TD1 expected to skirt East Coast on Independence Day

A developing tropical system is expected to shift northwestward toward the Southeast US coast over the next 24 hours, strengthening from a Tropical Depression into a Tropical Storm at some point during this week. This, almost all forecast models agree upon. What happens thereafter is another story. From Thursday morning forward, there is a considerable amount of spread amongst usually reliable guidance, as the tropical system will shift northeastward along the Mid-Atlantic states of the East Coast. Eventually, an incoming trough and shortwave will kick the tropical system to the north and east, but the timing of this depends highly on the positioning of said feature during the latter half of this week.

This means that our fourth of July forecast is up in the air — and at risk of being spoiled by tropical rains. Adding to the issue is the potential for rain along the front, even if the Tropical Storm is hundreds of miles to our east. We can thank extra lift from the incoming troughing system for this, and many models are picking up on the potential for heavy rain along this band of lift from Thursday Night into Friday. After that, the track of the exact low pressure center would obviously have more significant impacts on our weather.

Forecast track of Tropical Depression 1.

Forecast track of Tropical Depression 1.

Backtracking a bit, the main story for the next day or two will be heat and the potential for thunderstorms. A building ridge over our area will allow for developing heat, with temperatures rising into the 90’s for highs on both Tuesday and Wednesday. Wednesday will almost certainly be the more brutal of the two days, with dew points rising into the 70’s as a southerly flow increases and pumps in warm and moist air. This will bring heat index values higher than Tuesday and make the air feel both heavy and hot.

The aforementioned incoming shortwave could provide enough lift on Wednesday afternoon to aid in the development of thunderstorms. Given the favorable instability and moderately favorable wind fields, these storms could be severe if they do form. Capping in the atmosphere, however, is expected to mitigate the potential for organized thunderstorm development. Severe storms could, instead, be isolated to scattered on Wednesday afternoon and evening.

NAM model showing a tropical system off the Northeast Coast on Independence Day.

NAM model showing a tropical system off the Northeast Coast on Independence Day.

By Thursday, the frontal boundary will be near the area and increasing lift will support the development of widespread showers and storms. These will continue into the afternoon and evening hours — and the rain may even become heavier if lift and moisture increase, owing to the tropical system. The duration of the rain into Independence day becomes a wild card, and the exact track of the tropical system will have significant impacts.

If the system tracks nearer to the area, on the western fringe of guidance, heavy rain could continue during Independence Day and even into the weekend. But if the storm tracks farther east, drier air on the western fringes of the system could work into the area by Friday afternoon — saving at least the second half of Independence Day. Faster movement of the system could help clear things out by the holiday weekend.

We’ll keep a close eye on the exact track of the system — and keep you in the loop as well. Stay tuned over the next few days both here and on our social networks for the latest.