weather and water wisdom 261
Divide the number of seconds by 5, or
Multiply the number of seconds by 0.2.
You have timed the interval from boom to fl ash, and the time period is 26 seconds
26 ÷ 5 = 5.2 nautical miles.
You get the same result from using the second method
26 × 0.2 = 5.2 nautical miles.IS LIGHTNING HEADED YOUR WAY?
Storm clouds to the west or northwest of your position indicate that a storm
is headed your way. Take a series of bearings on successive bolts of lightning.
Constant bearings indicate the storm will pass overhead. If the storm lies to the
south or southeast, it should pass clear of you.
When a lightning storm approaches, monitor its progress by taking bearings on the
lightning strikes. Vessels A, B, and C are several miles apart. Th ey all sight a lightning
strike on the horizon at position 1. Using a handbearing compass and radar (if equipped),
each vessel tracks the lightning’s direction, or bearing drift (for more on bearing drift , see
Chapter 7), relative to their position. If unable to take a bearing at the moment of a strike,
they shoot the cloud surrounding the strike position. When lightning strikes at position 2,
vessel A notes that the bearing has changed to the left. Vessel B observes a bearing change
to the right. But vessel C shows a steady bearing. Th is indicates that the lightning is on a
collision course with vessel C. But vessels A and B should not relax yet. Th ey must continue
to take bearings until the lightning and associated clouds are well past their positions
(position 4). Vessel C must take evasive action now, changing course 90 degrees to the
north or south and increasing speed while continuing to take bearings visually and by
radar (if equipped) to ensure the bearing drift moves to the right or left.