Middle Tong-Tai Dialect a branch of the Tong-Tai Dialect

Tong-Tai Dialect

Tong-Tai Dialect, also named as Tai-Ru DialectTong-Tai Dialect(Chinese: 通泰方言), also named as Tai-Ru DialectTong-Tai Dialect(Chinese: 通泰方言), also named as Tai-Ru Dialect(Chinese: 泰如方言）is a particular dialect of Jianghuai Mandarin spoken in the middle-east of Jiangsu province. Tong stands for...

 is mainly used in the districts including Rugao

Rugao

Rugao is a city of Jiangsu province, People's Republic of China, located in the Golden Triangle region in the lower reaches of the Yangtze River. It is one of the historical and cultural city of Jiangsu province....

, Rudong (excluding Binfang), Taixin, east of Dongtai

Dongtai

Dongtai is a city under the jurisdiction of Yancheng, Jiangsu, in the People's Republic of China, located on the west coast of the Pacific ocean and 190 kilometers north of Shanghai. It has a population of roughly 1,170,000 estimated for 2007...

, east of Hai'an and southwest of Jinhai. Although it is divided into the category of Jianghuai Mandarin, interchange barrier still exists between it and other dialects of Jianghuai Mandarin like Yangzhou

Yangzhou

Yangzhou is a prefecture-level city in central Jiangsu Province, People's Republic of China. Sitting on the northern bank of the Yangtze River, it borders the provincial capital of Nanjing to the southwest, Huai'an to the north, Yancheng to the northeast, Taizhou to the east, and Zhenjiang across...

 Dialect. The reason could be that these areas are closely bonded on the Wu region in history. For example, there are lots of marked bottom preservation of Wu Chinese in vernaculars of Rudong.
So it can seem as a dialect based on Wu, but reformed by Jianghuai Mandarin later. Or as an interim zone between Wu and Jianghuai.