Good Evening everyone, I hope all of you have had a great day. I am going to write an informative blog about Hurricanes. I believe it is appropriate to write about Hurricanes because not only did Hurricane Season start on June 1st and ends on November 30th. This Hurricane is off to a fast start with Ana being our first named storm of the season. Ana was a sub-tropical storm at first, which had mid latitude storm characteristics which involved cold air aloft and tropical storm characteristics which had warm air at the surface. Ana did affect the Carolina coast south of Wilmington N.C. and north of Myrtle Beach S.C. with very heavy rain and gusty winds. It is unusual to have a storm to develop in early May but not extraordinary. The East Pacific is off to a fast start this year with Hurricane Blanca reaching major hurricane status. The Eastern Pacific starts a little earlier than the Atlantic side around May 15th.
Folks, what I am going to write and discuss about tonight is as follows: What a Hurricane is, the different Hurricane names in ocean basins, Hurricane frequency by month Factors that Develop Hurricanes, Factors that weaken and dissipate Hurricanes, Stages of Development in Hurricanes, How do Hurricanes cause damage, Factors that cause above average years for Hurricanes and Factors that cause below average year for Hurricanes in terms of number of storms, Deadliest Hurricanes on graph and the Saffir Simpson Scale.
1. WHAT IS A HURRICANE?
A. HURRICANES – The term Hurricane is derived from Huracan, a Carib god of evil. Hurricanes are intense low pressure centers focused at the surface that form over tropical or subtropical oceans characterized by intensive convective(thunderstorms) activity and very strong cyclonic circulation. Sustained winds must be 74mph or greater. Hurricanes lack contrasting air masses and fronts like midlatitude storms in the plains of the U.S. Hurricanes draw their energy from the warm ocean waters of the tropical and or subtropical oceans.
2. HURRICANE NAMES IN OCEANS THROUGHOUT THE WORLD
A. Atlantic and Eastern Pacific – Hurricanes
B. Northwest Pacific – Typhoons
C. Australia and Indian Ocean – Cyclones
3. HURRICANE FREQUENCY BY MONTH
Hurricanes vary in frequency by month. For example, June 1st is the start of the Atlantic Hurricane season, however June is a relatively quiet month compared to active months in the late summer. Hurricane frequency usually peaks in August to early October, with September 10th being the official peak day of the season. I have a graph by NOAA.gov that illustrates this point.
Notice how their is a secondary peak in Mid – October, Florida and the Gulf Coast need to be aware of this because at this point in the season most tropical systems tend to develop close to home in the Northwest Caribbean, Gulf of Mexico, and off the Southeast Coast of the U.S. The Cape Verde season starts in August and runs through the peak of the season due to the Atlantic Basin Sea Surface Temperatures being at its warmest. The Cape Verdes islands are located near the continent of Africa and these storms that originate near them make the long journey across the Atlantic Basin. Like Late October and November, June and July storms tend to develop close to home.
4. FACTORS THAT PROMOTE HURRICANE DEVELOPMENT
A. MOST Hurricanes not ALL – Tend to develop in tropical ocean basins around 5 – 20 degrees LATITUDE North or south of the equator. Someone asked me the other day, Brandon why don’t Hurricanes form on the equator. Well I remember Dr. Greg Nordstrom saying in my Meteorology class that the coriolis force is not present there. I know, I know you must being asking yourself “what is that” to keep it simple it is a force caused by rotation of the earth that gives or provides Hurricanes with its spin or rotation. Just a note, Hurricanes like low pressure systems in the Northern Hemisphere spin counterclockwise with the earths rotation. The opposite in the Southern Hemisphere.
B. Sea Surface Temperatures – Sea surface temperatures have to be at least 80 degrees Fahrenheit in order for Hurricanes to sustain themselves. The warmer the water the greater potential for strengthening. Why is this? Well basically a Hurricane is Heat Pump or a Heat Engine. It has to do with changing states or phases of water from gas to liquid. Some cool facts is this: Hurricanes are fueled by something called LATENT HEAT from that warm water and it is liberated or freed when huge amount of water vapor condense. The release of latent heat warms the air and provides buoyancy or lift for its upward flight(MSU notes). This results in a lowering of air pressure at the surface because most of the air is being evacuated from the surface to the top of the atmosphere, diverging or spreading out. An example of rapid intensification due to warm sea surface temperatures was in 2004 Hurricane Charley where it went from a strong tropical storm to a major Category 4 Hurricane in 24 hours. Here is a image of Hurricane Charley courtesy of the National Weather service. Charley affected SW Florida with 145mph winds with higher gusts.
