Friday, September 17, 2021

Circular Storms

Erin lives in hurricane territory and I live in tornado country. Both are destructive weather events, but they differ in several aspects while sharing a few others.

Hurricanes generally emerge from the Atlantic Ocean (they're called typhoons if they are in the Pacific Ocean) and are huge storms that move fairly slowly carrying lots of rain and high winds. When a hurricane makes landfall it wreaks havoc over a wide area; “storm surge” is the term for waves carried along by the hurricane that are many times as high as normal waves, carrying seawater inland and adding to the flooding caused by the torrential rain. Hurricanes are classified by their sustained wind speeds rather than their footprint, making comparisons difficult; A concentrated, high-energy storm may cause more extensive damage in a smaller area but a slightly “weaker” storm that covers a wide area will cause more total damage. Think of it as a rifle versus a shotgun; you don't want to get hit by either one, but the rifle has a much narrower path of damage whereas shotguns can hit multiple targets.

Strength Classification
The hurricane classification system uses five “categories” of sustained winds stronger than a typical storm:

  • A Tropical Depression is a storm with sustained winds below 38 mph.
  • Between 39 and 74 mph, it's called a Tropical Storm.
  • Between 74 and 95 mph, it's a Category (Cat) 1 hurricane.
  • Between 96 and 110 is Cat 2.
  • Between 111 and 129 is Cat 3.
  • Between 130 and 156 is Cat 4.
  • Anything over 157 mph is Cat 5.

Planning & Preparation
Hurricanes damage a wide area with wind and water, making recovery a state-level project. Restoring power is one of the main goals of hurricane recovery, since a large area is impacted and it's usually a heavily populated area as well. 

Preppers need to be able to take care of themselves and their families for days or weeks with limited power, services and transportation. Warnings are normally given a day to a week before the storm hits, so you can decide to leave or stay and you have time to top off supplies.

Tornadoes are mostly a Great Plains weather event, as the conditions for their formation are unlikely in mountainous or forested areas. Hurricanes often spin off tornadoes to add insult to injury, so the two can be found together, but the singular or small cluster versions are more common in the Central Plains of the USA. Europe has smaller tornadoes and they're very rare, while those of us in Tornado Alley get multiple severe ones every year. Being far from the coasts, flooding is less of a problem, so most of the damage they inflict is from wind.

Strength Classification
Tornadoes are ranked by both wind speeds and damage potential. Named the Fujita (F) Scale after the scientist that created it, it's a scale from 0 to 5. Wind speeds are easy to measure, but damage is a bit more random, so the F scale is more of a “rule of thumb”.

  • A normal thunderstorm will usually have winds under ~70 mph, with little to no rotation of the storm. Once it starts spinning on itself, the winds pick up rapidly and things start to fly.
  • At 73 mph, we've hit F0 and can expect light damage to trees and buildings.
  • Between 74 and 112 mph it's an F1. Shingles start leaving roofs, cars are pushed off roads, and mobile homes become more mobile.
  • Between 113 and 157 mph it's an F2. Entire roofs are ripped off houses, train cars are knocked over, and large trees uprooted or snapped. Lawn furniture and light objects become missiles.
  • Between 158 and 206 mph it's an F3. Walls start following the roofs into the air, locomotives are pushed over, and flying cars become reality.
  • Between 207 and 260 mph it's an F4. Wood-frame buildings demolished, airborne missiles cause major damage.
  • Between 261 and 318 mph it's an F5. Entire houses lifted into the air, car-sized missiles created by debris are common.

Looking at the two scales, you'll notice some overlap in wind speeds. A Cat 4 hurricane has roughly the same winds as a F2 tornado, as an example. The two aren't comparable, though, because a Cat 4 hurricane will have a diameter measured in dozens or hundreds of miles while any tornado will be measured in feet or yards (the largest tornado on record was about 1.5 miles in diameter). Tornadoes also have drastically shorter lifespans and paths; while a hurricane can last for a few days and travel a few hundred miles inland before dying out, most tornadoes last only a few minutes and travel a few miles. Hurricanes grow slowly and are tracked as they approach land, but tornadoes pop up suddenly, almost at random, and are over by the time they start to be tracked.

Planning and Preparation
Tornadoes devastate a small area with winds up to twice as high as a hurricane. The damage is more concentrated and more severe, meaning recovery is either minimal or impossible. 

Utilities are normally restored within hours or days, but if your house was in the path it may not exist any more. I've seen neighborhoods after a tornado, and you can have a house standing there with minor roof damage next to a vacant lot where his neighbor's house used to be. 

Warnings are given only slightly before (and sometimes after) the tornado hits. When conditions are ripe for their formation the local weather-people will give the normal watch/warning speeches, but like the little boy who cried “Wolf!” they are ignored. Local warning sirens are the best we have, and they give you minutes (at best) to find shelter. Having a suitable shelter close by and good insurance is about all you can do to prepare for a tornado.

Hurricane season has a few months left, but tornado season is drawing to a close. We had a fairly quiet summer in my area this year but we're still dealing with damage from last year's “inland hurricane” that hit a wide swath of the state with Cat 1 winds. Keep an eye on the sky, and research the weather patterns for your area, so  that you are less likely to be caught by surprise.    

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