DISCUSSION: When it comes to studying tropical cyclones, there is no debate that there are several very interesting features which to mind with some of the more intense tropical cyclones which come into existence. For example, within the heart of any intense tropical cyclone is the eye of a tropical cyclone. Within the confines of the eye of a tropical cyclone there can sometimes be a series of events which unfold in such a way that there can be smaller-scale features known as misovortices which form within the center and outer portions of the eye. Most often, such microscale features can form within an eye of an intense tropical cyclone due to rapid changes in intensity which occur within the core of an intensifying tropical cyclone.
As shown in the graphic and animated Twitter graphic below (courtesy of the NOAA Satellites Twitter account), you can clearly see one such example of this as found in association with Super Typhoon Jebi back on 31 August 2018. Note how within the eye of Super Typhoon Jebi you can clearly see the presence of what appears to be a four-pointed star cloud “dancing” around the center of Super Typhoon Jebi. Such small and interesting patterned clouds form within the eye of an intense tropical cyclone as a result of incredibly small-scale wind fluctuations and minor pressure fluctuations within the center of an intense tropical cyclone. As impressive as such gorgeous misovortices are, the presence of such cloud features within the heart of a tropical cyclone are a direct indication of an incredibly intense tropical cyclone being in place and/or quickly developing when such features are present.
Thus, despite the natural majesty and beauty associated with such features within intense tropical cyclones, the underlining message here is the fact that it is imperative to always respect the natural power of such storms. Moreover, in such situations when an intense tropical cyclone is developing such features, it is essential to respect and heed the advice of local emergency officials if such a storm is heading or is expected to head in your direction.
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© 2019 Meteorologist Jordan Rabinowitz
DISCUSSION: Although it has now already been a few months since Hurricane Florence smacked into the coastal and semi-coastal sections of the Carolinas, there is still much to be gained from this event and much learning which is still yet to come in the context of furthering current and future scientific knowledge. Having said that, it is worth noting that even though a good portion of the rainfall from Hurricane Florence unfolded somewhat closer to the Mid-Atlantic coastline, there was more to the Florence flooding situation that meets the eye. For example, as shown in the animated Tweet graphic attached below (courtesy of the United States Geological Survey), rainfall gauge measurements certainly are a useful reflection of the reality which unfolded in association with the coastal approach and eventual landfall of Hurricane Florence.
Regardless of how you approach the overall evaluation of this storm, Hurricane Florence was a storm which would forever change the lives and memories of millions of people living across coastal and semi-coastal sections of North Carolina, South Carolina, and beyond. Moreover, the fact that the major flooding event which ensued and progressed further inland with time is a testament of the mammoth extent of the deep moisture which flowed inland with the landfall of the mammoth circulation associated with Hurricane Florence. This is perfectly shown in the spiking of the rainfall accumulations which is shown by way of the highlighted dots within the map along the path of Hurricane Florence. You can also see how various rainfall gauges were observed to be below or above flood stage. By scanning the periphery of this animated graphic, you can see how the flooding extended far inland from the inland which exacerbated the complications associated with rescue and recovery operations to occur in the wake of the passage of a weakening Hurricane Florence.
Thus, this animated graphic just goes to show that tropical cyclone rainfall events can (as they have many times before) extend very far inland from a given coastline and Hurricane Florence was absolutely no exception to this rule in any context. Therefore, whenever you are presented with a situation defined by an incoming flooding event which is projected to have major impacts on a given region you are living in or visiting, it is imperative to always follow the recommendations and advice of regional emergency officials.
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© 2019 Meteorologist Jordan Rabinowitz
DISCUSSION: Even though a lot of the northern hemisphere is early in the heart of the 2018 – 2019 Winter season, it is still important to take in and reflect upon various aspects of the recently concluded 2018 Atlantic and East Pacific hurricane seasons. One of the bigger issues when it comes to intense tropical cyclones which many people do not consider right away is the inherent threat with coastal beach erosion as well as overall land destruction during a close encounter or even a direct landfall. During such events, whether it be a close call or a direct strike, tremendous coastal and even semi inland damaged can often quite easily occur as a result of both the wind and storm surge associated with a powerful tropical cyclone. One such example and incredibly humbling example of this scenario unfolding happened to occur in association with Hurricane Walaka over in the Central Pacific Ocean (i.e., the Central Pacific Ocean basin being considered to also be counted in conjunction with East Pacific tropical cyclones).
