Visible imagery from NASA’s Aqua satellite revealed that strong wind shear was adversely affecting Tropical Cyclone Liua in the Southern Pacific Ocean.
On Sept. 28 at 0315 UTC (Sept. 27 at 11:15 p.m. EDT) the Moderate Resolution Imaging Spectroradiometer or MODIS instrument aboard NASA’s Aqua satellite provided a visible image of Tropical Cyclone Liua. Liua appeared as a swirl of clouds around its center with most of its clouds and thunderstorms pushed southeast of center. Strong westerly to northwesterly vertical wind shear were tearing the storm apart.
In general, wind shear is a measure of how the speed and direction of winds change with altitude. Tropical cyclones are like rotating cylinders of winds. Each level needs to be stacked on top each other vertically in order for the storm to maintain strength or intensify. Wind shear occurs when winds at different levels of the atmosphere push against the rotating cylinder of winds, weakening the rotation by pushing it apart at different levels.
On Sept. 28, the Joint Typhoon Warning Center issued the final bulletin on Tropical Cyclone Liua. At that time, Liua was centered near 12.0 degrees south latitude and 161.1 degrees east longitude. That’s 540 miles northwest of Port Vila, Vanuatu. Liua was moving slowly to the west-northwest and had maximum sustained winds near 35 knots (40 mph/62 kph).
Liua is forecast to dissipate under adverse atmospheric conditions.
Sep. 27, 2018 – NASA Satellite Analyzes New Southern Pacific Ocean Tropical Cyclone
NASA’s Aqua satellite provided an infrared look at a new storm that formed in the southern Pacific Ocean called Liua and saw strongest storms off-center.
At 11 a.m. EDT (1500 UTC) on Sept. 27, the MODIS or Moderate Resolution Imaging Spectroradiometer instrument aboard NASA’s Aqua satellite looked at Tropical Storm Liua in infrared light. MODIS found two areas of coldest cloud top temperatures west and northeast of Liua’s center were as cold as or colder than minus 80 degrees Fahrenheit (minus 112 degrees Celsius). Those areas represented the strongest storms. Surrounding them were storms with cloud tops as cold as or colder than minus 70 degrees Fahrenheit (minus 56.6 degrees Celsius).
NASA research has found that cloud top temperatures as cold as or colder than the 70F/56.6C threshold have the capability to generate heavy rainfall.
At 11 a.m. EDT (1500 UTC), the center of Tropical Storm Liua was located near latitude 12.2 degrees south and longitude 162.5 degrees east. That’s about 471 miles northwest of Port Vila, Vanuatu. Liua was moving toward the south-southwest. Liua’s maximum sustained winds were near 40 mph (35 knots/62 kph) with higher gusts.
The Joint Typhoon Warning Center noted that the forecast takes Liua west over cooler sea surface temperatures and where outside winds will weaken the storm. Liua is forecast to dissipate by Sept. 29.