by When tropical meteorologists are bombarded with satellite imagery, they often see subtle cloud formations that indicate something more ominous is brewing.
The first signs of a potential hurricane can be detected days before a storm reaches its ferocious momentum. The exiting wispy cirrus clouds, the appearance of curved banded low-level clouds and a decrease in atmospheric pressure are all clues.
These early clues are critical to predicting what could be a catastrophic hurricane.
I’m a professor of meteorology at Penn State, and my research group uses satellites and computer models to improve forecasting of tropical weather systems. With a particularly fierce Atlantic storm season predicted for 2024, it is more important than ever to be able to detect these early signs and provide early warning. This is what forecasters look for.
Conditions ripe for a hurricane
Hurricanes typically begin as atmospheric tropical waves, areas of low pressure associated with clusters of thunderstorms. As these tropical waves move back across the tropical oceans, some of them can become hurricanes.
The formation of a hurricane is dependent on a number of specific conditions:
Distance from the Equator: Tropical cyclones usually form at least 5 degrees from the equator. This is because the Coriolis force, which is critical for the initial spin of the cyclonic system, is weaker near the equator. The Coriolis force is caused by the Earth’s rotation, causing air to spin and a moving vortex.
Warm sea surface temperatures: The sea surface temperature must be at least 26.5 degrees Celsius (about 80 Fahrenheit) for a hurricane to form. The warm water provides energy that drives the storm as the storm absorbs heat and moisture from the ocean.
Atmospheric and moisture instability: For tropical cyclones to form, the atmosphere must be unstable. This means that warm surface air rises and stays warmer than the surrounding air, allowing it to continue to rise and form thunderstorms. There must also be plenty of moisture, as dry air can evaporate the clouds and weaken the upward movements within thunderstorms. These factors are necessary for the development of cluster thunderstorms within the tropical waves.
Low vertical wind shear: Strong vertical wind shear can tear apart a developing hurricane. Vertical wind shear is changes in wind direction or speed at different altitudes. It interferes with storm formation and growth and makes it difficult for a hurricane to keep its vortex aligned.
Early forecasting requires more than satellites
Identifying the early stages of a hurricane’s life cycle has been very challenging because there are not a large number of surface stations and weather balloons to provide detailed atmospheric information over the open ocean.
As soon as a storm begins to form, National Oceanic and Atmospheric Administration hurricane-hunting planes will often fly through, taking measurements and dropping sensors to get more data. But that cannot happen for every wisepy cloud, especially when the developing system is far from the coast.
One of the primary tools meteorologists currently use to predict early hurricane formation is satellite imagery, which provides real-time data on cloud patterns, sea surface temperatures and other atmospheric conditions. For example, the GOES satellites operated by NOAA help meteorologists track hurricane development with unprecedented clarity. These satellites can capture images at multiple wavelengths, allowing forecasters to analyze different aspects of the storm, such as cloud formation, precipitation and lightning activity.
However, satellite observations alone do not provide enough information for meteorologists to know which tropical waves are likely to become hurricanes.
To improve forecast accuracy, our research group has developed methods to incorporate real-time satellite data, including moisture levels and cloud patterns, into computer forecast models. This process, known as data assimilation, enables a more accurate and consistent representation of atmospheric conditions. As a result, forecasters can benefit from greatly improved forecasting capabilities, especially when anticipating hurricane formation and progression.
We are currently working with NOAA to refine these techniques and use them more widely for better hurricane forecasting and earlier warnings so the public has more time to prepare.
As people in North America and the Caribbean brace for a particularly intense hurricane season in 2024, the need for early storm forecasting is greater than ever.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. It was written by: Xingchao Chen, Penn State
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Xingchao Chen receives funding from NOAA, DOE, NASA and ONR.
