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NATS 101 Lecture 30 Hurricanes. Supplemental References for Today’s Lecture. Aguado, E. and J. E. Burt, 2001: Understanding Weather & Climate, 2 nd Ed . 505 pp. Prentice Hall. (ISBN 0-13-027394-5)

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supplemental references for today s lecture
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
Types of Tropical Cyclones

Cyclone TypeWinds

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
Some Hurricane Extremes

Lowest Central PressurePressure

Pacific: Typhoon Tip 1979 870 mb

Atlantic: Hurricane Wilma 2005 882 mb

Costliest HurricanesCost-Loss

Hurricane Andrew 1992 $25 billion

Hurricane Katrina 2005 $200 billion?

Bangladesh Cyclone 1970 300,000 dead

andrew 1992 time sequence
Andrew 1992 Time Sequence

2005 Atlantic Hurricanes NASA

Note cooler water in wake of Dennis, Emily and Katrina

Link to Older NASA Satellite Animations

u s hurricane deaths and costs
U.S. Hurricane Deaths and Costs

Williams, The Weather Book

hurricane lecture overview
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
Strong Fronts

Cold at Storm Center Aloft

Strongest Winds Aloft

Forms outside Tropics

Diameter of 500-1000 miles

Energy Source: Horizontal Temperature Contrast

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

Differences Between Tropical and Extratropical Storms

Williams, The Weather Book

where hurricanes form
Hot Bed!

Tropical Cyclones




Williams, The Weather Book

Where Hurricanes Form?
  • 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 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 Frequency

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

Atlantic Hurricane Tracks

Danielson et al. Fig. 13.12

hurricane steering
Hurricane Steering

Large-scale flow controls where hurricanes go.

Williams, The Weather Book

hurricane necessary ingredients
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

Hurricane Necessary Ingredients

Williams, The Weather Book

where do seedling vortices come lots of places and ways
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
3D Flow within Hurricanes

Winds aloft spiral outward clockwise

Winds inside eye spiral downward clockwise

Eyewall winds spiral upward c’clockwise

Surface winds spiral inward c’clockwise

Aguado and Burt, Fig. 12-3

thermal structure of hurricane
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

Radar of Andrew’s Landfall

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
Eye of Hurricane Luis 1995

Luis Visible Eye Animation

asymmetry of hurricane winds
Asymmetry of Hurricane Winds

Region of Maximum Storm Surge

20 kts

100 kts

80 kts

80 kts

60 kts

Aguado and Burt, Fig. 12-10

hurricane intensity scale
Hurricane Intensity Scale

(> 980 mb)

(965-980 mb)

(945-964 mb)

(920-944 mb)

(< 920 mb)

Williams, The Weather Book

primary hurricane hazards
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.

Hurricanes Spawn Tornadoes

Aguado and Burt, Fig. 12-11

inland flooding agnes 1972
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 BookStorm Surge I
  • 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 BookStorm Surge II
  • 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 BookStorm Surge III
  • 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
Winds and Storm Surge

Floyd wave height forecast from RSMAS

Danielson et al. Fig. 13.20

surge damage
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.

hurricane decay
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
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 hurricanes1
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
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