Winds within a hurricane – both sustained winds and gusts – are
generally strongest in and near the eye wall, with wind speeds decreasing with distance from the center of the storm. The smaller
the hurricane, the more quickly winds decrease with distance.
For example, despite its Category 5 intensity, Hurricane Andrew
– a notoriously compact storm – had hurricane-force winds that
extended outward only 30-45 miles. Hurricane Irma’s hurricane-force winds extended outward more than twice that distance.
Tornadoes most often occur far from the center of a hurricane, in
the outer bands of thunderstorms that sweep counterclockwise
away from the eye. The vast majority of these tornadoes develop
in the right-front quadrant of the storm, relative to its direction
of motion. During Hurricane Irma, 23 tornadoes were identified
across the state of Florida – all of them in areas impacted by the
right-front quadrant of the storm – and all but four tornadoes
occurred along the Atlantic coast of the state.
Tornadoes that form in association with hurricanes are generally short-lived and relatively weak. Although they tend to form
near the coast, they can certainly occur further inland: during
Hurricane Harvey, more than two-dozen tornadoes were reported
in and around Houston, Texas. Some were nearly 80 miles inland.
Straight-line wind speeds can be assessed through in-situ
(weather station) observations, post-storm damage surveys and
weather radar data. Each data source has its own advantages and
disadvantages, so to obtain the most comprehensive and rigorous reconstruction of wind conditions, use all three data sources.
Weather station data provides on-the-ground observations (as
long as they continue operating during the peak of the storm),
while damage surveys assess the aftermath to determine the
wind speeds necessary to produce the observed damage. In areas
removed from weather stations or population centers, weather
radar offers data on winds aloft that can be extrapolated to esti-
mate winds near the surface.
The location and intensity of tornadoes are assessed through
storm reports, damage surveys and radar data.
As Hurricane Harvey demonstrated to devastating effect in August of last year, rainfall-induced flooding can be at least as destructive as extreme winds during tropical cyclones.
Although the more-than-four-feet of rain that Harvey
squeezed out of the skies over Texas was truly unprecedented,
most tropical cyclones produce prolonged, heavy rainfall that
can lead to flooding both during and after the storm, often far
inland of the landfall location.
Slower moving storms – which are often weaker in terms of
maximum wind-speeds – tend to produce greater flooding, as
do storms whose paths hug the coast, allowing the hurricane
to continue feeding on warm ocean waters while simultaneously dumping its precipitation load over land. Hurricane Harvey was a near-perfect example of the destructive potential of a
slow-moving, coast-hugging storm.
In-situ rain gauge data provide measured rainfall totals at specific
locations. In urban areas rain gauges may be only five to 10 miles
Rainfall-induced flooding in Simonton, TX, 40 miles
west of downtown Houston. The image to the left
shows Simonton before Hurricane Harvey while the
image to the right shows the town immediately after
HURRICANE HARVEY FLOODING
ATLANTIC TC DEATHS