Well to the north and west of the Hawaiian Islands (i.e., roughly 550 miles or so away), there is a more isolated and remote island known as East Island which was in the path of a departing Hurricane Walaka. As shown in the graphic above (courtesy of the NASA Earth Observatory), this island happened to be a remote sanctuary for local and regional wildlife from across parts of the Central Pacific. However, as Hurricane Walaka approached the island from the distance, the incoming storm surge was powerful enough (even at a substantial distance from the remote sanctuary island) to nearly completely overwhelm the associated inlets and coastal regions surrounding this island. In doing so, Hurricane Walaka proved that a given tropical cyclone does not need to even relatively close to inflict tremendous damage on an island or island chain for that matter.
Attached here is an excerpt from the original article which was published by the NASA Earth Observatory concerning the historical and ecological context behind East Island and what Hurricane Walaka meant to the situation overall:
“The Operational Land Imager on Landsat 8 captured these natural-color images of East Island on September 11 (left) and October 13, 2018 (right). The storm washed away the 11-acre strip of sand and gravel, and only two slivers of land have re-emerged since the hurricane struck. Storm surges also deposited sand and debris across Tern Island, which is northwest of East Island.
East Island is part of the French Frigate Shoals, one of the most significant coral reef systems in Papahānaumokuākea. The archipelago formed millions of years ago when a deep-sea “hotspot” created underwater volcanoes, which eventually rose to the ocean’s surface to became islands. While East Island was uninhabited by people, it provided nesting grounds for the threatened Hawaiian green sea turtles and pupping grounds for endangered monk seals, of which there are only 1,400 in the world.
Scientists believe many of the animals had already left the island before the hurricane hit because it was the end of turtle and seal breeding season. However, unhatched turtle nests were likely affected. Researchers must wait until next year to return to the islets for a more extensive survey of the impact on wildlife. In the meantime, a marine debris team worked within the Monument zone in early November to remove more than 160,000 pounds of lost or abandoned fishing nets and plastic that could endanger marine animals.
East Island is not the first island to disappear from the French Frigate Shoals. Whale-Skate Islet was lost to erosion in the 1990's, while Trig Island eroded earlier in 2018—a common occurrence in sand-dominated ecosystems. Scientists believe the mammals adapted to the ecosystem changes at Whale-Skate and Trig by finding new breeding locations, so they expect the same to happen now that East Island is gone.”
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© 2018 Meteorologist Jordan Rabinowitz
Taking a Look Back at the 2018 Atlantic Hurricane Season (Credit: NOAA NWS National Hurricane Center, NWS Key West)
Discussion: As November comes to a close, so does the 2018 Atlantic Hurricane Season. This season produced fifteen named storms. Among those fifteen storms, eight of them were hurricanes. This hurricane season produced two major hurricanes out of the eight that formed. A major hurricane is defined as a category three or higher on the Saffir-Simpson wind scale. The Saffir-Simpson wind scale measures a hurricane’s sustained wind speed.
This Hurricane season will be remembered in particular for Hurricanes Florence and Michael that caused significant damage to the southeastern United States. Hurricane Florence was one of two major hurricanes this season. It formed on August 31st, 2018 and as it made its way across the Atlantic it strengthened into a category 4 hurricane with sustained winds of 130 miles per hour. It maintained its strength until the track took the storm into an area of wind shear. Wind shear can tear apart the hurricane causing the structure to become asymmetrical and weaken. Florence made landfall in North Carolina on as a category one hurricane and moved slowly over the Carolinas producing torrential rainfall and devastating flooding. Many rivers across the Carolinas came close or actually broke their rainfall records. It took many weeks and in some places a month for the waters to recede and the rivers to fall below flood stages.
