What indicates that a tropical cyclone may be within 500 to 1,000 miles of your position?

Correct Answer: Option B — A pumping of the barometer up and down a few millibars

A diurnal pressure wave disruption causing the barometer to pump up and down by a few millibars is a classic meteorological indicator that a tropical cyclone is operating within 500 to 1,000 miles of the vessel's position.