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    • The size and strength of Hurricane Milton are influenced by wind shear
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    The size and strength of Hurricane Milton are influenced by wind shear

    Kathleen William Posted on

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    To use a fairytale analogy, potentially catastrophic Hurricane Milton could face the weather equivalent of the Big Bad Wolf as it approaches Florida – wind shear.

    This interaction could bring mixed blessings. The strength of the storm, its wind speeds, and the width of its storm surge depend on whether the winds blowing across the Gulf of Mexico are strong enough to collapse its house (structure).

    If the winds facing Milton as it approaches Florida are strong enough to destroy its inner core, the storm's strongest winds could weaken somewhat, said James Franklin, a retired hurricane specialist division chief at the National Hurricane Center. At the same time, the hurricane could grow in size, pushing more water toward the coast in a wave of ocean water, Franklin said.

    In any case, Milton is expected to be a dangerous and strong storm.

    How do hurricanes form? An insight into the formation and power of violent storms

    How does a hurricane work?

    A hurricane is essentially a heat engine, Franklin told USA TODAY on Monday. “It removes heat from the ocean and the heat is released in thunderstorms around the eye. Additionally, the air moving downward in the eye generates heat as it descends.”

    “All of this heat is released and generated in and around the eye in a fairly narrow vertical column,” he said. This heat lowers the pressure and “keeps the engine running,” allowing the hurricane to thrive and grow.

    How could wind shear help or hurt?

    Wind shear occurs when winds near the storm collide with winds blowing at different speeds or directions.

    When those winds interrupt or shift the release of heat from a hurricane's relatively small vertical column and spread it over a larger area, the pressure in that inner core stops falling, Franklin said. If wind shear is strong enough, “it essentially blows away the head of the hurricane and you no longer have an effective heat engine.”

    Low wind shear is a trigger for hurricanes

    Milton's explosive increase in wind speed and strength and drop in pressure on Monday was a classic example of how a hurricane works in a low wind shear environment.

    Moving over very deep, warm water with low wind shear, wind speed increased by 85 miles per hour in just 12 hours and pressure dropped by a staggering 64 millibars, according to the hurricane center. (Lower pressure typically means higher intensity and stronger winds.) That makes it one of the lowest pressure storms in modern history in the Gulf of Mexico.

    The low wind shear allowed heat to concentrate, allowing pressure to drop, Franklin said.

    Since 1979, only three hurricanes in the Gulf of Mexico have had pressure lower than Milton's on Monday, said Phil Klotzbach, a senior scientist at Colorado State University. These storms were Allen in 1980; Katrina in 2005 and Rita in 2005.

    Size is crucial to the intensity of a hurricane

    Small storms like Milton can increase intensity the fastest, Franklin said. “But they can also dissipate the quickest because smaller storms don’t have the same resilience to wind shear.”

    Meteorologists expect Milton's intensity starting Tuesday to be determined by eyewall replacement cycles, which could cause the system to gradually grow weaker but larger, Eric Blake, one of the center's hurricane specialists, wrote in a forecast discussion Monday afternoon .

    The replacement cycles occur when a secondary eyewall develops further from the center within a storm. That process could deprive the center of heat generation, Franklin said. The winds begin to strengthen and spread to match the areas where heat is being released.

    This happened in the hours before Hurricane Idalia made landfall in August 2023. Its “impact was likely somewhat mitigated by Idalia's inner core deteriorating rapidly as it underwent an eyewall replacement cycle immediately prior to landfall,” the National Weather Service in Tallahassee wrote in a report after the storm.

    After 36 hours, Milton is “expected to encounter a much less favorable environment with strong shear and dry air,” Blake said. “Therefore, some weakening is expected before the hurricane reaches the Gulf Coast of Florida.”

    However, if replacement cycles occur that make Milton larger before it reaches the coast, the storm could be more resilient to wind shear, Klotzbach said.

    Larger, stronger storms like Hurricane Helene are harder to stop.

    “All conditions being equal, you would rather have a small, severe storm than a large storm for several reasons,” Franklin said. Smaller compact storms are more prone to weakening quickly and do not produce the same type of storm surge as a large one.

    Milton is still expected to be “a large and strong hurricane making landfall in Florida, with life-threatening hazards on the coast and well inland.”

    Dinah Voyles Pulver covers climate change and the environment for USA TODAY. She has been writing about hurricanes, tornadoes and severe weather for more than 30 years. Reach her at [email protected] or @dinahvp.

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    Kathleen William
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