What is a ‘hurricane’? Where do they form? Why? Why do they move east to west rather than west to

east? Why do they have names?!? And how do they pick

the names? What is the ‘eye”? The ‘eye wall”? How do hurricanes compare to other storms?

Typhoons? mid-latitude cyclones? http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqHED.html

Sept 06 2004“IVAN IS FORECAST TO SLOWLY DEEPEN OVER THE NEXT 36 HOURS REACHING 130 KT IN 48 HOURS “

DEEPEN? What does this mean? How does it relate to hurricane intensity?

“ESTIMATED MINIMUM CENTRAL PRESSURE 951 MB MAX SUSTAINED WINDS 110 KT WITH GUSTS TO 130 KT. “

What is an “MB”? A “KT”? What is the significance of these values?

What does ‘warm water’ have to do with hurricanes? NWS TPC/NATIONAL HURRICANE CENTER

MIAMI FL 5 AM EDT MON SEP 06 2004 “NOW THAT FRANCES HAS MOVED OVER THE WARM WATERS

OF THE NORTHEAST GULF OF MEXICO...THUNDERSTORMS ACTIVITY HAS STEADILY INCREASED NEAR THE TIGHT CIRCULATION CENTER DURING THE PAST 6 HOURS. THE LAST RECON REPORT AT AROUND 05Z INDICATED A RAGGED EYE WAS TRYING TO FORM…

NOW THAT THE CENTER OF FRANCES IS BACK OVER WARM WATER...SOME RE-STRENGTHENING IS POSSIBLE. WATER TEMPERATURES ARE NEAR 83-84F AND UPPER-LEVEL OUTFLOW IS STILL QUITE IMPRESSIVE.”

What are the ‘levels’ or ‘layers’ of the of the atmosphere? “UPPER-LEVEL OUTFLOW IS STILL QUITE

IMPRESSIVE” “A STRONG DEEP-LAYER ANTICYCLONE

IS FORECAST TO REMAIN TO THE NORTH OF THE HURRICANE STEERING IVAN INTO THE EASTERN CARIBBEAN SEA BY DAY TWO AND TOWARD THE SOUTHWESTERN PORTION OF HISPANIOLA ON DAY FOUR.”

“STRONG UPPER LEVEL SHEAR…”

How are Hurricanes tracks established? THE NHC MODEL GUIDANCE IN GOOD

AGREEMENT ON FRANCES MOVING WEST-NORTHWESTWARD AROUND THE SOUTHWESTERN PORTION OF THE SUBTROPICAL RIDGE AXIS THAT EXTENDS EAST-WEST ALONG 32N LATITUDE. THE PRIMARY DIFFERENCE IN THE MODELS IS HOW SHARP OF A TURN FRANCES WILL MAKE UPON REACHING 32N. THE GFS APPEARS TO MAKE TOO SHARP OF A NORTHEASTWARD TURN GIVEN THE CURRENT LARGE DIAMETER OF FRANCES. THE OFFICIAL FORECAST IS CLOSE TO THE PREVIOUS FORECAST TRACK AND IS CLOSE THE GUNA MODEL CONSENSUS.

Huh? “THERE IS VERY GOOD AGREEMENT

THROUGH DAY FIVE WITH NOGAPS TO THE RIGHT OF THE AIDS ENVELOPE AND THE UKMET TO THE LEFT OF THE AIDS ENVELOPE. THE OFFICIAL FORECAST IS SLIGHTLY RIGHT OF THE PREVIOUS FORECAST TRACK AND IN VERY GOOD AGREEMENT WITH GUNS AND GUNA”.

So what is a ‘MODEL” and how does it work?

How does RADAR and Satellite imagery assist in evaluating hurricanes?

06 Sept. 04 Visible Satellite ImageA SMALL EYE IS EVIDENT ON THE VISIBLE IMAGERY. …. AND SOMEWHAT RAGGED-LOOKING BANDING FEATURES

06 Sept 04 IR Satellite Image

Francis

IVAN

Hermine?

