As Super Typhoon Halong tracks north through the Northwestern Pacific Ocean, NASA's Aqua and Terra satellites have seen the powerful storm appear to wink at space as it developed and "opened" an eye and then close its eye as clouds moved over it. That wink appears to be a sign of eyewall replacement in the powerful storm.
On August 2 at 01:45 UTC (August 1 at 9:45 p.m. EDT) NASA's Terra satellite captured a visible image of a wide-eyed Super Typhoon Halong moving through the Northwestern Pacific Ocean. At the time of the image, Halong was a powerful Category 5 Super Typhoon on the Saffir-Simpson Scale. Satellite data showed that Halong had a 10-nautical mile (11.5 mile/18.5 km) wide eye.
On August 4 at 04:40 UTC (12:40 a.m. EDT), NASA's Aqua satellite captured a visible image of Super Typhoon Halong that showed its eye had become cloud filled. The image also showed that the bulk of strongest bands of thunderstorms were over the southern quadrant of the storm.
Forecasters at the Joint Typhoon Warning Center or JTWC noted that microwave satellite imagery suggests an on-going eyewall replacement. That's when the thunderstorms that circle the eye of a powerful hurricane are replaced by other thunderstorms. Basically, a new eye begins to develop around the old eye. Many intense hurricanes undergo at least one of these eyewall replacements during their existence. JTWC noted that the eyewall replacement correlates to the recent weakening trend.
On Monday, August 4, Super Typhoon Halong's maximum sustained winds had dropped to near 105 knots (120.8 mph/190.4 kph), making it a Category Two hurricane on the Saffir-Simpson Scale. On August 3, Halong was a Super Typhoon with maximum sustained winds near 130 knots (149.6 mph/240.8 kph) on August 3, which made it a Category Four storm.
On August 4, Halong was centered near 17.3 north and 130.3 east, about 588 nautical miles (676.7 miles/1,089 km) south-southeast of Kadena Air Base, Okinawa, Japan. Halong was moving northwest at 4 knots (4.6 mph/7.4 kph). Because Halong is such a powerful storm, it is generating extremely rough seas. The Joint Typhoon Warning Center noted that wave heights were near 42 feet (12.8 meters).
The JTWC expects Halong to continue moving in a northerly direction for the next couple of days.
Explore further: NASA sees Tropical Storm Halong's 'best side'