Typhoon on the track ahead

Work it out rather than guessing from the wind alone.

Relative position. From 16°00'N 128°00'E to 14°30'N 131°00'E:

• Difference of latitude: 1.5° = 90 nm south.
• Difference of longitude: 3.0° at mean latitude 15.25°, so 3.0 × 60 × cos 15.25° = 180 × 0.965 = 173.7 nm east.
• Distance = √(90² + 173.7²) = √(8,100 + 30,172) = 196 nm.
• Bearing = 180° − arctan(173.7/90) = 180° − 62.6° = about 117°, that is east-south-east, 196 nm.

Buys Ballot check. In the northern hemisphere, standing with your back to the wind, the low is on your left. The wind is from 045°, so it travels toward 225°; 90° to the left of that is 135°. That agrees with the calculated 117° within the usual tolerance - the two methods confirm each other.

Semicircle. The storm track is 292°. The bearing of the ship from the centre is 117° + 180° = 297°, which is within a few degrees of the track direction. The ship is essentially dead ahead of the centre and slightly on the right-hand side of the track: the dangerous semicircle in the northern hemisphere, and in the path of the storm.

Wind sequence. In the dangerous semicircle the wind veers as the centre approaches and passes to the south: north-east, then east, then south-east, then south. Watch for the veer; it confirms the diagnosis. A backing wind would mean the centre is passing north of the ship.

The ship is 196 nm from a 90-knot typhoon that is closing, inside or at the edge of the 34-knot radius, and steering 070° straight toward the track. Doing nothing is the worst option: at 14 knots on 070° the ship gains about 4.8 nm per hour of northing and 13.2 nm per hour of easting, while the centre gains 4.5 nm per hour north and 11.1 nm per hour west - the ship closes the range.

Recommended action: alter to the northward, to about 350° to 010°, at best speed.

• This puts the north-east wind on the starboard bow, which is the classic northern-hemisphere handling in the dangerous semicircle, and it opens the distance between the ship and the forecast track.
• With a 14-knot ship against a 12-knot storm, the northward separation can be built at roughly 9 to 10 nm per hour once the vectors are resolved. Twelve hours of that gives about 110 nm of margin.
• The alternative - running south or east to pass behind the storm - means crossing ahead of the track and through the core. Reject it.

Supporting actions:

• Secure for heavy weather now: lashings checked, deck cargo re-secured, derricks and hatch covers, all watertight and weathertight closures, crew off the forecastle, engine room at standby.
• Three-hourly plots of the centre, not six-hourly, on the same chart, and plot the closest point of approach.
• Watch the barometer trend; a falling rate that accelerates means the centre is still approaching.
• Inform the company and, if the track becomes a direct threat, send an urgency broadcast.
• Have a shelter port identified before it is needed, in case the track shifts east.

The plan rests on a forecast position that is already up to six hours old and a track that will not be perfect. A 24-hour official track forecast carries a typical error of 100 nm or more, and the radius of 34-knot winds can be under-forecast. The typhoon warning is a snapshot, not a truth.

How to manage that:

1. Do not run the plan to the last mile. Keep a lateral margin between the ship and the forecast track that is larger than the expected track error - 100 nm or more if possible - and do not close that margin for commercial convenience.
2. Verify from the ship. Barometer trend, wind direction and force, swell direction, and cloud type. A heavy swell whose direction does not match the local wind is coming from the storm and is the most reliable early indicator of where the centre lies. Log the observations.
3. Replot on every new warning and reassess the evasion course each time; do not assume the first decision holds.
4. Recognise the asymmetry case. If the wind stops veering and begins to back, the centre is passing on the other side and the geometry has changed; the safe course changes with it.
5. Keep the engine room informed of the possibility of a long period at full power and the fuel implications for the diversion.

Finally, note that the vessel's speed advantage is small. If the ship can only make 12 knots for any reason - heavy weather, engine margin, fouled hull - the plan no longer separates from the track and the master must look for shelter rather than trying to outrun the storm.