More About Hurricanes

HURRICANES

Open Ended

This is our second week focusing on hurricanes.

Please tell me something you remember about hurricanes.

What is a Hurricane?

• A "hurricane" is the most severe category of the

meteorological phenomenon known as the "tropical
cyclone.”

• Hurricanes begin as a tropical disturbance (or wave).

– A tropical disturbance is a discrete tropical weather system of apparently organized convection originating
in the tropics or subtropics and maintaining its identity
for 24 hours or more.

What is a Hurricane?

• Tropical cyclones are low pressure systems that have thunderstorm

activity and rotate counterclockwise.

– winds of 38 mph or less is called a tropical depression.

– winds reach 39-73 mph, it is called a tropical storm (gets a name)

– winds exceed 74 mph, the storm is considered to be a hurricane (keeps given name)

– The wind speed mentioned here are for those measured or estimated as the top

speed sustained for one minute at 10 meters above the surface.

Hurricane Rating Scale

• The Saffir-Simpson Hurricane Scale defines hurricane strength by

categories.

– Category 1 — winds 74-95 mph

– Category 2 — winds 96-110 mph

– Category 3 — winds 111-130 mph

– Category 4 — winds 131-155 mph

– Category 5 — winds 156 mph and up

• The category of the storm does not necessarily relate directly to the damage it will inflict. Lower category storms (and even tropical storms)
can cause substantial damage depending on what other weather features
they interact with, where they strike, and how slow they move.

Hurricanes-Mass Movement of Energy:

Hurricane-Forming Winds

• Despite being a Category 1 storm, Hurricane Ophelia caused significant

damage to buildings along the Outer Banks of North Carolina as a result of
the storm surge. Damage from Ophelia was estimated at about $70 million.

When is Hurricane Season?

• The Atlantic hurricane season is officially from 1 June to 30 November.

–These dates were selected to encompass over 97% of tropical activity.

• The Atlantic basin shows a very peaked season from August through October.

–Maximum activity is in early to mid September.

• El Nino → less active season

• La Nina → more active season

Multiple Choice

When is hurricane season?

• January 1 to May 30

• June 1 to August 30

• June 1 to November 30

• December 1 to November 30

Multiple Choice

The Atlantic basin shows a very peaked season from August through October, with Maximum activity is in early to mid September.

El Nino → ? active season

La Nina → ? active season

• Less

  More

• More

  Less

• Less

  Less

• More

  More

Where Do Hurricanes Form?

• Hurricanes need specific conditions in order to form, including the right

combination of sea surface temperatures and winds.

• Hurricanes that come near the east coast of the United States form in the

Atlantic off the coast of Africa, and further develop in the Caribbean, or in the Gulf of Mexico.

– It is in these areas that water temperatures exceed 27oC (80oF) during

the summer and early fall months.

• Hurricanes that form in the Pacific move awayfrom the United States.

– The water along the west coast rarely warms above 21o C (70oF).

Main tropical storm and
hurricane formation region

Multiple Choice

Which color on the map is the best representation of the main tropical storm and hurricane formation region?

• Red

• Blue

• Purple

• Yellow

Multiple Choice

Hurricanes need a combination of specific conditions to form including

• atmospheric temperature and sun.

• sea surface temperatures and winds.

Hurricane Formation

• Tropical storms get their energy from warm, moist air in the lower atmosphere, near the surface of the ocean.

• As the warm, moist air rises, it cools in the upper atmosphere, condensing into ring-shaped clouds.

• During condensation, a great deal of heat energy is released, causing more warm air to rise even faster as the wind speed increases.

• This whirlwind of rising air moves in a spiral direction around a core of relatively calm air known as the eye of a hurricane.

• Just outside the core, the strongest winds within the storm surround the eye in a dense wall of thunderstorms (eyewall).

Multiple Choice

True or False:

Tropical storms form when the warm, moist air from the sea rises and collides with the cool, unstable upper atmosphere air condensing into ring-shaped clouds.

• True

• False

Multiple Choice

True or False:

During the condensing into the ring-shaped clouds heat energy is released which causes more warm air to rise faster as wind speed increases. This whirlwind of rising air forms a tropical cyclone.

• True

• False

Multiple Choice

True or False:

The eye of the tropical cyclone also known as the "eye of the storm" is where the strongest winds of the thunderstorms reside.

• True

• False

Hurricane-Forming Winds

• Whether or not a tropical disturbance develops into a hurricane depends to a great degree on wind shear.

• Wind shear is a change in the wind speed and/or direction over a short distance.

• For hurricane formation, it is the difference in wind velocity at upper and lower levels in the atmosphere that is of greatest concern.

– Hurricane formation requires light, upper-level winds that do not
change much in direction or speed
throughout the depth of the
atmosphere—low wind shear.

Multiple Choice

Whether or not a tropical disturbance develops into a hurricane depends to a great degree on __.

• wind depth

• wind heat

• wind shear

Multiple Choice

Wind shear is a change in the wind __ and/or __ over a short distance.

• wind speed

  and/or

  direction

• wind shape

  and/or

  direction

• wind tunnel

  and/or

  heat

• wind heat

  and/or

  atmospheric pressure

Multiple Choice

For hurricane formation, it is the difference in wind velocity at upper and lower levels in the atmosphere that is of greatest concern.

Hurricane formation requires light, upper-level winds that do not
change much in direction or speed
throughout the depth of the
atmosphere—low wind shear.

Based on the above information, what is the greatest concern in the formation of a hurricane?

• difference in wind velocity at upper and lower levels in the atmosphere

• similarity in wind velocity at upper and lower levels in the atmosphere.

Multiple Choice

Hurricane formation requires light, upper-level winds that do not
change much in direction or speed
throughout the depth of the
atmosphere—low wind shear.

Based on the above information, which is a more accurate situational description of low wind shear?

• A day that includes light breezes, low to no frontal activity, consistent temperatures, and minimum to no surface obstructions.

• A day that includes frontal activity, thunderstorms, temperature inversions, and surface obstructions.

How Does the Coriolis Affect

Hurricanes?

• Winds are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere as a result of the Coriolis Effect.

This means that hurricanes in the Northern Hemisphere spin counterclockwise while
hurricanes that form in the Southern Hemisphere rotate in the clockwise direction.

Multiple Choice

Winds are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere as a result of the Coriolis Effect.

This means that hurricanes in the Northern Hemisphere spin...

• counterclockwise direction.

• clockwise direction.

Multiple Choice

Winds are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere as a result of the Coriolis Effect.

This means hurricanes that form in the Southern Hemisphere rotate in the...

• counterclockwise direction.

• clockwise direction.

Multiple Choice

The hurricane to the left formed in which hemisphere, and how can you tell?

• Northern Hemisphere because it is spinning counterclockwise due to the Coriolis Affect.

• Northern Hemisphere because it is spinning clockwise due to the Coriolis Affect.

• Southern Hemisphere because it is spinning counterclockwise due to the Coriolis Affect.

• Southern Hemisphere because it is spinning clockwise due to the Coriolis Affect.