The Dvorak Technique Explained

The Dvorak technique is a method using enhanced Infrared and/or visible satellite imagery to quantitatively estimate the intensity of a tropical system. Cloud patterns in satellite imagery normally show an indication of cyclogenesis before the storm reaches tropical storm intensity. Indications of continued development and/or weakening can also be found in the cloud features. Using these features, the pattern formed by the clouds of a tropical cyclone, expected systematic development, and a series of rules, an intensity analysis and forecast can be made. This information is then standardized into an intensity code

How do statistics and probability relate to hurricane forecasts?Note the difference in size between the forecast cones… note the degradation of certainty over time, and the higher certainty of the track for hurricane ‘Ivan’

First question…. Where do hurricanes form? Why?

                                                                        

Atmospheric heating…. Imbalances in solar NRG are the driving

force behind all weather. Direct sunlight imparts more NRG to the

surface High angle sunlight has very much lower

NRG content The atmosphere is heated from below…

The Earth in Space

Figure 3.3Figure 3.3

June 22

Another way of looking at June 22…

www.time.gov

Daylight pattern on 22 September… near the equinox

What would December 22 look like?

What significance do the tropics of Cancer and Capricorn have?

Figure 3.4Figure 3.4

Figure 3.6Figure 3.6

Figure 3.2Figure 3.2

Figure 3.5Figure 3.5

Note the influence of clouds… which interrupts the latitudinal patterns

Figure 3.7Figure 3.7

DECEMBER 21

Figure 3.8Figure 3.8

Figure 3.10Figure 3.10

Figure 3.9Figure 3.9

Electromagnetic Radiation (EMR) can be described as waves.

Note the generation of a magnetic field at right angles to an electrical field and both are perpendicular to the direction of EMR propagation

http://micro.magnet.fsu.edu/primer/java/electromagnetic/index.html

 

The wavelength () of EMR is directly related to the amount of NRG in the radiation.

Short () (e.g. gamma rays) have a higher NRG content

Long () (e.g. thermal or microwave (Radio) have a lower NRG content

As the velocity of the propagation of EMR (the speed of light) is believed to be a constant (c)

The number of waves to pass a single point in a given period (the frequency, v) is much higher for shorter radiation

Blackbody radiance curves…

Wein’s Displacement Law

Figure 2.8Figure 2.8

Figure 2.9Figure 2.9

Figure 2.14Figure 2.14

When the sun is at very low angles, virtually all the shorter EMR is scattered, allowing only the longer, lower NRG waves (reds) to pass through.

Atmospheric scattering: (skylight or haze)

Rayleigh scatter (molecular scatter) primary factor in upper atmosphere (why the sky is blue)

Mie scatter (non-molecular scattering, water/ice/salt/smoke) primarly in lower atmosphere

Figure 2.15Figure 2.15

Figure 2.16Figure 2.16

Clouds and Ice have an Albedo approaching 100%

Global albedo is not constant… but the overall average is 35%

Figure 2.5Figure 2.5

NRG is transferred by:

Radiation: (sunlight)

Conduction (illustrated here)

Convection (description follows)

Figure 2.6Figure 2.6

Figure 2.13Figure 2.13

Atmospheric Windows

Some EMR passes through the atmosphere with no interference (an ‘atmospheric window’

Some EMR is absorbed (or blocked) by components in the atmosphere

The most significant absorbers of EMR in the atmosphere are O2 , N2, O3, CO2, H2O

 

Figure 2.11Figure 2.11

Figure 2.2Figure 2.2

Figure 2.3Figure 2.3

Figure 2.10Figure 2.10

45 degrees N… halfway between equator and pole

57.5 degrees North (same latitude as Moscow and Hudson’s Bay… semi-tropical gardens on the coast of Scotland

So how about those names? For several hundred years, hurricanes in the West

Indies were often named after the particular saint’s day on which the hurricane occurred.

Using women’s names became the practice during World War II

In 1979 male and female names were included in lists for the Atlantic and Gulf of Mexico

Names associated with storms that have caused significant death and/or damage are usually retired from the list.

name lists have been agreed upon at international meetings of the World Meteorological Organization

http://mywebpages.comcast.net/herbwx/hurrsixyr.html

Historical hurricane tracks and names http://weather.unisys.com/hurricane/atlantic/index.html

Tropical Weather & WavesTropical Weather & Waves

Figure 16.1Figure 16.1

Tropical winds Tropical winds typically blow typically blow from the east, from the east, and when they and when they encounter a encounter a slow moving slow moving trough of low trough of low pressure, pressure, called a called a tropical wave, tropical wave, the winds the winds initially initially converge and converge and lift to produce lift to produce showers and showers and thunderstorms.thunderstorms.

