Hurricanes

A ‘Survival Guide’ ProjectW4400: Dynamics of Climate Variability and Climate

ChangeEmily Firth, Bali White

What are hurricanes?(AKA cyclones and typhoons)

• intense low pressure disturbances • Form, migrate over tropical ocean regions• conditions required: high SST (> 26°C) and weak vertical wind

shears. • intense winds and very strong convective activity• -> thunderstorms and large amounts of rainfall.• takes days or a week to form• spreads over a radius of a few hundred kilometers. • surrounded by rings of towering thunder clouds spiraling up to a small

circle at the center of the storm--the eye. • winds here can reach a speed of 100+ km/hour and the most intense

rainfall occurs. • inside eye, air is still and convection suppressed by (subsidence). has a

radius of 30-40 km. • major damage potential / loss of life when they make landfall.

A regional snapshot

 This map shows the tracks of all Tropical cyclones which formed worldwide from 1985 to 2005

North Atlantic Ocean

SW Pacific Ocean

West Pacific Ocean

North Indian OceanEast Pacific Ocean

South Indian Ocean

 Typhoon Durian, Philippines Dec 2006

Migration of Hurricanes• hurricane tracks curve eastward and they speed up north

of ~30°N • active in the "trade wind" belts - north or south of the

equator where the winds blow steadily from east to west• initiated by weak pressure perturbations that exist in the

tropics. • move west with the trade winds in a steady, relatively

slow motion (10-20 km/hour). • intensify primarily through release of latent heat in

surrounding clouds; small percentage reach full hurricane intensity.

Global warming and hurricanes

• Tropical sea surface temperature (SST) increase of 0.25-0.5C over past several decades

• Future projections linking global warming to hurricane trends are hotly debated

• Role of Global Climate Models• Uncertainties and limitations

– Year-to-year and multidecadal variability in SST and hurricane activity

– Variation in historical and regional hurricane data– Temporal limitations: reliable satellite data only last 30 years

Three ‘take home’ points• A likely increase in hurricane intensity with rising

tropical SSTs• Regions of hurricane origin likely to remain

unchanged• Uncertainty surrounding impacts of increasing

SSTs on hurricane frequency

Useful resources

• HURDAT: Atlantic basin hurricane database www.aoml.noaa.gov/hrd/hurdat

• Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report. Climate Change 2001: The Scientific Basis. http://www.grida.no/climate/ipcc_tar/wg1/index.htm

• Wikipedia: The Free Encyclopediawww.wikipedia.org/wiki/Hurricanes

View of the eyewall of Hurricane Katrina taken on Aug 28, 2005.