Transcript lecture30
NATS 101 Lecture 30 Hurricanes Supplemental References for Today’s Lecture Aguado, E. and J. E. Burt, 2001: Understanding Weather & Climate, 2nd Ed. 505 pp. Prentice Hall. (ISBN 0-13-027394-5) Danielson, E. W., J. Levin and E. Abrams, 1998: Meteorology. 462 pp. McGraw-Hill. (ISBN 0-697-21711-6) Types of Tropical Cyclones Cyclone Type Tropical Depression Tropical Storm Hurricane/Typhoon Winds 25-39 mph 40-74 mph 75 mph Most Depressions do not develop into Storms Majority of Storms reach Hurricane status Some Hurricane Extremes Lowest Central Pressure Pressure Pacific: Typhoon Tip 1979 870 mb Atlantic: Hurricane Gilbert 1988 888 mb Costliest Hurricanes Cost-Loss Hurricane Andrew 1992 $25 billion Hurricane Katrina 2005 $200 billion? Bangladesh Cyclone 1970 300,000 dead Andrew 1992 Time Sequence 2005 Atlantic Hurricanes NASA Note cooler water in wake of Dennis, Emily and Katria Link to Older NASA Satellite Animations U.S. Hurricane Deaths and Costs Williams, The Weather Book Hurricane Lecture Overview • What are the primary differences between hurricanes and extratropical cyclones? • When and where do hurricanes form? • How do hurricanes intensify? • What is the structure of a hurricane? • What kind damage do hurricanes inflict? • When and where do hurricanes dissipate? Differences Between Tropical and Extratropical Storms Williams, The Weather Book No Fronts Warm at Storm Center Aloft Strongest Winds near Surface Forms over Tropical Oceans Diameter of 200-500 miles Energy Source: Energy Fluxes from Warm Ocean Strong Fronts Cold at Storm Center Aloft Strongest Winds Aloft Forms outside Tropics Diameter of 500-1000 miles Energy Source: Horizontal Temperature Contrast Where Hurricanes Form? Hurricanes Hurricanes Tropical Cyclones Hot Bed! Typhoons Williams, The Weather Book • Hurricanes go by different names in different regions of the world. • Form over warm tropical waters, equatorward of 20 latitude… Not on equator (poleward of 5 ) b/c non-zero Coriolis is needed. • Occur most frequently over Western North Pacific Ocean. Atlantic Hurricane Frequency Danielson et al. Fig. 13.2 Occur in Warm Season Maximum Likelihood when Sea Surface Temperatures are Warmest-September Average of ~6 Per Year Large Yearly Variability Fewer in El Nino Years More in La Nina Years Atlantic Hurricane Tracks Danielson et al. Fig. 13.12 • Atlantic hurricanes tend to form in the Middle Tropical Atlantic Ocean and Caribbean Sea • They usually propagate westward before turning northward • They dissipate rapidly over land Hurricane Steering Large-scale flow controls where hurricanes go. Williams, The Weather Book Hurricane Necessary Ingredients Williams, The Weather Book Warm Water with T 82oF Deep Warmth > 200 ft Converging Surface Winds Seedling Low Required Conditionally Unstable Air Supports Deep Convection Widespread, Deep Humid Air Supplies More Latent Heat Weak Vertical Wind Shear Shear Shreds Storm Apart Diverging Winds Aloft Where do Seedling Vortices Come? Lots of Places and Ways Remnant mid-lat circulation Remnant MCC circulation Danielson et al. Fig. 13.14 Vortices along ITCZ Easterly Waves 3D Flow within Hurricanes Winds aloft spiral outward clockwise Eyewall winds spiral upward c’clockwise Surface winds spiral inward c’clockwise Winds inside eye spiral downward clockwise Aguado and Burt, Fig. 12-3 Thermal Structure of Hurricane Aguado and Burt, Fig. 12-4 Radar of Andrew’s Landfall Most intense rainfall is along the eyewall. Fastest surface winds are along the eyewall. Region inside of eye is dry with light winds Rita TRMM "Hot Towers" Rita TRMM