Hurricanes Environmental Geology Lab PDF

Lab 10 -- Hurricanes Environmental Geology Lab GLY 3039L - Introduction Hurricanes are powerful weather phenomena that are well known for strong winds and torrential rainfall. Hurricanes often start out as tropical waves coming off the western coast of Africa into the warm open waters of the A...

Lab 10 -- Hurricanes Environmental Geology Lab GLY 3039L - Introduction Hurricanes are powerful weather phenomena that are well known for strong winds and torrential rainfall. Hurricanes often start out as tropical waves coming off the western coast of Africa into the warm open waters of the Atlantic Ocean. Given favorable conditions, they can intensify into Major Hurricanes. South Florida has endured many hurricane landfalls throughout the years, including notable hurricanes such as Andrew, Wilma, Charlie, the Labor Day Hurricane, Great Miami Hurricane and Michael. The objective of this lab is to cover the basics of hurricane dynamics including structure, formation, motion, intensity and landfall impacts. - Hurricane Structure There are many parts to a hurricane. The most infamous part being the eye, where the lowest pressure is found. The eye in some of the most powerful storms tends to be clear, however some features such as mesovortices can appear. The eye is also characterized by calm wind. The eyewall is the convective region that surrounds the eye and where the strongest of winds can be found. The location of the strongest winds in a hurricane is known as the radius of maximum wind (RMW). The swirling winds blow around the storm cyclonically (counterclockwise). The rainbands of a hurricane are the next convectively active region and can have some powerful wind gusts with them. The size of a hurricane can vary from a few 100 km to 1,000 km. There are two sides to hurricanes known as the hazards and navigable semicircles. The hazards semicircle is where the forward motion of the hurricane and the spiraling winds of the hurricane move in the same direction. The navigable semicircle is the side where the forward motion of the hurricane and the spiraling winds of the hurricane are opposite to each other. 1. In figure 1, what side of the motion arrow considered to be the hazardous side and navigable side? Explain your reasoning. - Hurricane Formation The necessary conditions for hurricane formation are: - Ocean temperatures must be greater than 26ºC - Relative humidity must be at least 80% between 2 -- 5km - Conditional instability - Wind shear must be less than 12.5 m/s - Pre-existing disturbance - Must be 5º or more away from Equator Most pre-exiting disturbances originate from the western coast of Africa as tropical waves, but this is not always the case. Hurricanes grow through enhanced evaporation due to high winds, unlike tropical squall lines which live off the energy stored in air above the sea instead the energy of the sea itself. For the average hurricane season in the Atlantic Ocean, there are 11 named storms, 6 hurricanes, and 2 major hurricanes.  - Hurricane Motion Hurricanes in the Atlantic Ocean tend to move East to West south of 30° latitude, West to East north of 30° latitude, re-curvature at about 30°. Most hurricanes have a northward degree of motion when making landfall in the US. Hurricanes tend to move with the steering flow around the storm, such as the Azores and Bermuda Highs. 