NASA Infrared Image Sees Tropical Depression 4 Form in South China Sea

Tropical Depression 04W formed out of disturbance 98W this weekend after this passed over Luzon, the Philippines. NASA's Aqua satellite captured an infrared image that showed strong convection and thunderstorms in its center, helping confirm its organization into a tropical depression.

The Atmospheric Infrared Sounder instrument uses infrared capabilities to take the temperature of various factors associated with a tropical cyclone, from cloud top temperatures which indicate strength of thunderstorms within to sea surface temperatures . When NASA's Aqua satellite flew over Tropical Depression 04W on July 18 at 0723 UTC , it saw an area of very high thunderstorm cloud tops from northeast to southwest around the center of TD4W. Those temperatures were colder than 63 Fahrenheit and indicate strong convection .

At 1500 UTC on July 19 TD4W had still not consolidated and strengthened into a tropical storm. However, the sea surface temperatures in the South China Sea are warm enough to enable strengthening, as long as the wind shear remains low . TD4W had maximum sustained winds near 34 mph and higher gusts. It was located about 285 nautical miles west northwest of Manila, the Philippines, near 15.9 North and 115.9 East. It was moving west-northwestward near 11 mph .

TD4W is expected to strengthen into a tropical storm and move toward the northwest for a landfall south of Hong Kong in a couple of days.

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