Hurricane Zeta’s winds caused tornado-like damage; where the strongest winds occurred and why

Hurricane Zeta's winds produced tornado-like damage

BILOXI, Miss. (WLOX) - Hurricane Zeta left a path of widespread damage as it zipped through South Mississippi Wednesday night, October 28, 2020.

While much of the damage resembled that of a tornado, it was mainly caused by Zeta’s hurricane force winds that carved a path through much of Hancock, Pearl River, western and northern Harrison, Stone, and George counties. According to the National Hurricane Center forecast Advisories issued as Zeta tracked through, the core of the hurricane force winds clipped Jackson County, but there were still damaging winds that caused considerable damage.

While it is possible there may have been a few tornadoes, the National Weather Service in Slidell and Mobile say the damage seen in South Mississippi is on par with a Category 1 and 2 hurricane. Preliminarily, there have been no confirmed tornadoes by either National Weather Service office. Much of the winds experienced in South Mississippi was close to an EF-1 tornado. That’s winds 86-110 mph, resulting in tornado-like damage.

Hurricane Zeta Wind Field shows a swath of damaging hurricane force winds (red) along and east of the track.
Hurricane Zeta Wind Field shows a swath of damaging hurricane force winds (red) along and east of the track. (Source: WLOX)

Why were Zeta’s winds so strong?

It was a fast mover. Racing 20-30 mph through South Mississippi with little time to weaken from its landfall around 5 PM Wednesday in Terrebonne Parish, Louisiana.

It was large. Tropical storm force winds extended about 140 miles away from the center. Large storms unravel slower as they travel across land.

South Mississippi was on the right side of the center. Its trajectory through Slidell into Hancock and Pearl River counties uniquely positioned South Mississippi on the side of the storm where the winds were blowing towards the same direction the storm was moving. The combined effect of the fast forward motion and the strong winds on the right side of the storm led to strong winds well inland into Stone and George Counties.

Maximum wind speed and wind gusts on October 28, 2020. While wind measurements could have been higher in other places, unfortunately, there are not anemometers in every back yard across South Mississippi to record and report winds.
Maximum wind speed and wind gusts on October 28, 2020. While wind measurements could have been higher in other places, unfortunately, there are not anemometers in every back yard across South Mississippi to record and report winds. (Source: WLOX)
Maximum wind speed and wind gusts on October 28, 2020. While wind measurements could have been higher in other places, unfortunately, there are not anemometers in every back yard across South Mississippi to record and report winds.
Maximum wind speed and wind gusts on October 28, 2020. While wind measurements could have been higher in other places, unfortunately, there are not anemometers in every back yard across South Mississippi to record and report winds. (Source: WLOX)
Maximum wind speed and wind gusts on October 28, 2020. While wind measurements could have been higher in other places, unfortunately, there are not anemometers in every back yard across South Mississippi to record and report winds.
Maximum wind speed and wind gusts on October 28, 2020. While wind measurements could have been higher in other places, unfortunately, there are not anemometers in every back yard across South Mississippi to record and report winds. (Source: WLOX)

The damage was bad, was it really JUST a Cat 1 or 2?

The Saffir-Simpson Scale, which rates hurricanes by wind ranks category 1 and 2 hurricanes with winds between 74-95 mph and 96-110 mph.

According to the Saffir-Simpson Scale, this is what a category 1 hurricane can do:  Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap, and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days.

Category 2: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks.

Winds damage increases exponentially

If you double the winds inside a hurricane from 75 mph to 150 mph. The damage it does is not doubled. As winds increase, damage potential increases exponentially. So, doubling from 75 mph to 150 mph would actually cause 256 times the damage.

A category 1 hurricane with 75 mph will cause widespread wind damage. However, a category 1 hurricane with 95 mph winds will cause almost 7 times as much wind damage as the 75 mph storm.

So, Zeta was a low-end category 2, high end category 1 hurricane when it came through. That means it caused 7 to 10 times as much damage as a minimal category 1 hurricane or strong tropical storm would have.

The wind damage potential with hurricane force winds increases exponentially. In other words, small increases in wind lead to very large increases in the damage it can cause.
The wind damage potential with hurricane force winds increases exponentially. In other words, small increases in wind lead to very large increases in the damage it can cause. (Source: National Weather Service)

Mesovorticies

Inside hurricanes, small-scale areas of concentrated spin rotate around the eye-wall. These are called mesovorticies. As hurricanes move inland, friction from land interaction can cause these to transport higher, swirling winds down to the surface. They can lead to isolated areas of increased wind damage and can resemble that of a tornado.

Hurricane Zeta Radar Loop October 28, 2020
Radar image of Hurricane Zeta moving into South MS after 7 PM as a Category 2 hurricane with 100 mph. The eye wall was moving into Hancock, western Harrison, and Pearl River Counties.
Radar image of Hurricane Zeta moving into South MS after 7 PM as a Category 2 hurricane with 100 mph. The eye wall was moving into Hancock, western Harrison, and Pearl River Counties. (Source: WLOX)

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