Tropical Cyclones & Societal Impacts

Tropical M. D. Eastin

Tropical Cyclones & Societal Impacts


Outline

Meteorological Impacts Landfall

• Winds and the Saffir-Simpson Scale• Storm Surge and Waves• Rainfall• Predecessor Rain Events (PREs) • Tornadoes• Death and Damage

Beyond Death and Damage

Are we affecting the TC climatology?


Winds and the Saffir-Simpson Scale

A Classification System for TCs

• Developed by Herbert Saffir (civil engineer) and Dr. Robert Simpson (NHC Director) in 1971 as a means to convey expected structural damage caused by a hurricane with a given maximum wind speed

• Initially designed to guide civil engineers in the establishment of building codes. Thus, damage estimates are for structures built to code (Was your residence built to code?)

• Modified versions of the Saffir-Simpson Scale are used worldwide

• NHC recently updated the scale with additional information on potential damage to various structures and infrastructure **

Dr. Robert Simpson

Herbert Saffir


Saffir-Simpson Scale



Category 1

• Maximum winds (74-95 mph; 64-82 knots)• No real damage to anchored structures. Some damage to unanchored mobile homes shrubs trees and signs.

Category 2

• Maximum winds (96-110 mph; 83-95 knots)• Some roof and window damage to anchored structures. Considerable damage to trees unanchored mobile homes, signs, and piers.

Category 3

• Maximum winds (111-130 mph; 96-113 knots)• Some structural damages to small structures. Most trees and mobile homes destroyed.



Category 4

• Maximum winds (131-155 mph; 114-135 knots)• Extensive damage to residential structures

Category 5

• Maximum winds (>156 mph; >135 knots)• Complete destruction of most structures


Storm SurgeBasic Concept:

• Rise in sea level and onshore rush of water caused by the “piling up” of water by the strong winds and a small rise due to the suction effect by the low pressure

• Ranges from < 10 cm to > 10 m

• Does not include waves

• Significant threat to coastal structures

Primary Factors in Surge Height:

• Maximum winds• Minimum surface pressure• Size of wind field• Storm speed• Coastline shape• Slope of the continental shelf• Tidal cycle

Shallow Sloped Shelf

Steep Sloped Shelf


Storm Surge

Forecasting Storm Surge:

SLOSH (Sea Lake and Overland Surges from Hurricanes) Model

• Run at NHC

• Uses storm pressure, winds, size, track, and forward speed as predictors

• Incorporates detailed ocean, coastal, and river bathymetry observations

• Forecasts are accurate to within 20%

• Highly dependant on track SLOSH Model run for a hypothetical weak hurricane


Waves

Waves are Superimposed upon the Storm Surge:

• Waves heights are greater at higher winds • Typical open-ocean wave heights are 5 to 15 meters (16-50 feet)• Maximum observed wave height 27.7 meters (97 feet) in Ivan (2004)• Significant threat to coastal structures and beaches

Hurricane Bonnie (1998)Mean Wave Heights (m)

at Landfall

Hurricane Bonnie (1998)Mean Wave Heights (m)

in the open oceanshown over the coastline

* *

Storm center

From Walsh et al. (2002)


Impact of Storm Surge and Waves


Result of a 25 foot surgeand 15-20 foot waves

Impact of Storm Surge and Waves


Rainfall

The greatest threat during a TC landfall:

• Significant in even weak TS

Spatial distribution is a function of:

• Intensity• Forward Motion• Terrain• Vertical Wind Shear• Environmental Moisture

Forecasts:

• Remains a difficult forecast challenge

• Old Rule: 100 inches / Speed (knots)

• Aided by NWS WSR-88D radar and the TRMM precipitation radar

Rainfall vs. Intensity

Average RainfallEntire TC

Average Rainfallby Region

Eyewall

Rainbands

From Cerveny et al. (2002)


Rainfall

Accumulated Rainfall

Storm Motionand Shear Vectors

Storm Motionand Shear Vectors

Accumulated Rainfall

Along-Track Shear Cross-Track Shear

From Rogers et al. (2003)


