A rather unusual setup, more typical in the wintertime than summer season, is likely going to take place near the Mid-Atlantic coast this weekend as an area of low pressure forms near the North Carolina coast and tracks either into the Mid-Atlantic or southern New England some time this coming weekend. This will mark the start of days of very unsettled weather across a large part of the Northeast as a constant feed of deep, tropical moisture from the Gulf of Mexico and Caribbean Sea streams up the East Coast along a stationary frontal boundary.
An incoming trough of low pressure over the midwestern US will become negatively-tilted this weekend. Meanwhile near the Southeast coast, a weak surface low pressure will gradually form beginning this Friday. That trough will catch the coastal storm and allow it to strengthen while steering it up the Eastern Seaboard Friday into Saturday. First bringing a widespread area of rain and thunderstorms to the coastal Carolinas, some of which will be heavy, on Friday, it will then bring a large shield of moderate rain to at least the coastal sections of the Mid-Atlantic on Saturday.
Similar to a tropical cyclone, this storm system will contain some tropical characteristics and may end up qualifying as a subtropical storm. Nonetheless, the impacts will be the same. Instead, this storm will act more like a nor’easter — the warm version that is. Nor’easters are quite uncommon in the summer but it can still happen, like during this weekend. Along with the heavy rain will also be gusty winds, large waves, and minor coastal flooding. It is worth noting how this storm will remain weak with pressures likely remaining above 1000 millibars.
On Saturday, the Mid-Atlantic will be in the crosshairs of this storm as the center of low pressure moves parallel to the coast not too far offshore. Like we mentioned earlier, rain and thunder will affect much of the area during the day Saturday, especially east of the Appalachian Mountains and on the DelMarVa and east of Interstate-95. Wind gusts may reach or potentially exceed 50 mph along the DelMarVa and New Jersey coastlines while inland locations experience gusts generally up to 25-40 mph.
Those winds along with the heavy rain will then move to the north overnight Saturday, affecting the New York City Tri-State area and southern New England as early as the late-afternoon on Saturday. Several hours of a steady rain will likely be in the cards while thunder occasionally occurs. Winds will be the strongest at the coast, reaching a magnitude of up to 50 mph while it’s 10-20 mph weaker elsewhere.
The center of low pressure will likely move inland into New England during the start of the day Sunday. This will keep the rain going across the greater New York City area in the morning while much of the Hudson River Valley and northern and central New England experiences a washout much of the day. Thankfully, winds should relax somewhat but it will still be a breezy, tropical-like day. Temperatures will be cooler than average — mainly in the 70s — but dew points also in the 70s will make it feel very muggy out there.
By the end of the day Sunday, the low pressure will likely weaken into a trough as it tracks into southeastern Canada. Meanwhile to the south, the tap of tropical moisture will be unleashed, making for a very stormy stretch of weather all of next week. The combination of a upper-level trough of low pressure and a cut-off low over the Midwest and a strong Bermuda High off the East Coast will funnel the abundant moisture up to the Interstate-95 corridor.
This forecast makes it quite difficult to specifically forecast. Similar to the Southeast in the summertime, storms will generally be hit or miss. You either get the storm or you don’t. These showers and storms will be quite widespread, however, so the chance for rain most of next week up and down the East Coast will be greater than 50 percent.
The westward extent of this Bermuda High will determine where the heaviest of rain will fall. It will fluctuate throughout the week, so while coastal areas of the Mid-Atlantic and New England have the best chance for heavy rain Monday and Thursday, the interior sections — basically the locations to the west — can expect Tuesday and Wednesday to be their wettest days as the high pressure extends its farthest west.
Because of this constant flow of highly-anamolous moisture, flooding will be a big threat. Analogs that compare this upcoming pattern with previous time periods featuring a similar atmospheric orientation highlight some of the greater Northeast flood events. We’re not saying that widespread, major flooding is expected next week, but some towns will definitely endure flooding.
The ensemble mean of all the European model’s members suggest an unusually high chance for at least 5 inches of rain in the New York City Tri-State area. Therefore, not only is this the area we’re most concerned about for heavy rainfall but also for flooding.
Our current rainfall forecast highlights a widespread area of 2 to 3 inches with pockets even greater than that within the next 7 days along the East Coast.
Based on the mid-range forecast, we don’t see this pattern breaking through at least the end of July, however, this content stream of moisture should come to an end next weekend, or the final weekend of July. Before then, it’s going to be very soggy and ugly, quite a difference compared to this week.