in this module we will cover Cyclones we'll start with an overall discussion of tropical and extratropical Cyclones and then Focus exclusively on tropical Cyclones so when you're thinking about Cyclones how do they form what are the drivers that create these systems tropical and extratropical Cyclones are driven by atmospheric Dynamics tropical Cyclones are fueled by warm water and extratropical Cyclones form due to interactions between different air masses and these are much more common in mid latitude regions you might have heard these called something else where do we often or typically think of cyclones occurring and based on where we think of them typically occurring sometimes they're called different things also are these low pressure or are these high pressure systems so Cyclones are often called by other names depending on the regions that they form they're typically called hurricanes or tropical storms or mid latitude Cyclones in the Atlantic or Northeast Pacific regions they can be called typhoons in the Northwest Pacific Ocean and they can be called Cyclones in the South Pacific and Indian Ocean Cyclones are low pressure systems they form when warm moist air rises and creates low pressure at the surface the surrounding air rushes in to fill this low pressure Zone and then the Earth's rotation the Coriolis effect causes the system to start spinning and it creates these characteristics that we know of as the swirling motion of a cyclone there are two major types of cyclones there are mid latitude Cyclones which we also call extratropical Cyclones and then there are tropical Cyclones and these include hurricanes and typhoons so this image on the left is an example of a mid latitude cyclone and this image on the right is an example of a typhoon this is off the coast of Australia and the mid latitude cyclone is over the land mass which is North America so let's focus a little on extratropical cyclones these are also known as mid latitude Cyclones or wave Cyclones and they're low pressure systems that occur in the earth's mid latitudes so outside of the tropics therefore extratropical Cyclones these Cyclones form along fronts where cold and warm air masses meet the interaction between these air masses creates instability in the atmosphere and this leads to the development of low pressure systems the winds around uh these low pressure systems rotate due to the Coriolis effect but the process is also driven by horizontal temperature contrasts not by ocean heat which we will see as the main driver in tropical Cyclones extratropical Cyclones do not have tropical characteristics they are everyday phenomenon that play major roles in driving weather patterns they produce a wide range of conditions from cloudiness to showers to heavy Gales to thunderstorms and they shape much of the Earth's daily weather and these storms can also be yearround so mid latitude Cyclones typically develop between 35° and 60° latitude in both the northern and southern hemispheres like I mentioned these driver much of the weather in these regions because they interact with cold and warm air masses to produce various conditions so anything from mild showers to intense storms mid latitude Cyclones are extratropical Cyclones they can form over both land and water and they're responsible for much of the precipitation that the mid latitudes experience we know that these systems can be disruptive sometimes they can cause travel delays due to stormy conditions if you fly during the winter you might have been delayed by a mid- latitude cyclone a defining feature of mid latitude Cyclones is that at their core they have cooler air and this is in contrast to Tropical Cyclones which have warmer cores so on this image in the lower left we see a mid latitude Cyclone which is moving across um from west to east across the uh United States and this nor Easter or this extr tropical Cyclone is affecting weather in New England here whereas this hurricane is down uh off the coast of Mexico and Texas and will impact weather in this area so mid latitude Cyclones like the one seen in this middle image can BRD conditions like the one we see in the right image heavy heavy snowfall trees down I as a Manor have experienced many extratropical Cyclones which we call nor Easter there's one in particular that I remember very very well and this is the Halloween nor Easter of 1991 it's also more famously known as The Perfect Storm it it was a very powerful and unique weather event that struck uh the Northeast United States in late October late October in early November in 1991 hence the name Halloween nor Easter there was a Confluence of weather systems that led to severe Coastal damage High uh Heavy Rain high winds and wave heights that are pretty unprecedented so what happened was there was a storm that developed in October 28th 1991 off the coast of Nova Scotia and this was a large extratropical low pressure system and it was fueled by the remnants of Hurricane Grace and this hurricane hurricane Grace had moved northwards into the North Atlantic at the same time there was a cold front moving down from Canada and there was a strong area of high pressure over Greenland which helped funnel cold air into this system the interaction of all these systems led to the creation of an extremely powerful nor Easter it earned its nickname The Perfect Storm because of the rare combination of these meteorological conditions and it became a popular um storm in in our cultural memory after this book by Sebastian younger was published in 1997 it details the impact on a fishing vessel the Andrea Gale and all the crew was tragically lost at sea and this movie has been made