Rainfall

Hugo at Landfall

Intensity: 120 knotsMotion: NW at 24 knotsShear: from the SE at 5 knots

Danny at Landfall

Intensity: 65 knotsMotion: NE at 3 knotsShear: from the E at 5 knots


Rainfall

Ivan at Landfall

Intensity: 105 knotsMotion: N at 12 knotsShear: from the SW at 7 knots

Floyd at Landfall



Rainfall

Allison at Landfall


Dean at Landfall

Intensity: 40 knotsMotion: NW at 6 knotsShear: from the NE at 5 knots


Predecessor Rain Events (PREs) Mesoscale region of heavy rainfall located ahead of an approaching TC Can “prime” a region for extensive flooding by saturating the soil before the TC-related rainfall arrives.

From Galarneau

et al.(2010)

TropicalStormErin

(2007)


Predecessor Rain Events (PREs)

Defining Criteria:

Radar dBZ > 35 within a coherent mesoscale area for at least 6 hr

Area-average rain rate > 100 mm/day

Well-defined separation (~1000 km) between the TC and PRE

Associated with a deep plume of tropical moisture intersecting a low-level baroclinic zone (or front) beneath a jet entrance region

From Galarneau et al. (2010)

Shading = Radar ReflectivityWind barbs = 0-6 km ShearContours = Surface TemperatureLine = Surface FrontLine = Upper-level Jet




Common Characteristics:

• PREs are located ahead of and to the left of the TC track (LOT)

• Upper-level jet is anticyclonically curved (AC)

• Moisture plume typically contains Total Precipitable Water (TPW) in excess of 50 mm

Notable PREs:

• Frances 2004 (in NY)• Marco 1990 (in TN, NC, VA)• Agnes 1972 (in DC, MD, and PA)

Erin

PRE





Tornadoes

Basic Statistics:

• Roughly 60% of landfalling TCs have at least one tornado reported• Hurricane Beulah (1967) had 113 tornadoes reported (the maximum)

• Over 70% of tornadoes are located in outer rainbands• Over 85% occur in the right-front quadrant with respect to the storm motion vector

• Over 90% are F0-F2 on the Fujita scale (max winds 32-90 m/s)

• Roughly 60% of tornadoes occur between 12-18 LST• Over 70% occur when the TC is within 250 km of the coast

From McCaul (1991)

Location of all Hurricane Tornadoes (1948-1986)

StormMotion


TornadoesRelationship to CAPE and Low-Level Shear:

• McCaul (1991) performed a census of 1296 soundings made within 3 hours and 185 km of a reported hurricane tornado.

• Hurricane tornadoes form in a low CAPE (~700 J/kg) but high vertical shear (~10 m/s between 0-6 km altitude) environments• [For comparison] Great Plains tornadoes form in high CAPE (~2500 J/kg) and high vertical shear (~12 m/s between 0-6 km) environments

From McCaul (1991)

Hurricane Tornado Locations Mean CAPE Mean 0-6 km Shear


Physical Mechanism for Hurricane Tornado Genesis:

• Proposed by Gentry (1983)

• Increased low-level vertical shear results from enhanced friction as air flows onshore• Produces low-level horizontal vorticity “tubes”

• If these “tubes are tilted into the vertical by an updraft/downdraft couplet• Further convergence into the updraft region could increase the (now) vertical vorticity and a tornado may forms

Tornadoes

Offshore Flow Onshore Flow

1

2

3


Tornadoes

Radar Signature of Hurricane Tornado Cells

• Tornado producing cells often exhibit “hook echoes”, suggesting a link to a mesovortex and the classic Great Plains supercell structure

• Hurricane supercells are often shallow with a mesovortex confined below 3 km

WSR-88D radar and Forecasts:

• Tornadoes are often associated small cells with > 50 dBZ echoes and storm relative rotational velocities of 6-15 m/s that persist for 1-2 hours

• The rotational features are often identifiable up to 30 min prior to the tornado sighting

From Eastin and Link (2009)

Tornadic CellsHurricane Ivan (2004)


Tornadoes

New Research: Hurricane supercells can form well offshore

From Eastin and Link (2009)

