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.
Eye (cyclone)
In the center of the eye, however, the waves converge from all directions, creating erratic crests that can build on each other to become rogue waves. 
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.
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Eye (cyclone) [SEP] Hazards
Though the eye is by far the calmest part of the storm, with no wind at the center and typically clear skies, on the ocean it is possibly the most hazardous area. In the eyewall, wind-driven waves all travel in the same direction. In the center of the eye, however, the waves converge from all directions, creating erratic crests that can build on each other to become rogue waves. The maximum height of hurricane waves is unknown, but measurements during Hurricane Ivan when it was a Category 4 hurricane estimated that waves near the eyewall exceeded 40 m (130 ft) from peak to trough.