(This post was originally posted at 3:03 p.m. Tuesday, and updated at 10:27 a.m. and 12:30 p.m. Wednesday)

Update 12:30 p.m. Wednesday: The China Meteorological Administration’s storm survey concludes a tornado, rated EF1 (on the 0-5 scale), struck the ferry. It says the tornado lasted 15-20 minutes and was less than 1 kilometer (0.6 miles) wide. It notes the Yangtze River Delta, where this storm occurred, is the part of China most frequently affected by tornadoes.

A stated limitation of the survey is that, because the tornado occurred over the water, officials could not evaluate damage to trees and structures – which is typically necessary to determine whether a tornado actually touched down and its strength.

Original post

The violent windstorm that tipped over a Chinese ferry boat carrying 458 people Monday evening originated from a towering group of thunderstorms that may have spawned a tornado.

The thunderstorms soared 40 to 50 thousand feet high in the atmosphere and were fueled by a very warm, humid stream of air from the China Sea.

Archived satellite imagery (see loop) shows the unmistakable cluster of vigorous storms over Jianli County, where the incident occurred at 9:30 p.m. local time Monday along the Yangtze River (detailed map).

The China Meteorological Administration says the storm reached level 12 on the Beaufort wind scale, which equates to wind of hurricane force, over 74 mph.

Many media outlets are reporting that a tornado struck the ship. China Daily says the twister lasted 15-20 minutes and was less than 0.6 miles (1 kilometer) in diameter. However, it is not out of the question that high winds were generated by a “microburst” rather than a tornado.

The storm not only unleashed devastating wind gusts but also unloaded over 2.5 inches (64.9 mm) of rain between 9 and 10 p.m. according to China Daily.

The storm complex developed during the rainy season on the Yangtze river, when large thunderstorms are common and tornadoes can occur. But conditions on Monday were particularly favorable for damaging storms.

Simulations from the GFS model portray hotter than normal temperatures, lower than normal pressures and abundant low level moisture in the region – ingredients which heightened the risk for severe weather.

Above normal temperatures provided heat necessary to destabilize the atmosphere

Lower than normal pressures promoted rising air motions for storm development

A deep plume of moisture originating from the China Sea helped energized the storms

The turbulent weather pattern has persisted since the accident and is hampering rescue efforts and the search for survivors.