ABSTRACT
The 1-2-3 rule consists in extending the forecast storm field of the cyclone with an approximated value of the forecast error based on 10 years of the relevant forecast time interval. The rule is recommended for the North Atlantic waters, but it can be easily adopted for other sea areas.The mean error of a given forecast is added to the largest forecast radius of the stormy area. Consistently, 100 Nm distance is added as the forecast error to the longest radius of the stormy area for 24 hour forecast for all quadrants. Similarly, 200 Nm is added for 48 hour forecast and 300 Nm for 72 hour forecast. The method does not take into consideration effects of sudden change in the intensification of the cyclone system, which consequently extends the stormy zone of winds≥34 knots. Besides, it does not account for the cyclone changes into extra-tropical stages, which also result in sudden changes of storm force winds. Additionally, it is recommended in the method description to further extend the dangerous area without specifying any values, particularly when forecasts are highly unreliable, captain and crews’ experience is limited, the vessel’s seaworthiness is restricted or there are other limiting factors defined by the captain. Therefore, the method does not precisely determine the area to avoid. If we combine the principle of avoiding the storm area where windW ≥ 34 knots with the extended zone where risk is high, we obtain a danger area to avoid by applying the 1-2-3 rule (Fig. 1) [1].
