Tropical
The storm originated in an upper-level low pressure system that moved southeastward from the central Great Plains into the Deep South of the United States. After reaching the southeast Gulf of Mexico, the disturbance underwent cyclogenesis, and the resultant system moved through Florida on December 22 in response to an approaching trough.[1] National Hurricane Center forecaster Jack Beven noted that "as it moved out into the Bahamas, it appeared to take on the characteristics of a tropical storm."[2] The uncertain nature of the storm prevented the NHC from issuing advisories on it, and forecasters lacked sufficient data to fully assess the cyclone for potential tropical characteristics. The same trough that pushed the storm across Florida had moved to the north, allowing for high pressure to develop in the upper levels of the atmosphere.[2]
Deemed a "hybrid storm", the cyclone rapidly intensified in warm waters of up to 80 °F (27 °C) from the Gulf Stream combined with a cold air mass over the United States.[3] The system continued to rapidly intensify while moving within the Gulf Stream; it developed central convection, an unusual trait for an extratropical cyclone, and at one point exhibited an eye.[1] Despite these indications of tropical characteristics, "There was no front associated with it and it had a warm core, but the radius of maximum winds was more than 150 nautical miles (170 mi; 280 km), so under the standard NHC criteria it didn't qualify as a tropical storm."[2] On December 23 and 24, the nor'easter intensified to attain a barometric pressure of 970 mb (29 inHg).[2] An upper-level low pressure system that developed behind the storm began to intensify and grew to be larger in size than the original disturbance. In an interaction known as the Fujiwhara effect, the broad circulation of the secondary low swung the primary nor'easter northwestward towards southern New York and New England.[3] The original low passed along the south shore of Long Island, and made landfall near New York City on December 24.[4]