Hurricane Charley was best described as the I-4 storm because it not only devastated SW Florida, places like Port charlotte, Fort Myers, and Punta Gorda, but Lakeland to Daytona Beach Fl felt His wrath as well right along the interstate 4.
C. LOW WIND SHEAR AND HIGH PRESSURE ALOFT
For a Hurricane to rapidly develop or get stronger its surrounding environment needs to be perfect. If winds aloft are light and High pressure is sitting on top of it Hurricanes tend to rapidly develop. WHY? Wind Shear is good if you want severe thunderstorms and tornadoes, but with Hurricanes you want light winds to develop its vertical beautiful structure, any shear will rip the developing thunderstorms apart. High Pressure on top of it fans, spreads or diverges the air aloft. Thus it becomes well vented. Its akin to putting a high performance air filter and exhaust into your car to make your car perform better. The more rapid you get air to rise and to spread or diverge out, the stronger the storm. I will attempt to show a graphic or MRI of a Hurricane.
Graphic display is done by www.drjudywood.com, this clearly shows the inflow at the surface and the outflow aloft. The center of the storm is the EYE – which is the center and is relatively cloud free with sinking air, surrounded by the EYEWALL – which is the worst part of the storm in terms of wind, rain,and storm surge. The Central Dense Overcast – compasses the whole storm.
5. FACTORS THAT CAUSE A HURRICANE TO DECAY –
A. Sea Surface Temperatures – If SSTs are cool or they are below 80 degrees, these conditions will weaken a hurricane.
B. Move Onto Land – When a Hurricane moves on land in causes devastation to coastal areas and surrounding areas, but at the same time it is weakening due to the loss of its fuel source the 80 degree water and the friction of the land.
C. Wind Shear – If winds aloft are strong it will cut the tops off the thunderstorms, thus cutting or putting a wrench in the heat engine, a Hurricane.
6. STAGES OF DEVELOPMENT
A. Tropical Disturbance – When a cluster a showers and thunderstorm are traversing the Atlantic in the tropics during hurricane season Meteorologists call them EASTERLY WAVES – why? because these clusters move east to west, with convergence on the east side and divergence on the west.
B. Tropical Depression – If the Wave or Tropical disturbance gets better organized the National Hurricane Center will call it a Depression or Tropical Depression. This is where the Wave starts to deepen or pressures fall, there is a closed surface low pressure and winds can reach 38mph. A Depression DOES not receive a name.
C. Tropical Storm – If a tropical depression continues to deepen or get stronger, pressures continue to fall, there is a well defined closed surface low, and wind speeds can reach between 39-73mph with torrential rain. At this point the storm RECEIVES a name.
D. Hurricane – If the storm continues to intensify and wind seeds reach or exceed 74 mph it has reach hurricane status. The low pressure is well organized and the storm begins displaying mature structure, for example an EYE can be seen, which is the center of the storm, Feeder Bans on the periphery of the storm are evident on radar or Doppler, and the strongest storms the Eye Wall is evident as well.
7. HOW DO HURRICANES DO THEIR DAMAGE
A. Storm Surge – The most devastating damage in the coastal zone is caused by storm surge. It not only accounts for a large share of coastal property losses but is also responsible for 90 percent of all hurricane-caused deaths. A storm surge is a dome of water 40-50 miles wide that sweeps across the coast near the point where the eye makes landfall. The storm surge is dictated by the strength of the Hurricane. The stronger the storm the higher the storm surge. An interesting fact is that if all the waves were smoothed out the storm surge would be the height of an above normal tide. The worst surges occur in places like the Gulf of Mexico where the continental shelf is very shallow and has a gentle slope.(The atmosphere 12th edition).
B. Wind – Wind is a significant factor because it causes damage to property and can loss to life. Wind damage is measured by the Saffir Simpson Scale that has a rating from a Category 1 to a Category 5. Cat 1 least and Cat 5 strongest. An interesting fact that I have come to learn is that the right front quadrant is the worst part of a landfalling Hurricane. The strongest wind and the highest storm surge is found there. Why? Lets take a look. Example, A Category 3 Hurricane in the Gulf of Mexico with winds at 125mph is headed for Houston at 15mph. The right front quadrant will get the worst wind because you take the Hurricanes top speed of 125mph and you add the 15 mph forward speed, you get a wind speed of 140 mph. Conversely, on the west side, the winds blow offshore and surge will be less. So the Cat 3 storm with winds at 125 will be less, because we subtract the forward speed 125-15mph= 110 mph. So it depends where you are geographically, where the worst of the storm is going to occur.
C. Inland Flooding Rain – Inland flooding can be devastating to people far displaced where the eye of the Hurricane came ashore. A well known example is in 1969 Category 5 Hurricane Camille, known for its storm surge in Mississippi and devastation to the coastal areas, in fact was most deadly in the Blue Ridge Mountains of Virginia where 12 inches of rain was reported killing 150 people.(The Atmosphere 12th edition).
Image by www.telegraph.co.uk shows inland flooding and storm surge damage done by Hurricane Sandy or Superstorm Sandy. many people argue a Hurricane/Midlatitude cyclone?
8. FACTORS THAT CAUSE HIGH AND LOW NUMBERS OF HURRICANES
A. Above Average Years –
Warm Atlantic Multidecadal oscillation – Are caused by a Positive or warm phase AMO or Atlantic multidecadal oscillation. Which means that the atlantic goes through cycles of cold and warm ocean waters. The warmer or more positive the ocean is the greater likelihood of frequency of hurricanes.
B. Neutral or La Nina – Neutral conditions are relatively normal or near normal sea surface conditions in the Pacific Ocean Basin. Causing lower wind shear in the Atlantic. La Nina is the opposite of El Nino which is a cooling of the Pacific Ocean temperatures causing NO wind shear at all over the atlantic basin. This phase is highly favorable for Atlantic Hurricane frequency in terms of numbers.
Low Numbers –
C. El Nino – The warming of the Pacific Ocean basin. Thunderstorms and precipitation form, the tops of the storms blow across the Atlantic Basin causing high wind shear cutting down the number of Hurricanes. This year we are in an El Nino year so most forecast agencies are predicting low numbers of storms to develop this year. I see a lot of 7-9 total storms, 3 Hurricanes, 1 major Hurricane. In a normal year there is about 11 named storms, 6 Hurricanes, and 3 major Hurricanes. So you can see the difference.
D. SAL- Recently, the past 2-3 years the SAL or the Saharan Air Layer has dominated the Atlantic basin choking off all Tropical development in the Main Development regions in the Atlantic. This dusty dry air originating from North African Sahara Desert is the Kiss of death for hurricanes. Hurricanes need moist, humid environment to develop and the SAL eliminates that.
9. DEADLIEST HURRICANES OF THE PAST CENTURY
The graphic will show the top 10 deadliest Hurricanes of the past century. Hint, most of the deaths occur early in the 20th century, but most of the property damage occurs later on
wattsupwiththat.com shows how hurricanes were so deadly early on in the 20th century due to lack of satellites, Doppler Radar, early wadvisories and forecasting issues. Galveston Hurricane in 1900 is responsible for the graph early on.
10. SAFFIR SIMPSON SCALE
The Saffir Simpson Scale is a tool to measure Hurricane Intensity. The national Hurricane center uses many devices, products and aircrafts to obtain measurements of the storm. Aircraft reconnaissance is used to measure and observe intensity. Scientists and meteorologists use Dropsondes to measure, humidity, pressure, temperature, wind speed and more of a Hurricane. The national hurricane Center can utilize satellite Radar composite Images, as well as the Doppler Radar an advanced radar system to help accurately predict the intensity of the storm, as well as computer forecast models such as the GFS, EURO, and the GEM to predict where the storm is headed. There are many more computer models but I will be here all day naming them.
I will display a graph depicting the Saffir Simpson scale. It is broken down in 5 categories 1 – 5. 1 being weakest 5 being strongest interms of wind speeds!!
earlyalert.com displays Saffir Simpson scale in an easy to read graphic, its all based on wind speed and potential damage from wind.
Well, I hope you enjoyed my blog today or tonight or whenever you get to read it. I want to thank all the companies or people that provided my graphics, and I hope this helps everyone prepare for hurricane season.
Remember to review your Hurricane survival guide : stock up with non-perishable items, water, generator if u can afford one, gas, and fill up the car with gas too.
Thank You for listening, Be safe and until next time BE GOOD
Brandon Brady