2. Below is a table containing the best track data for Hurricane Andrew. Starting at 17/000 UTC lot the location of the storm on the map included with this packet for every 24 hours. Make sure to use "D" for Tropical Depression, "S" for Tropical Storm, "H" for Hurricane, and "M" for Major Hurricane. Date/Time (UTC) Lat. (ºN) Lon. (ºW) Pressure (mb) Wind Speed (kt) Stage ----------------- ----------- ----------- --------------- ----------------- --------------------- 16/1800 10.8 35.5 1010 25 Tropical Depression 17/000 11.2 37.4 1009 30 0600 11.7 39.6 1008 30 1200 12.3 42.0 1006 35 Tropical Storm 1800 13.1 44.2 1003 35 18/0000 13.6 46.2 1002 40 0600 14.1 48.0 1001 45 1200 14.6 49.9 1000 45 1800 15.4 51.8 1000 45 19/0000 16.3 53.5 1001 45 0600 17.2 55.3 1002 45 1200 18.0 56.9 1005 45 1800 18.8 58.3 1007 45 20/0000 19.8 59.3 1011 40 0600 20.7 60.0 1013 40 1200 21.7 60.7 1015 40 1800 22.5 61.5 1014 40 21/0000 23.2 62.4 1014 45 0600 23.9 63.3 1010 45 1200 24.4 64.2 1007 50 1800 24.8 64.9 1004 50 22/0000 25.3 65.9 1000 55 0600 25.6 67.0 994 65 1200 25.8 68.3 981 80 Hurricane 1800 25.7 69.7 969 95 23/0000 25.6 71.1 961 110 Major Hurricane 0600 25.5 72.5 947 130 1200 25.4 74.2 933 145 1800 25.4 75.8 922 150 24/0000 25.4 77.5 930 125 0600 25.4 79.3 937 130 1200 25.6 81.2 951 115 1800 25.8 83.1 947 115 25/0000 26.2 85.0 943 115 0600 26.6 86.7 948 115 1200 27.2 88.2 946 120 1800 27.8 89.6 941 125 26/0000 28.5 90.5 937 125 0600 29.2 91.3 955 120 1200 30.1 91.7 973 80 Hurricane 1800 30.9 91.6 991 50 Tropical Storm 27/0000 31.5 91.1 995 35 0600 32.1 90.5 997 30 Tropical Depression 1200 32.8 89.6 998 30 1800 33.6 88.4 999 25 28/0000 34.4 86.7 1000 20 - Hurricane Intensity Hurricanes draw strength from warm water and given the correct atmospheric conditions, they will intensify. The strongest winds are in the part of the eyewall known as the radius of maximum winds (RMW), and the lowest pressure is found in the eye. Major hurricanes (Category 3 or above) are responsible for about 80% of damage. However, even if these conditions are met, it is possible for a hurricane to not reach what is known as maximum potential intensity. The determination of maximum potential intensity is done by comparing the ocean temperature [(*T*~in~)]{.math.inline} and outflow temperature [(*T*~out~)]{.math.inline}, as seen in figure 5. [\$M = \\frac{{(T}\_{\\text{in}} - T\_{\\text{out}})}{T\_{\\text{out}}}\$]{.math.inline}. Most hurricanes do not reach their maximum potential intensity because of wind shear, hurricane induced cooling of the sea, eyewall replacement cycles, and lifecycle duration. Two ways of measuring intensity of hurricanes is through wind speed and pressure. Wind speed and pressure happen to be related to each other as well. Hurricane winds circulate in gradient balance between Coriolis force and pressure. Starting from the eyewall of a hurricane outward, winds decrease as pressure increases. Hurricanes have low central hydrostatic pressure due to warm vortex-core. Energy is drawn from sea (mostly through evaporation) is balanced by loss to frictional work and heat carried away by upper-tropospheric exhaust. Energy is released through moist adiabatic expansion that changes stored latent heat obtained from the water vapor into sensible heat in the eyewall, see figure 5. 3. The table on the next page contains the minimum sea-level pressures for Hurricane Nemo at twelve-hour intervals. Use the standard pressure-wind relation [\$V\_{\\max}\\left( \\text{mph} \\right) = 16.725 \\times \\sqrt{1013 - p\_{c}(mb)}\$]{.math.inline}, to calculate the maximum wind in miles per hour for each minimum pressure. Then use Saffir-Simpson scale to assign categories for the times shown.  Figure 5: Thermodynamic cross section of how hurricanes obtain energy from the ocean. Also known as the \"Emanuel Cycle\" Day/Time [*P*~*c*~]{.math.inline}(mb) [*V*~max~]{.math.inline}(mph) Saffir-Simpson Category ---------- ------------------------------- -------------------------------- ------------------------- 01/00 Z 1007 01/12 Z 995 02/00 Z 960 02/12 Z 940 03/00 Z 931 03/12 Z 910 04/00 Z 920 04/12 Z 960 05/00 Z 985 What kind of relationship have you noticed between minimum pressure and maximum wind speed? At what times was Nemo intensifying? At what times was Nemo weakening? At what time did Nemo reach its maximum wind speed? - Landfall Impact Hurricanes have several negative impacts at landfall for people, which are storm surge, wind