Structure of a HurricaneStructure of a HurricaneTropical cyclones are Tropical cyclones are the international the international name of hurricanes, name of hurricanes, which typically form which typically form from an organized from an organized mass of storms formed mass of storms formed along a tropical wave.along a tropical wave.

In this image of In this image of Hurricane Elena, the Hurricane Elena, the central area of broken central area of broken clouds is the eye, clouds is the eye, surrounded by an eye surrounded by an eye wall cloud and spiral wall cloud and spiral rain bands, with a rain bands, with a total diameter nearing total diameter nearing 500 kilometers.500 kilometers.

Figure 16.2Figure 16.2

Hurricane Wind ProfileHurricane Wind Profile

Figure 16.3Figure 16.3

The low pressure core of the hurricane is surrounded by several The low pressure core of the hurricane is surrounded by several thunderstorms, each with updraft and downdraft cycles.thunderstorms, each with updraft and downdraft cycles.

The wind and moisture cycle is repeated as:The wind and moisture cycle is repeated as:surface moist air converges in a counterclockwise pattern at the eye, surface moist air converges in a counterclockwise pattern at the eye, rises to create high pressure aloft, condenses, precipitates, dries, rises to create high pressure aloft, condenses, precipitates, dries, diverges outward in a clockwise pattern, sinks, and warms.diverges outward in a clockwise pattern, sinks, and warms.

3-D Radar Image of Hurricane3-D Radar Image of Hurricane

Several key features of a hurricane are shown in this radar Several key features of a hurricane are shown in this radar composite image, including overshooting clouds, the area of composite image, including overshooting clouds, the area of strongest echoes (heaviest rain), and the eyewall.strongest echoes (heaviest rain), and the eyewall.

Figure 16.4Figure 16.4

Formation by Organized ConvectionFormation by Organized Convection

One theory explains that hurricane formation requires cold air above an One theory explains that hurricane formation requires cold air above an organized mass of thunderstorms, where the release of latent heat warms organized mass of thunderstorms, where the release of latent heat warms the upper troposphere, creates high pressure aloft, which pushes air the upper troposphere, creates high pressure aloft, which pushes air outward and causes a low to deepen at the surface.outward and causes a low to deepen at the surface.Air moving toward this low intensifies the cycle.Air moving toward this low intensifies the cycle.

Figure 16.5AFigure 16.5A

Figure 16.5BFigure 16.5B

Formation by Heat EngineFormation by Heat Engine

Another theory of hurricane development proposes that Another theory of hurricane development proposes that a heat engine cycle, fueled by warm moist input air and a heat engine cycle, fueled by warm moist input air and the release of heat when it converts to cool dry air.the release of heat when it converts to cool dry air.

Differences in the input and output temperatures Differences in the input and output temperatures determine the amount of work on the ocean and winds determine the amount of work on the ocean and winds that is performed.that is performed.

Hurricane Stages of DevelopmentHurricane Stages of DevelopmentThe initial The initial components of a components of a hurricane may hurricane may form as a tropical form as a tropical disturbance, grow disturbance, grow into a tropical into a tropical depression when depression when winds exceed 20 winds exceed 20 knots, become a knots, become a tropical storm tropical storm when winds when winds exceed 35 knots, exceed 35 knots, and finally then and finally then qualify as a qualify as a hurricane when hurricane when winds exceed 64 winds exceed 64 knots.knots.

Figure 16.6Figure 16.6

Erratic Paths of HurricanesErratic Paths of Hurricanes

Figure 16.8Figure 16.8

Historical charts of hurricane location may reveal Historical charts of hurricane location may reveal erratic, and hard to predict, patterns of movement.erratic, and hard to predict, patterns of movement.

As this figure shows, hurricanes may occasionally As this figure shows, hurricanes may occasionally double back.double back.

Further, when removed from the ocean and without a Further, when removed from the ocean and without a moisture source to supply energy, they may still moisture source to supply energy, they may still continue an inland journey.continue an inland journey.

