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Hurricanes act much the same as high latitude
depressions when it comes to force of their winds, and the dangerous
and navigable semicircles.
There are two reasons
for this. First, on the dangerous side of the storm, to escape from
the track of the storm and the dangerous center you must beat or
power into the winds and seas. On the navigable side, the wind is
at your back as you are running away from the storm center.
Then there are the
winds. What you feel on the boat is a function of the wind that
is circulating around the storm center and the increase or decrease
due to the direction in which the storm is traveling.
On the dangerous side
of the storm the winds are circulating at angles that are complemented,
and reinforced by the speed of travel. On the navigable side of
the storm, the speed of travel is opposite the circulating wind
direction and so reduces the wind you feel.
In the Northern Hemisphere,
if you face the storm center and the storm is coming right at you,
the dangerous quadrant is to your left and the navigable quadrant
is to your right. In the Southern Hemisphere, the dangerous quadrant
is to your right when you face the storm, and the navigable quadrant
is to your left.
Before we get carried
away with terms like dangerous quadrant and navigable quadrant,
keep in mind that these are relative terms. What is dangerous or
navigable is very much a function of the storm structure and distribution
of winds around its center. It is also a function of the seaworthiness
of vessel and crew.
It is far better to
take avoiding action early enough in the encounter so that the storm
passes harmlessly far enough away so as to make this discussion
academic.
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Finding
the navigable quadrant of a hurricane--face the storm center:
- In the
Northern Hemisphere the navigable quadrant is to your right.
- In the
Southern hemisphere the navigable quadrant is on your left.
What is
dangerous or navigable is very much a function of the storm structure
and distribution of winds around its center.
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In the Northern Hemisphere, hurricanes
rotate counterclockwise around their centers. Looking at
this top view of the storm, you can see that on the right-hand
side of the storm, the wind is blowing in the same direction
as the storm is traveling. When you feel this wind pressure
on a boat you have the total of the circulation winds about
the center plus the direction of travel speed.
If the wind were circulating at 100 knots,
and the storm moving at 15 knots, you would feel 115 knots
of wind force. On the left side you subtract motion speed
from wind speed, so in this example you would feel 85 knots.
In the Southern Hemisphere, winds circulate
clockwise around the low center (bottom drawing). In this
case, the dangerous side is to the left when looking at
the storm from the top. Here you add the speed of travel
to the circulating wind speed on the left side and deduct
it on the right-hand side.
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