DISASTER SEVERITY INDICES IN TROPICAL STORMS AND HURRICANES
COMPILED AND DISCUSSED BY LUCY WARNER
OCTOBER 7, 2016


I AM SITTING IN MY APARTMENT WAITING FOR A LARGE AND SCARY HURRICANE TO BRUSH OUR CITY, HOPEFULLY NOT TO COME DIRECTLY IN HERE, AND MY SISTER AND I BEGAN DISCUSSING THE NUMBER OF NEW AND LESS WELL UNDERSTOOD TERMS BEING USED ON OUR TV WEATHER REPORTS. THE RESEARCH ON THIS TURNED OUT TO BE FULL OF NEW INFORMATION. ONE REASON THAT SO MANY OF THE TERMS ARE NEW TO US LAYWOMEN IS THAT SCIENTISTS HAVE A TOTALLY NEW METHOD OF ANALYZING AND PREDICTING HURRICANES. AS I CAN'T SEEM TO AVOID THEM, I HAVE VERGED INTO A COUPLE OF SIDELINES, BUT JUST CONSIDER THAT TO BE EVEN MORE INTERESTING INFORMATION!

THESE ARE THE TWO MEASURES I FOUND OF THE PROBABLE DESTRUCTION THAT WILL BE CAUSED BY A HURRICANE, BOTH OF WHICH ARE IN USE TODAY. THE “SAFFIR-SIMPSON SCALE” IS THE OLD FAMILIAR METHOD, WHICH IS STILL IN COMMON USE BY TV WEATHER FORECASTERS AND OTHERS, BUT THE HURRICANE SEVERITY INDEX, OR “HIS,” CAN BE MORE PREDICTIVE OF TOTAL DAMAGE, ESPECIALLY IN THE SENSE OF FINANCIAL COST, BECAUSE THE AMOUNT OF SHEER DEVASTATION INVOLVE DEPENDS ON HOW LARGE A SWATH OF LAND AREA IS AFFECTED, AS WELL AS WIND SPEED. I LIKE THE PRESENTATION OF RESULTS IN THE SAFIR-SIMPSON DESCRIPTION BELOW, BECAUSE IT SPECIFIES WHAT DAMAGE IS DONE AT THE VARIOUS LEVELS OF WIND SPEED. IT GIVES ME A CLEAR WAY OF ESTIMATING WHETHER OR NOT I SHOULD TRY TO LEAVE MY APARTMENT FOR GREATER SAFETY, AND FOR HOMEOWNERS, IT TELLS THEM HOW TO BETTER PROTECT THEIR PROPERTY. SAFFIR-SIMPSON IS MUCH EASIER TO UNDERSTAND, BUT THE HIS METHOD GIVES SCIENTISTS MUCH BETTER DETAIL ON CERTAIN THINGS FOR PURPOSES OF WARNING THE PUBLIC AND MAKING BETTER PREDICTIONS. THE HIS METHOD WAS DEVELOPED IN 2005, AND HURRICANE PREDICTION REALLY IS MUCH MORE ACCURATE NOW THAN WHEN I WAS YOUNG ESPECIALLY, BUT EVEN AS RECENTLY AS THE LAST TEN YEARS, SO IT MAY BE RELATED TO THE USE BY SCIENTISTS OF THE NEW METHOD. ALSO, OF COURSE, EVERYTHING IS BEING DONE BY COMPUTERS WHICH CAN HANDLE HUGE AMOUNTS OF VARIABLE DATA. THOSE "CONES OF PREDICTIONS THAT ARE ALWAYS USED NOW TO FORETELL THE PATH ARE ACCURATE TO AN AMAZING DEGREE COMPARED TO THE OLD DAYS.

