LOCAL METEOROLOGY

Weather - a combination of temperature, humidity, and winds; a local and temporal phenomenon.

Climate - average of all weather for a particular area.

Aspects that affect our delta (local) climate:

Orientation - New Orleans is at 30 °N 90 °W

Kniffen, 1968 (Map 4).

other cities at 30 °N: Houston, Cairo, Shanghai

-others places at 90 °W: Memphis, St. Louis, Yucatan, the Galápagos.

atitude is very important. At 30 °N, we are outside of the tropical region, which is defined as being between the Tropics of Cancer and Capricorn (23.5 °N&S, respectively, or 6.5 ° off of direct incidence of solar radiation). At our latitude, weather is influenced by air mass movements. Winter starts when the first Polar Air Mass arrives and ends with the passing of the last one in the spring.

Our area is subtropical. The key to falling in this category is that the January average temperature must consistently fall between 32 ° & 64.4 °F. Louisiana is the only southeastern U.S. state that falls in this category. Its importance to agriculture and local vegetation is that it defines the length of the growing season. Burrwood, LA (not presently inhabited) has an average of 354 days without a frost; in one 10 year period, it had 6 yrs with no freeze and the other 4 yrs had only one freeze. New Orleans has a growing season averaging about 300 days.

Kniffen, 1968 (Map 8).

2. Location - situated between Lake Pontchartrain and the Gulf of Mexico. We are in a marine climate zone, a characteristic of most land within 100 mi of sea water. This and the subtropical status makes our region characteristically humid-subtropical. The New Orleans/delta zone has abundant precipitation (average 60-65 in/yr) that is relatively evenly distributed throughout the year. Though we tend to have drier and wetter spells, the importance is the availability of water to plants at different time periods. October averages about 3 in of precipitation, while July averages 7 in. However, low evaporation in October versus high evaporation in July tends to cause these figures to balance in terms of what is actually available for the plants to use.

Local high humidity in the air is good for plants since it tends to prevent excess evaporation. It also causes our skin to be less wrinkled over our lifetimes (compare to folks from Arizona).

One of the most important effects of being in this zone is local wind movement.

-During summer daytime, we experience onshore winds, i.e., wind moves from the sea (Gulf and Lake) onto the shore where we live. This is due to the fact that the land gets hotter and heats more rapidly than the water, causing the air over the land to rise (convection). As it does, it sucks in the cooler air from over the water to replace it. People in our area who lived around Lake Pontchartrain used to take advantage of this by placing their living quarters on the north sides of their houses in order to be evapo-cooled (one cools down as the sweat evaporates from the body) by cool day breezes blowing from the water. People who lived by other bodies of water placed their living quarters nearest the water.

-During summer nighttime, we experience offshore winds, i.e., wind moves from land toward the sea. This is caused by the land becoming cooler than and cooling more rapidly than the lake. The result is air over the lake being warmer, so it rises by convection and the cooler air over the land moves in to replace it. People who lived along Lake Pontchartrain took advantage of this nighttime air movement by placing their sleeping quarters on the south and southeastern sides of their homes in order to be evapo-cooled by cool night breezes blowing over their bodies as they rushed toward the lake.

As long as there is a heat differential between land and the lake, the direction the wind blows is predictable. Of course, this is true between different places on land, too (e.g., the concrete Central Business District heats much more rapidly than areas like the Louisiana Nature Center and surrounding neighborhoods, so which way does the air tend to move?). When there is no huge differential (usually in the winter), then other forces govern the direction of wind movement (e.g., storms, fronts, etc.).

Our position near large bodies of water has another influence, this time on the arrival of very cold weather. Large bodies of water hold heat longer than land. After months of heating, Lake Pontchartrain becomes thoroughly heated and functions much like a hot water bottle. As cold fronts begin to reach south Louisiana, their effects on north shore are very different than on south shore. The land on north shore tends to rapidly adjust to the cold air in the front. South shore, however, is buffered by the warm lake. In the fall and early winter, south shore normally is many degrees higher on a given night than north shore. The lake, however, cools more and more each day as winter approaches. When the lake reaches its low, then it may discontinue serving as our hot water bottle and the next cold front blows across the lake and affects south shore much as it does the north.

