Hurricanes and Tropical Hurricanes and Tropical StormsStorms

Naming ConventionNaming Convention

Hurricanes: extreme tropical storms over Atlantic and Eastern Pacific OceansTyphoons: extreme tropical storms over western Pacific OceanCyclones: extreme tropical storms over Indian Ocean and Australia

Ocean Temperatures and Ocean Temperatures and HurricanesHurricanes

Hurricanes depend on large pools of warm water

Annual Hurricane FrequencyAnnual Hurricane Frequency

There are no hurricanes in the southern Atlantic Ocean!The strongest hurricanes occur in the western Pacific Ocean (often referred to as “super-typhoons.”)

Hurricane CharacteristicsHurricane CharacteristicsDefinitionDefinition: Hurricanes have sustained winds of 120 : Hurricanes have sustained winds of 120 km/hr (74 mph) or greater.km/hr (74 mph) or greater.

SizeSize: Average diameters are approx. 600 km (350 : Average diameters are approx. 600 km (350 mi). This is 1/3 the size of a mid-latitude cyclone mi). This is 1/3 the size of a mid-latitude cyclone (synoptic storm system).(synoptic storm system).

DurationDuration: Days to a week or more. : Days to a week or more.

StrengthStrength: Central pressure averages 950 mb but : Central pressure averages 950 mb but may be as low as 870 mb (lower the pressure – may be as low as 870 mb (lower the pressure – stronger the storm).stronger the storm).

PowerPower: The power released by a single hurricane : The power released by a single hurricane can exceed the annual electricity consumption by can exceed the annual electricity consumption by the US and Canada combined. the US and Canada combined.

Hurricane SeasonsHurricane SeasonsHurricanes obtain their energy from Hurricanes obtain their energy from latent heatlatent heat release in cloud release in cloud formation processes. formation processes.

Hurricanes occur where a deep layer of warm water exists Hurricanes occur where a deep layer of warm water exists during the time of the highest SSTs (sea surface temps).during the time of the highest SSTs (sea surface temps).

Northern Hemisphere: August through September are most Northern Hemisphere: August through September are most active months. active months.

Southern Hemisphere: January through March are the most Southern Hemisphere: January through March are the most active months active months

Latent Heat: Release Me!Latent Heat: Release Me!

Hurricanes draw their power from Hurricanes draw their power from warm, extremely humid air found only warm, extremely humid air found only over warm oceans. over warm oceans.

The key energy source is the latent The key energy source is the latent heat that's released when water vapor heat that's released when water vapor condenses into cloud droplets and condenses into cloud droplets and rain. Tropical storms and hurricanes rain. Tropical storms and hurricanes grow best in a deep layer of humid air grow best in a deep layer of humid air that supplies plenty of moisture.that supplies plenty of moisture.

When a substance changes phase, When a substance changes phase, energy must be supplied in order to energy must be supplied in order to overcome the molecular attractions overcome the molecular attractions between the constituent particles. This between the constituent particles. This energy must be supplied externally, energy must be supplied externally, normally as heat, and does not bring normally as heat, and does not bring about a change in temperature. about a change in temperature.

When water is in the vapor state, as a gas, the water molecules are not bonded to each other. They float around as single molecules.

When water is in the liquid state, some of the molecules bond to each other with hydrogen bonds.  The bonds break and re-form continually.

Latent HeatLatent Heat

We call the energy needed to change We call the energy needed to change phases phases latent heatlatent heat (the word "latent" (the word "latent" means "invisible"). The latent heat is the means "invisible"). The latent heat is the energy released or absorbed during a energy released or absorbed during a change of state. change of state. To get the molecule of water vapor to To get the molecule of water vapor to become liquid again, we have to take the become liquid again, we have to take the energy away, that is, we have to cool it energy away, that is, we have to cool it down so that it down so that it condensescondenses (condensation is (condensation is the change from the vapor state to the liquid the change from the vapor state to the liquid state).  When water condenses, it releases state).  When water condenses, it releases latent heat. latent heat.