into a movie with George Clooney and Mark Walberg um and it does a pretty good job of talking about the storm and the Confluence of these events this is some of the damage from the storm this is along the Massachusetts coast and here are some facts from Massachusetts so 78 MH wind so hurricane force winds storm surge of 14 ft 30 ft Seas a hundreds of homes destroyed and pretty low pressure in the area and this damaged uh Coastal Massachusetts Coastal Maine and there was flooding up into other parts of New England in total I think it caused about $20 million in damage it was a weird storm too in that as it was weakening it actually transitioned back into a tropical storm as this storm moved Southward into tropical warmer Waters and this storm actually was never named they just named this storm unnamed which is kind of interesting in the National Hurricane Center records so what causes extra TR tropical Cyclones extratropical Cyclones are caused by the interaction of warm and cold air masses typically along a frontal boundary like what we see here they develop when cold air masses that are usually from polar regions meet warmer air masses that are typically from tropical or subtropical regions and we talked a lot about this when we discussed the different patterns of fronts and winds that exist around on the globe when this meeting of cold and warm air masses occurs along a front we see cold fronts and warm fronts in mid latitude regions the temperature difference between these air masses creates a significant pressure gradient and this sets the stage for the development of a low pressure system which is the core of EXT tropical Cyclones the warm air is less dense than the cold air which means it's Li so when these air masses Collide the colder denser air pushes underneath the warmer air and the lighter air for is forced upwards warm air has more energy as it expands it becomes more buoyant and it causes it to rise above the cold air in extratropical Cyclones we see that this clash between these two air masses creates conditions where the warm air is dramatically lifted along this frontal Zone when it rises and cools it loses its ability to hold moisture and as a result we get condensation and this process releases latent heat and it further Powers the Cyclone it's a positive feedback loop uh the lifting of this warm air creates subsequent cooling it creates clouds it creates precipitation and leads to stormy weather patterns so in areas like Corpus Christi when we get a cold front that moves in it's pushing warm moist air ahead of it and upward and this rapid lifting of warm air leads to Cooling and condensation which can cause thunderstorms and potentially heavy precipitation the intensity of the storm just depends on how much moisture and warm air is contained in that air mass and how sharp the temperature contrast is between those warm and cold air masses so what's our forecast for tomorrow what do we see well we do see a cold front coming through here so it's very good timing that we're talking about this right now because we see this mass of air this low pressure system forming as a result of the conditions that we just discussed and how much rain and how much Thunder is going to be dependent on how much moisture this warm air contains and just how sharp the temperature contrast is so let's go over some key differences between extratropical Cyclones etc's and tropical Cyclones which I note as TCS in the lecture outlines the first thing is extratropical Cyclones have fronts and tropical Cyclones don't so extratropical Cyclones have fronts like cold fronts and warm fronts and this is where those different air masses interact tropical Cyclones on the other hand don't have fronts and they're formed in more of a homogeneous air mass over warm ocean waters and they rely on different developmental factors for their growth there's also a difference with where the strongest winds are in an extratropical Cyclone the strongest winds are found in the upper atmosphere because most of these Cyclones are driven by the jet stream and temperature contrasts between air mattress air mat masses not mattresses in a tropical Cyclone the strongest winds are near the surface this is because the uh storm is going to be fueled by energy from warm ocean water and this drives circulation of the Cyclone close to the surface they also have different formation processes like we just talked about extr tropical iCal Cyclones form due to temperature contrast between cold and warm air masses and they are typically found in the mid latitudes these are much more dependent on the Dynamics of air masses and fronts whereas tropical Cyclones form through latent heat release from warm moist air rising and condensing over warm ocean waters etcs and TCS also have different locations in which they originate and track e TCS originate in the mid latitude regions and track along fronts their paths are influenced by the jet stream and larger Global circulation patterns whereas tropical Cyclones originate in the tropics or subtropical oceans and they track Westward and poleward due to global wind patterns as well as the Coriolis effect so let's get into tropical Cyclones hurricanes are tropical Cyclones and we can see two such examples on this page and we'll talk about the anatomy of hurricanes and the factors that drive them in more depth going forward here tropical Cyclones are storm systems that are characterized by low pressure centers that are surrounded by spiral Arrangements of thunderstorms that produce strong winds and heavy rain tropical Cyclones strengthen when water is evaporated from the ocean and is released as the saturated air rises