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.