In maritime radio communications, what is the hierarchy of urgency among the standard procedural words 'MAYDAY', 'PAN PAN', and 'SECURITE'?

1. SECURITE is the highest distress priority, followed by PAN PAN, then MAYDAY
2. PAN PAN is used only for weather forecasts, while SECURITE is for fire
3. MAYDAY indicates grave and imminent danger threatening life or vessel; PAN PAN indicates an urgent situation concerning vessel/person safety; SECURITE indicates a navigational or meteorological warning
4. All three signals mean exactly the same thing and can be used interchangeably