For this strange practice we can actually thank Prohibition. Prior to prohibition, the Coast Guard (USCG) had more-or-less the same radio equipment as the navy: marine telegraph.. just Morse code.
So in 1924, about 3 years after crime surged, there was a response from the Coast Guard. They opened shore radio stations at a dozen ports: Fort Tilden, NY, Nahant, MA; New London, CT; Cape May, NJ; Cape Henry, VA; Fernandina, FL; Fort Lauderdale, FL; Mobile, AL; San Francisco CA; San Pedro, CA; Port Angeles, WA; and Anacortes, WA. All of this was to help handle all the communications from all of their new ships. More here.
here. NMF was decommissioned in November 18th, 1996. It's last broadcast words were as follows:
"Camslant Chesapeake this is commsta Boston, transferring communications watch at this time, over. Camslant's reply: "Roger, we have the watch, thank you for you dedicated service throughout the years - out."
The NMF calls are still used by NMN Chesapeake, VA when sending Boston Weatherfax. Some marine Radio texts, such as Reed's Nautical Almanac even note those calls for that purpose. NMG in New Orleans delivers similar maps by radio fax for the Gulf region. You can see the NOAA weather maps here.