In the spring, the lake works just the opposite. It warms gradually, so it keeps south shore cooler longer than north shore.

The following average minimum temperatures (compiled by Nash C. Roberts, Jr. Consultants, Inc.) for 1989 show this protective action of the lake (during this season, however, the weather was mild so the lake acted as a buffer all year long):

Covington New Orleans

Dec 30.5 °F 38.3 °F

Jan 47.6 °F 53.2 °F

Feb 43.9 °F 48.4 °F

June 68.6 °F 72.7 °F

July 71.5 °F 74.4 °F

Aug 70.1 °F 74.3 °F

3. Position on the continent - At our orientation, the general air flow is from the west. These winds travel over the highly variable interior of the continent, so they carry that weather variability to our region. Colder air arrives in the winter and warmer air in the summer. The western side of the continent receives winds from the sea, so it has a relatively consistent temperature.

HURRICANES (for more and current info, visit the National Hurricane Center – http://www.nhc.noaa.gov, the U.S. Geological Survey – http://coastal.er.usgs.gov/hurricanes/, and the L.S.U. Hurricane Center – http://hurricane.lsu.edu.

Our most powerful weather systems are hurricanes. They go by the following names:

hurricanes: Atlantic, Caribbean, Gulf of Mexico, and eastern Pacific

tropical cyclones: most of S. Pacific & Indian Oceans

typhoons: western N. Pacific

baguios: Philippines

willy-willy and cyclones: Australia

A hurricane can release enough energy in one day to supply U.S. electrical needs for 6 months.

The following is a selection of terms that one should know in order to understand the nature of hurricanes.

Cyclone - low pressure zone with air rising in a counterclockwise spiral.

Anticyclone - high pressure zone with air descending in a clockwise spiral.

Convection - the movement of air upward, due to thermal qualities or updrafts.

Bermuda High - an anticyclone that, from early summer until mid-autumn, locates over the mid-Atlantic Ocean and southeastern U.S.

The Charlotte Observer, Wednesday, June 25, 1986.

Easterlies (tradewinds) - south of the Bermuda high, these winds normally flow from southeast to the northwest. Easterlies may reach as high as 40,000 ft or more and travel over great expanses of the Atlantic Ocean into the Gulf of Mexico. See the illustration below.

Easterly (=tropical) waves - Low pressure areas that normally originate over equatorial Africa and move westward in the easterly tradewinds. They are oriented north-south, are about 20 ° latitude long, and are spaced about every 15 ° longitude. Associated clouds are easily spotted on the 6 o'clock news aerial photos by their northeast to southwest orientation on the west of the wave and southeast to northwest on the east. Sometimes they are the result of a polar trough separating at its tip, but they still move in the easterlies.

Westerlies - winds of the temperate zone that blow from northwest to southeast. See the illustration below.

Polar trough - an area of low pressure embedded in the westerlies that may be pushed south.

http://www.hpc.ncep.noaa.gov/international/training/synopt/sld010.htm

Intertropical convergence zone (ITCZ) (=equatorial trough, doldrums) - a low pressure zone located around the equator between the easterly tradewinds of the northern and southern hemisphere. It varies from being almost undetectable to being a zone of intense storms. Its location varies from day to day, but its seasonal variation is from the vicinity of the equator in February to about 12 ° N latitude in August. See the illustration below.

WHERE DO CYCLONES OCCUR IN THE WORLD?

POSSIBLE HURRICANE STARTER MECHANISMS:

The following are three ways cyclonic wind circulation may begin that may lead to a hurricane.

