Download Meteorology Chapter 11 – Hurricanes Profile of a Hurricane

Meteorology Chapter 11 – Hurricanes Profile of a Hurricane ‐ Most hurricanes form between the latitudes of 5O and 20O over all the tropical oceans except the South Atlantic and eastern South Pacific • These tropical storms are known in various parts of the world by different names. ⇒ In the western Pacific they are called typhoons; in the Indian Ocean they are called cyclones; the tropical storms in the Atlantic are called hurricanes. • By international agreement a hurricane has sustained wind speeds of at least 119 kilometers per hour (74 mph) and a rotary circulation. They can range in diameter from 100‐km up to about 1500‐
km. From the outer edge of the hurricane to the center, the barometric pressure can drop 60 millibars. • A hurricane is a heat engine that is fueled by the latent heat liberated when huge quantities of water vapor condense. ⇒ The release of latent heat warms the air and provides buoyancy for its upward flight. ⇒ The upward movement of air reduces the pressure near the surface, which results in a more rapid inflow of air • Hurricanes develop most often in the late summer when ocean waters have reached temperatures of 27OC (80OF) or higher and are able to provide the necessary heat and moisture to the air • Hurricanes do not form within 5 degrees of the equator because the Coriolis force is too weak to initiate the necessary rotary motion Hurricane Formation ‐ In the Atlantic, most hurricanes occur in the west along the coast of North America and in the Caribbean Sea. The origin of these hurricanes is far to the east. • In the eastern Atlantic, disorganized arrays of clouds and thunderstorms, called tropical disturbances, sometime develop and exhibit weak pressure gradients and little or no rotation. ⇒ Occasionally, these disturbances grow larger and develop a strong cyclonic rotation. • Tropical disturbances that produce many of the strongest hurricanes often begin as large undulations or ripples in the trade winds known as easterly waves. ⇒ To the east of the wave the air converges, rises and clouds form. Tropical disturbances are located on the east side of the wave. • Not all tropical storms strengthen to hurricane status. ⇒ If a temperature inversion forms surface air will not be able to rise, and thunderstorms will not develop. ⇒ Another factor that can inhibit hurricane formation is the presence of a strong wind aloft. This wind will disperse the latent heat created when clouds form which limits cloud growth. • In order for a tropical storm to achieve hurricane status, the combination heat released by the thunderstorms and the decrease in surface pressure cause surface winds to increase bringing in more moisture which nurtures the storm growth. ⇒ A cycle of water vapor condensation and the adiabatic cooling of rising air fuels storm growth. • By international agreement, lesser tropical cyclones are given different manes based on the strength of their winds: ⇒ Tropical depression – strongest winds do net exceed ;61 kilometers per hour ⇒ Tropical storm – sustained winds between 61 and 119 kilometers per hour. Hurricane Decay ‐ Hurricane diminish in intensity whenever they: 1. Move ocean waters that cannot supply warm, moist tropical air 2. Move onto land 3. Reach a location where the large‐scale flow aloft is unfavorable • Whenever a hurricane moves unto land, it loses energy quickly. The primary reason for this is the fact that the storm’s source of warm, moist air is cut off. Hurricane Destruction ‐ Based of the study of past storms, the Saffir‐Simpson scale was established to rank the relative intensities of hurricanes. • When a tropical storm becomes a hurricane, the National Weather Service assigns its scale (category) number. ⇒ Category assignments are based on observed conditions at a particular stage in the life of a hurricane. ⇒ As conditions change, the category of the storm is reevaluated. ⇒ A rating of 5 on the scale represents the worst storm possible, and a 1 is the least severe. • Damage caused by hurricanes can be divided into three classes: (1) storm surge, (2) wind damage, and (3) inland freshwater flooding.