A storm attempting to garner tropical characteristics will brush the mid-Atlantic coast and sweep over New England Friday into Saturday with locally heavy rain and flooding risk.
While widespread flooding problems are not expected in the Northeast, a system from the Gulf of Mexico will travel northeastward along the coast to bring tropical downpours and urban flooding concerns to end the week.
Travel delays from blinding tropical downpours, poor drainage area flooding and locally gusty thunderstorms are possible. A brief period of stiff winds will sweep northward, brushing the coast.
Coastal Rain, Urban Flooding
The heaviest rain from the Gulf system will likely swing east of Washington, D.C., and perhaps Philadelphia. However, disruptive downpours can occur around New York City, Boston, Hartford, Providence, Portsmouth, N.H., and Portland, Maine.
Indications are most locations in this swath will be in for a 2- to 4-inch rainfall, but locally heavier amounts are possible.
Coastal Wind, Above-Normal Tides
A brief period of onshore winds will make for locally rough surf and strong rip currents. Bathers should exercise caution Friday and Saturday as the system approaches then swings by.
A water rise causing significant coastal flooding is not expected, due to the increasing forward speed and relatively weak nature of the tropical part of the system.
However, tides will be higher than average for the month with the new moon Saturday. Brief, minor flooding at time of high tide is possible later Friday into Saturday morning. Water levels can be as high as a foot or two above published levels.
Appalachian Rain, Flooding Concerns
Another component of the rain will be from a storm system moving in from the Midwest. The combination of tropical moisture and the presence of the Midwest system can enhance rainfall over the Appalachians, potentially leading to localized flash and urban flooding problems. Rainfall in this area can top 2 inches in some locations.
Widespread flooding of streams and major river flooding are not expected, due to the forward motion of both systems.
In between both main areas of heavy rain on the coast and over the mountains, downpours which are more spotty in nature can also occur. However, rainfall will be on the order of an inch or less and could be under one-quarter of an inch in some locations.
Finally, the combination of the tropical part and non-tropical part of the storms can lead to locally strong thunderstorms, of which a handful could be severe at the local level. The greatest risk for locally severe thunderstorms would be near and just east of the track of the tropical system's center of circulation.
Incidents of power outages and property damage would be very sporadic and should be relatively minor. However, since forecasting the exact location of individual thunderstorms is nearly impossible days in advance, there is the risk of a severe thunderstorm hitting a major population center with more widespread consequences.
The bulk of the rain is forecast to have departed Long Island in time for the Belmont Stakes late Saturday. However, there is a risk of spotty showers in the area during the early evening.
Heavy rain and locally gusty winds and thunderstorms will focus over Nova Scotia, New Brunswick and Newfoundland Saturday night, as both the Midwest and Gulf systems merge into one.
On a positive note for lawn, garden and agricultural interests, the combination of the two storms will bring a dose of rain to many areas. Recent sunshine, low humidity and breezes have dried out the topsoil leaving shallow root vegetation in need of moisture.
The bulk of the rain will leave the mid-Atlantic by Saturday morning and New England by Saturday evening. Showers more spotty in nature will trail, but will allow most outdoor activities to resume for the balance of the weekend.