THE "HIS" METHOD WAS DEVELOPED IN 2005 BY TWO SCIENTISTS WORKING WITH A PRIVATE CORPORATION CALLED “IMPACTWEATHER” IN DIRECT COMPETITION WITH THE NATIONAL WEATHER SERVICE’S “ACCUMULATED CYCLONE ENERGY INDEX.” BOTH OF THOSE MEASUREMENTS ARE MEANT FOR ALL TROPICAL STORMS RATHER THAN MERELY HURRICANES. THE HURRICANE SEVERITY INDEX INCLUDES BOTH THE PHYSICAL SIZE OF THE STORM AS WELL AS THE WIND SPEED. IT IS DESCRIBED IN TERMS OF A “SIZE POINT” SCALE COVERING 50 SIZE POINTS AND DESCRIBED IN TERMS OF “WIND RADII” AND “SIZE POINT RANGE.” SEE THE WIKIPEDIA ARTICLES BELOW. ALL THESE ARTICLES HAVE ENOUGH SCIENTIFIC LANGUAGE TO MAKE THEM INSCRUTABLE IN PARTS, OR AT LEAST TRICKY TO UNDERSTAND; BUT THEY ARE EXPLAINED WELL ENOUGH FOR ME TO GET A GOOD GRASP ON WHAT THEY ARE ACTUALLY SAYING, AND I ALWAYS USE THAT AS A COMPARISON POINT FOR MY ASSUMPTIONS OF WHAT THE AVERAGE COLLEGE EDUCATED PERSON WILL BE ABLE TO ABSORB. IT IS MY POLICY, WHEN I DON’T UNDERSTAND A TERM, TO GOOGLE THAT AS WELL. I DO LOVE THE INTERNET!! I HOPE YOU ENJOY THIS INFORMATION.



http://www.nhc.noaa.gov/aboutsshws.php

Saffir-Simpson Hurricane Wind Scale

MUST SEE -- ANIMATION ON THIS WEBSITE SHOWING PHYSICAL EFFECTS AT EACH LEVEL OF SEVERITY. IF YOU ARE PLANNING TO BUY A HOME IN FLORIDA, YOU SHOULD LOOK AT THIS.


Category Sustained Winds Types of Damage Due to Hurricane Winds

1 74-95 mph
64-82 kt
119-153 km/h Very dangerous winds will produce some damage: Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days.

2 96-110 mph
83-95 kt
154-177 km/h Extremely dangerous winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks.

3
(major) 111-129 mph
96-112 kt
178-208 km/h Devastating damage will occur: Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes.

4
(major) 130-156 mph
113-136 kt
209-251 km/h Catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.

5
(major) 157 mph or higher
137 kt or higher
252 km/h or higher Catastrophic damage will occur: A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months.




Hurricane Severity Index
From Wikipedia, the free encyclopedia

The Hurricane Severity Index (or HSI) is a hurricane rating system which defines the strength and destructive capability of a storm. The HSI uses equations which incorporate the intensity of the winds and the size of the area covered by the winds.[1] The HSI attempts to demonstrate that two hurricanes of similar intensity may have different destructive capability due to variances in size, and furthermore that a less intense, but very large hurricane, may in fact be more destructive than a smaller, more intense hurricane. HSI was developed by a private company program in competition with the National Weather Service's Accumulated cyclone energy index.

History[edit]

Development of the Hurricane Severity Index began in 2005 after the 2005 Atlantic hurricane season by Chris Hebert and Bob Weinzapfel, two ImpactWeather meteorologists and hurricane experts. ImpactWeather officially announced the HSI in 2006. Their goal was to create a new index that rates the severity of all types of tropical cyclones (not just hurricanes) based on both their intensity and size of wind field.[1]

Components of the Index[edit]

Visual comparison of Hurricane Floyd with Hurricane Andrew while at similar positions and nearly identical intensities. Floyd was, however, 3-4 times larger and posed a much greater threat.

The idea behind the Hurricane Severity Index is that the size of a hurricane is as important as the strength of its winds. Thus, the index uses a 50-point scale, with half of the total based on wind intensity, and half based on the wind fields.

Size (1-25 points)

Examines the total coverage of the 39+, 58+, 74+ and 100+ mph wind fields.
Intensity (1-25 points)

Points assigned using the relationship between wind speed and the force exerted on an object.
Determining Size Points[edit]

Wind radii data from every named storm since 1988 was studied. From these data, average wind radii ranges of four wind fields (39, 58, 74, and 100 mph) were calculated. Once the typical ranges were established, each wind field range was divided into sections. Since hurricane-force winds are much more damaging than tropical storm-force winds, the size scale is weighted more toward the 74 and 100 mph wind fields. With the HSI, a tropical storm can receive no more than 7 total points for size.

HSI Size Points[2]
A total of 25 size points is possible.

Wind Radii Size Point Range
35 kts 1–3
50 kts 1–4
65 kts 1–8
87 kts 1–10



[WHAT ARE “WIND RADII?”]

https://en.wikipedia.org/wiki/Radius_of_maximum_wind

Radius of maximum wind
From Wikipedia, the free encyclopedia

Photograph -- The radius of maximum wind of a tropical cyclone lies just within the eyewall of an intense tropical cyclone, such as Hurricane Isabel from 2003
Two images -- Radar imagery of a tornado and associated mesocyclone in Wyoming on June 5, 2009. Reflectivity data on the left show the calm interior of the tornado. Velocity data on the right show where the strongest winds are located.