Polar trough - In early summer, the Bermuda high slips south and weakens. This may allow a polar trough to move farther south. If the southern tip of the trough gets trapped in the prevailing easterlies of the tropics, it may break loose and develop into an easterly wave. It is already a low pressure cyclone, so if the right circulation increases, it may become a hurricane.

Easterly wave - Here we are discussing those that originate off the coast of Africa and travel westward. Many of these change little in form and simply dissipate. Occasionally, however, one develops greater cyclonic circulation and may become a hurricane.

ITCZ - an area of circulation may develop at the periphery, break loose and move into the easterly tradewind belt and intensify.

STEPS THAT OCCUR AFTER A VORTEX IS FORMED

1. Initial vortex creates a region into which air from the surroundings flow, accelerating the convection already occurring. If the air has become warm and moist from flowing over tropical waters, it adds energy to the system.

2. As the warm, moist air rises in the cyclone, it cools and water vapor and heat energy are released. The heat energy drives the wind system and the vertical circulation acquires greater organization.

3. If high altitude winds of the proper speed blow over the vortex, they draw the air, now drier and with decreased energy, upward more quickly and distribute it in a anticyclonic fashion away from the vortex. This pumping action 1) continues to decrease the pressure in the cyclone and 2) prevents the cyclone from being filled with cool air and thus deteriorating. It is possible only if a convective chimney has developed.

4. MOVEMENT. The cyclone continues to move northwestward in the easterlies on a curved course. When it arrives at 30-35 °N latitude (the horse latitudes), the general area where it encounters the westerlies, the hurricane may stall (and, if the water is warm, pick up energy) or begin to move northeastward. This is called the point of recurvature. Before this point, hurricane linear movement may be at about 30 mph; after, up to 60 mph.

WHAT MIGHT STOP A HURRICANE FROM FORMING?

1. Wind circulation never gets organized.

2. Not enough energy in the system to carry its development.

3. Other meteorological events that bump them off.

4. The convective chimney does not form.

5. Jet stream or other strong wind shears off the top.

6. Two sticks crossed with salt poured in the center.

7. You have adequate canned goods, stored water, gas tanks filled, windows boarded, and a precise plan of action ready to implement.

Anatomy of a Hurricane

This is a vertical cross section through the eye of a hurricane.

A plan view of a hurricane shows the location of the eye, convective chimney, and the rainband pattern

Views of Hurricanes

Hurricane Gladys, October 17, 1968.

Hurricane anatomy from above.

Hurricane Hugo (Category 4), September 1989.

In August 1980, Typhoon Isis (Category 2) was in the Pacific while Hurricane Allen (Category 5) ravaged the Texas Coast. UPI.

HOW DO WE CLASSIFY CYCLONES?

As low pressure zones (=cyclones) become better organized, 1) their circulation becomes more obvious, 2) there is more organization to their atmospheric pressures (an isobar is a line that separates two areas with consistent pressures; if the isobar forms a circle, then all the area within the circle has the same pressure), and 3) their wind speeds increase. Hence, these are the three criteria used to identify the levels of development ranging from a Tropical Disturbance to a Hurricane.

Isobars for Hurricane Camille, August 17, 1969.

Stages of Tropical Cyclones

STAGE	SURFACE CIRCULATION	CLOSED ISOBARS	WIND SPEED (MPH)
Tropical Disturbance	absent - slightly	0-1	some-22
Tropical Depression	some	1+	23-38
Tropical Storm	well developed	several	39-73
Hurricane	very well developed	more	74+

HURRICANE CATEGORIES: Once a cyclone is classified as a Hurricane, then attention focuses on 1) barometric pressure, 2) wind speed, and 3) storm surge. We used the Saffir/Simpson Scale to rate hurricanes from Category 1 to Category 5.

