NASA’s Aqua satellite saw icy cold cloud top temperatures in Tropical Storm Ethel on January 19, which hinted at intensification. Infrared satellite imagery gives forecasters a clue to how high the cloud tops are that belong to thunderstorms that make up a tropical cyclone. The rule is the higher the cloud top, the stronger the uplift and the stronger the thunderstorm. When NASA’s Aqua satellite passed over Ethel on January 19 at 09:17 UTC (4:17 a.m. EST) the Atmospheric Infrared Sounder (AIRS) instrument measured the temperatures of Ethel’s cloud tops. Thunderstorm cloud tops around the entire center of circulation and in some of the bands of thunderstorms that circled the center to the east and north, were colder than -63 Fahrenheit (-52 Celsius).
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On January 20 infrared satellite data showed a symmetrical tropical cyclone with very strong convection (rising air that forms the thunderstorms that make up the cyclone) and strong thunderstorms around the center of circulation. A comparison of infrared satellite imagery from January 19 and 20 showed that the area of strong thunderstorms has expanded, hinting that the hurricane-force winds are expanding in coverage from the center. On January 20, 2012 at 1500 UTC (10 a.m. EST) the Joint Typhoon Warning Center (the organization that forecasts tropical cyclones in the Southern Indian Ocean) noted that Ethel had maximum sustained winds near 65 knots (75 mph/120 kmh) and was the strength of a Category one hurricane on the Saffir-Simpson Scale. Ethel was located about 410 nautical miles (471 miles/759 km) east of Port Louis near 19.7 South latitude and 64.5 East longitude.