Friday, September 6, 2013

8:53 News is on. The weather forecast for the next week has the temperature starting at 91 for today and progressively going down to 86 for most of the next seven days. Is this autumn coming, or a hurricane brewing? We have had no hurricanes this year, though there have been half a dozen or so named storms. If the weather is going to be cooler from now on I wouldn't mind, as long as it doesn't get cold until November. The sun is shining and rain isn't predicted.

I just took some time to delete quite a number of files off my desktop and in my “Work after 55” folder. I'm not looking for work anymore. I'm keeping my resumes and list of jobs just because I can't make the break emotionally yet. I haven't been retired long enough to adjust my ideas to my new condition. I'm enjoying my new freedom, though, and am more relaxed during the day.

I called Raquel and told her about the web sites offering low cost cat rabies vaccinations, and she said she would look at it. I got her email address so we can keep in touch.

Reading now. This book is called Florida's Hurricane History and is written by Jay Barnes, director of the North Carolina Aquarium. It was published by the University of North Carolina Press at Chapel Hill, NC. This is not a subject that I will probably read in complete detail like the book on dogs. I will skim parts of it.

The term hurricane is probably derived from the word Hurukan, the name of the Mayan storm god, and some other Caribbean words meaning “big wind” and “evil spirit.” In the western Pacific they are called typhoons, and in the Indian Ocean, cyclones. A “cyclone” is a low pressure area in which the winds rotate inward and upward, moving counterclockwise in the Northern Hemisphere and clockwise in the Southern. An anticyclone is a high pressure system and rotates in the opposite directions, bringing clear and sunny weather. All hurricanes no matter what their location or the term used for them are cyclones. They form in all tropical oceans except the South Atlantic and the Southeastern Pacific, and can come in various strengths. It begins with the “tropical wave” which is a low pressure trough drifting westward at the equator. Within it thunderstorms form, and it is then called a “tropical depression.” If it intensifies, developing wind as high as 39 mph it is then a “tropical storm.” If its wind reaches 74 mph, its air pressure continues to lower and the winds become organized in a circular pattern, it is a hurricane. The spinning of the winds is caused by the rotation of the earth and is called the Coriolis effect. The winds start to spiral inward in response to the friction with the water surface, pulling in more warm, moist air from the surrounding area and the storm strengthens. When the circle of winds is complete and an eye has formed, the winds next to the eye in the eyewall are at their most destructive. They require warm water to strengthen, and will weaken when they move over cooler water or land. Typically hurricanes are formed in the Atlantic between June and November, but they have been known to occur either prior to or after that time. September is the peak of the hurricane season in the waters off Florida. The Cape Verde Islands off the coast of Africa are the source of the most dangerous storms that strike Florida, occurring most often in August and September. Earlier or later in the season the source of storms is more likely to be the Gulf of Mexico or the Caribbean, and they aren't usually as severe. The “nor'easters” developing in the winter off the Florida coasts can be damaging, but are not true hurricanes. They are called “extratropical cyclones” and lack the warm central air mass and the eye. Every year about 60 tropical waves form off the coast of Florida or Africa, but only about 6 make it to hurricane status.

The “Saffir-Simpson scale is used to rate the intensity of a hurricane. It goes from the numbers 1 through 5, based on the gradation of sustained wind strength. Gusts of wind in the storm, or particular structures such as a “suction vortex” which can occur in the eye wall and act like a tornado, can be much higher than the sustained wind. Some storms have totally broken the instruments measuring wind speed due to their strength. In this measuring scale wind of 74-95 mph is classed as a number 1. A number 5 has sustained wind of over 155 mph and a tidal surge of over 18 feet. The terrible storm Andrew was only a category 4. A storm simply called the Labor Day storm in 1935 was a number 5, and had sustained winds estimated at 200 mph. This is stronger wind than the average tornado contains. Some storms like Camille go inland for great distances retaining severely damaging winds, in spite of the fact that passing over land tends to weaken them. Camille went through Tennessee, Kentucky and Virginia. Its tidal surge was 25 feet high. It dropped 27 inches of rain in eight hours in Virginia and caused flash floods there that killed 109 people. That was in 1969, and was the last storm of that strength to come ashore in the US, up to the 1998 publication date of this book.