-SAFFIR/SIMPSON HURRICANE SCALE RANGES

HURRICANE SCALE NUMBER (CATEGORY)	CENTRAL BAROMETRIC PRESSURE (INCHES)	WINDS (MPH)	STORM SURGE (FT)	DAMAGE
1	>28.94	74-95	4-5	Minimal
2	28.50-28.93	96-110	6-8	Moderate
3	27.91-28.49	111-130	9-12	Extensive
4	27.17-27.90	131-155	13-18	Extreme
5	<27.17	>155	>18	Catastrophic

Though we tend to think of severity on the basis of the category, the truth is that lesser hurricanes can be more dangerous under certain conditions. For example, a very fast moving Category 5 hurricane moving into a sparsely settled area will be much less devastating than a very slow moving Category 3 that has lots of rain hitting and hovering over a major metropolitan area.

-FREQUENCY OF RETURNS FOR HURRICANES WITHIN 80 MILES OF NEW ORLEANS

CATEGORY	FREQUENCY OF RETURN
1	8 years
2	19 years
3	32 years
4	70 years
5	180 years

-Fujita Scale for Damaging Wind (Used for Tornadoes)

The Fujita Scale, a system similar to the Saffir/Simpson Scale, is used for tornadoes. Fujita is based solely on wind speed – which is much higher than for hurricanes and certainly more concentrated. Remember: tornadoes are almost always produced by hurricanes.

· SCALE	MPH	DAMAGING WIND
F 0	40-72	Light damage
F 1	73-112	Moderate damage
F 2	113-157	Considerable damage
F 3	158-206	Severe damage
F 4	207-260	Devastating damage
F 5	261-318	Incredible damage

Anatomy of a Thunderstorm

Thunderstorms

Storm Season 1989: Mapping the Risk in Greater New Orleans

America's WETLAND Pea Soup (fog and what causes it)

WAYS HURRICANES CAUSE DAMAGE:

1. Winds. Pressure against structures mounts disproportionately with wind velocity.

Example: a 20 knot wind increases atmospheric pressure by 2 lb/sq ft. A 200 knot wind increases atmospheric pressure by 225 lb/sq ft.

We noted that the speed of wind in a hurricane is derived from the storm =s travels over warm water, where it picks up energy. Normally, the power (=energy) of the storm is dissipated once it hits land. Hurricane Danny, which crossed southeast Louisiana on July 18, 1997, was the first hurricane to actually increase in power once it crossed the state =s barrier islands. This was because it was the first storm to travel across this section of our coastal wetlands since most of the marsh became open water, thus presenting the storm not with friction and terra firma to slow it, but with shallow, warm water from which it gained more strength.

2. Storm surge. This is a "bulge" of water being pushed in front of the eye of the hurricane. This is on top of increased tide. For Hurricane Camille, the surge was 25 ft!

The next time you visit Gulfport, MS, go by the marina just east of the junction of US 49 at the coastal highway. Beside the boat ramps, there is a pole that marks the storm surges from several storms that have affected that area. It is quite impressive. At about eye level is Hurricane Juan (1985), then Hurricane Betsy (1965), then the unnamed hurricane of 1947, then, 25 ft above your head, is Hurricane Camille (1969). This pole gives you an excellent idea of the enormous amount of water that a hurricane can push ahead of its eye.

Gulfport, Mississippi, Marina "hurricane pole," showing the height of tidal surges of various hurricanes.

Floods in the lower Mississippi River area caused by Hurricane Camille.

Based on information obtained by the U.S. Army Corps of Engineers in the Terrebonne estuary after Hurricane Andrew, a general rule-of-thumb is that for every three miles of healthy coastal marsh that a hurricane crosses, one foot of its storm surge is dissipated. Since Hurricane Camille emerged directly from the Gulf of Mexico to hit the Mississippi Gulf Coast, it had a 25 ft storm surge. Had it crossed a healthy marsh some 75 mi wide, it may have had no surge. This is critical for coastal Louisiana when we consider the speed at which we are losing our Astorm buffer. @

3. Wave activity. There may be 5-10 ft waves on top of the surge. Water weighs 1700 lb/cu yd, so the pounding waves can be deadly.

4. Misplaced currents. These occur because of the dynamic movement of water during the storm; existing currents are simply pushed closer to the shore. These will erode beaches and foundations.

