what is the physical structure of this above type of cyclone just mentioned?
Its formation was unusual, originating from a tropical disturbance that crossed from the eastern Pacific Ocean into the Caribbean Sea; few Atlantic hurricanes develop in this manner.
Tropical Storm Arlene (1981)
Its formation was unusual, originating from a tropical disturbance that crossed from the eastern Pacific Ocean into the Caribbean Sea; few Atlantic hurricanes develop in this manner. 
what is tropical storm arlene (1981)? It was a rare off-season tropical cyclone.
wiki:20422543
Tropical Storm Arlene (1981) [SEP] Introduction
Tropical Storm Arlene was a rare off-season tropical cyclone that hit Cuba and the Bahamas in May 1981. Its formation was unusual, originating from a tropical disturbance that crossed from the eastern Pacific Ocean into the Caribbean Sea; few Atlantic hurricanes develop in this manner. On May 6, a tropical depression developed, and the next day it became Tropical Storm Arlene near the Cayman Islands, three weeks before the start of the hurricane season. This marked the first Atlantic tropical storm in May since 1970's Hurricane Alma. Arlene moved northeastward throughout its life, bringing rainfall and locally gusty winds as it crossed Cuba and the southeastern Bahamas.