That's the normal header for declaring a Tropical Depression~Without Reconnaisance.
The mileage is probably due to the scaling and skew of the satellite images.
It gives a rough idea of the area, if you are in or near the depression though.
However...Most mariners and locals would probably know that a depression was forming from the winds and weather.

Interesting note. Jim Cantore just mentioned the three above systems on the Tropical Update on TWC.

Link for climatology of tropical systems passing through or near Martinuqe from 1888-1996.
http://www.cgste.mq/meteorologie/images/ouragan.gif