Hurricane Michael was the second of two major hurricanes this season. It formed in the Caribbean Sea on October 2nd, 2018 and traveled slowly through the Gulf of Mexico. Once in the Gulf of Mexico, it rapidly intensified and became a major hurricane on October 9th, 2018. Hurricane Michael reached a peak intensity of a high-end category four hurricanes with maximum sustained winds of 155 miles per hour. On October 10th, 2018, Hurricane Michael made landfall on the Florida panhandle near Mexico Beach, Florida. Michael caused widespread damage across the panhandle with a fourteen-foot storm surge that washed houses away and strong winds that destroyed buildings and foundations. Michael was the fourth strongest storm to make landfall in Florida since Hurricane Andrew in 1992 in regard to its wind speed. It was also the third strongest hurricane in regard to its central pressure with a minimum central pressure of 919 millibars to make landfall since Hurricane Camille in 1969.
Overall this Hurricane season was pretty active this year. Tropical Storm Alberto kicked the season off early on May 25th, 2018 making landfall in Florida. Seven of the fifteen named storms were subtropical at a point in their lifetime. A named storm that has characteristics of a non-tropical storm is called a sub-tropical storm. These seven storms this season all became tropical storms and three of them intensified to hurricane status. For the first time since 2008, the Atlantic saw four named storms existing in the Atlantic basin together. Florence, Helene, Isaac, and Joyce all co-existed for a period of time this season. With the 2018 Hurricane season finished, it is never too early to begin making preparations for next summer. It’s important to have a plan in place if you live in hurricane-prone areas because it only takes one storm to cause significant damage. Being prepared and tuned into your local and government weather service offices is a great way to be ready for the 2019 season! For more information on having a hurricane ready plan click here!
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© 2018 Meteorologist Shannon Scully
What is the Meaning and Importance Behind a Tropical Cyclone's Outflow? (Imagery credit: Himawari-8 Satellite Imager)
DISCUSSION: Year in and year out, millions of people all over the world bear witness to the formation of tropical cyclones in tropical ocean basin across the globe. During some of the more intense tropical cyclones which form during a given year, there are often some neat satellite imagery-based signature features which can be greatly appreciated even by the general public. One such example of an interesting feature which will often occur in association with tropical cyclones of variable intensities, but most often in association with major hurricanes (i.e., across the tropical Eastern and/or Central Pacific Ocean as well as the tropical Atlantic Ocean is upper-level outflow.
Upper-level outflow associated with a tropical cyclone is particularly interesting since it will always flow in the opposite direction from the more intense cyclonic (anticyclonic) winds which occur with tropical cyclones which form within the Northern (Southern) Hemisphere. However, the big question which many people will often inquire about in association with upper-level outflow tied to more intense tropical cyclones is why the upper-level winds from in the opposite direction of the low/mid-level wind flow regime. As is often the case with many interesting scientific conundrums in life, the answer to this question is actually very simple. And that answer is a result of a basic atmospheric dynamics principle and fundamental law of atmospheric physics. This basic atmospheric dynamic principle is the fact that above any low-pressure center is a high-pressure center and above any high-pressure center is always going to be a nearby low-pressure center. Effectively, this fundamental principle is what allows the atmosphere to always remain at or closer to a dynamically-stable state of atmospheric balance over both shorter-term and longer-term periods.
When it comes to observing upper-level outflow associate with a tropical cyclone via satellite imagery, it is often photogenic and almost mesmerizing to watch. Moreover, upper-level outflow is often found to be quite attention-grabbing despite the storm encapsulated within the symmetric outflow (or sometimes asymmetric outflow depending on the given situation at hand) being quite powerful towards the surface of the Earth. Thus, this just goes to show that even the more interesting and curious details of a larger weather event can be quite interesting to understand on a more profound level.
To learn more about this particular issue, please also visit our GWCC Kid's Corner, which can be found right here!
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© 2018 Meteorologist Jordan Rabinowitz
How Historic Was Hurricane Michael Really? (Photo Credit: The Weather Channel and the National Hurricane Center)
DISCUSSION: Earlier this month, on October 10, 2018, Hurricane Michael made landfall along the Panhandle of Florida, over the city of Mexico Beach. Michael made landfall as a strong Category 4 storm, with maximum sustained winds of 155 mph. In addition to the strong winds, Hurricane Michael’s central pressure was exceptionally low, at 919 mb. The winds, combined with storm surge as high as 12 feet in some areas, lead to devastating destruction of land and property along the path of the hurricane. Due to all of this, Hurricane Michael is already being called a historical event, but just how rare is an event like Hurricane Michael.