Secondary weather. These arise from the hurricane and include rain (flooding) and tornadoes.

HURRICANES ALSO CAUSE EARLY BIRTHS: The rapid drop in barometric pressure associated with hurricanes fills the hospitals with ladies who are close to birth time. After Hurricane Andrew, this sign showed up on Veterans Boulevard in Metairie:

Note the name of the baby - Andrew!

On July 11, 1979, the first hurricane named for a man, Bob, formed near the mouth of the Mississippi River and the eye swept over Metairie. My wife was very pregnant, and her water broke. On July 13 th, my son Patrick was born, several weeks early due to my namesake – Hurricane Bob.

How do we determine the impact of a Hurricane? (all 8/30/02)

-Deadliest Hurricanes in the U.S. 1900-1996 - http://www.nhc.noaa.gov/pastdead.html

-Costliest Hurricanes in the U.S. 1900-1996 - http://www.nhc.noaa.gov/pastcost.html

-Most intense Hurricanes in the U.S. 1900-1996 -http://www.nhc.noaa.gov/pastint.html

The many lessons learned from Hurricane Andrew, one of only three Category 5 storms to hit the U.S. (it was a Category 3 when it hit Louisiana), visit http://www.lacoast.gov/wetlands/willfulwinds/index.htm (8/30/02).

Hurricane tracks.

When a hurricane has completed its destructive course, a plot of its travels becomes its hurricane track. These have been plotted for most hurricanes and look like spilled spaghetti in the Gulf of Mexico (see the slides we show).

Typhoon tracks in the western Pacific.

Hurricane tracks for the eastern Pacific.

Hurricane tracks in the Atlantic Ocean and Gulf of Mexico between 1886-1969.

Hurricane tracks in Louisiana 1831-1975.

-Hurricane strikes in the U.S. between 1900-1996 - http://www.nhc.noaa.gov/pastdec.html

-Hurricane Strikes in the U.S. by State - http://www.nhc.noaa.gov/paststate.html

Critical Path Hurricane for New Orleans.

The worst case scenario hurricane (based on a Category 3 storm) for New Orleans will basically follow a path whereby the eye, traveling from the southeast, passes between the Mississippi River and the mouth of Lake Pontchartrain from the Gulf. Since hurricanes have a counterclockwise wind motion, this path would result in the storm pushing water into Lakes Pontchartrain, Borgne, Catherine, and Maurepas.

U.S. Army Corps of Engineers.

As the eye nears the center of the lake, the storm would kick to the northeast, thus causing the counterclockwise winds to push the copious amounts of water south and over the levees into Greater New Orleans.

Imagine what happens when you get into a full bathtub too quickly. As you plop in, the water races to the other end of the tub, then sloshes back and usually over the edge of the tub. This is called a seiche, and such a phenomenon would be the primary culprit for filling up the bowl of Greater New Orleans.

It is projected that such a storm would put about 18-20 ft of water throughout Greater New Orleans.

What have we done to prevent this?

We can't stop the storm, so we have to protect ourselves otherwise. The current plan is to encircle the region with 17 ft high levees (the high level plan).

Times-Picayune.

There was a plan proposed by the Corps of Engineers to place control structures at the entrance of the Lake (see slides) that could be closed as a storm appoaches (the Environmental Impact Study was finished in 1974). This was not implemented because environmentalists did not want to see the lake ecosystem interrupted in such a way that marine larvae (such as crabs, shrimp, menhaden, etc.) could not move into and out of the lake.

The overall plan for the lake. U.S. Army Corps of Engineers.

This was the plan for the Chef Menteur Pass. U.S. Army Corps of Engineers.

So, when does one evacuate?

This is the hardest question to answer, and it should definitely be an individual decision. Many say they will never evacuate. Here is my rule of thumb.