The radius of maximum wind (RMW) is the distance between the center of a cyclone and its band of strongest winds. It is a parameter in atmospheric dynamics and tropical cyclone forecasting.[1] The highest rainfall rates occur near the RMW of tropical cyclones. The extent of a cyclone's storm surge and its maximum potential intensity can be determined using the RMW. As maximum sustained winds increase, the RMW decreases. Recently, RMW has been used in descriptions of tornadoes. When designing buildings to prevent against failure from atmospheric pressure change, RMW can be used in the calculations.[2]

Determination[edit]

The RMW is traditionally measured by reconnaissance aircraft in the Atlantic basin.[1] It can also be determined on weather maps as the distance between the cyclone center and the system's greatest pressure gradient.[3] Using weather satellite data, the distance between the coldest cloud top temperature and the warmest temperatature within the eye, in infrared satellite imagery, is one method of determining RMW. The reason why this method has merit is that the strongest winds within tropical cyclones tend to be located under the deepest convection, which is seen on satellite imagery as the coldest cloud tops.[1] Use of velocity data from Doppler weather radar can also be used to determine this quantity, both for tornadoes and tropical cyclones near the coast.

Tornadoes
See also: Tornado

In the case of tornadoes, knowledge of the RMW is important as atmospheric pressure change (APC) within sealed buildings can cause failure of the structure. Most buildings have openings totaling one square foot per 1,000-cubic-foot (28 m3) volume to help equalize air pressure between the inside and outside of the structures. The APC is around one-half of its maximum value at the RMW, which normally ranges between 150 feet (46 m) and 500 feet (150 m) from the center (or eye) of the tornado.[4] The widest tornado as measured by actual radar wind measurements was the Mulhall tornado in northern Oklahoma, part of the 1999 Oklahoma tornado outbreak, which had a radius of maximum wind of over 800 metres (2,600 ft).[5]

Tropical cyclones[edit]
See also: Tropical cyclone, Storm surge, and Ocean swell

An average value for the RMW of 47 kilometres (29 mi) was calculated as the mean (or average) of all hurricanes with a lowest central atmospheric pressure between a pressure of 909 hectopascals (26.8 inHg) and 993 hectopascals (29.3 inHg).[6] As tropical cyclones intensify, maximum sustained winds increase as the RMW decreases.[7] The heaviest rainfall within intense tropical cyclones has been observed in the vicinity of the RMW.[8]

The radius of maximum wind helps determine the direct strikes of tropical cyclones. Tropical cyclones are considered to have made a direct strike to a landmass when a tropical cyclone passes close enough to a landmass that areas inside the radius of maximum wind are experienced on land.[9] The radius of maximum wind is used within the maximum potential intensity equation. The Emanuel equation for Maximum Intensity Potential relies upon the winds near the RMW of a tropical cyclone to determine its ultimate potential.[10]

The highest storm surge is normally coincident with the radius of maximum wind. Because the strongest winds within a tropical cyclone lie at the RMW, this is the region of a tropical cyclone which generates the dominant waves near the storm, and ultimately ocean swell [sic] away from the cyclone.[11] Tropical cyclones mix the ocean water within a radius three times that of the RMW, which lowers sea surface temperatures due to upwelling.[7]

Much is still unknown about the radius of maximum wind in tropical cyclones, including whether or not it can be predictable.[12]



[WHAT IS A KNOT AND HOW DOES THIS MEASURING SYSTEM DETERMINE SPEED?

[NOTE: INTERPRETING SPEED FROM THIS SYSTEM WOULD TAKE CONSIDERABLE EXPERIENCE, MATHEMATICAL SKILL AND CREATIVE GUESSWORK, I WOULD THINK. I HAVE A MUCH GREATER RESPECT FOR SAILORS NOW, THOUGH I HAVE ALWAYS THOUGHT THEY WERE VERY ROMANTIC AND APPEALING AS A PROFESSION! THE WORDS I HAVE UNDERLINED ALSO NEED TO BE DEFINED FOR ME TO UNDERSTAND THIS INFORMATION FULLY, BUT I DIDN’T TAKE THE TIME TO DO THAT, SO IF YOU WANT TO LOOK THOSE UP AS WELL, I HOPE YOU WILL DO THAT ON YOUR OWN.]


