nats 101 lecture 20 hurricanes. supplemental references for today’s lecture aguado, e. and j. e....
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NATS 101
Lecture 20Hurricanes
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 Winds
Tropical Depression 25-39 mph
Tropical Storm 40-74 mph
Hurricane/Typhoon 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 Wilma 2005 882 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
Link to Older NASA Satellite Animations
2005 Atlantic Hurricanes NASA
Note cooler water in wake of Dennis, Emily and Katrina
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?
Strong FrontsCold at Storm Center AloftStrongest Winds AloftForms outside TropicsDiameter of 500-1000 milesEnergy Source: Horizontal
Temperature Contrast
Differences Between Tropical and Extratropical Storms
Williams, The Weather Book
No FrontsWarm at Storm Center AloftStrongest Winds near SurfaceForms over Tropical OceansDiameter of 200-500 milesEnergy Source: Energy Fluxes
from Warm Ocean
Where Hurricanes Form?
Williams, The Weather Book
HurricanesHurricanes
TyphoonsTropical Cyclones
Hot Bed!Hot Bed!
• 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
Occur in Warm SeasonMaximum Likelihood
when Sea Surface Temperatures are Warmest-September
Average of ~6 Per Year Large Yearly Variability
Fewer in El Nino YearsMore in La Nina Years
Danielson et al. Fig. 13.2
Atlantic Hurricane Tracks
• 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
Danielson et al. Fig. 13.12
Hurricane Steering
Williams, The Weather Book
Large-scale flow controls where hurricanes go.
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
Vortices along ITCZ Easterly Waves
Remnant MCC circulationDanielson et al. Fig. 13.14
3D Flow within Hurricanes
Aguado and Burt, Fig. 12-3
Surface winds spiral inward c’clockwise
Winds aloft spiral outward clockwise
Eyewall winds spiral upward c’clockwise
Winds inside eye spiral downward
clockwise
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
Danielson et al. Fig. 13.25
Floyd hourly rain loop from RSMAS
Rita TRMM "Hot Towers"Rita TRMM Rain Rate
Eye of Hurricane Luis 1995Luis Visible Eye Animation
Asymmetry of Hurricane Winds
20 kts
80 kts80 kts
60 kts
100 kts
Aguado and Burt, Fig. 12-10
Region of Maximum
Storm Surge
Hurricane Intensity Scale
Williams, The Weather Book
(> 980 mb) (965-980 mb) (945-964 mb) (920-944 mb) (< 920 mb)
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 a hurricane after landfall 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. Fig. 13.20Floyd wave height forecast from RSMAS
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, many died.
http://en.wikipedia.org/
Hurricane Decay
Hurricanes weaken when they make landfall (or go over cool water).Intense surface energy fluxes are cut off and friction increases.
Andrew Central Pressure
Danielson et al. Fig. 13.26
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