For starters, it is rare for a hurricane to make landfall in the continental United States as a Category 4 or greater. Since 1851 there have only been 27 hurricanes to do so, with the greatest number making landfall over Florida, as can be seen in the image above. However, despite this, since the United States began keeping a record of hurricanes there has never been a Category 4 or 5 hurricane to make landfall along the Florida panhandle. Therefore, the location that Michael made landfall by itself makes it historic.
Aside from its location, it was also the first hurricane to make landfall in the United States in the month of October as a Category 4 or higher storm since Hurricane Hazel 64 years ago. Hurricane Hazel was a Category 4 hurricane when it made landfall near the border of North Carolina and South Carolina on October 15, 1954. Its estimated maximum winds were between 130 mph and 150 mph and had storm surge that reached 18 feet along portions of North Carolina. The storm then moved northward into Canada, where it dropped 11 inches of rainfall in Toronto.
Hurricane Michael’s minimum central pressure also makes it unique. Since 1851 there have only been two storms, The Florida Keys Labor Day Storm in 1935 and Hurricane Camille in 1969, that had a lower central pressure at landfall. The Labor Day storm made landfall as a Category 5 storm with a central pressure of 892 mb in the Florida Keys. It then turned to the northeast and made a second landfall as a Category 2 storm near Cedar Key Florida. Hurricane Camille was also a Category 5 when it made landfall along the Mississippi coast with a central pressure of 900 mb. Its maximum wind speed was not recorded because the wind instruments in the path of the storm were destroyed but winds along the coast were estimated to be 200 mph. Hurricane Michael also beat Hurricane Katrina’s minimum central pressure which was 920 mb, though not by much. Katrina, which devastated New Orleans in 2005, had been a Category 5 storm with a minimum pressure of 902mb the day before landfall but at the time of landfall on Aug 29 it had weakened to a Category 3 and its minimum pressure increased.
The location, time of year, and the minimum central pressure of the Hurricane Michael for sure make it an historical event. However, these factors alone will likely not be the only reasons Hurricane Michael will live in infamy. In the following weeks, months, and years we will continue to examine the storm and likely find other factors that will add to the historic nature of this event. Even more, we do not know the economic impact the storm had, and the amount of property and loved ones lost.
Additional information about memorable hurricanes to hit the US can be found at: https://www.nhc.noaa.gov/outreach/history/
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© 2018 Meteorologist Sarah Trojniak
Inside Edge on What Helped Hurricane Michael to Rapidly Intensify Leading up to Landfall. (Imagery credit: Meteorologist Stu Ostro)
DISCUSSION: There is no question that Hurricane Michael shocked the state of Florida and the rest of the world for that matter on the morning of October 10th, 2018. It goes without saying that Hurricane Michael will undoubtedly go down in history as one of the top five most intense hurricanes to make a direct hit on the contiguous United States as far back as records go. Having said that, it is even more interesting to learn more about and why Hurricane Michael managed to intensify so quickly and so close to the official point of landfall in northeast Florida as this system did. This is complicated and yet, at the same time represents a perfect example of a classic tropical cyclone intensification scenario.
To get into the factors which went into how and why Hurricane Michael intensified as quickly and abruptly just before its landfall near Mexico Beach, Florida, there are some atmospheric and environmental fundamentals which must exist. It is imperative to establish the fact that for a hurricane to intensify and/or rapidly intensify at any point in time, there must always be sufficiently warm sea-surface temperatures in place both under and out ahead of an approaching tropical cyclone. In the case of Hurricane Michael, there was more than sufficiently warm sea-surface temperatures spread across the northeastern Gulf of Mexico out ahead of the forward approach of Hurricane Michael. Hence, the first major piece was most certainly in place for this tropical cyclone.
