and will merge with a larger storm system approaching Ireland and the UK tomorrow into Wednesday.

About the Author:

Michael Lowry is Local 10's Hurricane Specialist and Storm Surge Expert.