damage, inland flooding, beach erosion, and high seas. Hurricanes often disrupt communications, utilities, transportation schedules and infrastructure. Landfall is also bad for hurricanes. Surface winds decrease quickly inland due to friction from rougher land surface. The hurricane starts to weaken since it is cut off from the oceanic heat source. Wind speed decreases exponentially inland. Kaplan and DeMaria's rule for inland decay reduces the wind speed of a hurricane by half every seven hours. For example, after seven hours the hurricanes wind speed would be half of what it was when it made landfall. After fourteen hours, the wind speed would be a fourth of the landfall value, and after twenty-one hours, the winds would be an eighth of the landfall value. 4. Hurricane Nemo made landfall at 00h UTC (midnight) on the 19^th^ with 72 m/s maximum winds. Using Kaplan and DeMaria's rule for inland decay (and neglecting immediate frictional effects on the surface winds), what would Nemo's winds in m/s be? a. At 07h UTC? Hint: [\$V\_{\\max}\\left( \\text{decay} \\right) = \\frac{1}{2} \\times V\_{\\max}\\left( \\text{landfall} \\right)\$]{.math.inline} b. At 14h UTC? Hint: [\$V\_{\\max}\\left( \\text{decay} \\right) = \\frac{1}{4} \\times V\_{\\max}\\left( \\text{landfall} \\right)\$]{.math.inline} c. At 21h UTC? Hint: [\$V\_{\\max}\\left( \\text{decay} \\right) = \\frac{1}{8} \\times V\_{\\max}\\left( \\text{landfall} \\right)\$]{.math.inline} - Hurricane Rainfall Hurricane rainfall is a major hazard to life. Inland flooding caused by torrential hurricane rainfall has accounted for 60% of hurricane related deaths from 1970 to 2004. Low-level convergence feeds moisture into the storm, rising motion cause condensation to form. Convective (heavy, brief) and stratiform (light, long lasting) rain. Hurricane precipitation efficiency is enhanced by low evaporation in hurricanes.  Figure 7: Cross section of rain in a hurricane showing where convective and stratiform rainfall 5. Hurricane Nemo is moving at 10 kt when it makes landfall. d. Using Kraft's equation [\$R\_{\\text{TOT}} = \\frac{100}{C}\$]{.math.inline} where [*R*~TOT~]{.math.inline} the storm-total rainfall in inches and C is the storm's speed of motion in knots, what is the expected storm-total rainfall? e. If Nemo slows down to 5 kt just before landfall what will the storm-total rainfall be? f. What do you notice about the relationship between the speed of the Nemo and the total rainfall? - Hurricane Storm Surge A diagram of waves with arrows Description automatically generated Figure 8: Shows that storm surge is resultant of the winds from a hurricane pushing the water onshore Storm surge is simply water pushed toward the shore by the force of the winds swirling around the storm. This advancing surge combines the normal tides to create the hurricane storm tide, which can increase the mean water level 18 feet or more. In addition, wind driven waves are superimposed on the storm tide. This rise in water level can cause severe flooding in coastal areas, particularly when the storm surge coincides with high tide. Much of the densely populated Atlantic and Gulf Coast coastlines lie less than 10 feet above sea level, which makes the dangers of storm surge tremendous. The amount of storm surge is influenced by the slope of the continental shelf and the wind field of the hurricane, which ties into the wind speed intensity and size of the hurricane. 6. Using figure 9 and your knowledge about hurricane wind fields. Determine where the greatest impacts of storm surge will most likely occur and explain why? 7. Conversely, using figure 9 explain where the weakest impacts of storm surge will occur and explain why? 8. How does your answer correlate with the hazardous and navigable sides of Katrina? 9. With sea level rise being an important topic for Miami, how does sea level rise make storm surge an even greater issue for the city?