JACKSONVILLE, Fla. – Overnight Thursday, for about 6 hours, there was a deep burst of thunderstorms near the center of the nor'easter. The nor'easter formed earlier this week off the coast of New England. There was just enough convection for the National Hurricane Center to declare sub-tropical Melissa had formed.
Nor'easters are cold-core systems that derive their energy from the contrast of warm moist air in the atmosphere and cold dry air pushing into that warm moist air. Sub-tropical storms are cold-core that become warm-core, where thunderstorms do develop near the circulation center.
That happened for a very brief period Thursday night into sunrise Friday morning,
During that very brief time that the convection (thunderstorms) developed near the center, satellite imagery briefly showed an eye-like feature before the convection around the center weakened. Additionally, a large convective area persisted for 6 hours over the northern semicircle, and this structure indicated the system has transitioned to a subtropical cyclone.
A trough (cold front) will begin to lift Melissa northeastward later Friday with strong upper-level wind which will begin to affect the storm tonight. This is expected to cause a weakening trend and Melissa is forecast to become post-tropical Saturday.
Coastal flooding impacts along portions of the U.S. East Coast from the mid-Atlantic states to southeastern New England has not changed.
Weakening is expected to gradually weaken and begin moving away from the East Coast by Friday night, resulting in a gradual decrease in wind and coastal flooding impacts.
Locally, wave models show a bump in the surf late Sunday and early next week. Get on it while it lasts as this will be a short run of waves.