what is the size range of these formations?
Anywhere from the radius of the outermost closed isobar being less than two degrees of latitude to being more than eight degrees of latitude.
Tropical cyclone
. If the radius of outermost closed isobar is less than two degrees of latitude (), then the cyclone is "very small" or a "midget". A radius of 3–6 latitude degrees () is considered "average sized". "Very large" tropical cyclones have a radius of greater than 8 degrees (). 
what is the pressure at the center of a hurricane The cyclone's lowest barometric pressure occurs in the eye(the center) and can be as much as 15 percent lower than the pressure outside the storm. why are they considered to be a threat? In the center of the eye, however, the waves converge from all directions, creating erratic crests that can build on each other to become very high rogue waves. what are other twisters that have similar formations? UNANSWERABLE what indicates the strength of a cyclone? The Maximum Potential Intensity.
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Tropical cyclone [SEP] Size
A radius of 3–6 latitude degrees () is considered "average sized". "Very large" tropical cyclones have a radius of greater than 8 degrees (). Observations indicate that size is only weakly correlated to variables such as storm intensity (i.e. maximum wind speed), radius of maximum wind, latitude, and maximum potential intensity. Size plays an important role in modulating damage caused by a storm. All else equal, a larger storm will impact a larger area for a longer period of time. Additionally, a larger near-surface wind field can generate higher storm surge due to the combination of longer wind fetch, longer duration, and enhanced wave setup.