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Tropical Storm Irma was the ninth tropical cyclone as well as the ninth named storm in the 1978 Atlantic hurricane season. Irma developed from a subtropical system that was located about 500 miles (805 km) south of to the Azores. The system gained more tropical characteristics and was classified as Tropical Depression Nine beginning on October 2. The storm strengthened into a tropical storm before it tracked in between the western and central sections of the Azores.

As it passed through the Azores, some islands reported gale-force winds on October 5. Later that day, Tropical Storm Irma became absorbed by a cold front. Despite passing through the islands, there were no reports of damages or fatalities associated with the storm.

Meteorological History

The origins of Tropical Storm Irma can be traced to a subtropical system that formed about 500 miles (805 km) south of the Azores on October 2.[1] During the next two days, thunderstorm activity gradually increased around the circulation center as the storm drifted northward.[1] On October 2, the storm had taken the appearance of a tropical storm on satellite photographs, and upper-level anticyclonic flow over the center of the storm was evident on satellite time-lapse movies. Though because winds were not 39 miles per hour (63 km/h) or greater, the system had been classified as a tropical depression, [1] operationally, public advisories were not issued on this system until it was already a tropical storm. [2]

By the afternoon of October 4, the system had strengthened and acquired more characteristics of a tropical storm. It had strengthened into a tropical storm and received the name Irma. [1] [2] At this time, the storm had winds of 45 mph (70 km/h) and gale-force winds extended 150 miles (240 km) from the center of circulation.[2] The storm was expected to accelerate and strengthen slightly during the night while approaching the Azores.[2] Six hours after being named, Tropical Storm Irma reached its peak intensity of 50 mph (80 km/h).[3]

On October 5, Tropical Storm Irma turned towards the north-northeast and passed about midway between the central Azores and the two westernmost islands of Corvo and Flores.[1] Soon after passing in between these two groups of islands, Irma became less organized on satellite images due to an approaching cold front.[4] That evening, Tropical Storm Irma was absorbed into the cold front and low pressure system while 450 miles (725 km) northeast of the Azores.[5]


Upon becoming a tropical storm on October 4, Tropical Storm Irma had posed an immediate threat to the Azores.[6] Although Irma passed near parts of the western and central Azores with a few reports of gale-force winds in some areas, no reports of damage or casualties in association with Tropical Storm Irma. Despite few reports on gale-force winds on land, several ships in the vicinity of Tropical Storm Irma reported winds around 46 mph (74 km/h). [1] It was noted that heavy rains may have occurred on some of the mountainous islands of the Azores as Tropical Storm Irma passed. Other than that, there were no affects associated with Tropical Storm Irma. [1]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 "Preliminary Report: Tropical Storm Irma". National Hurricane Center. Retrieved 5 March 2010. 
  2. 2.0 2.1 2.2 2.3 Pelissier (4 October 1978). "Advisory 1". National Hurricane Center. Retrieved 5 March 2010. 
  3. "Preliminary Best Track: Tropical Storm Irma". National Hurricane Center. Retrieved 5 March 2010. 
  4. Pelissier (5 October 1978). "Advisory 5". National Hurricane Center. Retrieved 5 March 2010. 
  5. Lawrence, Miles B. (5 October 1978). "Advisory 6". National Hurricane Center. Retrieved 5 March 2010. 
  6. Pelissier (4 October, 1978). "Tropical Storm Alma Discussion Number 1". National Hurricane Center. Retrieved 30 March 2010.