Boston NPR news station 90.9 WBUR-FM is wading into the Cape Cod resort market and going toe-to-toe with WGBH’s network of stations with its planned purchase of 92.7 WMVY-FM on Martha’s Vineyard. WBUR is buying the Tisbury, Mass.-based station for an undisclosed amount from Housatonic, Mass.-based Aritaur Communications Inc. The sale is expected to close in early 2013 pending FCC approval. Now broadcasting an adult alternative format, WMVY, known as mvyradio, will switch to WBUR’s news format, reaching up to 60,000 listeners with a 3,000-watt signal. The market includes Cape Cod, Martha’s Vineyard, and coastal towns including New Bedford, Fall River, Falmouth and Westport. “We believe that the islands, Cape Cod and SouthCoast are important parts of the community we cover and serve,” said WBUR General Manager Charlie Kravetz, in a statement.