Structure of a TRS
A well-developed TRS has three distinct parts:
- The eye or vortex: A calm central area of lowest pressure, having a diameter between 4 miles and 30 miles, the average being about 10 miles. It is a roughly circular area of comparatively light winds and fair weather, available at the center of a severe tropical cyclone.
Weather in the eye is normally calm but the sea can be extremely violent. There is little or no precipitation and sometimes blue sky or stars can be seen. The eye is the region of lowest surface pressure than the surrounding environment.
In severe cyclones, the eye usually looks like a circular hole in the central cloud mass.
- The eye-wall: An inner ring of hurricane-force winds having a width usually between 4 miles and 30 miles. The winds in the eye-wall blow in a perfectly circular path with a speed as high as 130 knots with occasional gusts up to 150 knots.
The pressure gradient in the eye wall is very steep and, therefore, the barograph would register a near-vertical trend, downward before the eye and upward behind it, as shown in the figure.
The eye wall consists of a dense ring of clouds and tall thunderstorms that produce heavy rains and usually the strongest winds (about force 6 or 7) at about circular paths.
Changes in the structure of the eye and eyewall can cause changes in wind speed, which is an indicator of the storm’s intensity.
- The Outer Storm area: The area surrounding the eye-wall, having a diameter between 50 miles and 800 miles, the average being about 500 miles. Winds in this region are strong (about force 6 or 7) and the pressure gradient is much less than in the eye-wall.
Here the angle of indraft of wind is about 45º and this gradually decreases to 0º in the eye wall. In this area, the cirrus cloud can be in the form of strands or filaments with aligned conditions and points toward the storm center.
Here visibility is excellent, except in occasional shower areas.