resulting in condensation of water vapor that's contained in that moist air they're fueled by different heat mechanisms than other cyclonic windstorms like nor easers and we'll talk about that in a second but I want to point out this image here and looking specifically at the Equator so we'll talk about the Coriolis effect but note this image and the lack of hurricanes as we get very close to the equator so let's talk about hurricane formation this is the hurricane formation life cycle the first step is the evaporation of warm ocean water water the process begins with evaporation of warm oce water that provides moisture and heat needed for storm development typically this occurs over Waters with temperatures of at least 80° F or higher the next step is that we have uplift of warm moist air that forms a surface low this warm moist air rises from the ocean surface and it creates a low pressure Zone at the surface as the air rises it cools and condenses and forms clouds and thunderstorms there's an immense amount of latent heat so as that air rises and cools water vapor condenses into liquid water and it releases latent heat and this release of heat provides additional energy to the storm and acts to intensify it in the fourth step we see high pressure that forms above the release of heat causes the air at the top of the storm to warm up and it creates an area of high pressure at the upper atmosphere here in step five we see air reaches the tropo the tropopause and moves out laterally what happens is this air rises until it hits the tropopause and if we remember this is the boundary between the troposphere and the stratosphere and at this point air can no longer rise and as a result it begins to spread out laterally in Step six we see that as the air moves outward it starts to descend it warms again and is pulled back into the low pressure area at the surface and it perpetuates the cycle it creates a positive feedback loop in step seven something really interesting happens the Coriolis Force which is formed or created due to the earth rotation causes the storm to spin in a counterclockwise Direction in the Northern Hemisphere and a clockwise Direction in the southern hemisphere we actually don't get enough of the Earth's rotation of the Coriolis Force at the equator to see tropical storms form there has to be enough of this Force as we move move away from the equator on either side of the Equator and the Tropic of Cancer or Tropic of Capricorn to start this rotation in Step eight we see that as the pressure in the center of the storm decreases wind speeds increase towards the center and this further intensifies the Cyclone step nine it's all about that positive feedback loop we have the uplift of warm air and that warm moist moist air continues to perpetuate itself the interaction between the ocean's surface area wind speeds and low pressure creates a positive feedback loop and it causes the storm to intensify as long as the ocean remains warm and moisture is available in Step 10 we see that dissipation can occur we can see negative feedback introduced and this happens when the storm moves over cooler water which reduces the Heat and its supply of moisture or when the storm makes landfall and this cuts off its moisture source and then we see the friction force that it encounters with land that further acts to dissipate the storm so what are the general conditions for Hurricane formation the first thing or the first ingredient is that we need warm ocean water they generally require a sea surface temperature of at least 80° F this warm water provides their energy source and it fuels the Cyclone by evaporating moisture from the ocean that condenses and releases uh as heat in the atmosphere they also have to be a minimum distance away from the equator we need about 5 of latitude or a distance of about 300 miles and this is needed for the Coriolis Force to act as the Coriolis effect is responsible for the rotation of the Cyclone without it the storm can't gain the necessary spin that it needs and this is why we see the absence of cyclones on that map we also need surface disturbance we need a pre-existing disturbance and this comes in the flavor of tropical waves or groups of unorganized thunderstorms and this is the initial Catalyst these are the initial conditions for cyclonic formation this disturbance triggers convection it helps develop that low pressure center of the storm and things move from there we also need low vertical wind shear so what this means is that we need to see low wind shear which is the difference in wind speed or Direction with height this is critical for cyclone development they form when wind shear is less than 23 mph if we have high wind shear this can disrupt the storm's structure it can weaken the vertical development of the Cyclone so we need low wind shear which allows for it to meet that tropopause and move out and la and laterally build we also need the season so most of us are very familiar with what tropical storm or hurricane season is they typically form um between June 1st and November 30th which is hurricane season so we're still in hurricane season and this is when ocean temperatures are warm enough to support cyclonic formation between about 5 to 25° North and South away from the equator all of these factors together create conditions that are necessary for tropical Cyclones to develop intensify and potentially become powerful storms there are three basic stages in the life of a tropical Cyclone its origin or source the mature stage and the dissipation stage where it dies out these occur in a continuous process not as separate in distinct stages each stage may occur