Meteorology · Tropical Cyclones — 1-2-3 Rule
The mariner's '1-2-3 rule' for tropical cyclone avoidance refers to:
- AWind speeds of 1, 2, and 3 knots
- BThe forecast track error radius added at 24, 48, and 72 hours (roughly 100, 200, 300 nm)✓ Correct
- CThree days of fuel reserve
- DBarometer readings
Explanation
The 1-2-3 rule adds the historical forecast-track error to the storm's wind radius — about 100 nm at 24 h, 200 nm at 48 h, 300 nm at 72 h — to define a danger area to avoid.
Authority: NWS/NHC mariner guidance; Bowditch (Pub. No. 9)
Practice the full Meteorology bank
Free spaced-repetition quizzing across 2190 USCG exam questions — it schedules your reviews so the ones you miss come back until they stick.
Related Meteorology questions
- Atmosphere & Pressure
Standard atmospheric pressure at sea level is approximately:
- Atmosphere & Pressure
One millibar (mb) is equal to:
- Atmosphere & Pressure
A barometer that is falling rapidly most likely indicates:
- Atmosphere & Pressure
On a surface weather chart, isobars spaced very close together indicate:
- Wind
By convention, a wind is named for:
- Wind
In the Northern Hemisphere, the Coriolis effect deflects moving air: