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'TROPICS IN DEPTH' PART 3: Becoming a Major Hurricane

When hurricanes become a Category 3 or greater, we are talking about a potentially life-changing event.

Last week, we focused on systems that have the key in the ignition and look as if they are ready to wrap up. Most likely, these are the sort of systems in which watches and warnings may be issued. 

But this week, we are taking things a step further and taking a look at major hurricanes.

Hurricanes have five categories. Category 1 and Category 2 are both serious events. The scale of damage for these storms in exponential, not linear.

Once a storm reaches the status of a Category 3, 4, or 5, we are talking about a potentially life-changing event for an entire community.

The average first major hurricane of the year occurs on Sept. 4. This is because that is when the oceans are the warmest. Climatologically speaking, the second major hurricane of the year occurs around Oct. 3.

SIDE NOTE: On average, there are 10-11 named storms in an Atlantic hurricane season. Of those 10-11, 5-6 of them become hurricanes. Then, of those 5-6, only 1-2 of them typically strengthen to a major hurricane.

It doesn't just take warm oceans to help a hurricane turn major. It also takes ventilating winds at 30,000 feet.

1. A major hurricane will only occur with high pressure on top of low pressure.

  • This is the only low pressure system on Earth like this!
  • An environment with little to no wind shear helps storms organize best and get their act together. However, anti-cyclonic flow is one step beyond this.
  • A tropical cyclone with anti-cyclonic flow means the system is able to breath. It's like opening the vent to a fireplace.
  • The heat system then has the ingredients in place to become one of the most ferocious natural events on Earth.

2. The clear eye and completed eyewall is visual verification of a major hurricane.

  • When a major hurricane is breathing healthy thanks to anti-cyclonic flow and is vertically stacked thanks to low wind shear, rapid intensification can and oftentimes occurs.
  • This is truly like the movies when a storm strengthens significantly with every National Hurricane Center update. Even meteorologists get a pit in their stomach when they see the evidence from Hurricane Hunter data, satellite images, or radar.
  • Rapid intensification, by definition, is an increase in the maximum sustained winds of a tropical cyclone of at least 30 knots, or 35 mph, in a 24-hour period.

3. Rapid intensification does not last forever and is actually an unstable environment for cyclones.

  • After some time during rapid intensification with major hurricanes, a double eyewall will form. We call this eyewall replacement.
  • This typically signals a halt to any further rapid intensification.
  • While the intensity of the major hurricane may have seemed like it has hit its peak, the scope of impacts expands.
  • Storm surge can become much larger. Even the storm itself can become much larger after eyewall replacement.

Also to note, the warmer the ocean is down to 600 feet below sea level, the higher the risk for major hurricanes and rapid intensification to occur.

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