From the National Weather Service:
Special Weather Statement National Weather Service Boston/Norton MA 906 PM EDT Tue May 15 2018 MAZ020-022>024-RIZ006>008-160400- Southern Bristol MA-Barnstable MA-Dukes MA-Nantucket MA- Washington RI-Newport RI-Block Island RI- Including the cities of Fall River, New Bedford, Chatham, Falmouth, Provincetown, Vineyard Haven, Nantucket, Narragansett, Westerly, Newport, and New Shoreham 906 PM EDT Tue May 15 2018 ...ABNORMAL OCEAN SURGES ARE EXPECTED THIS EVENING ALONG THE OCEAN_EXPOSED SOUTH COAST OF MASSACHUSETTS AND RHODE ISLAND... Air pressure sensor and tide gage readings near Block Canyon off the Mid Atlantic coast indicated that a weather-generated abnormal rise is water levels was triggered by a storm system as it moved over the ocean. Water level fluctuations of several inches to one foot above normal tide in localized areas can be expected at the shore for the next several hours as a series of surges strike the coast. While No coastal flooding is expected, the strong currents associated with these surges could pose danger to those in or near the water. Recommended actions are listed below. Impacts are expected along the ocean-exposed south coast of Massachusetts and Rhode Island. Boat owners... * Prepare now for the following hazards... * Strong, unpredictable currents. * Surging up to one foot above normal sea level. Swimmers, surfers and boaters... * It is recommended you leave the beach now to avoid the following hazards... * Strong currents. * Potentially dangerous surges of water. This kind of tsunami is generated by abrupt changes of atmospheric pressure in the causative storm system, which is a line of thunderstorms that moved over the ocean in this case. The combination of the air pressure effect on the ocean surface, and the speed at which the pressure disturbance travels, can generate abnormal waves in certain situations. The National Tsunami Warning Center is monitoring this event. Additional statements will be issued if necessary through National Weather Service Office Forecast Office in Norton, MA.