Latent Heat ValuesLatent Heat ValuesThe amount of latent heat involved depends to some extent on the The amount of latent heat involved depends to some extent on the temperature at which the process is occurring. The figures below temperature at which the process is occurring. The figures below are those normally found in meteorology texts and are for are those normally found in meteorology texts and are for temperatures found in the atmosphere, such as 0 Celsius (32 F).temperatures found in the atmosphere, such as 0 Celsius (32 F).Latent heat of condensationLatent heat of condensation (Lc): Refers to the heat gained by (Lc): Refers to the heat gained by the air when water vapor changes into a liquid. Lc=2500 Joules per the air when water vapor changes into a liquid. Lc=2500 Joules per gram (J/g) of water or 600 calories per gram (cal/g) of water. gram (J/g) of water or 600 calories per gram (cal/g) of water. Latent heat of fusionLatent heat of fusion (Lf): Refers to the heat lost or gained by the (Lf): Refers to the heat lost or gained by the air when liquid water changes to ice or vice versa. Lf=333 Joules air when liquid water changes to ice or vice versa. Lf=333 Joules per gram (J/g) of water or 80 calories per gram (cal/g) of water. per gram (J/g) of water or 80 calories per gram (cal/g) of water. Latent heat of sublimationLatent heat of sublimation (Ls): Refers to the heat lost or gained (Ls): Refers to the heat lost or gained by the air when ice changes to vapor or vice versa. Ls=2833 by the air when ice changes to vapor or vice versa. Ls=2833 Joules per gram (J/g) of water or 680 calories per gram (cal/g) of Joules per gram (J/g) of water or 680 calories per gram (cal/g) of water. water. Latent heat of vaporizationLatent heat of vaporization (Lv): Refers to the heat lost by the air (Lv): Refers to the heat lost by the air when liquid water changes into vapor. This is also commonly when liquid water changes into vapor. This is also commonly known as the latent heat of evaporation. Lv= -2500 Joules per known as the latent heat of evaporation. Lv= -2500 Joules per gram (J/g) of water or -600 calories per gram (cal/g) of water. gram (J/g) of water or -600 calories per gram (cal/g) of water.

Latent HeatLatent Heat

As water vapor evaporates from the warm ocean As water vapor evaporates from the warm ocean surface, it is forced upward in the convective clouds that surface, it is forced upward in the convective clouds that surround the eyewall and rainband regions of a storm. surround the eyewall and rainband regions of a storm. As the water vapor cools and condenses from a gas As the water vapor cools and condenses from a gas back to a liquid state, it releases latent heat. The release back to a liquid state, it releases latent heat. The release of latent heat warms the surrounding air, making it lighter of latent heat warms the surrounding air, making it lighter and thus promoting more vigorous cloud development. and thus promoting more vigorous cloud development. The release of latent heat warms the surrounding air, The release of latent heat warms the surrounding air, making it lighter and thus promoting more vigorous cloud making it lighter and thus promoting more vigorous cloud development.development.

Animation: Animation: http://svs.gsfc.nasa.gov/vis/a000000/a001600/a001605/chttp://svs.gsfc.nasa.gov/vis/a000000/a001600/a001605/cloud.movloud.mov

Energy of Latent HeatEnergy of Latent Heat

Condensation releases latent heat. This causes the temperature of a Condensation releases latent heat. This causes the temperature of a cloud to be warmer than it otherwise would have been if it did not cloud to be warmer than it otherwise would have been if it did not release latent heat. Anytime a cloud is warmer than the surrounding release latent heat. Anytime a cloud is warmer than the surrounding environmental air, it will continue to rise and develop. environmental air, it will continue to rise and develop. The more moisture a cloud contains, the more potential it has to release The more moisture a cloud contains, the more potential it has to release latent heat. latent heat. Temperatures in the middle of the rising air in cumulonimbi there may be Temperatures in the middle of the rising air in cumulonimbi there may be as much as 15-20C (28-38F) warmer than air outside the storm. For as much as 15-20C (28-38F) warmer than air outside the storm. For Hurricane Rita, observations showed that, at 700 mb (approximately Hurricane Rita, observations showed that, at 700 mb (approximately 10000 feet), the interior temperature of Rita was 31C and about 20C 10000 feet), the interior temperature of Rita was 31C and about 20C warmer than the outside of the storm at the same elevation. warmer than the outside of the storm at the same elevation.

Air parcel dew point temperature (oC)

Approximate amount of water vapor (g) in an air parcel (kg) at saturation (by the way, in text books referred to as the saturation mixing ratio)

Approximate amount of potential heating due to latent heat release (calories) if all the water vapor condenses

0 4 2360

10 8 4720

20 16 9440

30 32 18880

40 64 37760

Hurricane StructureHurricane Structure

A central eye is surrounded by large cumulonimbus thunderstorms occupying the adjacent eyewall.Weak uplift and low precipitation areas are separated by individual cloud bands.

Temperature StructureTemperature StructureHurricanes characterized Hurricanes characterized by a strong thermally direct by a strong thermally direct circulation with rising of circulation with rising of warm air near center of warm air near center of storm and sinking of cooler storm and sinking of cooler air outside.air outside.

The “warm core” of the The “warm core” of the hurricane serves as a hurricane serves as a reservoir of potential reservoir of potential energy which is continually energy which is continually being converted to kinetic being converted to kinetic energy by thermally direct energy by thermally direct circulation circulation

Pressure StructurePressure Structureof Hurricanesof Hurricanes

The horizontal The horizontal pressure gradient with pressure gradient with altitude decreases altitude decreases slowlyslowly

At about 400 mb, the pressure At about 400 mb, the pressure inside the storm is approx. that of inside the storm is approx. that of outside of the storm.outside of the storm.

From surface to From surface to 400 mb: cyclonic 400 mb: cyclonic circulation.circulation.

From 400 mb to From 400 mb to tropopause: anticylonic tropopause: anticylonic circulation.circulation.The upper portions of the storm The upper portions of the storm

are blanketed by a cirrus cloud are blanketed by a cirrus cloud cap due to overall low cap due to overall low temperatures.temperatures.

Hurricanes and Tropical Hurricanes and Tropical StormsStorms

Naming ConventionNaming Convention

Hurricanes: extreme tropical storms over Atlantic and Eastern Pacific OceansTyphoons: extreme tropical storms over western Pacific OceanCyclones: extreme tropical storms over Indian Ocean and Australia

Ocean Temperatures and Ocean Temperatures and HurricanesHurricanes

Hurricanes depend on large pools of warm water

Annual Annual HurricaneHurricane Frequency Frequency

There are no hurricanes in the southern Atlantic Ocean!The strongest hurricanes occur in the western Pacific Ocean (often referred to as “super-typhoons.”

Hurricane CharacteristicsHurricane CharacteristicsDefinitionDefinition: Hurricanes have sustained winds of 120 : Hurricanes have sustained winds of 120 km/hr (74 mph) or greater.km/hr (74 mph) or greater.

SizeSize: Average diameters are approx. 600 km (350 : Average diameters are approx. 600 km (350 mi). This is 1/3 the size of a mid-latitude cyclone mi). This is 1/3 the size of a mid-latitude cyclone (synoptic storm system).(synoptic storm system).

DurationDuration: Days to a week or more. : Days to a week or more.

StrengthStrength: Central pressure averages 950 mb but : Central pressure averages 950 mb but may be as low as 870 mb (lower the pressure – may be as low as 870 mb (lower the pressure – stronger the storm).stronger the storm).

PowerPower: The power released by a single hurricane : The power released by a single hurricane can exceed the annual electricity consumption by can exceed the annual electricity consumption by the US and Canada combined. the US and Canada combined.

Hurricane SeasonsHurricane SeasonsHurricanes obtain their energy from Hurricanes obtain their energy from latent heatlatent heat release in cloud release in cloud formation processes. formation processes.

Hurricanes occur where a deep layer of warm water exists Hurricanes occur where a deep layer of warm water exists during the time of the highest SSTs (sea surface temps).during the time of the highest SSTs (sea surface temps).