Intense Convective Cells

Tornadic Cells in Hurricane Ivan (2004)

Dual DopplerAnalysis Box(1804 UTC)


Tornadoes

Radar ReflectivityCell-relative Winds

Dual-Doppler Analysis Z = 1.5 km

Each cell exhibits

an inflow notch or hook echo

From Eastin and

Link (2009)


Updrafts > 2 m/sVorticity > 2x10-3 s-1

Downdrafts < -2 m/sVorticity < -2x10-3 s-1

Dual-Doppler Analysis Z = 1.5 km


Tornadoes

From Eastin and

Link (2009)

Collocated updrafts and cyclonic vorticity

indicative of supercells


Updrafts > 2 m/sVorticity > 2x10-3 s-1

Downdrafts < -2 m/sVorticity < -2x10-3 s-1

Dual-Doppler Analysis


Tornadoes

From Eastin and

Link (2009)

Shallow updrafts

and vorticity indicative of

mini-supercells


Death and Damage

Tropical cyclones are arguably the greatest natural threat to mankind:

Notable Tropical Cyclones of History:

Deaths Damage*Bangladesh 1970 > 300,000Bangladesh 1991 > 138,000 > $1.5 billionChina 1922 > 50,000Hurricane Mitch 1998 ~11,000 > $1.0 billionTyphoon Vera 1958 > 5,000Galveston Hurricane 1900 ~6000Hurricane Katrina 2005 ~2000 > $92.0 billionHurricane Sandy 2012 72 > $50.0 billionHurricane Andrew 1992 23 > $25.0 billion

* Value at time of occurrence

Comprehensive global statistics of death and damage for an “average” TC are unavailable.


Death and Damage

Death Statistics for the U.S.

Based on statistics from Rappaport (2000) for the period 1970-1999:

• A total of 600 people died directly from tropical cyclones• Greatest loss of life was 125 in Hurricane Agnes (1972) 59% Fresh-water flooding 23% Drowning after leaving a vehicle 12% Winds 10% Offshore 7% Surf / riptides 4% Tornadoes 1% Storm surge 2% Other

Note: Over 2000 deaths occurred from Katrina 2005 alone


Death and Damage

Damage Statistics for the U.S.

All Natural Disasters (1960-2002)

From Cutler and Emrich (2005)


Death and Damage

Damage Statistics for the U.S.

Based on statistics from Pielke and Landsea (1998) for the period 1925-1995:

• All damages were normalized to 1995 dollars ($) based on changes in coastal populations and changes in wealth (both have dramatically increased in the past two decades)

• Average annual impact of landfalling TCs is ~$4.8 billion• Over 83% of all damages are from Cat - 345 storms (21% of all TCs) • Costliest Tropical cyclones in US history:

1. Katrina 2005 $76 billion 2. SE FL-AL 1926 $72 billion 3. Andrew 1992 $33 billion 4. SW FL 1944 $17 billion 5. New England 1938 $16 billion

11. Sandy 2012 $11 billion (adjusted to 1995 dollars)12. Hugo 1989 $9 billion


Death and Damage

Damage Statistics: The Importance of Building Codes

• Statistics are skewed due to poor building codes (or their non-compliance) in coastal communities

• Huge need for improvement!

• Inexpensive – could save $4 in damages for every $1 spent to “hurricane-proof” a structure

Galveston, TexasHurricane Ike (2008)

Home of a retired coupleTheir son is an architect

and he made sure the house was built to code

Evidently the others were not!





Tropical Cyclone Impacts:

International National Local

Trade (port closures) Price of gasoline / heating oil Loss of basic utility services Stocks Markets Price of consumable goods ATMs inoperable Currency Values Cost of construction Cash registers inoperable Aid / Supplies Cost of insurance policies No credit card transactions

Legislation No working gas pumpsGovernment self-studies Perishable food spoils

Loss of infrastructure No food deliveries Loss of civil order (police/fire) Limited medical services Schools destroyed Businesses destroyed

Need for psychological servicesNeed for social services


Our Affect on Tropical Cyclones

Is human activity changing the frequency or intensity of TCs?