more than once during the life cycle as the strength of the Cyclone Rises and falls it may reach land weaken then go back out to sea where it strengthens once more the formation of a cyclone depends upon the following conditions coinciding a large still and warm ocean area with a surface temperature that exceeds 26.5 de C over an extended period this allows a body of warm air to develop above the ocean's surface low altitude winds are also needed to form a tropical Cyclone as air warms over the ocean it expands becomes lighter and Rises other local winds blow in to replace the air that has risen then this air is also warmed and Rises the rising air contains huge amounts of moisture evaporated from the ocean's surface as it rises it cools condensing to form huge clouds about 10 km up in the troposphere more warm air rushes in and Rises drawn by the draft above the rising drafts of Air carry moisture High High into the atmosphere so that these clouds eventually become very thick and heavy condensation then releases the latent heat energy stored in the water vapor providing the Cyclone with more power this creates a self- sustaining heat cycle drawn further upwards by the new release of energy the clouds can grow to 12 to 15 km High the force created by the Earth's rotation on a tilted axis the coris effect causes rising currents of air to spiral around the center of the tropical Cyclone it is at this stage that the Cyclone matures and the eye of the storm is created as the air rises and cools some of this dense air descends to form the clear still eye as the Cyclone rages around it the eye wall where the wind is strongest behaves like a whirling cylinder Cyclones rotate clockwise in the southern hemisphere anticlockwise in the northern the lowest air pressure in a tropical Cyclone is always found at the center and is typically 950 mbars or less the average air pressure at the earth's surface is about 1,0 mbars tropical Cyclones have significantly lower air pressure than the air that surrounds them the bigger the pressure difference the stronger the wind Force one of the lowest air pressures ever recorded was 877 mbars for typhoon Ida which hit the Philippines in 1958 where winds reached 300 km an hour once formed the Cyclone's movement or track follows a pathway away from its source driven by global wind circulation there warm ocean waters feed it heat and moisture the Cyclone continues to enlarge I also like this diagram which really simplifies the entire process of hurricane formation so let's talk about the stages of tropical Cyclone development these represent increases in wind speed and also a drop in barometric pressure pressure the first level or stage is tropical wave this is going to be the initial disturbance and we characterize this by weak low pressure areas and clusters of disorganized thunderstorms this is really the precursor of the Catalyst to what can become more intense Cyclone development the next stage is tropical depression as the system becomes more organized and wind starts circulating around a low press Center it becomes a tropical depression and at this stage we see winds that are under 39 mph the next stage is tropical storm here the storm has become more organized and we see wind speeds that are about 39 to 73 mph at this point storms get an aim and I'll talk about that in a second the next stage is the hurricane stage if the storm intensifies further and we see winds in excess of 74 mph it gets classified as a hurricane they have a well-defined eye they're surrounded by tropical or sorry uh strong winds and uh thunderstorms and then we start measuring it using something called The saffer Simpson hurricane wind scale and from here we go from category 1 to category 5 category 1 are winds that are 74 to 95 mph Category 2 96 to 110 Category 3 111 to 129 category 4 130 to 156 and then Category 5 is anything with a wind speed greater of 157 miles hour at Category 3 hurricanes start being referred to as major hurricanes and this is due to the likelihood that they'll cause significant damage every year at the end of May or the beginning of June your local weather station will put up this graphic and it'll talk about the stages of development and it usually will just say tropical depressions tropical storms and hurricanes but if you listen during weather reports it will say we have this tropical wave down here it's just a bunch of unorganized thunderstorms at the moment we're going to keep our eye on it you don't really need to worry about it at that point but later in the season when water start getting really really warm it's very impressive how fast storms can go from tropical waves to tropical storms or hurricanes so I mentioned that at the tropical storm stage storms get named these are the 2024 and 2025 lists of hurricane names usually When Storms become major hurricanes or have a significant amount of damage associated with them the names will get retired so names like Katrina Harvey we won't see again they'll be taken off the list so these are the 2024 names and if there is a storm that us the next storm after Milton it'll become naen and then Oscar so we're pretty far down in the list there is a convention for naming storms after we run out of names I think we move to the Greek alphabet so let's talk about the anatomy of hurricanes the first feature that I want you all to know is the eye and the ey is the low pressure center at the center of the storm it's the calmest part of the cyclone and wind speeds here are pretty low the weather is often clear and the eye can range for smaller storms to a couple of miles from larger storms to 40 mi in diameter and this really depends on the intensity of the storm it's not uncommon during night hurricanes or hurricanes that come on Shore at night to be in the eye and be able to look straight up through the eye of the storm and see stars it's pretty disconcerning knowing that you're only halfway through the eye ey wall is the area that's immediately around the eye it consists of rings of intense thunderstorms and they produce the most severe weather the strongest winds the heaviest rainfall this is one of the most dangerous parts of a hurricane the wind speeds and the pressure gradients are going to be the highest right here and we can see this within the diagram uh right here on the on the right side the next part that I want you to be aware of in terms of the anatomy of a hurricane are the rain bands they're long bands of clouds and thunderstorms that spiral out from the center of the storm they're associated with the rising warm moist air that cools and precipitates as it moves upwards they can extend hundreds of miles away from the center of the storm so we can get heavy rains and Gusty winds and even tornadoes can form as a result of these rain uh rain bands even if we're pretty far away from the eye or the eyewall of the storm and we can see the anatomy pretty well here uh this is a hurricane hunter or hurricane tracker that's flying into the center of the hurricane to take uh conditions uh barometric pressure wind speed measurements inside a large hurricane so right in the center area we'd be able to see down to the ocean or to land this is the eyew wall and what we don't see coming off of it are the um rain bands that could be hundreds of miles in diameter this is a video of Milton and the hurricane hunter so hurricane hunters will fly into the Hurricanes to collect this very important data so this is the National Oceanic and Atmospheric Administration [Music] good grab my phone real quick [Music] on holy crap all [Music] [Music] right to [Music] so here you can see that they're entering the eye of the storm they'll typically so as you can see from that video a lot of action a really important job but definitely something most of us wouldn't want to fly through I want to also talk about steering factors for hurricanes and hurricanes are influenced by large scale wind and pressure systems in the atmosphere so I want to talk about some of the variables that impact these storms things like sea surface uh temperatures and hurricanes are are definitely impacts but other things like Trade Winds can push hurricanes westward in the tropics the Bermuda high can influence whether hurricanes move towards the Gulf Coast or curve into the Atlantic Wester Lees can steer hurricanes poleward and out uh out to sea the polar jet stream can interact with hurricanes as they move higher in Latitude it can steer them or help them transition like we saw with the nor Easter into extr tropical Cyclones also transient low and high pressure systems can affect short-term changes in hurricanes tracks this can cause potential shifts in directions or speed so this this is an image from Hurricane Fay we have high pressure and we have low pressure and so the high pressure is going to um basically allow for this tropical storm to move west under the ridge it's going to prevent it from moving to the Northeast and allow for it to move towards this area of low pressure what we also see in our neck of the woods is meteorologists usually say that when we have our first cold front in Texas hurricane season is usually over for us what they mean by that is when we start seeing low pressure move in that high pressure that would act to steer hurricanes and low pressures that would act as troughs um they really change things around and we start seeing water start to cool off and provide less fuel we know there's a time lag in this so we can't be completely off our guards until November 30th but the first cold front is a very welcoming sign for Texas and hurricanes other things that impact uh hurricanes in terms of steering factors are sea surface temperatures so this is an image that shows uh Fabian tropical storm Fabian and tropical storm Isabel so here's the origin of Fabian and we see the track of Fabian down here we see the origin of Isabelle and she might have not have very much luck moving the same direction even though steering factors will be forcing her to move in that path she might not have very good luck staying a storm um or intensifying as a result to uh as a result of the decrease in water temperatures so it needs that warm ocean water and because we see cold water in fabian's Wake she's going to have less success so this is 2023 and I can't pull up 2024 yet because we still have quite a bit of hurricane season left to go but for 2023 what we see is there were a number of name storms but we did not see a ton of interaction with the United States with the exception of Harold we didn't even have any hurricanes that interacted with Texas and this is because we had an El Nino system so El Nino was officially declared on June 8th 2023 and this happened a week into hurricane system a season the transition to El Nino LED people to believe that the Western Gulf of mexic Mexico would be quiet so even if things became active like they did in the Atlantic our neck of the woods was going to be pretty quiet and this is because El Nino tends to deliver a lot more wind shear over the Western Gulf and wind shear inhibits storms from forming and hurricane season did wind up being more active than average for this season but it stayed in the Atlantic and with the exception of heral which came on Shore August 22nd we didn't see much in the way of action several factors