Knot (unit)
From Wikipedia, the free encyclopedia


The knot (/nɒt/) is a unit of speed equal to one nautical mile (1.852 km) per hour, approximately 1.151 mph.[1] The ISO Standard symbol for the knot is kn.[2] The same symbol is preferred by the IEEE; kt is also common. The knot is a non-SI unit that is "accepted for use with the SI".[3] Worldwide, the knot is used in meteorology, and in maritime and air navigation—for example, a vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour.

Etymologically, the term derives from counting the number of knots in the line that unspooled from the reel of a chip log in a specific time.


[WHAT IS A CHIP LOG?]

https://en.wikipedia.org/wiki/Chip_log

Chip log
From Wikipedia, the free encyclopedia

A chip log, also called common log, ship log, or just log, is a navigation tool mariners use to estimate the speed of a vessel through water. The word knot, to mean nautical mile per hour, derives from this measurement method.

Construction[edit]

Diagram of a chip log [TO UNDERSTAND THIS BETTER, GO TO THE WIKIPEDIA SITE AND EXAMINE THE DIAGRAMS, WHERE THERE IS ALSO MORE TEXT.]

Ship log and associated kit. The reel of log-line is clearly visible. The first knot, marking the first nautical mile is visible on the reel just below the centre. The timing sandglass is in the upper left and the chip log is in the lower left. The small light-coloured wooden pin and plug form a release mechanism for two lines of the bridle.
From the Musée de la Marine, Paris.

A chip log consists of a wooden board attached to a line (the log-line). The log-line has a number of knots at uniform intervals. The log-line is wound on a reel so the user can easily pay it out.

Over time, log construction standardized. The shape is a quarter circle, or quadrant, and the log-line attaches to the board with a bridle of three lines that connect to the vertex and to the two ends of the quadrant's arc. To ensure the log submerges and orients correctly in the water, the bottom of the log is weighted with lead. This provides more resistance in the water, and a more accurate and repeatable reading. The bridle attaches in such a way that a strong tug on the log-line makes one or two of the bridle's lines release, so a sailor can retrieve the log.

*** [NOTE: SAILORS HAVE USED “CHIP LOGS” TO MEASURE SPEED FOR HUNDREDS OF YEARS. IT IS ONE QUARTER SECTION OF DIAMETER A GENUINE LOG , OR QUADRANT, WHICH IS WHIMSICALLY CALLED A “LOG.” THE ANGLE OF THE SIDES IS 90 DEGREES. ROPE LINES ARE ATTACHED TO ALL THREE POINTS AND THEN TO ONE, PROBABLY TO CONTROL THE WAY IT FLOATS OR TO REEL IT IN EVENLY. THIS SINGLE LINE IS KNOTTED IN A SPECIFIC WAY TO MEASURE THE DISTANCE, AND AS THE LINE IS REELED IN THE KNOTS ARE COUNTED. I ASSUME A TIME PIECE OF SOME KIND IS ON HAND TO ADD THE TIME FACTOR TO THE DISTANCE, AS MEASURED BY THE KNOTS. IN THOSE DAYS (CIRCA 1600) THERE WERE NO WRIST WATCHES, BUT THERE WERE SUNDIALS AND "HOUR GLASSES" MENTIONED IN THE ARTICLE ABOVE AS A "SAND GLASS", BOTH FAIRLY ACCURATE WAYS OF DETERMINING THE TIME IF THE SUN IS SHINING. AS A GIRL SCOUT WE WERE TAUGHT TO DRAW A CIRCLE IN THE GROUND WITH LINES IN IT TO SHOW THE HOUR MARKS. THEN YOU PICK A STRAIGHT STICK OR A LIMBER YOUNG BRANCH OF A LIVING TREE AND, AFTER STRIPPING OFF THE LEAVES, STICK THAT INTO THE SOIL AS FIRMLY AND VERTICALLY AS POSSIBLE. THIS SHOULD BE DONE IN A SUNNY PLACE, OF COURSE. THERE HAVE ALSO BEEN HOUR GLASSES IN USE FOR HUNDREDS OF YEARS AS WELL. THIS COULDN’T HAVE PROVIDED A VERY PRECISE MEASURE OF SPEED, BUT ENOUGH TO ESTIMATE WHEN YOU SHOULD GET TO THE NEXT PORT. THAT IS IMPORTANT IN ORDER TO PREDICT THE TIDES, BECAUSE IF THE TIDE IS GOING OUT, A SAILING SHIP WOULDN’T BE ABLE TO COME INTO THE PORT. IN THE OLD PIRATE STORIES, THEY WOULD WAIT OFFSHORE UNTIL IT WAS THE RIGHT TIME TO COME IN.

