The National Hurricane Center indicated on Monday that a strong extratropical cyclone over the Atlantic Ocean south of Nova Scotia is unlikely to make a transition to a tropical cyclone. At 1:00 p.m. EST on Monday the center of the extratropical cyclone was located at latitude 37.8°N and longitude 63.8°W which put it about 460 miles (745 km) south of Halifax, Nova Scotia. The extratropical cyclone was moving toward the north-northeast at 10 m.p.h. (16 km/h). The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h). The minimum surface pressure was 986 mb.
The National Hurricane Center (NHC) issued a special Tropical Weather Outlook on Monday morning for a strong extratropical cyclone over the Atlantic Ocean south of Nova Scotia. NHC indicated in the Tropical Weather Outlook that it was unlikely the extratropical cyclone would make a transition to a tropical cyclone or a subtropical cyclone. The extratropical cyclone was subsequently designated at Invest 90L.
A circular area of showers and thunderstorms developed at the center of a large, occluded extratropical cyclone south of Nova Scotia on Monday. A clear circular area was visible at the center of the area of showers and thunderstorms on satellite images. The clear area resembled the appearance of an eye in a tropical cyclone. The thunderstorms did not extend high into the troposphere because the center of the extratropical cyclone was over water where the Sea Surface Temperatures are near 20˚C. The circular area of showers and thunderstorms in the middle of the extratropical cyclone was surrounded by a large area of cold, dry air. Bands of low clouds and showers were occurring in the cold, dry air. The extratropical cyclone was producing a large area of winds to tropical storm force.
The extratropical cyclone will move through an area that is only marginally favorable for a transition to a subtropical cyclone or a tropical cyclone. The extratropical cyclone will move over over water where the Sea Surface Temperatures are colder than 20˚C. It will move under the eastern part of an upper level low south of Nova Scotia. The upper level low will produce southerly winds that will blow toward the top of the extatropical cyclone. However, the upper level low is almost stacked vertically with the surface low pressure systems. So, the winds at different levels of the atmosphere are similar and there will be little vertical wind shear. Cold, dry air will continue to surrounded the circular area of thunderstorms at the center of the extratropical cyclone. Cold Sea Surface Temperatures and cold, dry air around the area of thunderstorms will inhibit a transition to a subtropical cyclone. There is a slight chance the extratropical cyclone could make a transition to a subtropical cyclone during the next 24 hours before it moves over even colder water.
The upper level low will steer the extratropical cyclone toward the north during the next 24 hours. On its anticipated track the extratropical cyclone could reach Nova Scotia on Tuesday. It will bring gusty winds and locally heavy rain to Nova Scotia.