shape whether a hurricane season will be active or inactive and their influence varies each year based on complex interactions of atmospheric and oceanic and even solar conditions so let's talk about the degree to which these different variables are going to influence whether we have an active or an inactive season as discussed global warming can increase the potential for more intense hurricanes global warming is increasing sea surface temperatures and this provides more heat energy to fuel tropical Cyclones when we get warmer oceans this can lead to more intense storms Saharan dust can suppress hurricane activity this leads to less active Seasons due to drier air and increased atmospheric stability we also see that natural climate Cycles like elino and linia can have statistically significant influence on whether we have active or inactive Seasons so in alino years wind shear in the Atlantic tends to increase this disrupts hurricane formation and results in fewer hurricanes in linia years we see lower wind shear this leads to more favorable conditions for Hurricane development and can be uh one of those things that can create more active seasons for us and interestingly Sun uh spot Cycles can actually have subtle influences on Hurricane frequency Sunspot Cycles follow 11-year patterns and can affect hurricanes through subtle changes in solar radiation these can influence atmospheric pressure systems ocean circulation and temperatures but there is more research being done on the degree to which this really impacts anything one thing we do hear a lot about is how our area is impacted by Saharan dust so this is the beginning of the 2024 hurricane season and this is the main development region where we see hurricanes or disorganized bins of rain clouds form and move towards the tropics and then move into the Gulf of Mexico and what we see is this is the Saharan dust it comes from the areas of the Sahel and uh the Sahara Desert and this dust acts to dry out the atmosphere and create stability within the atmosphere and we see less thunderstorms uh and disorganized rain clouds as a result when Sahara dust dies down we see hurricane season moves into its more active uh part of the season so let's talk about hurricane impacts this is Hurricane uh this is the impact of hurricane Harvey on the downtown Houston area and I lived in Houston during Hurricane Harvey I had just moved there from Corpus Christie and we were not prepared for the impact that this region had so as a question as a hurricane makes landfall where do we see the severity of the greatest impacts well these are generally going to be greatest on the right hand side of the storm's eye and this is going to be the case for the Northern Hemisphere this area is known as the right front quadrant and this is why this region experiences the most severe impacts in the right front quadrant we see in the northern hemisphere that hurricanes rotate uh counterclockwise as the storm moves forward the winds on the right hand side are going to be moving in the same direction as the Hurricane's forward motion and this combines the storm's rotational winds with its movements so this leads to the strongest winds on the right side of the eye we also see this impacting storm surge the strongest winds push more water towards the coast in the right front quadrant and result in higher storm surge which can be a more deadly aspect of hurricanes this quadrant is also typically associated with heavy rainfall and a greater likelihood for tornadoes forming on the left hand side of the storm winds are lower um cuz the forward motion subtracts from the wind speed and Storm surges is less severe also near the center of the eye it's relatively calm compared to the surrounding areas but as the eye passes winds quickly increase how much rain so this is Hurricane Harvey oh sorry this is Hurricane Harvey and it made landfall on August 25th 2017 near Rockport Texas and it did so as a category 4 um it caused catastrophic flooding in Southeast Texas particularly in the Houston area it stalled over the region and it led to $1.5 billion in damage 100 people lost their lives dur due to flooding and storm related incidents and it dropped 27 trillion gallons of water on the Houston area how much rain fell in Texas when hurricane Harvey struck in August scientist have inferred the weight of the Water by measuring how much the Earth was compressed up to half an inch meaning somewhere up to 34 trillion gallons or 127 billion tons or 26,000 super doomes filled with water according to Adrien borer from the scrips Institute the American geophysical Union met this week in New Orleans where researchers told the Gathering that Harvey's heavy rainfall was aggravated by the extra warming of greenhouse gases there were record-breaking global temperatures in 2016 which helped raise ocean temperatures in the Atlantic and Gulf of Mexico warm water fuel storms the rainfall was especially intense along the Texas Coastline hurricane Harvey stall with stinging wind and ceaseless rain but simply they say it was one of the heaviest precipitation events in recorded human history how much rain how much rain fell in Texas sorry about that so these are some images from Harvey there are water rescues everywhere our neighborhood um was flooded all around and we had to walk out with our dogs and our our stuff we were we thought that we were going to lose uh the house we were in a rental but we were worried we were going to lose all of our all of our possessions we did not flood we were one of the only streets in the neighborhood not to flood um this is what many areas in Houston look like and I like this image from