9:30 PM EDT Update 21 October 2016
While official odds of 99L becoming "Otto" have been falling throughout the day, and are now just 20%, the cyclone has actually been intensifying, and most likely has sub-994mb central pressure, with maximum sustained winds of at least 35 knots.
This Low is a truly unusual bird, in that it has been so hybrid, 99L has failed to fit the commonly accepted definition for a subtropical storm. However, it looks as though 99L has been taking on more tropical characteristics today/tonight, and provided it does not shear out, and can stay far enough ahead of the front, may still get a name.
Regardless of named/not-named, this hybrid storm is producing a rather large area of stout winds, some to tropical storm force, with pockets of moderate to heavy showers, and a much larger area scattered to numerous light to moderate rain, while already out at sea and tracking north-northeast.
99L (or possibly Otto) is expected to work with two other weather features this weekend to bring as much as 80mm of rain to parts of Nova Scotia, some in the form of torrential downpours, prompting heavy rain and flood warnings over the weekend there.
2PM EDT Update 20 October 2016
Recon has found that the surface circulation of 99L, which briefly appeared well defined earlier today, has given way to a general state of elongated troffiness with multiple cyclonic swirls, and together with the diminished convection, does not yet meet the definition of a subtropical or tropical cyclone. However, recon is finding some near tropical storm-force winds, and there is still a window for this feature to become Otto before it probably meets up with an approaching front, by Saturday.
Convection has been consolidating about a well-defined surface circulation that exists within a broad and elongated region of lower pressure. This disturbance, tagged as Invest 99L, may become a subtropical or tropical storm later today. The bulk of reliable models and model runs keep this feature offshore of the United States, but it is worth watching.
Recon is scheduled to fly in this afternoon. The next name on the list is Otto.
Elsewhere of interest, a convectively active tropical wave continues plowing west through the Central Atlantic, and a region of persistent lower pressure exits along and either side of Central America.
99L Event Related Links
Animated Model Plot of 99L
SFWMD Model Plot (Animated Model Plot) SFWMD Hurricane Page
Clark Evans Track Model Plot of 99L
(Animated!) Model Plots in Google Earth - In Google Maps
Clark Evans Intensity Model Plot of 99L (Animated!)
Clark Evans Track Plot of 99L
Other Model Charts from Clark
Clark Evans Top 10 Analog Storms for 99L
More model runs on from RAL/Jonathan Vigh's page
NRL Info on 99L -- RAMMB Info
Floater Satellite Images: