Terms in this set (29)
Impacts of Hurricanes
- high winds
- heavy rains
- injuries and loss of life
- economic losses
- Rebuilding of damaged infrastructure (biggest)
- cost of evacuation
- impact on energy production
- the cost of severe coastal eroision
- warm core, low pressure system
- no "fonts" attached
- develops over the tropical or subtropical waters
- has an organized circulation with winds of at least 120 km per h (74 miles per h, or 63 knots)
What do we mean by warm core?
1. Warm moist air moves over the ocean
2. Water Vapor rises into the atmosphere
3. As the water vapor rises, it cools and condenses into liquid droplets.
4. Condensation releases heat into the atmosphere making air lighter.
5. The warmed air continues to rise with moist air from the ocean taking the place creating more wind.
- another mechanism of warming in the tropical cyclone's center
- at the air in the eye of the cyclone sinks, it warms due to compression
(Tropical cyclones (TCs) always originate over the tropical oceans (in maritime tropical air masses)
- Hurricanes are used to describe TCs that occur over the Atlantic and the Eastern Pacific Ocean
- Typhoons- the same as hurricanes, but occurring in the western pacific ocean
- Cyclones- occur over the Indian Ocean region
- The material discussed in this lecture will refer to Hurricanes as the general term for Hurricanes, Typhoons, and Cyclones
The beginning stage, tropical depression
- first appearance of a lowered pressure and wind rotation
- winds near the center are consistently between 23 and 38 mph
Tropical Storm (next stage)
- 39-73 mph
- it is now named
Minimum Strength Hurricane
- sustained winds of at least 74 mph or 120 km per h
The Saffir-Simpson Intensity Scale
Where do hurricanes occur?
- note that tropical cyclones do not form near the equator
- also storms tend to curve to the north and east as they interact with the westerlies
- in general, sea surface temperatures are warmer along eastern coasts than western coasts and are warmest near Indonesia accounting for the strongest and most frequent activity
When do hurricanes occur?
- wordwide, tropical cyclone activity peaks in the later summer when water temperatures are the warmest
- in the North Atlantic Basin, They mostly occur in September, and Range from August to November.
Six Important Points about Worldwide hurricane occurrences
1. About 66% occur in the Northern Hemisphere
2. Hurricanes never originate within 5 degrees of the equator
3. Hurricanes rarely originate poleward of 25 degrees (North or South)
4. Of the 80 tropical storms that develop annually around the globe, between 50 and 70% develop into hurricanes (or cyclones or typhoons)
5. The western Pacific in the Northern Hemisphere produces the largest number of tropical cyclones (winter and summer)
6. Hurricanes form over all tropical oceans except the south Atlantic and the southeast Pacific oceans
Lists of Name for Hurricane
- list of names is alphabetical, alternates male and female names, and uses names from the French, English, and Spanish languages.
- with the exception of retired names, the list repeats itself every six years.. 2021 will have the same list as for 2015.
Tropical Cyclone Development (the enviroment)
- There are at least three main requirements for an environment to allow tropical cyclogenesis
- enough Coriolis force to develop a low pressure center
- sufficiently warm sea surface temperatures approximately 27 C at least 60 m deep
- low vertical wind shear
- these conditions are necessary but NOT sufficient conditions for the formation of tropical cyclones
Why is the Coriolis force so crucial to the rotation seen in hurricanes?
- By looking downward onto the ocean (or land) surface in the Northern Hemisphere, consider the following winds
- later as the Coriolis force deflects the winds to the right
- we need warm sea surface temperatures
- there is a direct relationship between the intensity (central pressure) of the most intense hurricanes and the temperature of the sea-surface over which the storms are moving.
- note from the following table that the six strongest hurricanes all occurred in the western pacific where the sea-surface temperatures are warmest
- Important to have warm ocean for hurricane formation
- we not only need to know how warm the ocean surface is, but how deep is the warm water
- this is because the storm itself can cool the sea surface by bringing up cooler water through upwelling
Weak Wind Shear
- it is necessary to focus the energy as shown below
- Low wind shear- storm's latent heat is focused over small volunteer
- high wind shear- storm's latent heat is spread over larger volume
Summary of Hurricane Formation Components
1. Enough Coriolis Force to facilitate rotations e.g. a location at least 5C (550km) from the Equator
2. Sufficiently warm sea surface temperatures approximately 27C atlas 60 m deep.
3. Weak vertical wind shear
Tropical Development (three trigger mechanisms) #1
1. intertropical convergence zone
- The intertropical convergence zones, migrates with the sun towards the summer hemisphere. Note that the ITCZ is slightly displaced towards the Northern Hemisphere since there is more land mass.