Northern Hemisphere: August through September are most Northern Hemisphere: August through September are most active months. active months.

Southern Hemisphere: January through March are the most Southern Hemisphere: January through March are the most active months active months

Latent Heat: Release Me!Latent Heat: Release Me!

Hurricanes draw their power from Hurricanes draw their power from warm, extremely humid air found only warm, extremely humid air found only over warm oceans. over warm oceans. The key energy source is the latent The key energy source is the latent heat that's released when water vapor heat that's released when water vapor condenses into cloud droplets and condenses into cloud droplets and rain. Tropical storms and hurricanes rain. Tropical storms and hurricanes grow best in a deep layer of humid air grow best in a deep layer of humid air that supplies plenty of moisture.that supplies plenty of moisture.When a solid substance changes When a solid substance changes phase, energy must be supplied in phase, energy must be supplied in order to overcome the molecular order to overcome the molecular attractions between the constituent attractions between the constituent particles. This energy must be particles. This energy must be supplied externally, normally as heat, supplied externally, normally as heat, and does not bring about a change in and does not bring about a change in temperature. temperature.

When water is in the vapor state, as a gas, the water molecules are not bonded to each other. They float around as single molecules.

When water is in the liquid state, some of the molecules bond to each other with hydrogen bonds.  The bonds break and re-form continually.

Latent HeatLatent Heat

We call the energy needed to change We call the energy needed to change phases phases latent heatlatent heat (the word "latent" (the word "latent" means "invisible"). The latent heat is the means "invisible"). The latent heat is the energy released or absorbed during a energy released or absorbed during a change of state. change of state. To get the molecule of water vapor to To get the molecule of water vapor to become liquid again, we have to take the become liquid again, we have to take the energy away, that is, we have to cool it energy away, that is, we have to cool it down so that it down so that it condensescondenses (condensation is (condensation is the change from the vapor state to the liquid the change from the vapor state to the liquid state).  When water condenses, it releases state).  When water condenses, it releases latent heat. latent heat.

Latent Heat ValuesLatent Heat ValuesThe amount of latent heat involved depends to some extent on the The amount of latent heat involved depends to some extent on the temperature at which the process is occurring. The figures below temperature at which the process is occurring. The figures below are those normally found in meteorology texts and are for are those normally found in meteorology texts and are for temperatures found in the atmosphere, such as 0 Celsius (32 F).temperatures found in the atmosphere, such as 0 Celsius (32 F).Latent heat of condensationLatent heat of condensation (Lc): Refers to the heat gained by (Lc): Refers to the heat gained by the air when water vapor changes into a liquid. Lc=2500 Joules per the air when water vapor changes into a liquid. Lc=2500 Joules per gram (J/g) of water or 600 calories per gram (cal/g) of water. gram (J/g) of water or 600 calories per gram (cal/g) of water. Latent heat of fusionLatent heat of fusion (Lf): Refers to the heat lost or gained by the (Lf): Refers to the heat lost or gained by the air when liquid water changes to ice or vice versa. Lf=333 Joules air when liquid water changes to ice or vice versa. Lf=333 Joules per gram (J/g) of water or 80 calories per gram (cal/g) of water. per gram (J/g) of water or 80 calories per gram (cal/g) of water. Latent heat of sublimationLatent heat of sublimation (Ls): Refers to the heat lost or gained (Ls): Refers to the heat lost or gained by the air when ice changes to vapor or vice versa. Ls=2833 by the air when ice changes to vapor or vice versa. Ls=2833 Joules per gram (J/g) of water or 680 calories per gram (cal/g) of Joules per gram (J/g) of water or 680 calories per gram (cal/g) of water. water. Latent heat of vaporizationLatent heat of vaporization (Lv): Refers to the heat lost by the air (Lv): Refers to the heat lost by the air when liquid water changes into vapor. This is also commonly when liquid water changes into vapor. This is also commonly known as the latent heat of evaporation. Lv= -2500 Joules per known as the latent heat of evaporation. Lv= -2500 Joules per gram (J/g) of water or -600 calories per gram (cal/g) of water. gram (J/g) of water or -600 calories per gram (cal/g) of water.

