11.0 hurricanes

Typhoons, and Cyclones

By

Kella Randolph M.Ed.

HURRICANES

Air pressure is measured in millibars (mb).

Air pressure is equal to the weight of a vertical column of air divided by the area of the base of the column.

AIR PRESSURE – THE FORCE OF AIR ON A SURFACE.

• A HURRICANE WARNING issued for your part of the coast indicates that sustained winds of at least 74 mph are expected within 24 hours or less. Once this warning has been issued, your family should be in the process of completing protective actions and deciding the safest location to be during the storm.

• A HURRICANE WATCH issued for your part of the coast indicates the possibility that you could experience hurricane conditions within 36 hours. This watch should trigger your family's disaster plan, and protective measures should be initiated, especially those actions that require extra time such as securing a boat, leaving a barrier island, etc.

WATCH VS WARNINGKNOW THE DIFFERENCE

• Typhoon — (the Northwest Pacific Ocean west of the dateline)

• Severe Tropical Cyclone — (the Southwest Pacific Ocean west of 160E or Southeast Indian Ocean east of 90E)

• Severe Cyclonic Storm — (the North Indian Ocean)

• Tropical Cyclone — (the Southwest Indian Ocean)

• A hurricane is a severe tropical storm that forms in the North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline, or the South Pacific Ocean east of 160E. Hurricanes need warm tropical oceans, moisture and light winds above them. If the right conditions last long enough, a hurricane can produce violent winds, incredible waves, torrential rains and floods. In other regions of the world, these types of storms have different names.

• A tropical storm becomes a hurricane when winds reach 74 mph. There are on average six Atlantic hurricanes each year; over a three-year period, approximately five hurricanes strike the United States coastline from Texas to Maine. The Atlantic hurricane season begins June 1 and ends November 30. The East Pacific hurricane season runs from May 15 through November 30, with peak activity occurring during July through September. In a normal season, the East Pacific would expect 15 or 16 tropical storms. Nine of these would become hurricanes, of which four or five would be major hurricanes.

HURRICANES ROTATE IN A COUNTERCLOCKWISE DIRECTION AROUND AN "EYE."

• NOAA

• Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides.

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• Storm surge should not be confused with storm tide, which is defined as the water level rise due to the combination of storm surge and the astronomical tide. This rise in water level can cause extreme flooding in coastal areas particularly when storm surge coincides with normal high tide, resulting in storm tides reaching up to 20 feet or more in some cases.

Storm tideStorm surge

STORM SURGE VS. STORM TIDE

• Storm surge is the abnormal rise in seawater level during a storm, measured as the height of the water above the normal predicted astronomical tide. The surge is caused primarily by a storm’s winds pushing water onshore. The amplitude of the storm surge at any given location depends on the orientation of the coast line with the storm track; the intensity, size, and speed of the storm; and the local bathymetry. NOAA

HURRICANE STORM SURGE

• Storm tide is the total observed seawater level during a storm, resulting from the combination of storm surge and the astronomical tide. Astronomical tides are caused by the gravitational pull of the sun and the moon and have their greatest effects on seawater level during new and full moons—when the sun, the moon, and the Earth are in alignment. As a result, the highest storm tides are often observed during storms that coincide with a new or full moon.

• NOAA

STORM TIDE IS THE TOTAL OBSERVED SEAWATER LEVEL DURING A STORM

NWS CHARLESTON, SC - HURRICANE HUGOHURRICANE HUGO'S MAXIMUM STORM TIDES ACROSS SOUTH CAROLINAWWW.ERH.NOAA.GOV1087 × 764SEARCH BY IMAGE

STORM SURGE DAMAGE

AT SEA LEVEL, AIR PRESSURE AVERAGES 1,013 MILLIBARS.

HIGH AND LOW AIR PRESSURE AREAS

CORIOLIS EFFECT – THE CURVING OF MOVING OBJECTS, INCLUDING WIND, FROM A STRAIGHT PATH DUE TO EARTH’S ROTATION.

• o In addition to causing winds to blow in a curved path, the Coriolis effect causes ocean currents to flow in a curved path.

• In the Northern Hemisphere, the Coriolis effect causes moving objects to curve to the right. In the Southern Hemisphere, the Coriolis effect causes moving objects to curve to the left.

• CORIOLIS EFFECT – THE CURVING OF MOVING OBJECTS, INCLUDING WIND, FROM A STRAIGHT PATH DUE TO EARTH’S ROTATION.

• The Coriolis effect causes winds to curve to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This results in a counterclockwise rotation for Northern Hemisphere hurricanes and a clockwise rotation for Southern Hemisphere hurricanes.

• Hurricanes form when an area of low pressure forms over warm water. Winds blow toward the low pressure, but are deflected by Earth’s rotation.

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HURRICANES FORM OVER WARM WATER

Eye – the core of warm, relatively calm air with low pressure and light winds at the center of a hurricane.

Eye

The most violent storms in a hurricane generally surround the eye in an area known as the eye wall.

Eye Wall

• In the western Pacific Ocean, hurricanes are called typhoons,

• and in the Indian Ocean and around Australia, hurricanes are called tropical cyclones.

typhoons, and tropical cyclones

HURRICANE – A LARGE, ROTATING TROPICAL STORM WITH WIND SPEEDS OF AT LEAST 74 MPH.