Rain Rate Danielson et al. Fig. 13.25 Floyd hourly rain loop from RSMAS Eye of Hurricane Luis 1995 Luis Visible Eye Animation Asymmetry of Hurricane Winds 20 kts Region of Maximum Storm Surge 100 kts 80 kts 80 kts 60 kts Aguado and Burt, Fig. 12-10 Hurricane Intensity Scale (> 980 mb) (965-980 mb) (945-964 mb) (920-944 mb) (< 920 mb) Williams, The Weather Book Primary Hurricane Hazards • Wind Damage Large-Scale Hurricane Circulation Itself Embedded Tornadoes • Flooding Heavy Rains Far Inland, 5”-10” Common Storm Surge along Shoreline Hurricanes Spawn Tornadoes • Tornadoes embedded within an overland hurricane tend to be weak (category F1-F2) • But they are embedded within an environment with 65+ kt winds. • Causes hurricane wind damage to be localized. Aguado and Burt, Fig. 12-11 Inland Flooding-Agnes 1972 • Even weak hurricanes can be catastrophic, hundreds of miles inland. • Agnes 1972, category 1 storm for a few hours. • Agnes merged with a slow-moving ET cyclone. • Up to 15” of rain in 24 h fell over Pennsylvania. • Previous flood records exceeded by 6 ft. • Damage > $10B in inflation adjusted dollars. • Costliest U.S. storm prior to Andrew and Katrina. Storm Surge I Williams, The Weather Book • Low atmosphere pressure raises a mound of water inside eye. • Water rises about 1 cm for every 1 mb decrease in pressure. • Inward spiraling winds push more water toward hurricane eye. • Deep hurricanes only raise about 1 meter of water over deep ocean. Water can sink downward and flow away from the surface. Storm Surge II Williams, The Weather Book • In shallow water near land, water can not flow away under surface. • But winds continue to push water inward towards storm’s center. • Winds along hurricane’s right flank also push water against shore. • Water piles up along shoreline and rushes inland. The big effect! • Effect is worse where ocean floor slopes gently - Gulf of Mexico! Link to COMET Surge Animation Storm Surge III Williams, The Weather Book • If hurricane hits at high tide, the two effects superimpose. • A 2 ft tide plus a 10 ft surge rises water 12 ft above mean sea level. • Penetration of storm-whipped waves inland worsens damage. • Waves cause far more destruction than the high water alone. Winds and Storm Surge Danielson et al.RSMAS Fig. 13.20 Floyd wave height forecast from Surge Damage • Richelieu Apartments before and after landfall of Camille 1969. • Camille was a Category 5 hurricane. • Sustained winds > 180 mph! • Storm surge was 24 feet along the coast! • Many tired citizens took refuge in apartments. Sadly, several died. http://en.wikipedia.org/ Hurricane Decay Andrew Central Pressure Danielson et al. Fig. 13.26 Hurricanes weaken when they make landfall (or go over cool water). Intense surface energy fluxes are cut off and friction increases. Summary: Hurricanes • What are differences between hurricanes and extratropical cyclones? Many significant ones! See earlier slide. • Where and when do hurricanes form? 5-20 latitude over oceans during warm season • How do hurricanes intensify? Energy source is surface energy fluxes from the underlying warm ocean Summary: Hurricanes • What is the structure of a hurricane? Eyewall - strongest winds, heaviest rain Eye - dry with light winds • What kind damage do hurricanes inflict? Can be catastrophic due to high winds, torrential rains, and coastal storm surges • When and where do hurricanes dissipate? At landfall or when they go over cold water Assignment for Next Lecture • Topic – Air Pollution • Reading - Ahrens, pg 317-324, 327-340 • Problems - 12.1, 12.5, 12.14, 12.15, 12.19, 12.23