Latent HeatLatent Heat

As water vapor evaporates from the warm ocean As water vapor evaporates from the warm ocean surface, it is forced upward in the convective clouds that surface, it is forced upward in the convective clouds that surround the eyewall and rainband regions of a storm. surround the eyewall and rainband regions of a storm. As the water vapor cools and condenses from a gas As the water vapor cools and condenses from a gas back to a liquid state, it releases latent heat. The release back to a liquid state, it releases latent heat. The release of latent heat warms the surrounding air, making it lighter of latent heat warms the surrounding air, making it lighter and thus promoting more vigorous cloud development. and thus promoting more vigorous cloud development. The release of latent heat warms the surrounding air, The release of latent heat warms the surrounding air, making it lighter and thus promoting more vigorous cloud making it lighter and thus promoting more vigorous cloud development.development.

Animation: Animation: http://svs.gsfc.nasa.gov/vis/a000000/a001600/a001605/chttp://svs.gsfc.nasa.gov/vis/a000000/a001600/a001605/cloud.movloud.mov

Energy of Latent HeatEnergy of Latent Heat

Condensation releases latent heat. This causes the temperature of a Condensation releases latent heat. This causes the temperature of a cloud to be warmer than it otherwise would have been if it did not cloud to be warmer than it otherwise would have been if it did not release latent heat. Anytime a cloud is warmer than the surrounding release latent heat. Anytime a cloud is warmer than the surrounding environmental air, it will continue to rise and develop. environmental air, it will continue to rise and develop. The more moisture a cloud contains, the more potential it has to release The more moisture a cloud contains, the more potential it has to release latent heat. latent heat. Temperatures in the middle of the rising air in cumulonimbi there may be Temperatures in the middle of the rising air in cumulonimbi there may be as much as 15-20C (28-38F) warmer than air outside the storm. For as much as 15-20C (28-38F) warmer than air outside the storm. For Hurricane Rita, observations showed that, at 700 mb (approximately Hurricane Rita, observations showed that, at 700 mb (approximately 10000 feet), the interior temperature of Rita was 31C and about 20C 10000 feet), the interior temperature of Rita was 31C and about 20C warmer than the outside of the storm at the same elevation. warmer than the outside of the storm at the same elevation.

Air parcel dew point temperature (oC)

Approximate amount of water vapor (g) in an air parcel (kg) at saturation (by the way, in text books referred to as the saturation mixing ratio)

Approximate amount of potential heating due to latent heat release (calories) if all the water vapor condenses

0 4 2360

10 8 4720

20 16 9440

30 32 18880

40 64 37760

Hurricane StructureHurricane Structure

A central eye is surrounded by large cumulonimbus thunderstorms occupying the adjacent eyewall.Weak uplift and low precipitation areas are separated by individual cloud bands.

Temperature StructureTemperature StructureHurricanes characterized Hurricanes characterized by a strong thermally direct by a strong thermally direct circulation with rising of circulation with rising of warm air near center of warm air near center of storm and sinking of cooler storm and sinking of cooler air outside.air outside.

The “warm core” of the The “warm core” of the hurricane serves as a hurricane serves as a reservoir of potential reservoir of potential energy which is continually energy which is continually being converted to kinetic being converted to kinetic energy by thermally direct energy by thermally direct circulation circulation

Pressure StructurePressure Structureof Hurricanesof Hurricanes

The horizontal The horizontal pressure gradient with pressure gradient with altitude decreases altitude decreases slowlyslowly

At about 400 mb, the pressure At about 400 mb, the pressure inside the storm is approx. that of inside the storm is approx. that of outside of the storm.outside of the storm.

From surface to From surface to 400 mb: cyclonic 400 mb: cyclonic circulation.circulation.

From 400 mb to From 400 mb to tropopause: anticylonic tropopause: anticylonic circulation.circulation.The upper portions of the storm The upper portions of the storm

are blanketed by a cirrus cloud are blanketed by a cirrus cloud cap due to overall low cap due to overall low temperatures.temperatures.

