II. Hurricanes
A. Other names
B. Source regions for hurricanes
C. Formation
Easterly Waves, storm levels
D. Months of frequent hurricanes
E. Compared to tornados
F. Anatomy
eyewall, eye
G. Favorable Conditions and Seasons
H. Destruction
track, Saffir-Simpson scale
I. Watch vs. Warning
A. Other Names…
“typhoon” (W. North Pacific Ocean, South Pacific)
Typhoon Angela
“baguio” (Philippines)
“tropical cyclone” (Indian Ocean)
Tropical Cyclone Hondo
“taino” (Haiti)
“cordonazo” (W. coast, Mexico)
B. Source regions
C. Formation
US hurricanes usually begin as “Easterly Waves” in tropics, off west coast of Africa:
Trough of low pressure over tropical oceans
East side: convergence, rain
Storm Levels:
1.Tropical disturbances
(10% become hurricanes)
2.Tropical depressions: < 36 mph
3.Tropical Storms: 39 mph, named
4. Hurricanes (Tropical Cyclone): 74 mph
D. Months of frequency
Originate in tropics over warm oceans:
N. Hem: August – September
S. Hem: January - March
E. Comparisons:
10’s of meters wide; higher wind speeds; < 2 hours
Hurricane: 100 -1000 mi. wide; lower wind speed (90 - 200); several days - week
F. Anatomy of a hurricane:
Spiral bands of cumulonimbus clouds
Low pressure center
(lowest 870 mb)
Eyewall : most intense rainfall
100 in / day
Highest wind speeds
Eye: clear, calm center
Average: 15 miles wide (1 hour duration)
Descending air
Source of fuel: latent heat of condensation!!
G. Favorable conditions:
Vast, warm ocean surface
Converging surface winds
Coriolis spin
Divergence (outflow) aloft
H. Hurricane destruction
High winds (>120 km / hr)
Heavy rainfall (25 cm - several meters / day)
Storm surge : sudden rise of water level
Responsible for most deaths
Hurricane intensity scale:
Saffir-Simpson Scale :
based on pressure, wind speed and storm surge
Categories 1 – 5 : weak, moderate, strong, very strong, devastating
I. Watch/Warning
Hurricane watch: landfall > 24 hours
Hurricane warning: landfall < 24 hours