This diagram shows a simplified version of a nor'easter approaching Massachusetts. The winds are blowing counter-clockwise around a low pressure system that has worked its way up the Atlantic seaboard. The storm system pulls water out of the Atlantic and dumps it (in the form of rain or snow) on the mainland. Nor'easters vary in size and can be as much as 1000 miles across. If a stationary high pressure system is off the coast, the low pressure system can stall and remain in position over New England for several days. These sustained onshore winds usually bring the most seabirds close to land, including, on occasion, the continental slope inhabitants. 
     As the storm system approaches New England the southeast coast of Rhode Island is receiving winds from the east and southeast. Point Judith in southeast Rhode Island is a good location to conduct a sea watch during these conditions.

In this diagram we see that the nor'easter has moved closer to the Massachusetts coastline. The islands of Martha's Vineyard and Nantucket are bearing the full force of the southerly winds on the leading edge of the storm system. It is precisely during conditions as these that numbers of Cory's Shearwaters may be seen off the southern shores of these islands.  Cory's Shearwaters breed in Equatorial waters, and are usually encountered after their breeding season. They prefer the warmer waters south of Massachusetts, and are possible from July to early November, some years in greater number than others, depending on the availability of prey food.

If this hypothetical storm traveled due east, the eastern shores of Cape Cod would be receiving easterly winds. These conditions are favorable for bringing seabirds closer to shore for viewing from land. Chatham is one such location. 

In this example we see the effects of a classic nor'easter. Easterly winds are blowing directly at Cape Ann. There is a good chance that seabirds are being blown toward land. Halibut Point and Andrews Point in Rockport are two locations to conduct a seawatch during these conditions. The northeasterly winds of the storm are also beginning to blow into Cape Cod Bay. Seabirds may get blown into this natural basin and fly in a counter-clockwise location looking for exit to the open ocean. There is a good chance that observers at Sandy Neck in Barnstable  will be getting good views of a variety of pelagic birds. 

As time passes the storm system moves further out to sea. Now the winds are directly northeast off of Cape Ann. If the system is stalled for a few days and the easterly winds continue, there is always the possibility that the pelagic birds usually found along the continental slope will eventually be blown toward land.

Meanwhile, the winds have shifted to the northwest in Cape Cod Bay. The seabirds which are "trapped" in the bay will be blown toward Eastham and Wellfleet. Traditionally, if there has been a strong nor'easter overnight, birders will try to get to First Encounter Beach in Eastham at dawn to see these trapped pelagic birds seeking exit to the open ocean.

Richard S. Heil has conducted over twenty-five years of seawatches at Andrew's Point on Cape Ann. Of the many important observational discoveries he has made the following is of special interest.  When Cape Anne is receiving winds from the south, shearwaters and other pelagic birds often seek shelter in Ipswich Bay (located to the northwest of Cape Ann.) Here in these relatively calm waters the birds wait out the storm. After the winds have died down, the pelagics will return to the open ocean, often passing by Andrew's Point. Conditions as these can produce spectacular flights of shearwaters, and it is worth keeping abreast of weather conditions during peak migration times to increase ones chances of witnessing such a flight.