I’M GUESSING THAT THE TERM LOG COMES FROM THE SECTIONING OF A TREE TRUNK TO PRODUCE SUCH A SHAPE. THAT TREE TRUNK, A “LOG” IN TRADITIONAL ENGLISH USAGE, WAS CUT THROUGH THE DIAMETER TO PRODUCE A CIRCULAR SECTION AND THEN INTO EVEN QUARTERS. I DIDN’T SEE THE IDEAL SIZE MENTIONED IN THE INFORMATION ABOVE, BUT I WOULD SAY THAT THE WEIGHT OF THE “LOG” WOULD HAVE TO BE JUST RIGHT FOR IT TO OPERATE WELL. IN ONE OF THESE TWO ARTICLES IT IS ALSO CALLED A CHIP LOG. AGAIN, THIS ISN’T MY IDEA OF A “CHIP,” WHICH IS SMALLER, BUT I’LL LET THAT GO. THE LINE, ATTACHING THE LOG OR CHIP TO A WINDABLE REEL ON THE SHIP, IS KNOTTED AT SPECIFIC LENGTHS WHICH ARE THEN COUNTED AS THE ROPE IS PULLED IN, THUS GIVING THEM A REASONABLE MEASURE OF THE SPEED. THE METHOD REQUIRES CONSIDERABLE EXPERIENCE TO PRODUCE GOOD RESULTS. SEE THE “USE” SECTION BELOW.]


Use[edit]

A navigator who needed to know the speed of the vessel had a sailor drop the log over the ship's stern. The log acted as a drogue – see https://en.wikipedia.org/wiki/Drogue for an explanation of what it is and how it is used -- remaining roughly in place while the vessel moved away. The sailor let the log-line run out for a fixed time while counting the knots that passed over. The length of log-line passing (the number of knots) determined the reading.

. . . .

Accuracy and considerations by the navigator[edit]

Use of a log did not give an exact speed measure. The sailor had to incorporate a number of considerations:

The amount of "following sea”
The effect of currents
“Stretch” of the line
Inaccuracy in the time measurement—because ambient temperature, humidity, and sea state affected the “sandglass”

Frequent measurements helped mitigate some of these inaccuracies by averaging out individual errors, and experienced navigators could determine their speed through the water with a fair degree of accuracy. Because a log measures the speed through the water, some errors—especially the effect of currents, the movement of the water itself—could not be corrected for. Navigators relied on position fixes to correct for these errors. Modern navigation tools, such as GPS, report speed over ground, and in general do not give the same result as a log when currents are present.

More modern logs and replacements[edit]

A patent or taffrail log

Mechanical speed logs called patent logs or taffrail logs, operating on physical principles in a manner similar to a car's odometer by towing a vane or rotor from the stern (or taffrail) by a long line, were developed in the eighteenth century (or earlier) but became practical in the nineteenth century and replaced the traditional chip log.[9] Since the second half of the twentieth century, sailors continue to use more modern mechanical and electro-mechanical versions based upon a small impeller or paddle wheel attached to (or through) the bottom of the hull, especially on smaller yachts.

In recent years ultrasonic speed sensors have become available. These use two ultrasonic transducers—one forward, one aft—that send ultrasonic pulses through the water flow past the hull. By calculating the time differential in pulse propagation from one sensor to the other, the device calculates the speed of the hull through the water.

Today, the most accurate maritime speed measurement comes from Doppler measurement, either derived acoustically with Doppler Sonar—or with radio interferometrically by Doppler measurement of satellite signals, such as those from Global Positioning System (GPS). Most commercial GPS systems are not configured to operate in this mode, however.


EVEN THOUGH THIS TOOL IS IMPROVISED, THE USE OF IT DOES SHOW THAT THE HUMAN MIND IS EVER CREATIVE AND RESOURCEFUL. GO TO THE WIKIPEDIA ARTICLE ON THE SUBJECT. I HAD NO IDEA OF WHAT THESE LOGS WERE AND HOW THEY WORKED, AND IT'S VERY INTERESTING TO ME. IT'S ALMOST AS GOOD AS CROSSING THE ATLANTIC FROM EUROPE WITH THE FIRST EXPLORERS.