In the North Atlantic, on average 3 storms per year In the North Atlantic, on average 3 storms per year move inland and bring damaging winds and rain.move inland and bring damaging winds and rain.

North Atlantic HurricanesNorth Atlantic HurricanesComposite infrared Composite infrared imagery of imagery of Hurricane Georges Hurricane Georges reveals the pattern reveals the pattern of a seasonal threat of a seasonal threat for Central and for Central and North America North America coastlines.coastlines.

Tropical cyclones at Tropical cyclones at the same latitude the same latitude survive longer in survive longer in the Atlantic than the Atlantic than Pacific Ocean Pacific Ocean because of warmer because of warmer Atlantic Ocean Atlantic Ocean waters.waters.

Figure 16.9Figure 16.9

Hurricane Damage & WarningHurricane Damage & Warning

Hurricanes have their highest wind speeds on the side where Hurricanes have their highest wind speeds on the side where storm pushing winds amplify cyclonic, or counterclockwise, storm pushing winds amplify cyclonic, or counterclockwise, rotational winds. In coastal areas, flooding is aggravated by the rotational winds. In coastal areas, flooding is aggravated by the hurricane low pressure triggering higher tides and Ekman hurricane low pressure triggering higher tides and Ekman transport piling up water.transport piling up water.

Figure 16.10Figure 16.10

Figure 16.11Figure 16.11

Hurricane Watch & WarningHurricane Watch & Warning

The National Hurricane Center in Florida issues a hurricane watch 24 to The National Hurricane Center in Florida issues a hurricane watch 24 to 48 hours before a threatening storm arrives, and if it appears that the 48 hours before a threatening storm arrives, and if it appears that the storm will strike within 24 hours, a hurricane warning is issued.storm will strike within 24 hours, a hurricane warning is issued.While some consider the warning area too large, causing unneeded While some consider the warning area too large, causing unneeded evacuation, such evacuations have saved many lives.evacuation, such evacuations have saved many lives.Hurricane Hugo, with peak winds near 174 knots, caused tremendous Hurricane Hugo, with peak winds near 174 knots, caused tremendous damage.damage.

Figure 16.5AFigure 16.5A

Hurricane Saffir-Simpson WindsHurricane Saffir-Simpson Winds

Figure 16.13AFigure 16.13A Figure 16.14Figure 16.14

In 1989 Hugo caused nearly $7 billion in damages in the U.S., In 1989 Hugo caused nearly $7 billion in damages in the U.S., killing 49 in the Caribbean and United States. killing 49 in the Caribbean and United States.

Current classification of hurricanes is based on their wind speed, Current classification of hurricanes is based on their wind speed, however, and not on human or property damage.however, and not on human or property damage.

Hurricanes range from category 1 to 5, with winds of 64 to more Hurricanes range from category 1 to 5, with winds of 64 to more than 135 knots.than 135 knots.

Hurricane Names and CostHurricane Names and Cost

Category 5 Hurricane Category 5 Hurricane Andrew (1992) was Andrew (1992) was the costliest US storm, the costliest US storm, but it ranks as less but it ranks as less intense than 1935 and intense than 1935 and 1969 hurricanes.1969 hurricanes.

Hurricane names are Hurricane names are chosen from an chosen from an alphabetical list of alphabetical list of male and female male and female names for the Atlantic names for the Atlantic and Pacific, some of and Pacific, some of which are retired if which are retired if the storm was the storm was especially damaging.especially damaging.

Figure 16.14Figure 16.14

Hurricane Andrew Devastation in Homestead, Florida Hurricane Andrew Devastation in Homestead, Florida August 24, 1992August 24, 1992

Figure 16.15Figure 16.15

Likelihood for LandfallLikelihood for Landfall

Between 1900 and Between 1900 and 1999, only two 1999, only two category 5 category 5 hurricanes have hurricanes have made landfall made landfall along the Gulf or along the Gulf or Atlantic.Atlantic.

Numerous Numerous category 1, and category 1, and less damaging less damaging storms, that do storms, that do make landfall may make landfall may not cause much not cause much damage, but bring damage, but bring needed rainfall.needed rainfall.

Figure 16.16Figure 16.16