V it shows Katrina how much water there was Harvey how much water there was and what that footprint looks like over an area about the size of Manhattan so that video showed us how storm surge combined with the levies failing had such catastrophic effects there are several key factors that control storm surge and storm sures the abnormal rise in seawater during a hurricane or storm and this is shaped first by barometric pressure so lower barometric pressure in a hurricane core can lead to the ocean surface rising and this happens because low pressure allows for water to essentially be pulled up the more intense the storm or the lower the barometric pressure the higher the potential for storm surge land elevation is crucial um this really affects how far inland water can reach low-lying areas are more vulnerable to flooding higher elevations provide natural protection wind direction determines where storm surge will be the greatest so winds are going to blow towards the shore and push water onto land and these contribute to a rise in sea level along the coast so that right front quadrant of a hurricane is going to have winds that are going to cause the most severe storm surge the storm speed is a huge factor it's going to affect how long surge conditions persist slow moving storms can cause more prolonged surge events and lead to Greater levels of inundation whereas fast storms can produce short but intense surge also we have to see where the storm comes on land in terms of time with tidal levels if storm surge coincides with high tide we can have significantly higher surge so the water levels are already elevated because we're at high tide surge is added on top of that and it can drastically worsen coastal flooding heavy rainfall can also compound storm surge by adding to the flood waters in low-lying areas where rivers and streams overflow we can get more widespread and severe flooding and also the shape of the coastline can amplify or reduce storm surge narrow bays and estuaries can funnel water and increase storm STM uh surge height and this can result in more widespread or severe flooding so each one of these factors can significantly influence the height the duration and extent of storm surge and this makes storm surge one of the most dangerous aspects of hurricanes especially in lowline coastal areas this is a map that shows the flooding extent and depth caused by Hurricane Katrina and this is from the National Oceanic and Atmospheric Administration and I'm going to explain the color coding here green is um the red that we see here is going to be zero to about two orange 2: 4 the yellows 4 to 6 green 6 to9 and then the blues are going to represent anything from about 10 to 20 ft so we do see some areas where we have the purple and blues that are going to represent the deepest flooding zones we can see those right in here so these green areas um are definitely um impacted by the depth and extent of the flooding we also see Heavy Coastal rainfall and coastal flooding compounding each other so this is the path of Hurricane Fay so as it came on Shore we saw in the Coastal Bend area 12 to 18 inches of flooding and then in tallaha see 24 in of flooding which is um extreme amount of rain for that area we also have to note and I think recent events have shown us that heavy rainfall can impact locations that are distant from a hurricane and Inland so so this is Hurricane Agnes on the left we have a historic photograph that shows severe damage caused by flooding in wils Bear uh Pennsylvania and this is a result of Hurricane Agnes's rainfall but also River flooding subsequently we see destruction of homes due to the overwhelming force of water that swept through neighborhoods and on the right we have a map that depicts the track of Hurricane Agnes and it illustrates Journey from the Gulf of Mexico up the East Coast from Storm uh from major hurricane to Hurricane to Depression more recently we see the impacts of hurricane Helen and this had a devastating impact on Mountain areas in Western North Carolina and the Appalachian region there was extreme rainfall some areas receiving 30 in of rain we saw catastrophic flooding in the Black Mountain region so certain towns saw entire neighborhoods destroyed severe flooding in landslides and 200 over 200 water resc uh rescues in the mountains we saw occurrences of mudslides and landslides that contributed to roads and bridges washing out and this severely puts back response efforts to these areas where response efforts could only occur by a helicopter so more effects of hurricanes um especially impacting our areas are overwash so overwash on barrier islands is a significant what we call geomorphic process that occurs when storm surge and high energy waves in and dat Islands what happens is the storm surge comes on Shore and it transports sand from the ocean side to the Bay Side and this reshapes the Island's landscape so let's talk about how this works a little bit so the first process of overwash occurs when storm surge combined with high waves pushes seawater and cament over this low-lying section of the island and this water flows across the island and it deposits sand and other debris Inland so this water comes in and it deposits sediment on on the Bayside overwash can lower Dunes it can flatten the island and it can cause significant what we call geomorphological change this overwash transports large amounts of sediment we can get new land forms like overwash fans we can get Island migration which deposits sand landward and it also can impact vegetation so vegetation gets buried under the sand and habitats can be severely altered we also see uh breaches in the