Hurricane Eye and Hurricane Eye and EyewallEyewall

A shrinking eye A shrinking eye indicates storm indicates storm intensificationintensification

The hurricane eye is an area of The hurricane eye is an area of descending air, relatively clear sky and descending air, relatively clear sky and light winds: 25 km (15 mi) diameter on light winds: 25 km (15 mi) diameter on average. average.

The eyewall is The eyewall is moves at a speed moves at a speed of 20 km/hour and of 20 km/hour and the calm weather the calm weather associated with the associated with the eye will last less eye will last less than 1 hourthan 1 hour

The eyewall is comprised of the strongest winds, the largest The eyewall is comprised of the strongest winds, the largest clouds and the heaviest precipitation with rainfall rates as high clouds and the heaviest precipitation with rainfall rates as high as 2500 mm/day (100 inches/day).as 2500 mm/day (100 inches/day).

Hurricane FormationHurricane Formation

Tropical DisturbanceTropical Disturbance: Clusters of small : Clusters of small thunderstorms.thunderstorms.

Tropical DepressionTropical Depression: When at least 1 closed : When at least 1 closed isobar is present (organized center of low isobar is present (organized center of low pressure).pressure).

Tropical StormTropical Storm: Further intensification to wind : Further intensification to wind speeds of 60 km/hr (37 mph).speeds of 60 km/hr (37 mph).

HurricaneHurricane: Hurricane status is gained when the : Hurricane status is gained when the winds reach a sustained 120 km/hr (74 mph).winds reach a sustained 120 km/hr (74 mph).

Tropical Disturbances and Easterly WavesTropical Disturbances and Easterly Waves

Some tropical disturbances form from mid-latitude troughs migrating towards lower latitudes, some form from ITCZ convection, but most develop from “easterly waves.”Easterly Waves, or undulations in the trade wind patterns, spawn hurricanes in the Atlantic. Only 10% of tropical disturbance become more organized, rotating storms.

Conditions necessary for Hurricane FormationConditions necessary for Hurricane Formation

Hurricanes only form over deep (several 10s of meters) Hurricanes only form over deep (several 10s of meters) water layers with temperatures in excess of 27 degrees water layers with temperatures in excess of 27 degrees C. C. Poleward to about 20 degrees, water temperatures are Poleward to about 20 degrees, water temperatures are usually below this threshold. usually below this threshold. Coriolis effect is an important contributor, hurricanes do Coriolis effect is an important contributor, hurricanes do not form from equator to 5 degrees.not form from equator to 5 degrees.Need unstable atmosphere: available in western parts of Need unstable atmosphere: available in western parts of oceans but not in eastern parts of ocean. oceans but not in eastern parts of ocean. Strong vertical shear must be absent. (both magnitude Strong vertical shear must be absent. (both magnitude and direction).and direction).Vertical shearVertical shear: changing of wind speed and/or direction : changing of wind speed and/or direction with height of the atmosphere. with height of the atmosphere.

Hurricane MovementHurricane Movement

Tropical depressions and Tropical depressions and disturbances are largely disturbances are largely regulated by trade wind regulated by trade wind flow – move westward.flow – move westward.Tropical storms & Tropical storms & hurricanes: upper-level hurricanes: upper-level winds and ocean winds and ocean temperatures gain temperatures gain importance.importance.Fully developed Fully developed hurricanes will move hurricanes will move poleward (stronger upper poleward (stronger upper winds will steer the winds will steer the hurricanes northward).hurricanes northward).

