Hurricanes key terms

Question 1

Cyclone

Answer 1

large low pressure system with circulating winds

Question 2

what classes as a Hurricane

Answer 2

winds over 74 mph

Question 3

wind intensification order

Answer 3

• tropical disturbance
• tropical depression
• tropical storm
• hurricane

Question 4

hurricane facts

Answer 4

• largest hurricane on record winds up to 190 mph (Alan, 1980)
• typically 500-1000km in diameter
• can be associated with heavy rains, tornados and storm surges on the coast

Question 5

hurricane season

Answer 5

• For the N.H., August and September are the most active months.
• For the S.H., the hurricane season is January to March.

Question 6

how do hurricanes occur

Answer 6

• Hurricanes obtain their energy from
latent heat release in the cloud
formation process
• Hurricanes occur where a deep layer
of warm waters exists and during the
times of highest SSTs.

Question 7

hurricane characteristics

Answer 7

• High-pressure air masses flow towards
low-pressure zone
• Wind created is deflected to the right
by Coriolis effect
• Counter-clockwise rotation
• Tropical cyclones
• 5-20˚ latitude
• Extra tropical cyclones
• 30-70˚ latitude (associated with
frontal systems – discussed last
week)
• Dependent on large area of warm water – min 26˚C

Question 8

Structure of a hurricane

Answer 8

• clouds and wind patterns
• warm moist surface water rises = rain bands (thunderstorm)
• sinking dry air = areas of fewer clouds
• the eye of a hurricane

Question 9

the eye of a hurricane

Answer 9

- is an area of descending air,
relatively clear sky, and light winds
which is about 25 km (15 mi) in
diameter on average
- a shrinking eye indicates intensification 
- The eye wall is comprised of the
strongest winds, the largest clouds,
and the heaviest precipitation with
rainfall rates as high as 2500 mm/day
- Eye is fast moving – 20km/hr

Question 10

hurricane source areas

Answer 10

• deep water areas (several 10’s of metres)
• beyond 20oN, waters usually too cool
• needs unstable atmosphere
• needs air movement via Coriolis effect (not present 0-5oN)

Question 11

hurricane formation

Answer 11

• instability generated from storms (low pressure areas) in easterly trade winds (easterly waves)
• moves westwards via trade winds
• 10% of tropical disturbances develop into organised rotating storms
• disturbance = depression if winds increase and warm moist air drawn in (energy)
• wind shear

Question 12

wind shear

Answer 12

• difference in wind speed between the sea surface and upper tropsphere must be very low
• strong winds prevent development

Question 13

hurricanes in a warming climate

Answer 13

• conditions necessary for hurricane formation restrict location to certain latitudinal location to certain latitudinal boundaries
• formation area highly unusual (warm moist gulf stream, unusually cool upper atmosphere)
• as world warms, range of regions with conditions suitable for hurricane formation and persistence may grow

Question 14

Extended Hurricane Activity (EHA) index

Answer 14

• Burns and Palmer, 2015
• Caribbean region
• Last 1000 years