| Category 1 hurricane (SSHWS/NWS) | |
 Andy at peak intensity with a well-defined eye | |
| Formed | December 17, 2017 |
|---|---|
| Dissipated | December 29, 2017 |
| (Extratropical after December 22) | |
| Highest winds | 1-minute sustained: 90 mph (150 km/h) Gusts: 105 mph (165 km/h) |
| Lowest pressure | 970 mbar (hPa); 28.64 inHg |
| Fatalities | 61 |
| Damage | $7.17 billion (2017 USD) |
| Areas affected | Northeast United States, Canada, Nova Scotia, Newfoundland |
| Part of the 2017-18 North American Winter, 2017 Atlantic Hurricane Season | |
Winter Cyclone Andy, referred to in the Atlantic as Hurricane Tammy was an extremely rare tropical cyclone, forming in the great lakes. A powerful anticyclone lessened shear to about 10 kt, and the warm lakes allowed for tropical development. This system was Michigan's worst storm in recorded history, dropping as much as 40 feet of snow in some places. The system was known as "the terrible nor'easter of 2017" before it became a tropical cyclone.
The track of Andy, showing its rare transition into a Tropical Cyclone.
Subtropical Depression Twenty, Andy's precursor, located in the Gulf of Mexico on December 13, 2017.
Andy as a Subtropical Storm on December 17, shortly after classification.