Subtropical Storm Otto Forms, Likely to Become a Hurricane

(Oct. 6) -- Subtropical Storm Otto has formed in the western Atlantic, and it is expected to become a Category 1 hurricane this week.

Otto will head northeastward into the open Atlantic in the coming days, so it is not expected to pose a direct threat to the Bahamas, the United States or even Bermuda.

As of 11 p.m. EDT, Otto had a sustained wind of 65 mph and was located about 230 miles to the northeast of Grand Turk Island.

A subtropical storm is a storm that has the intensity of a tropical storm but also has some characteristics of a nontropical storm. National Hurricane Center forecasters expect that Otto will make the transition into a standard tropical storm by early Thursday, when it will be renamed Tropical Storm Otto. Otto is then expected to strengthen into a full-fledged hurricane by Thursday night.


(Image courtesy of NOAA)

Otto will move little tonight and then turn more northeastward Thursday and remain on a northeastward track through the weekend. This path means that Otto will remain well to the east of the Bahamas tonight into Thursday and well to the south of Bermuda on Friday. What's left of Otto, most likely a nontropical entity, will approach the Azores on Monday.

Heavy thunderstorms are a threat in the northern Leeward Islands, the Virgin Islands and Puerto Rico for the day next or so, and presence of the storm in the western Atlantic might increase the risk of riptides along the southeastern coast of the United States and in Bermuda.

Otto formed as a result of a combination of an upper-level low-pressure system, which is the nontropical aspect of the storm, and the warm water in the western Atlantic, the tropical aspect of the storm. The low-pressure system began to weaken today, and as it continues to dissipate, the tropical driving forces of the storm will take over. The result will be the transition from a subtropical storm to a tropical storm and, government forecasters expect, a hurricane.

While subtropical storms have the same intensity in terms of wind speed as more traditional tropical storms, the center is typically not as compact. The result is often a larger wind field with rain bands extending farther outward from the center than with a standard tropical storm -- often appearing more diffuse than a standard tropical storm.

As Subtropical Storm Otto continues its transition, it will likely take on the more symmetrical appearance that is associated with tropical storms and hurricanes.