Hurricane DissipationHurricane Dissipation

After making landfall, a hurricane may die After making landfall, a hurricane may die completely within a couple of days (no longer completely within a couple of days (no longer has moisture to feed into storm).has moisture to feed into storm).Even as storm weakens, it can still have large Even as storm weakens, it can still have large effects on land (especially flooding).effects on land (especially flooding).Hurricanes will also dissipate over cooler waters Hurricanes will also dissipate over cooler waters or if they encounter strong vertical shear.or if they encounter strong vertical shear.Animation: Animation: http://svs.gsfc.nasa.gov/vis/a000000/a001600/ahttp://svs.gsfc.nasa.gov/vis/a000000/a001600/a001605/coldwater.mov001605/coldwater.mov

Hurricane DamageHurricane Damage

Heavy rainfallHeavy rainfall

Strong windsStrong winds

Tornadoes (generally F0-F2)Tornadoes (generally F0-F2)

Storm surge – rise in water level induced Storm surge – rise in water level induced by the hurricane.by the hurricane.

Tornado formation in hurricanesTornado formation in hurricanes

Most hurricanes Most hurricanes contain clusters of contain clusters of tornadoes.tornadoes.

Most tornadoes occur Most tornadoes occur in right front quadrant in right front quadrant of the storm.of the storm.

It appears that slowing It appears that slowing of wind by friction at of wind by friction at landfall contributes to landfall contributes to the formation of these the formation of these tornadoes.tornadoes.

Storm SurgesStorm Surges

Process 1: Hurricane winds drag surface Process 1: Hurricane winds drag surface waters forward and pile water near coasts.waters forward and pile water near coasts.Process 2: Lower atmospheric pressure Process 2: Lower atmospheric pressure raises sea level (for every 1mb pressure raises sea level (for every 1mb pressure decrease, sea level raises 1 cm)decrease, sea level raises 1 cm)Storm surges raise sea level by a 1-2 m Storm surges raise sea level by a 1-2 m for most hurricanes, as much as 7 m (a for most hurricanes, as much as 7 m (a real problem when coastal locations are at real problem when coastal locations are at or below sea-level)or below sea-level)

Hurricane Wind Hurricane Wind StructureStructure

Winds and surge Winds and surge are typically are typically strongest at strongest at right right front quadrant front quadrant of of storm where wind storm where wind speeds combine speeds combine with speed of with speed of storm’s movement storm’s movement to create the to create the highest area of highest area of potential impact.potential impact.

Trends for AtlanticTrends for Atlantic

Mid 1990s-now: A significant increase in Mid 1990s-now: A significant increase in the numbers of hurricanes and intense the numbers of hurricanes and intense hurricanes making landfall in US.hurricanes making landfall in US.

1970s-mid 1990s: Lower than normal 1970s-mid 1990s: Lower than normal incidence of Atlantic Hurricanes.incidence of Atlantic Hurricanes.

Debate: Is the recent increase in Debate: Is the recent increase in hurricanes part of a natural cycle, global hurricanes part of a natural cycle, global climate change or a combination?climate change or a combination?

ForecastingForecasting

National Hurricane Center responsible for National Hurricane Center responsible for Atlantic and eastern/central Pacific.Atlantic and eastern/central Pacific.

Data gathered through satellite, surface Data gathered through satellite, surface observations and aircraft using observations and aircraft using dropsondes (dropping of instruments dropsondes (dropping of instruments through hurricane)through hurricane)

Computer models assist in predictions.Computer models assist in predictions.

Hurricane Watch and WarningHurricane Watch and Warning

Hurricane WatchHurricane Watch: if an approaching : if an approaching hurricane is expected to make landfall hurricane is expected to make landfall within 24 hours. within 24 hours.

Hurricane WarningHurricane Warning: if the time frame is : if the time frame is less, then it’s a warning. less, then it’s a warning.

Naming of HurricanesNaming of Hurricanes

When a tropical disturbance reaches a When a tropical disturbance reaches a tropical depression, the storm will be given tropical depression, the storm will be given a name.a name.

The name comes from an “A-W” list given The name comes from an “A-W” list given by World Meteorological Organization by World Meteorological Organization (WMO).(WMO).

The names of hurricanes with devastating The names of hurricanes with devastating effects are retired. effects are retired.

Hurricane Intensity ScaleHurricane Intensity Scale

Saffir-Simpson Scale

Five Categories: the larger numbers indicate lower central pressures, greater winds and stronger storm surges