HURRICANE

• Category 1: 74-95 mph (119-153 km/hr)




• Category 5: greater than 155 mph (249 km/hr)

Hurricanes are categorized based on their wind speeds:

PASTE URL INTO A NEW WINDOW TO PLAY.HTTP://OCEANEXPLORER.NOAA.GOV/EDU/LEARNING/14_HURRICANES/ACTIVITIES/HURRICANE_CATEGORIES.HTML

http://oceanexplorer.noaa.gov/edu/learning/14_hurricanes/activities/hurricane_categories.html

http://oceanexplorer.noaa.gov/edu/learning/14_hurricanes/activities/hurricane_categories.html

Category 1: A Minimal Hurricane

Winds: 74-95 mph, 64-83 kts, 119-153 km/h

Minimum surface pressure: higher than 980 mbar

Storm surge: 3-5 ft, 1.0-1.7 m

Damage primarily to shrubbery, trees, foliage, and unanchored homes. No real damage to other structures. Some damage to poorly constructed signs. Low-lying coastal roads inundated, minor pier damage, some small craft in exposed anchorage torn from moorings. Example: Hurricane Jerry (1989).

Category 1: 74-95 mph (119-153 km/hr)

• Category 2: A Moderate Hurricane

• Winds: 96-110 mph, 84-96 kts, 154-177 km/h

• Minimum surface pressure: 979-965 mbar

• Storm surge: 6-8 ft, 1.8-2.6 m

• Considerable damage to shrubbery and tree foliage; some trees blown down. Major damage to exposed mobile homes. Extensive damage to poorly constructed signs. Some damage to roofing materials of buildings; some window and door damage. No major damage to buildings. Coast roads and low-lying escape routes inland cut by rising water 2 to 4 hours before arrival of hurricane center. Considerable damage to piers. Marinas flooded. Small craft in unprotected anchorages torn from moorings. Evacutation of some shoreline residences and low-lying areas required. Example: Hurricane Bob (1991).


• Category 3: An Extensive Hurricane

• Winds: 111-130 mph, 97-113 kts, 178-209 km/h


• Storm surge: 9-12 ft, 2.7-3.8 m

• Foliage torn from trees; large trees blown down. Practically all poorly constructed signs blown down. Some damage to roofing materials of buildings; some wind and door damage. Some structural damage to small buildings. Mobile homes destroyed. Serious flooding at coast and many smaller structures near coast destroyed; larger structures near coast damaged by battering waves and floating debris. Low-lying escape routes inland cut by rising water 3 to 5 hours before hurricane center arrives. Flat terrain 5 feet or less above sea level flooded inland 8 miles or more. Evacuation of lowlying residences within several blocks of shoreline possibly required. Example: Hurricane Gloria (1985).


• Category 4: An Extreme Hurricane

• Winds: 131-155 mph, 114-135 kts, 210-249 km/h


• Storm surge: 13-18 ft, 3.9-5.6 m

• Shrubs and trees blown down; all signs down. Extensive damage to roofing materials, windows, and doors. Complete failure of roofs on many small residences. Complete destruction of mobile homes. Flat terrain 10 feet or less above sea level flooded inland as far as 6 miles. Major damage to lower floors of structures near shore due to flooding and battering by waves and floating debris. Low-lying escape roues inland cut by rising water 3 to 5 hours before hurricane center arrives. Major erosion of beaches. Massive evacuation of all residences within 500 yards of shore possibly required, and of single story residences within 2 miles of shore. Example: Hurricane Charley (2004).


• Category 5: A Catastrophic Hurricane

• Winds: greater than 155 mph, 135 kts, 249 km/h

• Minimum surface pressure: lower than 920 mbar

• Storm surge: higher than 18 ft, 5.6m

• Shrubs and trees blown down; considerable damage to roofs of buildings; all signs down. Very severe and extensive damage to windows and doors. Complete failure of roofs on many reisdences and industrial buildings. Extensive shattering of glass in windows and doors. Some complete building failures. Small buildings overturned or blown away. Complete destruction of all structures less than 15 feet above sea level within 500 yards of shore. Low-lying escape routes inland cut by rising water 3 to 5 hours before hurricane center arrives. Massive evacuation of residential areas on low ground within 5 to 10 miles of shore possibly required. Example: Hurricane Camille (1969).

Category 5: greater than 155 mph (249 km/hr)

A nautical mile measures distance and a knot measures speed (NOAA)

A nautical mile is based on the circumference of the earth, and is equal to one minute of latitude. It is slightly more than a statute (land measured) mile (1 nautical mile = 1.1508 statute miles). Nautical miles are used for charting and navigating.

Knot – a unit of speed equal to 1.151 miles per hour.

• A knot is one nautical mile per hour (1 knot = 1.15 miles per hour). The term knot dates from the 17th century, when sailors measured the speed of their ship by using a device called a "common log." This device was a coil of rope with uniformly spaced knots, attached to a piece of wood shaped like a slice of pie. The piece of wood was lowered from the back of the ship and allowed to float behind it. The line was allowed to pay out freely from the coil as the piece of wood fell behind the ship for a specific amount of time. When the specified time had passed, the line was pulled in and the number of knots on the rope between the ship and the wood were counted. The speed of the ship was said to be the number of knots counted (Bowditch, 1984).

METEOROLOGIST – A SCIENTIST THAT STUDIES WEATHER AND EARTH’S ATMOSPHERE.

• Types of precipitation include rain, sleet, snow, hail, and mist.

PRECIPITATION – WATER THAT FALLS TO EARTH’S SURFACE.

• Related Links

• Multimedia Discovery Missions: Lesson 14 - Hurricanes

• Multimedia Discovery Missions: Home

• NOAA Ocean Explorer: Education

RELATED LINKS

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