In its early stages, a storm is less defined, consisting mostly of cloud cover and no obvious eye. See the unmistakable eye of Dorian below, on Sept 1. “Dorian was able to maintain category 5 intensity while it was stationary.” The Eyeīraun also pays close attention to the formation of a well-defined eye, another indicator of the storm’s power. “That is very unusual because stationary or very slow-moving tropical cyclones generate upwelling, cooling the sea surface temperature, which leads to weakening,” he said. Zachry said, was its ability to maintain its strength while stalled over the Bahamas. One of the most surprising aspects of Dorian, Dr. On Sept 1, the same day the storm made landfall on Grand Bahama Island, winds surged from 150 mph to 185 mph in only nine hours. ![]() With Dorian, rapid intensification occurred twice: Once between Aug 30 and 31, when winds jumped from 105 mph to 140 mph. A jump of 35 mph or more in less than 24 hours is considered rapid intensification. That decrease can be equivalent to one or more categories on the Saffir-Simpson hurricane intensity scale.īut the opposite is also true. You can see a ragged eye and a drop in symmetry compared to the earlier image.Ī hurricane that encounters strong shear can drop in intensity by as much as 35 mph or more in the span of a day. 6 image above was taken, the storm was experiencing an increase in wind shear and crossing into cooler waters, Straka said. When wind shear is high, it distorts the storm and pushes the thunderstorm activity to one side, which can start to weaken the hurricane.Ĭompare, for example, these side-by-side images of Dorian from Sept. When wind shear is low, storms tend to be more symmetric. That’s a sign that wind shear-a change in wind speed or direction with height-is minimal. 2 above, have a round, almost circular shape. The most powerful hurricanes, like Dorian on Sept. One of the first things that satellites can quickly determine is a hurricane’s shape. "Rotation around a central core corresponds with the eye wall and spiral rain bands," said William Straka III, a researcher for the Cooperative Institute for Meteorological Satellite Studies at the University of Wisconsin-Madison. “So essentially, the convection surrounding the circulation acts as the engine that sustains a hurricane.” The Shape ![]() The eye is surrounded by a wall of deep clouds and deadly winds. At 74 mph, it officially becomes a hurricane, one of the most violent storms on Earth.Ī hurricane’s eye is its clear center, and the calmest part of the storm. When winds form a closed circle with speeds exceeding 39 miles per hour, the cluster of storms becomes a tropical storm. The warm air rises high into the atmosphere, where it condenses into liquid and freezes to ice, forming giant rain-producing clouds. As it strengthens, drawing energy from warm ocean water and warm, moist air, it begins to organize and rotate. Hurricane 101Ī tropical cyclone, known as a hurricane in the Atlantic, a typhoon in the Pacific and a cyclone in the southern hemisphere and Indian Oceans, typically begins as a cluster of thunderstorms that form over the ocean. Using a series of images from Hurricane Dorian, we’ve created this guide. But without the trained eye of a meteorologist, it can be a challenge for most people to know what to make of them. Brian Zachry, Technology and Science Branch Chief at NOAA’s National Hurricane Center in Miami, Fla.ĭuring major storms, it’s common for these images to circulate on social media and surface in news articles and on television reports. ![]() “This imagery is fundamental to determining where the storm is located, knowing what direction it’s moving, and estimating its strength,” said Dr. These measurements tell us about wind at various levels in the atmosphere, sea surface temperatures and cloud properties. NOAA’s GOES East and West satellites also show the storm’s evolution by measuring infrared and visible radiation from the atmosphere and surface in real-time. These data are converted into brightly colored pictures that reveal the structure, intensity and temperature of a storm, along with other features, such as lightning and gravity waves. It was the strongest storm on record to hit the island nation.ĭuring a hurricane, instruments on NOAA-20 and S-NPP capture data twice a day. That week, the world watched as Hurricane Dorian slammed into the Bahamas and then stalled for more than 36 hours, leaving an estimated 200 people dead and 70,000 homeless. The image above shows this remarkable storm structure from S-NPP at 3:03 am EDT on that morning. ![]() These images, caught from the NOAA-20 and NOAA/NASA Suomi-NPP (S-NPP) satellites, showed a nearly perfect circular eye inside a powerful Category-5 storm.
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