island potentially and this can form new inlets so this can happen when the water scour enough of the sediment that this moves um ex towards the bay and scour the island predicting hurricane tracks and intensity involves a combination of advanced meteorological models real-time data and historical patterns so here's a breakdown of the process meteorologists are going to use computer models to determine and predict where hurricanes will move and they focus on different environmental factors that steer the storm these are are going to be atmospheric steering currents Global circulation models they're going to do realtime data collection from satellites and buoys they're going to use the hurricane hunter aircraft that provides real-time data on the storm's position and then they're also going to use consensus models they're going to use multiple consensus models that allows for us to determine how we weigh or emphasize different variables like wind shear sea surface temperature and upper level winds our understanding of hurricanes has changed over the past 60 years in 1946 scientists began to use radar and aircraft reconnaissance to study hurricanes and this significantly improved our understanding on their internal structure hurricane Donna that made landfall on September 10th 1960 with an eye located near Tampa was really notable for its strength and path it caused widespread damage across the US and Caribbean this is an image that shows hurricane Donna and one of our first um broadcasts where we see the use of this radar data and how we in conveyed this information to the public to make them aware of those conditions this is Doppler radar of Katrina we've gotten much more sophisticated in our models and our tools but dopplers remained very much the same um this shows where we have heavy or extreme uh winds and you can see the eyewall the eyewall as it moves on Shore and the radiating bands outward from that intensity rather than track is the more difficult aspect of hurricane forecasting this is an urgent need which requires more data that is at a finer detail than what we need to track storm direction for example this is Hurricane Charlie and it hit landfall in Florida in August of 200 four and it was supposed to be a minimal Category 3 uh which is still a major hurricane but a minimal Category 3 um but instead it came on Shore as category 4 and there was a widespread damage as a result another thing that can change intensity is the loop current so this image highlights the loop current and loop current edies in the Gulf of Mexico and these are known to play a critical IAL role in Hurricane intensification when hurricanes pass over these warm ocean currents they can draw up additional energy and this leads to the process of Rapid intensification the loop current is warm water that flows from the Yucatan Peninsula into the Gulf of Mexico and then it moves through the Florida Straits and into the Atlantic and it carries this warm water from the Caribbean and has deep reserves of heat so there's these large spinning warm water masses that break off from this Loop current and find their way into the Gulf of Mexico and we know that hurricanes rely on warm ocean water for energy and when they pass over the loop current or some of its edies what we see is that can this can lead to Rapid intensification as in the case of Hurricane Katrina in 20 05 and also hurricane readen 2005 and both of these intensified after passing over the loop current and they transformed from category 3es to category five storms within a short period of time scientists also use numerical Dynamic U models which are essential tools for predicting hurricane tracks and intensity these models rely on real-time data from various sources Like Satellites and buoys as well as aircrafts and they also simulate atmospheric and oceanic conditions based on the uh principles of physics models like the global forecast system or the GFS as well as the European model the ecmwf are particularly effective for predicting hurricane tracks and very accurate at capturing large scale weather patterns that influence the movement of storms there are other models like the hurricane weather research and forecasting model that has a high resolution and is better suited for predicting storm intensity including complex processes like we just talked about with rapid intensification the one that you all might be more aware of are statistical models and these use historical data and establish correlations between various storms and environmental parameters like ELO or linia to predict the behavior of hurricanes they rely on patterns found on past storms and are based on the statistical relationship between those patterns and future tracks or intensities of storms another interesting way that we can examine the past intensities of storms is through dendrochronology this is the study of tree rings and is a very effective tool for studying plast past climate events so each year trees produce growth rings and the characteristics of these Rings such as their width density and isotopic composition can give us detailed records of environmental conditions so when a hurricane brings heavy rainfall it leaves a distinct isotopic signature in the rings that form during that summer this isotopic signature typically reflects the unusual water content brought on by these storms this method of using TR treer ring isotopic data gives us pretty valuable insights especially in regions where instrumental weather records are sparse or non-existent this also allows for us to understand hurricane records far beyond the reach of what we now use for Hurricane and meteorological observations