By June 1 st of each year, I am prepared for the hurricane season. I update my belongings inventory (I always pay my flood insurance on time), have at least 10 five gallon bottles of water in my garage, 20 or so butane cylinders for my butane lights and stove, at least 2 large butane tanks for my barbeque grill, lots of batteries and several good flashlights, plenty of matches, lots of canned foods (many of which I would only eat in a crunch - most of it goes to charity after the season), an axe in my attic (in Hurricane Betsy, a number of people drowned when they crawled in their attics to avoid rising water and became trapped and drowned), a couple of snake bite kits, extra medications that we need, and the like. Once a storm enters the Gulf, my cars have full tanks, I monitor the forecast at least hourly, I constantly tell my family members what I am thinking, I begin to put yard things away, and the like. If it really looks bad, just before I evacuate I fill my bathtubs and all containers in the house with water, get together the things I simply must save and keep them in a place where they can easily be packed in the cars (yes, I have an official list of what I can =t live without so that I don =t have to think about it; I review it at the beginning of the season), call my out-of-town family to tell them what we are thinking and planning, and further batten down the hatches.

If I am absolutely certain that a hurricane will be a Category I when it hits land, I don =t leave (but I am ready to if needed). Even at a moderate to low Category II, I would be hesitant to leave. I would be comfortable if such a storm was approaching from due south, i.e., targeted to cross the coast near Grand Isle.

My family is on stand-by any time a hurricane is heading toward the Gulf of Mexico. If it is a Category II when it enters, I assume it will escalate so I begin preparing to leave.

When do I absolutely, definitely, always leave? Anytime we have a Category III or above (or a lesser that appears to be escalating to that level) nearing the middle of the Gulf and heading toward New Orleans on a critical path, I =m gone before it hits the center of the Gulf. It is just plain dumb to wait too long and not be able to get out, and it is just plain dumb to stay. Life is not a gamble.

By the way, I also don =t run in front of Big Mack trucks or stick my head in a tiger =s mouth. One of my best friends stayed in his house during a direct hit by Hurricane Andrew. His roof was completely torn off, and he told me that for every minute for many, many hours he expected to die and to see his family die. It was the most terrifying time of his life and he will never make that mistake again.

What is the biggest present fear?

There has not been a major storm in the immediate Greater New Orleans area since Hurricane Betsy in 1965. The population has increased markedly, with most residents not really knowing the power of a storm. If a hurricane approaches New Orleans, many would stay here thinking that a hurricane is no big deal. Also, evacuation would be tough with this many people. And, very important, the poor have no options of escape!

Hurricane Andrew (1992) may have educated the masses. Witness, though that one of the City of New Orleans' four escape routes, I-10 West, was not available due to construction! Today, if a hurricane evacuation is declared, all lanes of I-10 will be available for northbound traffic from the western edge of Kenner.

Damage Scenes from Hurricane Camille, August 17, 1969

Hotel Richelieu before Camille.

Hotel Richelieu after Camille.

Damage Scenes from Hurricane Andrew in Louisiana, August 26, 1992

Huricane Andrew's track.

Chuncks of marsh thrown onto high ground. Photo Shea Penland.

More marsh damage. Photo by Shea Penland.

The bark was literally blown off cypress trees. Photo by Shea Penland.

Huge amounts of mud were left behind. No big deal in the marsh, but terrible when in your backyard. Photo by Shea Penland.

Floatant marsh was ripped off on the southern edge and pushed up like a blanket at the foot of the bed on a hot night. Note the folds. It was suggested that these floatant marshes would never recover.

Photo by Shea Penland.

This photo was taken just south of Houma in a floatant marsh 6 months after Hurricane Andrew. Note the narrow open areas of water. This floatant marsh had been bunched up like the one above, but within this short period of time, it reestablished. The narrow open water areas were the creases in the bunched up marsh, and the intervening green areas were the folds. Wetlands are more resilient than we often admit.

EXCELLENT SERIES BY THE TIMES PICAYUNE:

ttp://www.nola.com/hurricane/?/washingaway/