SECTION 3. TROPICAL CYCLONES

Severe weather, strong gusts and heavy rain, and high seas associated with TCs are critical parameters affecting the Navy's operations. Calhoun (1981) documented the damages to the Third Fleet due to a north Western Pacific tropical cyclone (TC). The methods of operational forecasts for onset, motion, wind and gusts, and decay of TCs are key subjective decisions made based on various objective forecast aids in a man-machine environment.


3.1 Classifications of Tropical Cyclones

Tropical cyclone is a general term for a cyclone that originates over the tropical oceans. The TC is a nearly circular storm with a mean diameter of about 5 degrees latitude and an extremely low-pressure center into which the horizontal winds spiral. The mean life span of a TC is about 5 to 10 days. Tropical cyclones usually contain a central region, known as the "eye" (Huschke, 1959). The diameter of the eye is in the order of some tens of kilometers, and with light winds, lightly clouded to clear sky, and light to no rain.

There is a regional variation in the classification and terminology of TCs. Table 2.2 is the World Meteorological Organization (WMO), USA and Japan classifications of TCs according to their intensity, which is the maximum wind speed near the surface (Huschke, 1959; WMO, 1966; Neumann, 1993). Table 2.3 shows the WMO and Indian Ocean Regional Tropical Cyclone Classifications (Neumann, 1993).

Mature TCs (i.e., typhoons or hurricanes), range in size from 100 km to well over 1500 km in diameter. The distribution of tangential winds, pressure and temperature tends to be radially symmetric. However, asymmetric components are frequently detected by radar precipitation reflections and satellite cloud images. Strong wind speeds are present in most cases when the central pressure of the cyclone falls below 990-hPa level, although there is no exact balance between the low-level mass and velocity fields.

Section 2.7 Section 3.2

Chapter 2