One approach: Does the GFDL hurricane model produce more intense tropical cyclones in a high-CO2 world?

• From Knutson et al. (2001)

• GFDL hurricane model: Limited area (global models provide BCs)Employs three nested grids

Inner two grids follow the TCHighest resolution is 1/6º (~18

km)Coupled to the oceanComplex bogus vortex scheme

• Two Environments Control (Present day ocean-atmosphere)

High-CO2 (in 70-120 years with double CO2)



Knutson et al. (2001)

• The High-CO2 ocean-atmosphere boundary conditions were obtained from the mean conditions during forecast years 71-120 of a coupled simulation of the GFDL global climate model using a +1% increase in CO2 per year as “forcing”

• Forcing was based on observations and previous modeling efforts**

• In the high-CO2 “world” tropical SSTs are ~2.5ºC warmer

From Meehl et al. (2004)



Knutson et al. (2001)

• Performed numerous simulations in both environments with a spectrum of bogus vortices incorporating random perturbations to the maximum wind

• Repeated the process in the six global tropical cyclone basins

• The net global mean result was a ~5% increase in maximum intensity

• Since the high-CO2 environment occurs 70-120 years in the future, detecting a trend in TC intensity due to global warming would be nearly impossible

From Knutson et al. (2001)


Summary:

• Meteorological Impacts Landfall

• Winds and the Saffir-Simpson Scale (origin)• Storm Surge and Waves (primary factors, forecasting)• Rainfall (primary factors, forecasting)• Tornadoes (statistics, environment, processes, forecasting)• Death and Damage (diversity and contributions to totals)

• Beyond Death and Damage

• Are we affecting the TC climatology? (current results)

Tropical Cyclones & Societal Impacts


ReferencesEastin, M.D., and M. C. Link, 2009: Miniature supercells in an offshore outer rainband of Hurricane Ivan (2004),

Mon. Wea. Rev., 137, 2081-2104.

Galarneau, T. J., L. F. Bosart, and R. S. Schumacher, 2010: Predecessor rain events ahead for tropical cyclones. Mon. Wea. Rev., 138, 3272-3297.

Gentry, R. C. , 1983: Genesis of tornadoes associated with hurricanes, Mon. Wea. Rev., 115, 1206-1223.

Houston, S. H., and M. D. Powell, 1994: Observed and modeled wind and water-level response from Tropical StormMarco (1990), Wea. Forecasting, 9, 427-439.

Houston, S. H., W. A. Schaffer, M. D. Powell, and J. Chen, 1999: Comparisons of HRD and SLOSH surface wind fieldsin hurricanes: Implications for storm surge forecasting. Wea. Forecasting, 14, 671-686.

Knutson, T. R., and Coauthors, 2001: Impact of CO2-induced warming on hurricane intensities as simulated in ahurricane model with ocean coupling. J. Climate, 14, 2458-2468.

McCaul, E. W., Jr, 1991: Buoyancy and shear characteristics of hurricane-tornado environments. Mon. Wea. Rev.,119, 1954-1978.

Pielke, R. A., Jr., and C. W. Landsea, 1998: Normalized hurricane damages in the United States: 1925-95. Wea.Forecasting, 13, 623-631.

Rappaport, E. N., 2000: Loss of life in the united states associated with recent Atlantic tropical cyclones.Bull. Amer. Met. Soc., 81, 2065-2073.

Rogers, R, S. Chen, J. Tenerelli, and H. Willoughby, 2003: A numerical study of the impact of vertical shear on thedistribution of rainfall in Hurricane Bonnie (1998). Mon. Wea. Rev., 131, 1577-1599.

Spratt, S. M., D. W. Sharp, P. Welsh, A. Sandrik, F. Alsheimer, and C. Paxton, 1997: A WSR-88D assessment oftropical cyclone outer rainband tornadoes. Wea. Forecasting, 13, 479-501.

Walsh, E. J., and Coauthors, 2002: Hurricane directional wave spectrum spatial variation at landfall. J. Phys. Ocean.,32, 1667-1684.

Documents

Tropical Cyclones & Societal Impacts