NASA - National Aeronautics and Space Administration

Typhoon Sepat Remnants Lingering Over Eastern China


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On Tuesday, August 21, the remnants of the once powerful Typhoon Sepat were dissipating over the east China coast, as seen in this infrared image at 5:47 UTC (1:47 a.m. EDT) created by data from the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite.

This AIRS image shows the temperature of the cloud tops or the surface of the Earth in cloud-free regions. The lowest temperatures (in purple) are associated with high, cold cloud tops that make up the top of the storm's remnants. The infrared signal does not penetrate through clouds. Where there are no clouds the AIRS instrument reads the infrared signal from the surface of the Earth, revealing warmer temperatures (red). This infrared image shows an area of stronger convection (rapidly rising air) in purple.

Sepat made landfall in the Fujian province on Sunday, August 19, and has been bringing rains and winds to east China's Fujian, Jiangxi and Zhejiang provinces. Local meteorologists predict Sepat will linger in the province for another two days before dissipating. Reports attribute 29 deaths to the storm, and 17 million dollars in damages.

Rob Gutro
Goddard Space Flight Center
Image credit: NASA/JPL

Remnants of Super Typhoon Sepat Hanging Off China's Coast



Super Typhoon Sepat came ashore in Taiwan on August 17, 2007, after bringing torrential rain and flooding to the Philippines the day before. Flights to and from Taipei, Taiwan‚s capital, were canceled and Chinese authorities were taking emergency measures in anticipation of the powerful typhoon coming ashore on the mainland, said news reports. The typhoon was classified as Category Five typhoon, at the very top of the scale, with sustained winds of 184 kilometers per hour (114 miles per hour), according to CNN.

NASA's Aqua Satellite Peers at Sepat's Cloud Tops

On Monday, August 20, the remnants of Sept were hanging around the coast of China, as seen in this infrared image at 5:05 UTC (1:05 a.m. EDT) created by data from the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite.

These AIRS images show the temperature of the cloud tops or the surface of the Earth in cloud-free regions. The lowest temperatures (in purple) are associated with high, cold cloud tops that make up the top of the storm's remnants. The infrared signal does not penetrate through clouds. Where there are no clouds the AIRS instrument reads the infrared signal from the surface of the Earth, revealing warmer temperatures (red). This infrared image shows an area of strong convection (rapidly rising air) in purple. However, it's evident that Sepat has lost its circulation, as the purple areas, which depict the clouds in Sepat, appear elongated and not circular.

Image credit: NASA/JPL

NASA's QuikSCAT Captures Sepat's Winds on August 17



This data visualization of the storm shows observations from the QuikSCAT satellite on August 17, 2007, at 5:39 p.m. local time (9:39 UTC). At this time, Sepat was poised to come ashore onto Taiwan. Peak winds were around 220 km/hr (130 mph; 120 knots), according to Unisys Weather‚s Hurricane information, a Category Four strength typhoon. The image depicts wind speed in color and wind direction with small barbs. White barbs point to areas of heavy rain.

QuikSCAT measurements of the wind strength of Sepat and other tropical cyclones can be slower than actual wind speeds. QuikSCAT‚s scatterometer sends pulses of microwave energy through the atmosphere to the ocean surface and measures the energy that bounces back from the wind-roughened surface. The energy of the microwave pulses changes depending on wind speed and direction.

To relate the radar signal to actual wind speed, scientists compare measurements taken from buoys and other ground stations to data the satellite acquired at the same time and place. Because the high wind speeds generated by cyclones are rare, scientists do not have corresponding ground information to know how to translate data from the satellite for wind speeds above 50 knots (about 93 km/hr or 58 mph).

Also, the unusually heavy rain found in a cyclone distorts the microwave pulses in a number of ways, making a conversion to exact wind speed difficult. Instead, the scatterometer provides a nice picture of the relative wind speeds within the storm and shows wind direction.

Image credit: NASA/JPL/Brigham Young University, David Long

Rob Gutro
NASA Goddard Space Flight Center