The author mentions that damage from increasingly high winds does not increase in direct proportion to the change in wind speed, but to the square of the change, or “quadratically.” A 140 mph wind will do four times as much damage as a 70 mph wind. Tree branches, road signs, lawn furniture, lumber and other items are airborne in a 100 mph gust of wind. At 96 to 110 mph roofs, doors and windows are damaged, as are mobile homes, trees, signs, piers and small boats, with flooding of coastal routes. 111 to 130 mph brings structural damage to buildings, destroys mobile homes and causes substantial regional flooding along beaches and rivers.
Sustained winds of 131-155 mph cause extensive structural damage and complete roof failures. with all terrain under 10 feet above sea level flooded. Finally, the strongest winds of greater than 155 (and recorded as high as 200 mph) cause complete roof failures on many homes and businesses with complete structural failure on many buildings. While the strongest tornadoes do more damage than a number 5 hurricane where they hit, most do not, and at least tornadoes rarely affect as wide a swath of land as a large hurricane does. So hurricanes get the prize for being the worst. Luckily, less than 5% of Atlantic storms reach the category 5. Since 1900, six category 4 storms have hit Florida and a category 5 in 1935.

Like tornado winds, hurricanes have picked up objects like planks and driven them through structural walls, trees or posts. In Hurricane Andrew “a massive concrete and steel beam measuring eighteen feet in length, with part of a roof section still attached, was carried through the air more than 150 feet. In the same storm, a possible vortex near the Hurricane Center lifted cars off the ground and dropped them onto other cars.”

Despite the damage of the winds, the storm surge is the most dangerous part of a hurricane. The winds and lowered barometric pressure in the storm cause the water they cross to rise up into a swirling column, and it is then driven over the land. While the storm is still out at sea the dome of water may be only a few feet high, but when it reaches the shallow water near the shore it rises up higher like a tsunami. In strong hurricanes the storm surge once it reached land has been more than 20 feet above sea level, destroying all structures on the beach. While still at sea the storm surge produces large swell of water which travel ahead of the storm by as much as several days and create huge surf on the shore. The swells tend to be evenly spaced and be as high as ten feet. The shape of the sea floor and coastline can cause storm surge damage to be worse. In the Bay of Bengal an event called the Hooghly disaster, from the presence of the Hooghly River, in 1737, in which a storm “wave” estimated at 40 feet came ashore and killed 300,000 people. At Martinique, St. Eustatius and Barbados the Great Hurricane of 1780 killed 22,000. Hurricane winds have also been known to pull the water back from the shore out to sea exposing the sand of the sea bottom and taking boats from the harbor with it. The storm surge usually builds gradually over a span of minutes to hours, but it has been known to come in suddenly. In the Galveston hurricane of 1900 over 8,000 people were killed when this happened. The author also mentions something called a “bore,” which is “a high, abrupt tidal wave that sweeps through narrow channels.” It occurred in a 1926 hurricane on the Miami River, destroying a number of boats that were moored there to keep them safe from the storm. It was caused by the shifting of the wind when the eye passed over the city. Florida's greatest flood disaster was the loss of 2,000 people when the waters of Lake Okeechobee were driven over the levee by hurricane winds.

And then there is rain. Wherever the storm passes, there are huge quantities of rain. Typically at least 6 to 12 inches of rain falls, as the downpour may go on for days if the storm is slow to move through the area. Even after it was diminished to a tropical storm, Hurricane Agnes in 1972 caused flooding all the way from Florida to New York state. On the other hand a hurricane passed over the city of Miami depositing only 0.35 inches of rain! Some of what controls that is how soon the storm moves out of the area. A hurricane that drifted in circles for three days over Cedar Key dropped 38.70 inches. City flooding in Florida is often a problem because most of Florida is flat, and the water can't run off as easily as in hilly areas. Fouled drinking water, power outages and stalled traffic flow cause problems.

Tornadoes are often spawned by hurricanes, usually striking on the fringes of the storm rather than near the center. Florida averages 44 tornadoes a year, which is more than Kansas. A simple severe thunderstorm can develop a tornado. The tornadoes in Florida are not as large and destructive as those in the Midwest, but they still destroy homes and other structures. In 1972 Hurricane Agnes spawned 15 tornadoes, destroying 80 mobile homes at one site and causing $4,000,000 in damages.

The right front quadrant of the eyewall in a hurricane produces the greatest amount of damage in the Atlantic Ocean and Gulf of Mexico. The radiating arms of the storm can cause rain and wind even if the eye never comes ashore. How much damage from wind and rain are caused has a great deal to do with how fast the storm is progressing forward. Over tropical water, they tend to be moving between 8 and 15 mph, but may accelerate up to 30 to 50 mph over cooler northern water. Fast-moving hurricanes have sometimes caused great damage in New England where their forward speed increased. In Florida they are usually moving about 15 mph.

The end of reading and writing for this day. Goodbye.