Tropical Development (three trigger mechanisms) #2
2. Easterly waves: Thunderstorms forming on the convergent side (to the east) have the potential to organize into hurricanes
Tropical Development (three trigger mechanisms) #3
3. Middle latitude cold fronts, which are more common in the autumn months
- ex hurricane kyle (2002) formed from the thunderstorms developing from a cold front
- the effect of wind shear on tropical storm development.
How Thunderstorms organize into a hurricane?
1. Large scale convergence associated with ITCZ, wave, or front triggers convection
2. Surface winds increase, significantly increasing flux of heat and moisture (latent heat) from ocean to atmosphere, destabilizing atmosphere
3. Subsidence in center of cloud cluster leads to warm an lowering of central pressure
4. Rate of heat and moisture transfer to atmosphere greater for higher sea surface temperatures and wind speeds
5. Strong surface winds mounts large flux of heat and moisture (latent heat) from ocean to atmosphere, destabilizing atmosphere.
6. central low pressure in eye associated with warm core created by subsidence
7. warm water supplies heat and moisture at an increasing rate as the winds become stronger
Summary of Necessary Conditions for Hurricane Formation
1. Enough Coriolis force to facilitate rotation ex- a location at least 5C from the Equator
2. Sufficiently warm sea surface temperatures approximately 27C at least 60 m deep
3. Weak vertical wind shear
The Triggering Mechanisms
1. The intertropical convergence zone (ITCZ)
2. Easterly Waves
3. Cold fronts extending into the tropics
Hurricane Structure- The Eye
The hurricane's center is relatively calm, generally clear area of sinking air and light winds that usually do not exceed 15 mph and is typically 20-40 miles across. An eye will usually develop when the maximum sustained wind speeds are hurricane force.
Hurricane Structure- The Eye Wall
Consists of a ring of tall thunderstorms that produce heavy rains and usually the strongest winds. Changes in the structure of the eye and eyewall can cause changes in the wind speed, which is an indicator of the storm's intensity. The eye can grow or shrink in size, and double (concentric) eyewalls can form.
Hurricane Structure- Rainbands
Curved bands of clouds and thunderstorms that trail away from the eye wall in a spiral fashion. These bands are capable of producing heavy bursts of rain and wind, as well as tornadoes. There are sometimes gaps in between spiral rain bands where no rain or wind is found.
Tropical Cyclone Size
Typical hurricane strength tropical cyclones are about 300 miles wide although they can vary considerably. The relative sizes of the largest and smallest tropical cyclones on record as compared to the United States.
1. storm surge
2. wind damage
3. heavy rains (flooding
4. associated tornados
About 90% of fatalities are caused by coastal and inland storm surge
What is Storm Surge?
it is a 8-160 km wide dome of water that sweeps over the coastline during landfall
- Strong onshore winds and relatively low air pressure are responsible for a storm surge
- a sea-level rise of about .5 m for every 50 mb of pressure loss
- a surge is superimposed on the normal tidal oscillation, so that the danger is greatest at high tide
- plus wind-driven waves up to 3 m
- The level of surge in a particular area is also determined by the slope of the continental shelf.
- A shallow slope off the coast (right, top picture) will allow a greater surge to inudate coastal communities,
- Communities with a steeper continental shelf (right, bottom picture) will not see as much surge inundation, although large breaking waves can still present major problems.
Katrina's landfall was at a category 3, but with a comparable storm surge to that of Camille..?
Katrina had weakened to a Category 3 hurricane with maximum sustained winds estimated at 145 mph as it made landfall early Monday.
However, the storm surge of 8.4 m, generally found in category 5 storms, was maintained during Katrina's weakening to a category 3.
Camille (1969): 7.3 m
Katrina (2005): 8.4 m