Super Typhoon Choi-wan had just become a monstrous Category 4 super typhoon on the morning of September 15, 2009, when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this photo-like image. Choi-wan is a perfect circle with bands of clouds pin-wheeling around the dense center. The dark blue surface of the Pacific Ocean is visible through the clear eye, which is defined by a towering wall of clouds.

At the time the image was taken, Choi-wan had sustained winds estimated at 230 kilometers per hour (145 miles per hour or 125 knots), according to the Joint Typhoon Warning Center. Choi-wan was strengthening. Twenty-four hours later, the storm reached Category 5 status with sustained winds of 260 km/hr (160 mph or 140 knots). The Joint Typhoon Warning Center expected the storm to intensify a little more.

While the storm raked across the Northern Mariana Islands and was targeting the small islands of Iwo To and Chinchi Jima, it was not forecast to hit any major land mass. In this image, Super Typhoon Choi-wan is centered over the northern arc of the Mariana Islands in the western Pacific Ocean, with the larger islands of Guam, Saipan, and Tinian located on the southern edge of the storm. The islands north of Saipan are volcanic and are either unoccupied or sparsely populated.

The large image provided above is at MODIS’ maximum resolution of 250 meters per pixel. The MODIS Rapid Response System provides the image in additional resolutions.

The once mighty Super Typhoon Choi-Wan that reached Category 5 strength on the Saffir-Simpson hurricane/typhoon scale has become extratropical and is fading in the northern Pacific Ocean. The U.S. Navy’s Joint Typhoon Warning center issued a final warning on Saturday, September 19, when Choi-Wan was making the extra-tropical transition.

On Saturday, September 19, Choi-Wan still had maximum sustained winds of hurricane strength, near 86 mph, still at Category One typhoon strength. At one time, the storm’s maximum sustained winds had clocked at 161 mph. On Saturday, it was located about 410 miles southeast of Tokyo, Japan and moving further into the open North Pacific Ocean near 21 mph.

On Friday, NASA’s Aqua satellite flew over Typhoon Choi-Wan and captured infrared and microwave images on September 18 at 12:29 p.m. EDT (16:29 UTC). Microwave images are created when data from NASA’s Aqua satellite Atmospheric Infrared Sounder (AIRS) and Advanced Microwave Sounding Unit (AMSU) instruments are combined. These microwave images indicate where there is precipitation or ice in the cloud tops and the images from last Friday revealed Choi-Wan still had cold, high thunderstorms.

The infrared imagery revealed that there were also some towering, strong thunderstorms around Choi-Wan’s center on Friday.

Over the weekend, Choi-wan lost strength in the adverse atmospheric conditions as wind shear battered the storm. Choi-wan made the transition to extra-tropical status over the weekend.

A conversion to “extratropical” status means that the area of low pressure (known as Choi-Wan) eventually loses its warm core and becomes a cold-core system. During the time it is becoming extratropical the cyclone’s primary energy source changes from the release of latent heat from condensation (from thunderstorms near the storm’s center) to baroclinic (temperature and air pressure) processes. When a cyclone becomes extratropical it will usually connect with nearby fronts and or troughs (extended areas of low pressure) consistent with a baroclinic (pressure) system. When that happens it appears the system grows larger while the core weakens.