(WGHP) – Met Hurricane Milton in the Gulf of Mexico and several southeastern cities clearing from Helene, meteorologists have used several important weather terms that are difficult for the average person to understand.
Let’s take a look at some common words and phrases that are repeated repeatedly during this busy week of hurricane season.
Structure of a hurricane: eye, eyewall, outer bands
A hurricane consists of three basic parts: the eye, the eyewall and the outer rain bands.
The eye of a hurricane is the clear and calm central part of a hurricane. It looks like a ‘hole’ in the center of the storm. The inside of the eye is usually associated with light winds and fair weather.
A small eye usually means the hurricane is stronger. This is because it can rotate faster around the center point.
Think of it like a figure skater spinning around. If they bring their arms closer to their bodies, they can spin faster. The faster a storm can rotate around a center, the stronger the winds with the system can be.
The eye wall of a hurricane is the ring of thunderstorms that surrounds the eye. The eyewall has the strongest wind and heaviest rain. The eyewall and eye can enlarge or shrink, and when these changes occur it can affect the storm’s wind speeds, which is a measure of the storm’s intensity/strength.
We’ll talk more about the changes in eye/eyewall size and its impact on the strength of a hurricane in the region. eye wall replacement cycle section.
The outer bands of a hurricane are actually the rest of the storm. They are the areas of rain, storms and clouds that are further from the center of the storm and resemble a spiral.
The outer bands can produce very heavy rain showers, as well as strong winds and tornadoes. However, sometimes there are gaps between the rain bands, where there is no rain and the wind may be lighter.
Maximum sustained wind versus gust
Maximum sustained wind is the highest steady wind that lasts for at least 20 seconds and is measured at 33 feet above the surface. The maximum sustained wind determines the strength of a hurricane on the Saffir Simpson bowl.
A gust of wind is a sudden increase in wind speed that is at least 10 miles per hour faster than the sustained wind and lasts less than 20 seconds.
Saffir Simpson bowl
The Saffir Simpson bowl is the rating system for hurricanes based on their sustained wind speed.
A Category 1 hurricane has wind speeds of 120 to 150 km per hour.
A Category 2 hurricane has wind speeds of 96 mph to 180 mph.
A Category 3 hurricane has wind speeds of 180 to 200 km/hour.
A Category 4 hurricane has wind speeds of 210 to 250 km/hour.
A Category 5 hurricane has wind speeds of more than 250 km per hour.
Any hurricane rated Category 3 or higher is considered a hurricane major hurricane.
Cone of uncertainty
The cone of uncertainty is the name for the predicted path of a hurricane or tropical system, issued by the National Hurricane Center.
The cone only shows the most likely path from a hurricane’s center. It doesn’t show how big a hurricane is, or how far its effects can extend from the center.
The forecast path shows the trajectory every 12 hours until three days before landfall and then at 24-hour intervals for five days before landfall.
If the edges of the cone are closer together, it means forecasters have more confidence in the path the storm’s center will take. Whereas, if the two parties are further apart, it means there is little confidence in the path.
The cone of uncertainty is updated every six hours by the National Hurricane Center. The updates will take place at 5:00 AM, 11:00 AM, 5:00 PM and 11:00 PM. However, updates on the storm’s intensity occur every three hours.
Sea surface temperatures
The surface temperature of the sea water is the temperature of the upper meters of the ocean. It is influenced by the sun, wind and ocean currents.
Hurricanes need warm ocean water to develop. Typically, tropical systems require temperatures around 80 degrees or warmer from the surface to 50 meters below.
The warmer the surface temperatures of the sea water and the deeper these warm temperatures go below the surface can provide ‘fuel’ in the form of heat and moisture for the development of hurricanes.
Wind shear
According to the National Weather Service, wind shear is the change in wind speed and direction over a short distance. It has a major impact on hurricanes and tropical systems.
Strong wind shear means that there are constant changes in wind speed and direction in an area. This can essentially “tear up” or “tear apart” a hurricane. Weak wind shear is an essential part of the development and survival of a tropical system.
Wind shear affects the winds in a tropical system and the way heat and moisture are transported within the hurricane. This disruption of energy transfer essentially kills a tropical system.
Storm surge
According to NOAA, storm surge is the abnormal rise in sea level that occurs during a hurricane and is caused by strong winds pushing water toward the coast.
Storm surge is measured as the height of the water above the normal tide. The height of the storm surge at any location depends on the shape of the coastline, the course of the storm and the intensity, size and speed of the storm.
According to FEMAThe storm surge is known to travel 25 miles inland, completely submerging cars and inundating homes. The storm surge with Hurricane Ike in 2008 reached as far as 30 miles inland.
If the land is below sea level or relatively close to sea level, a storm surge can reach further inland.
To calculate what the storm surge might be at your location, you need to know what the National Hurricane Center’s predicted peak storm surge at sea level is, as well as your location’s elevation above sea level. The predicted peak storm surge at sea level minus your location’s elevation above sea level equals the predicted storm surge at your location.
For example, if the National Hurricane Center predicts a storm surge of 8 feet at sea level and your home is 4 feet above sea level, then the predicted storm surge at your location is 4 feet.
Rapid intensification
Rapid intensification is defined by the National Hurricane Center as an increase in the maximum sustained wind of a tropical system with at least 55 km/h in a 24-hour period.
An increase in wind speeds of 55 km per hour would change the strength of a hurricane from one category to another. Saffir Simpson bowl.
An example would be if a hurricane had winds of 90 miles per hour and increased to winds of 125 miles per hour. That’s an increase from a Category 1 hurricane to a major Category 3 hurricane within 24 hours.
Certain conditions are needed for a storm to intensify quickly. Those conditions are, among other things, weak wind shearlots of moisture and warm sea surface temperatures (more than 80°).
All of these weather conditions were in place as we saw Hurricane Milton rapidly intensify this week.
In fact, Milton rapidly intensified from a Category 1 hurricane to a Category 5 hurricane in just 18 hours, making it the third fastest rapid intensification in the Atlantic Ocean, behind Wilma (2005) and Felix (2007).
Eye wall replacement cycle
In strong tropical systems, the outer rain bands can form an outer ring of thunderstorms that moves toward the center, drawing moisture from the hurricane’s main eyewall and causing the eyewall to “collapse” in on itself.
As this happens, the hurricane weakens and the new eyewall “replaces” the original. Once the replacement has occurred, the storm returns to its original strength or may even become stronger.
This process of forming a new eyewall from outer rainbands, coupled with the weakening and strengthening of a tropical system, is known as the eye wall replacement cycle.
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