(Scroll down for a detailed forecast for storm effects in the Washington and Baltimore regions.)
The storm will develop along a cold front diving southeastward from the upper Midwest, where it is dumping record snow in northern Minnesota, around Duluth. Once the front arrives along the East Coast, it is forecast to draw northward a disturbance developing in the Caribbean, which may become Tropical Storm Philippe on Saturday after it moves north of Cuba.
The connection between the East Coast storm and this tropical-weather-maker will establish the equivalent of a superhighway for atmospheric moisture, starting in the Caribbean and pointed directly at the northeastern states. In the Pacific Ocean, these narrow but intense firehose-like streams of moisture are called atmospheric rivers, and they can unload tremendous rainfall in a short amount of time.
Widespread rainfall totals of one to five inches are predicted from central Virginia to Maine, but the zone of heaviest rainfall — where at least two or three inches are likely — should focus between northeastern Pennsylvania and southern Maine.
After the mid-latitude and tropical weather systems come together in the Mid-Atlantic, the storm will become a powerhouse — its pressure plunging fast enough over a 24-hour period to meet the criteria of a meteorological “bomb.” This means winds — particularly in coastal areas in New England — will crank up as Sunday progresses. Gusts from Long Island to eastern Massachusetts could easily reach 50 to 60 mph Sunday night into early Monday. Even in interior sections of the Northeast, gusts at times could near 50 mph, causing isolated to scattered power outages.
The lower the pressure, the more intense the storm, and models project that the storm’s pressure could fall below 980 millibars late Sunday night over New England.
“Readings this low have never been observed in southern New England during October, although even lower values were recorded from the New York area southward during Hurricane Sandy (2012),” writes meteorologist Bob Henson on Weather Underground’s Category 6 blog.
The howling southeast winds bombarding the coast of New England will push excess ocean water toward the coast, but due to astronomically low tides and the storm’s rapid movement, the risk of significant coastal flooding seems low.
Cold air will spill southeastward in the storm’s wake, and the high elevations of western New York, Pennsylvania, western Maryland and West Virginia could see some snow Monday morning.
D.C. and Baltimore area forecast
Rain is expected to begin during the predawn hours Sunday, picking up early Sunday morning, when it may be heavy for a time.
From Sunday late morning to Sunday evening, there are two scenarios:
1. The rain tapers off by midafternoon — which is predicted by the American model.
2. The rain eases for a time late morning into the midafternoon, before picking back up — heavy at times — well into the evening, tapering off around midnight. The European model forecasts this situation.
Rainfall totals in the first scenario would average 0.5 to 1.5 inches, but could double in Scenario 2, reaching the 1 to 3 inches range.
American model rainfall forecast
European model rainfall forecast
The European model forecasts more rain, lasting longer, because it intensifies the storm more quickly and closer to the coast. The American model doesn’t strengthen the storm until it has mostly passed the D.C. region — so most of the rain it forecasts is limited to whatever the cold front produces early in the day.
Our forecasts over the weekend will update on which model and scenario is most likely — but plan on Sunday being rainy and unfit for most outdoor plans.
It will become increasingly windy Sunday — with gusts of 20 to 30 mph in the morning and afternoon, increasing to 30 to 40 mph in the evening.
Temperatures are also going to turn quite chilly. While they may start the day in the 60s, as those winds crank up from the north and northeast, they will drop through the 50s during the day.
With that strong wind coming in Sunday evening, for the first time this season it will feel like winter.