Category strengths of a hurricane and wind shear ... How do they relate?

HNN provides hourly updates on Facebook and the mobile news app. (Image: Hawaii News Now)
HNN provides hourly updates on Facebook and the mobile news app. (Image: Hawaii News Now)
Updated: Aug. 23, 2018 at 1:22 AM HST
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HONOLULU (HawaiiNewsNow) - With Hurricane Lane breathing down Hawaii's neck, it's important to know how strong the storm is and the factors surrounding the system.

The first thing to note is the difference between the various hurricane strengths and categories 1 through 5.

It's simple: The higher the number, the stronger the storm. Here's how the categories breakdown:

  • Tropical Storm: Heavy rain, gusty winds between 39 and 73 mph.
  • Category 1: Winds between 74 and 95 mph.
  • Category 2: Winds of 96 through 110 mph.
  • Category 3: Sustained winds of 111 through 129 mph. (Hurricanes Category 3 and higher are considered "major" hurricanes.)
  • Category 4: Strong winds sustained between 130 and 156 mph.
  • Category 5: This is the top of the scaled, the strongest a storm can get with winds sustained of 157 and higher.

Hurricane Lane alarmingly reached Category 5 strength briefly on its path toward Hawaii. The National Weather Service said Lane was just the second Category 5 storm to come within 350 miles of Hawaii since Hurricane John in 1994.

Factors for hurricanes to strengthen include warm sea surface temperatures (80 degrees Fahrenheit and higher), and a lack of wind shear.

Wind shear is important to the life (or death) of a storm. Little to no wind shear means a hurricane has a better chance at living and strengthening while strong wind shear can completely rip a storm apart.

Shear is defined as, "A change in wind speed and/or direction over a short distance. It can occur either horizontally or vertically and is most often associated with strong temperature inversions or density gradients," according to the FAA.

In the case of Lane, forecasters are counting on the shear to weaken the system before it comes too close to the islands Thursday into Friday.

"If you have winds aloft, that kind of acts like a blender that will disrupt the structure of the system," HNN Meteorologist Jennifer Robbins explained in this Facebook live report. "That's what we want to weaken the system."

Forecasters say the area where Hurricane Lane was on Wednesday night was in an area of moderate shear — but it wasn't enough to kill the storm significantly.

Instead, later in the week, forecasters expect Lane to encounter a stronger area of shear from the north. That's when the winds will hopefully rip the storm down to a Category 3, then a Category 2 and eventually a Category 1.

Be sure to stay with Hawaii News Now for the latest developments on Hurricane Lane.

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