Koppu (Western Pacific)

Koppu briefly reached typhoon status before it made landfall just south of Hong Kong. Koppu’s eye made landfall around 7 a.m. local time (Hong Kong) today, September 15 (11 p.m. EDT, September 14) and brought winds gusting to near 78 mph (Category one typhoon strength) to the southern Guangdong Province.

NASA’s Aqua satellite captured an image of Koppu about 8 hours before its center made landfall, and revealed strong thunderstorms with very cold cloud tops as cold as -63F. Cloud top temperatures are important because they tell forecasters how high thunderstorms are, and the higher the thunderstorm, the more powerful. Those thunderstorms brought heavy downpours which led to minor flooding.

Prior to the Aqua’s flight over Koppu at 8 p.m. EDT (4 a.m. local time, Hong Kong), Koppu had maximum sustained winds near 69 mph (60 knots), tropical storm strength. It was 75 miles southwest of Hong Kong, China and moving west-northwest near 14 mph. The Hong Kong Observatory had issued a “No. 8 Southeast Gale or Storm Signal, meaning that winds with mean speeds of 63 kilometres per hour (39 mph) or more are expected from the southeast quarter (of Hong Kong).”

At 2:45 a.m. local time (Hong Kong), the Hong Kong Observatory noted “the maximum sustained winds recorded at Cheung Chau, Chek Lap Kok and Kai Tak were 110, 75 and 71 kilometres per hour (68, 46 and 44 mph) with maximum gusts 131, 108 and 115 kilometres (81, 67, and 71 mph) per hour respectively.”

NASA’s Aqua, CloudSat and the Tropical Rainfall Measuring Mission (TRMM) captured stunning satellite images and different views of Super Typhoon Choi-Wan this week. Aqua provided cloud temperatures, CloudSat provided a side look into the storm at convection, precipitation and hot towers, and TRMM provided a look at the extent and intensity of rainfall in Choi-Wan.

NASA’s Aqua satellite flew over Choi-Wan on September 15 at 1:30 p.m. local time, and captured an infrared image of the storm using the Atmospheric Infrared Sounder (AIRS) instrument. The infrared instrument provides valuable data on a tropical cyclone’s cloud top temperatures. They’re important because they tell forecasters how high thunderstorms are, and the higher the thunderstorm, the more powerful it is, and the data helped forecasters see Choi-Wan’s cloud tops were as cold as or colder than minus 63 degrees Fahrenheit (F).

AIRS infrared images depict different cloud temperatures in purple and blue. Those cloud that appear in purple on AIRS imagery have temperatures as cold as or colder than 220 degrees Kelvin or minus 63 degrees Fahrenheit (F). The blue areas are around 240 degrees Kelvin, or minus 27F. The colder the clouds are, the higher they are, and the more powerful the thunderstorms are that make up the cyclone. Areas that are false colored as purple, are where meteorologists would also find the “hot tower” clouds that the TRMM and CloudSat satellites see. In fact, in Choi-Wan, CloudSat identified several hot towers.

A hot tower is a tropical cumulonimbus cloud that penetrates the tropopause, i.e. it reaches out of the lowest layer of the atmosphere, the troposphere, into the stratosphere. In the tropics, the tropopause typically lies at least 15 kilometers (over 9 miles high) above sea level. These towers are called “hot” because they rise high due to the large amount of latent heat released as water vapor condenses into liquid.

NASA’s CloudSat satellite completed an eye overpass of Super Typhoon Choi-Wan in the Western Pacific Ocean on September 15, at 0352Z (Sept. 14 at 11:52 p.m.). The CloudSat overpass shows the vertical cross section right through the center of the storm. The eye center is free of cirrus clouds with eye wall edges sloping outwards towards the top of the storm and with hot towers on both sides.

Natalie D. Tourville, of the Atmospheric Science Department at Colorado State University Fort Collins, Colo. is a member of the CloudSat team. Tourville said, “The storm has a well developed, fully enclosed circular eye wall (red circle in the image) around the eye center with intense convection and precipitation (orange and red reflectivities) extending outwards. The Aqua Infrared (AIRS) depicts cloud cover throughout the overpass but the CloudSat image reveals moats (convection free areas) containing a thick cirrus canopy between the spiral rain bands.”

This is one a few inner eye images CloudSat has managed to capture of a Category 5 tropical cyclone.

Data from TRMM over flights are used in making the rainfall analysis at NASA’s Goddard Space Flight Center in Greenbelt Md. The rainfall analysis showed that Choi-Wan is a large and well-organized. TRMM’s Microwave Imager and Precipitation Radar instruments revealed that Choi-Wan has bands of heavy rainfall.

NASA’s TRMM satellite captured an image of Choi-Wan’s rainfall on September 13, as it was approaching Super Typhoon status. Rainfall in some areas exceeded 50 mm/hr, that’s almost 2 inches per hour!

NASA satellites provide daily information to the National Hurricane Center, the Central Pacific Hurricane Center, and the U.S. Navy’s Joint Typhoon Warning Center, all of whom forecast tropical cyclones.