Transcript Hurr Bill `09

Earth Science: Unit 1 (mini-unit)
Hurricanes
and Global Winds
Hurricanes
 Whirling tropical cyclones –intense low
pressure storms that produce winds of at
least 74 miles per hour are known in the
United States as hurricanes.
 Hurricanes form ONLY ON WARM WATER!
• Water must be >80 F. Because this is where
they get their energy from: between about 5 and
20 degrees north and south latitude.
(The North Pacific has the greatest number of
storms, averaging 20 per year, called typhoons)
2Air Mass needed for fueling
the energy of a hurricane.
 Maritime Tropical Air
• Maritime tropical air masses are warm, loaded
with moisture, and usually unstable*
• Warm air rises, cools and condenses, releasing
heat (energy) in the form of latent heat of
condensation.
•*Maritime
.
tropical air is the source of much, if not
most, of the precipitation received in the eastern
two-thirds of the United States.
Note the location of mT air masses
Upper Air Winds
The Role of Airflow Aloft
 More often than not, air high up in the
atmosphere fuels a middle-latitude cyclone
---(These are called “low pressure storms”)
 In hurricanes, fast upper-level wind sheer
off the tops of thunderstorms, preventing
the growth of tropical waves, depressions
or storms.
Severe Storm Development
Development of Thunderstorms and Waves
• Thunderstorms form when warm, humid air rises.
• Moving off Africa, clusters of storms are called
tropical “WAVES” –these often stay together
and become a tropical depression- especially in
late summer.
 Occurrence of Thunderstorms• At any given time, there are an estimated 2000
thunderstorms in progress on Earth. The
greatest number occur in the tropics where Air is
warm, moist, and unstable.
A wave exits the west coast of Africa and
begins to circulate.
• A wave starts to get together:
Review of the Conditions
needed for Hurricanes to
develop:
• Warm, humid air (over the water)
• Warm water (>80 degrees F) ..
• Thunderstorms to coordinate/circulate
(“Waves” coming off of Africa)
• Little to no wind sheer (in upper atm.)
greater than!
Parts of a hurricane:
Identify the following in the picture of Hurricane
Floyd.
EYE
EYE WALL
FEEDER BANDS
CENTRAL DENSE OVERCAST
-OR “CDO”
Satellite View of Hurricane Floyd
Cross Section of a Hurricane
Parts of a storm:
•Rain FEEDER bands ”Spiral arms”) are curving
lines of thunderstorms attached to the center.
• The eye is a zone of scattered clouds and calm
averaging about 20 kilometers in diameter at the
center of a hurricane.
• The eye wall is a doughnut-shaped area of
intense cumulonimbus development and very
strong winds that surrounds the eye of a
hurricane. Outside the eye wall is the
CENTRAL DENSE OVERCAST
Evolution and life cycle of a
Hurricane
• Hurricanes develop most often in the late
summer when water temperatures are
warm enough to provide the necessary
heat and moisture to the air.
• Tropical Wave…Tropical Depression…
• Tropical Storm (39 mph)
• Hurricane (74 mph) is when an eye can
form.
• Eventually, the storm will die (Land friction
and/or loss of energy)
Classifying Hurricanes
 Hurricane Intensity
• The Saffir-Simpson scale describes the intensity
of the hurricane. It is based on sustained wind
speed.
• A storm surge is the abnormal rise of the
oceans surface. (Think of it as a higher high tide
like a spring tide)
- This is due to the lower air pressure pushing
down on the water and also as a result of strong
winds.
Saffir-Simpson Hurricane Scale
Eye of hurricane (Not always seen)
Hurr. Bill- Sat. Aug 22, ’09
Why will Ct./New England be spared from a direct hit?
Sat
Hurricane Bill –Aug 23rd races past Nova
Scotia and Newfoundland.
SEPT 7
1) N. Carolina Coast (Non-tr.?Cold core)
2) T.S. FRED
SEPT 8 (TUE.) T.S. Fred 50 mph moving w-15
Wed. Cat. 2
105 mph
Starting to turn to the northwest. Cat 3 soon- before
weakening,turning.
Th.Sept
th
105
mph
nw-12
10