Hurricane Circulation and Movement
In the northern hemisphere, hurricane winds circulate around
the center in a counter-clockwise fashion. This means that the
wind direction at your location depends on where the hurricane's
eye is. A boat on the northern edge of the orange area in Hurricane
Fran (right) would experience winds from the east, while a boat
on the southern edge would have westerly winds.
Test Your Understanding: Which Way Is the Wind Blowing?
Track of Hurricane Gordon, 1994
A hurricane's speed and path depend on complex interactions
between the storm with its own internal circulations and the
earth's atmosphere. The air in which the hurricane is embedded
is a constantly moving and changing "river" of air. Other features
in that flow, such as high and low pressure systems, can greatly
alter the speed and the path of the hurricane. In turn, it can
modify the environment around the storm.
Typically, a hurricane's forward speed averages around 15-20
mph. However, some hurricanes stall, often causing devastatingly
heavy rain. Others can accelerate to more than 60 mph. Hurricane
Hazel (1954) hit North Carolina on the morning of 15 October;
fourteen hours later it reached Toronto, Canada where it caused
80 deaths. Some hurricanes follow a fairly straight course,
while others loop and wobble along the path. These seemingly
erratic changes are difficult to forecast and will be discussed
in more detail in the Forecasting section of this module.
The Right Side of the Storm
As a general rule of thumb, the hurricane's right side (relative
to the direction it is travelling) is the most dangerous part
of the storm because of the additive effect of the hurricane
wind speed and speed of the larger atmospheric flow (the steering
winds). The increased winds on the right side increase the storm
surge described in the Hazards section of this module. Tornadoes
are also more common here.
Looking at the figure above, pretend you are standing behind
the hurricane with your back to the steering flow. In this case,
the right side is the eastern section of the hurricane. (If
it were travelling east to west, the right side would be the
north section.) The winds around the hurricane's eye are moving
in a counterclockwise fashion.
At Point A, the hurricane winds are nearly in line with the
steering wind, adding to the strength of the winds. For example,
if the steering currents are 30 mph and the average hurricane
winds are 100 mph, the wind speed would be 130 mph at Point
A. On the other hand, the winds at Point B are moving opposite
those of the steering wind and therefore slow to 70 mph (100
- 30 mph). Incidentally, NHC forecasts take this effect into
account in their official wind estimates.