1. Tropical Meteorology Jeff Gawrych Met. 10

2. Introduction Tropical weather is very different than our mid-latitude weather. –No fronts, little day-to-day variation Tropical weather systems form due to warm air rising (convection). Thermodynamics says –Heat added to system will increase the temperature and increase ability to perform work Warm oceans are fuel Latent heat release when warm air rises and condenses Tropical storms and hurricanes act like heat engines

3. In a nutshell Thunderstorms release large amounts of latent heat which warms the mid- and upper-troposphere. As a result of this heating, air begins to diverge consequently lowering the surface pressure. Surface convergence is enhanced by friction. However, because of the warm waters, the adiabatic cooling as the air crosses the isobars is balanced by conductive heating. A warm core is thus maintained, perpetuating the storm. Friction therefore balances the storms strength by limiting its intensity but maintaining its fuel supply (latent heat). I.e. CISK

4. Background Tropical cyclones/Hurricanes are perhaps the most severe of the weather phenomena. They can cause both massive property damage and loss of life.Tropical cyclones/Hurricanes are perhaps the most severe of the weather phenomena. They can cause both massive property damage and loss of life. –in 1972 a TC killed an estimated 300,000-500,000 people in Bangladesh. –in 1992 Hurricane Andrew hit the southern US. –in 1999 created massive flooding & mud slides in Honduras and Guatemala –in 2004, 4 hurricanes hot the Florida coast. Charley, Frances, Ivan, Jeanne. –http://www.cnn.com/SPECIALS/2004/hurricanes/interactive/hurrican e.paths/index.html http://www.cnn.com/SPECIALS/2004/hurricanes/interactive/hurrican e.paths/index.htmlhttp://www.cnn.com/SPECIALS/2004/hurricanes/interactive/hurrican e.paths/index.html

6. ITCZ Inter-Tropical Convergence Zone –defined as the result of the equatorial Hadley cell where air converges near the equator, rises and diverges near the tropopause Creates large thunderstorms called hot towers. Usually between 5 and 10 degrees latitude.

7. Definition These phenomena are commonly known asThese phenomena are commonly known as _______________ (Indian Ocean & South Pacific),_______________ (Indian Ocean & South Pacific), _______________ (Atlantic and Eastern Pacific)_______________ (Atlantic and Eastern Pacific) _______________ (North Pacific)._______________ (North Pacific). Tropical storms differ considerably from mid- latitude cyclones: For example, tropical storms haveTropical storms differ considerably from mid- latitude cyclones: For example, tropical storms have – – –

8. Definition These phenomena are commonly known asThese phenomena are commonly known as _______________ (Indian Ocean & South Pacific),_______________ (Indian Ocean & South Pacific), _______________ (Atlantic and Eastern Pacific)_______________ (Atlantic and Eastern Pacific) _______________ (North Pacific)._______________ (North Pacific). Tropical storms differ considerably from mid- latitude cyclones: For example, tropical storms haveTropical storms differ considerably from mid- latitude cyclones: For example, tropical storms have – – – Tropical Cyclones Hurricanes* Typhoons Warm core No fronts Strongest wind near the surface * Named for Carib god of evil: Huracan

11. Stages of development Tropical Disturbance:Tropical Disturbance: Tropical depression:Tropical depression: Tropical storm:Tropical storm: Hurricane:Hurricane:

12. Stages of development Tropical Disturbance:Tropical Disturbance: Tropical depression:Tropical depression: Tropical storm:Tropical storm: Hurricane:Hurricane: some closed isobars and winds 20-34 knots (more organization) mass of thunderstorms with slight wind circulation Some organization packed isobars, winds 35-64 knots when winds above 64 knots (74 mph)

13. Atlantic Hurricanes… Begin with easterly waves –Form as the Sahara Desert intensely warms up in the summertime –Wind blows to the west at ~ 15 deg. N –Triggers thunderstorm formation

14. Hurricane Classification

17. Recipe for Tropical Cyclone Formation 1.Warm ocean temperatures (T> 80F): –Typical in subtropical Atlantic/Pacific in summer/early fall –N. H. hurricane season: 2.Rotation: –Thunderstorms must organize to produce converging air –Cannot form at equator 3.Weak winds:

18. Recipe for Tropical Cyclone Formation 1.Warm ocean temperatures (T> 80F): –Typical in subtropical Atlantic/Pacific in summer/early fall –N. H. hurricane season: 2.Rotation: –Thunderstorms must organize to produce converging air –Cannot form at equator 3.Weak winds: June-November Coriolis force=0 Strong wind can disrupt organization

19. Hurricane movement Steered by prevailing windsSteered by prevailing winds – – Middle latitude high/low pressure systems can cause quick changes in hurricane position.Middle latitude high/low pressure systems can cause quick changes in hurricane position. Often challenging to predict!!Often challenging to predict!!

20. Hurricane movement Steered by prevailing windsSteered by prevailing winds –Easterly winds of tropical latitudes –Westerly winds of middle latitudes Middle latitude high/low pressure systems can cause quick changes in hurricane position.Middle latitude high/low pressure systems can cause quick changes in hurricane position. Often challenging to predict!!Often challenging to predict!!

21. Hurricane George

23. Evolution Tropical cyclones are driven by the warm ocean temperatureTropical cyclones are driven by the warm ocean temperature Thus, they will weaken and eventually die when they move overThus, they will weaken and eventually die when they move over – –

24. Evolution Tropical cyclones are driven by the warm ocean temperatureTropical cyclones are driven by the warm ocean temperature Thus, they will weaken and eventually die when they move overThus, they will weaken and eventually die when they move over –land or –colder waters.

25. Formation 30%12% 15%12% 7% 12%

26. Hurricane Structure Eye of hurricaneEye of hurricane – – Eye wallEye wall –Intense thunderstorms – Spiral rain bandsSpiral rain bands –Areas corresponding to upward motion and heavy rain –Alternating with rain free areas

27. Hurricane Structure Eye of hurricaneEye of hurricane –Extremely low pressure, –weak winds and generally clear skies Eye wallEye wall –Intense thunderstorms –Strongest winds, heaviest precip Spiral rain bandsSpiral rain bands –Areas corresponding to upward motion and heavy rain –Alternating with rain free areas

28. Why is eyewall the most intense part of the Hurricane? Law of Conservation of angular momentum –Wind speed (v) X distance from axis of rotation (r) must remain constant Close to eye --> r is small --> v must be large Far from eye --> r is large --> v is small

30. Hurricane Destruction Winds can have speeds over 100mph.Winds can have speeds over 100mph. –Extensive damage to buildings and vegetation. Storm surge:Storm surge: Hurricane may spawn tornadoes.Hurricane may spawn tornadoes.

31. Hurricane Destruction Winds can have speeds over 100mph.Winds can have speeds over 100mph. –Extensive damage to buildings and vegetation. Storm surge:Storm surge: Hurricane may spawn tornadoes.Hurricane may spawn tornadoes. abnormal rise in ocean level responsible for most damage via flooding