What these rules mean
Some companies tell ships to start detailed avoidance planning once a tropical storm is inside 1500 nautical miles. The better-known 1-2-3 rule uses expanding danger circles of about 300, 600 and 900 NM around the forecast position at 24, 48 and 72 hours. The idea is to stay outside the circle that matches how far ahead you are looking. Storm forecasts can be wrong, so extra margin is wise.
How this checker works
Enter the present distance from the ship to the storm centre. The page shows whether you are inside the 1500-mile planning circle and inside the 1-2-3 radii. It does not plot the dangerous semicircle or the forecast track. Use official tropical cyclone warnings, the routing service and the Master’s decision.
Who should use it
Useful for a first look during passage planning. It is not a weather-routing service and it does not replace the company’s heavy-weather procedure.