Watching for a Coastal Storm Late this Weekend in New England

After the freezing start, Friday's recovery will be quick, so the sub-freezing temperatures won't last very long for southern and central New England. Afternoon highs will likely bounce back into the upper 50s and 60s. Saturday will be slightly warmer and dry with high pressure remaining in charge. At the same time, a coastal storm system will begin to take shape off Florida's coast along a frontal boundary. This will be the next system to watch for New England.

This system will work up the east coast Saturday and Sunday. Its movement will likely be quick initially, but it will slow down as it reaches the Mid-Atlantic. The most likely timing for the system to reach toward New England will be later Sunday and Monday. This system will be the first fall nor'easter of the season and may bring heavy rain, winds and the potential for coastal flooding to at least a part of New England. The main question will be how far north it can get with a strong area of high pressure to the north of New England.

The high pressure around New England during this time is a rather strong one, and its position and exact strength will determine what kind of impacts New England sees from the nor'easter. Trends over the past couple days have pushed the system farther north, allowing southern New England to get into a batch of heavy rain. It's farther north in New England that remains the question mark. A slightly weaker high pressure system would allow the heavier bands of rain to push farther north while a stronger high would allow only for some lighter showers.

This overall setup is very much like a Rex-Block, where an area of high pressure sits directly north of an area of low pressure. The high pressure tries its best to block the low pressure from advancing northward. The fact that this is a blocking pattern adds inherent uncertainty to the forecast. Individual Euro ensemble members, for example, shows the system as far north as the New Jersey coast by early Monday morning and as far south as the South Carolina coast. This is quite a spread and reminiscent of winter time nor'easters.

Below: Current weather map for Monday morning, showing the high and low pressure systems around New England forming a Rex Block:

More solutions continue to paint a picture that will see the system impact southern New England with a potentially sharp cutoff in rainfall moving north in the region. Confidence is increasing that southern and central New England will see a bout of steady to heavier rainfall moving south to north later Sunday and lasting through much of Monday. Rainfall amounts will likely gradually taper off moving north in New England.

At this point, there is much higher uncertainty regarding rainfall amounts north of a line from Rutland to Lake Winnipesaukee to Sebago Lake. South of this line could see a good 1 to 3 inches of rain, with the highest amounts across eastern Massachusetts. Less than an inch remains the favored outcome for areas north of the previously stated line across northern New England. With the blocking pattern and uncertainty, these numbers (and locations) are not locked in, they just give a good visual of current trends.

Below: Current 5-day rainfall outlook from the Weather Prediction Center:

Any rain this system produces is still much-needed. All of New England is now officially abnormally dry, with extreme drought conditions continuing to expand across northern New England. Unfortunately, the areas with the worst drought conditions are far less likely to see a good hit of rainfall with this system, but wherever the heaviest rain ends up will be welcomed. The only issue would be the potential for torrential downpours resulting in localized flash flooding, especially if it were to set up over an urban area.

Below: Current US drought monitor:

The other impact from this system could be the potential winds. A nor'easter off the coast and a rather strong area of high pressure to the north will lead to a tight pressure gradient. This will be supportive of strong wind gusts across the region. These winds would, naturally be strongest at the coast, but the tight gradient would support at least breezy conditions region-wide. Winds in excess of 40mph will be possible for coastal areas of southern and central New England.

A gusty northeast wind and rough seas will also promote the potential for some coastal flooding. At this time, the coastal flood threat does appear to be closer to the minor side. The CMC's most southerly solution would represent the worst-case scenario for coastal impacts as the storm stalls to the south and allows seas to continue to build after the "king tides".