Weather for New England and the Northeast

Area Forecast Discussion, National Weather Service Boston/Norton MA, 723 AM EDT Monday, September 21, 2026

**What has Changed**

Inner southern waters have been added to the Gale Watch.

**Key Messages**

1. Light showers will exit early this morning, moving offshore of Cape Cod and the Islands by late morning. Breezy and cool conditions are expected this afternoon.

2. Dry and cool conditions will persist through midweek. Forecasters are monitoring a potential late-week coastal low that could bring rain, strong winds, and coastal impacts depending on its track.

**Discussion**

**Key Message 1, Showers End This Morning, Then Cooler and Breezy**

Light showers will move eastward across the eastern portions of the region early this morning, with the remaining showers likely moving offshore of Cape Cod and the Islands by late morning. Areas of patchy fog are also possible early today.

A strong area of high pressure will build in behind the departing system, bringing a dry and cooler than normal air mass into the region. Drier air in the middle levels of the atmosphere will move in quickly from the north, with lower levels of the atmosphere also becoming drier through the morning. This should gradually improve the low clouds, with some breaks developing from midmorning into the afternoon. Low clouds may linger longer across Cape Cod and the Islands.

Another cool day is expected, with high temperatures mainly in the low to mid 60s. Some valley locations could reach the upper 60s. Forecast temperatures about 5,000 feet above the ground are expected to be around 50 to 55 degrees, supporting the cooler conditions at the surface.

Northeasterly winds will develop today as high pressure builds to the northwest. The increasing difference in air pressure, known as the pressure gradient, will support breezy north to northeast winds along the south coast, Cape Cod, and the Islands, with gusts of 20 to 25 mph.

Tonight will be mostly cloudy. Despite limited cooling under the clouds, temperatures should fall into the 40s across most inland areas. Urban locations and areas near the coast should remain milder, with temperatures in the 50s.

**Key Message 2, Cool and Mostly Dry Through Midweek, Coastal Storm Late Week**

Forecast model guidance remains in good agreement that an unusually strong area of high pressure will develop over Quebec and persist through late week. This will bring a cooler than normal air mass into the region, with high temperatures generally in the upper 50s and 60s and a prolonged period of northeasterly winds.

A weak low pressure system will move through the Mid-Atlantic on Tuesday. There remains some uncertainty about how far north this system will track. If it moves far enough north, a few light showers could occur, with the better chances across Connecticut, the south coast, Cape Cod, and the Islands. Otherwise, mainly dry conditions are expected through midweek.

**Potential Coastal Storm Late This Week**

Attention then turns to a developing coastal low pressure system late in the week. Both individual computer forecast models and larger groups of model forecasts, known as ensemble guidance, continue to show a slow-moving low developing and tracking northward toward the Northeast coast late this week.

There is still considerable uncertainty regarding the exact track and strength of this system. The average of the ensemble forecasts has generally settled on a middle-ground scenario, with the low developing off the Mid-Atlantic coast Wednesday and then tracking northward toward southern New England Thursday and Friday.

Individual model forecasts show a wide range of possible tracks, from as far west as Long Island and near Cape Cod to considerably farther offshore southeast or east of southern New England.

Recent ECMWF ensemble forecasts, which use multiple slightly different versions of the European forecast model, have shown subtle shifts east and west within the group of possible tracks. The GEFS, the Global Ensemble Forecast System, has shown a subtle but fairly consistent trend toward a farther-west track.

Regardless of the eventual track, the ensemble forecasts bring the low close enough to potentially produce strong wind gusts, rain, and coastal impacts including erosion and coastal flooding. The exact track and strength of the storm will strongly influence the strength of the winds, the amount of precipitation, and how far inland the rain reaches.

**Increasing Wind and Marine Concerns**

Although the center of the coastal low is not expected to arrive until later in the week, marine and coastal impacts could begin as early as Wednesday.

As the low strengthens over the Mid-Atlantic, the strong area of high pressure to the north will increase the difference in air pressure across the region. This tightening pressure gradient, particularly across the southern coastal waters, will support strong winds beginning Wednesday morning, well ahead of the main low pressure system.

The exact position and strength of the high and low pressure systems will determine how strong the winds become. Confidence is increasing in gale-force winds, meaning sustained or gusty winds capable of creating hazardous marine conditions, across the southern coastal waters. The ECMWF and its ensemble forecasts have strongly supported this scenario, although the GEFS and GFS, the Global Forecast System, remain somewhat weaker.

A Gale Watch has been issued for these areas.

As the system moves northward, strong wind gusts are expected to continue and could strengthen or spread across additional portions of the coastal waters. The ECMWF ensemble shows a 10 to 25 percent chance of wind gusts exceeding 45 mph Thursday into Friday.

Inland winds will also become gusty, although they should be lighter than over the water. Gusts of 25 to 35 mph are possible, with the strongest winds near the immediate coast.

**Rain and Coastal Impacts**

The prolonged period of gusty northeast winds will produce increasingly rough seas and raise the threat for coastal erosion and flooding. The severity of these impacts will depend heavily on the eventual track of the storm.

Because forecast models continue to show considerable variation in the track and strength of the system, rainfall amounts remain uncertain. Most guidance suggests that the main area of rain will at least reach the far eastern portions of Massachusetts, while some of the higher-end forecasts bring the rain shield farther west.

Some individual model runs and ensemble members indicate rainfall amounts greater than 1.0 inch. This possibility will need to be monitored because the system is expected to move slowly.

**What to Expect**

Confidence is steadily increasing that a coastal storm will affect at least the coastal waters and coastal areas of southern New England late this week. However, the storm is still several days away, and important details remain uncertain, including the track, strength, and larger-scale atmospheric pattern.

Those factors will determine the eventual magnitude of the rain, wind, rough seas, coastal erosion, and potential coastal flooding. Further forecast updates will provide a better indication of where the greatest impacts are likely to occur.