Tropical Cyclones. Part 10

Transcription

1 Tropical Cyclones Part 10

2 What is a Tropical Cyclone? A tropical cyclone is the general term for all rotating weather systems that originate over warm tropical waters. Tropical cyclones are classified as follows: Tropical Depression: Maximum sustained winds of 38 mph (33 knots) or less. Tropical Storm: Maximum sustained winds of 39 to 73 mph (34-63 knots). Hurricane: Maximum sustained winds of 74 mph (64 knots) or higher. In the northwestern Pacific, hurricanes are called "typhoons," and similar storms in the Indian Ocean and southwestern Pacific are called "cyclones."

3 Stages of Hurricane Growth

4 General Characteristics Approximate average diameter of hurricanes is 500 km circulation of largest systems extend for thousands of kilometers The overall lifecycle of tropical cyclone growth from tropical depression to hurricane and subsequent dissipation is on the order of days Generally classified as very large mesoscale systems (meso-α) that are inertially stable vortices at maturity Most tropical cyclones form between 5 and 20 latitude (more form poleward in NH) The majority of tropical storms form in the summer hemisphere North Atlantic hurricane season is June through November with a peak around September 10

5 General Characteristics General Characteristics Hurricanes are warm core lows Low pressure at the surface High pressure aloft Decreasing intensity with height Weak vertical wind shear exists Form over warm ocean waters Latent heat of condensation very important to the formation and maintenance of tropical storms

6 Tropical Storm Circulation High warm Low

7 Vertical Cross Sections

8 Infrared Satellite Pictures of Hurricane Mitch October 26-27, 1998

9 Differences between Hurricanes and Extratropical Cyclones: Hurricane warm ocean/latent heat release Energy Source Extratropical Cyclone temp difference between air masses warm core/decays with height Vertical Structure cold core/strengthens & slopes with height smaller size/just maritime Tropical air mass Horizontal Structure larger size/fronts (boundaries between 2 different air masses)

10 Parameters Important for Tropical Cyclone Formation Large values of low-level vorticity (ζ) likely from a pre-existing tropical disturbance Large values of Coriolis parameter (f) Minimum of vertical wind shear Sea surface temperatures >26 C to a depth of 50 m Large values of moist lapse rate instability Large values of mid-troposphere ( mb) relative humidity

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12 Organized Convection Theory of Tropical Cyclone Development 1 - surface convergence leads to rising motion / increase in moisture content. 2 - rising air condenses, releases large amount of latent heat. 3 - latent heating aloft leads to high pressure and divergence aloft (organizes the large scale circulation) 4 - divergence aloft leads to lower surface pressure. 5 - lower surface pressure increases surface convergence. 6- stronger surface winds increase wave height; increase friction and convergence; also increase ocean-air moisture flux. 7 - rotation serves to organize flow.

13 Easterly Wave Atlantic hurricane development initiated by the passage of a wave disturbance in the tropics/subtropics (e.g., easterly waves).

14 Easterly Wave [From Gray (2000)] Top panel (a): Conditions favorable for an easterly wave to develop into a hurricane Bottom panel (b): Conditions unfavorable for hurricane development

15 Typical Tropical Cyclone Tracks

16 World-Wide Wide Tropical Cyclone Frequency

17 Tropical Cyclones by Basin Tropical Storms Hurricanes Average % of Total Average % of Total Atlantic NE Pacific NW Pacific N Indian SW Indian SE Indian SW Pacific Global

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20 NHC Track Forecast Error h OFCL 48 h OFCL 72 h OFCL Year Track Error (nm)

21 Hazards from Tropical Cyclones Storm Surge Ocean can rise up to 25 feet High Wind Gusts up to 200 mph Flooding from rainfall Up to 40 inches of rain Tornadoes Spawned by the hurricane up to 1000 miles inland

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23 U.S. Landfalling Hurricanes

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25 Atlantic Hurricane Names Alberto Allison Arthur Ana Alex Arlene Beryl Barry Bertha Bill Bonnie Bret Chris Chantal Cristobal Claudette Charley Cindy Debby Dean Dolly Danny Danielle Dennis Ernesto Erin Edouard Erika Earl Emily Florence Felix Fay Fabian Frances Franklin Gordon Gabrielle Gustav Grace Gaston Gert Helene Humberto Hanna Henri Hermine Harvey Isaac Iris Isidore Isabel Ivan Irene Joyce Jerry Josephine Juan Jeanne Jose Keith Karen Kyle Kate Karl Katrina Leslie Lorenzo Lili Larry Lisa Lee Michael Michelle Marco Mindy Matthew Maria Nadine Noel Nana Nicholas Nicole Nate Oscar Olga Omar Odette Otto Ophelia Patty Pablo Paloma Peter Paula Philippe Rafael Rebekah Rene Rose Richard Rita Sandy Sebastien Sally Sam Shary Stan Tony Tanya Teddy Teresa Tomas Tammy Valerie Van Vicky Victor Virginie Vince William Wendy Wilfred Wanda Walter Wilma Typical Year: 10 Named Storms 6 Hurricanes 2 Major Hurricanes

26 Where are the winds likely to be strongest? Prevailing wind

27 The Coriolis Force Affects Ocean Currents Too wind Rotation of the Earth deflects ocean currents to the right of the wind in the Northern Hemisphere Current (N.H.)

28 Storm Surge Surface wind converges Surface water diverges Makes a huge pile of water Causes terrible damage and loss of life!

29 Hurricane Storm Surge Makes the Ocean Level Rise STORM SURGE HIGH TIDE MEAN TIDE (MSL) DUNE LOW TIDE

30 Folly Beach, South Carolina (Before Hugo)

31 Folly Beach, South Carolina (After Hugo)

32 x

33 Hurricane Andrew 1992 Wind Damage

34 Hurricane Andrew 1992 Wind Damage

35 Hurricane Floyd 1999 Rainfall Damage

36 North Carolina Rainfall Damage from Hurricane Floyd 1999

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38 (Rappaport, Fuchs and Lorentson, 1999) U.S. Loss of Life from Tropical Cyclones (517 Total) 2% 1% 4% 13% Freshwater Shoreline Offshore 13% 53% Wind Tornado Stormsurge Other 14%

39 Summary Tropical Cyclones are warm core rotating weather systems that derive their energy from the warm ocean Counter-clockwise in N. hemisphere, clockwise in S. hemisphere Tropical storm winds > 39 mph, Hurricane winds > 74 mph Formation requires warm ocean, weak upper level winds, moist mid-troposphere, moist lapse rate instability, earth s rotation, and pre-existing disturbance They occur in most tropical and sub-tropical ocean basins Motion is usually east to west in tropics, west to east in higher latitudes Track forecasting has greatly improved in last few decades Hazards include storm surge, wind, rainfall and tornadoes