The second major environmental factor which is key and essential for tropical cyclone intensification is the presence of little to no vertical wind shear both surrounding the immediate location of the intensifying tropical cyclone and out ahead of the given tropical cyclone. In the case of Hurricane Michael, the main concern regarding the presence of vertical wind shear was when this system was developing both near and just to the north of the Yucatan Peninsula in eastern Mexico. However, as this storm continued to move northward with time, the issues pertaining to the presence of vertical wind shear subsided rather quickly as the storm’s inner and outer core organized rather quickly with time which limited the vertical wind shear threat and concerns thereof. Thus, the second piece of the puzzle was most certainly in place for then intensification of Hurricane Michael.
The third major piece which is important and is critical both ahead and during a period of intensification and/or rapid intensification of a tropical cyclone is to have an effective and consistent outflow channel both surrounding and out ahead of a strengthening tropical cyclone. This consistent outflow surrounding an intensifying tropical cyclone is important since this allows a tropical cyclone to vent all the excess “cloud debris” and excess heat energy which is always being released both above and surrounding the convective inner and outer portions of a developing and/or mature tropical cyclone. As shown in the animated graphic attached above, there was most certainly an effective outflow channel in place with Hurricane Michael which allowed for this outflow channel to be maintained incredibly well with Michael right up to the point of landfall.
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© 2018 Meteorologist Jordan Rabinowitz
DISCUSSION: The Global Precipitation Measurement (GPM) Core Satellite was launched in 2014 as a joint project between NASA and the Japan Aerospace and Exploration Agency (JAXA). The two primary instruments carried on the satellite are the GPM Microwave Imager and the Dual-Frequency Precipitation Radar (DPR). The GMI measures naturally emitted radiation in 13 channels, while the DPR measures scattered radiation at two microwave frequencies. The combination of information from these instruments provides critical information necessary to create a globally-consistent measure of precipitation. Rain gauges and ground-based radar are useful tools for estimating precipitation, but these are only available on land and coverage is not uniform. Only from a satellite can a truly consistent, global measure of precipitation be obtained. The GPM mission actually consists of a constellation of satellites, but the GPM Core Satellite provides the basis against which all the other satellite instruments are compared or calibrated against.
Hurricane Walaka is currently a Category 1 hurricane located northwest of Hawaii. The storm formed southwest of Hawaii and moved west of the islands without any direct impacts there. The storm is currently weakening as it moves over cooler water and into the mid-latitude westerlies. When the storm was still an intensifying tropical storm on 30 September, the GPM satellite passed over the storm center. The above figure shows a 3-D depiction of the 17-dBZ surface from the Ku Band of the DPR instrument. This basically shows how the precipitation is distributed around the storm and in the vertical. The figure also shows the intense and deep (up to 8.5 miles [13.7 km] above the sea surface) convection in the southeastern and northwestern section of the eyewall of the storm. The DPR also observed intense rainfall in a rainband northeast of the storm center with an estimated rain rate of nearly 6.5 inches (165 mm) per hour. Without satellite microwave instruments, acquiring estimates of such intense rainfall in the middle of the ocean would be much more difficult if not impossible.
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© 2018 Meteorologist Dr. Ken Leppert II
Hurricane Rosa Expected To Make Landfall in Baja California! (Photo Credit: National Hurricane Center)
Hurricane Rosa is located in the Eastern Pacific Ocean and it moving towards Baja California. Rosa is a category 1 hurricane with sustained winds of 85 mph. While expected to continue to weaken, Rosa will bring torrential downpours as well as damaging winds to the Southwest. Rosa is expected to downgrade to a tropical storm by the time it makes landfall on Monday. After making landfall, Rosa is expected to continue on a northeastward track towards Arizona. Currently, hurricane force winds extend outward of 30 miles form the center. Due to the mountainous region, the heavy rainfall can produce life-threatening flash flooding and landslides. High surf as well as storm surge is also a threat as Rosa moves closer to land.
The key messages from the National Hurricane Center are as follows:
The main hazard expected from Rosa or its remnants is very heavy rainfall in Baja California, northwestern Sonora, and the U.S. Desert Southwest. These rains are expected to produce life-threatening flash flooding and debris flows in the deserts, and landslides in mountainous terrain.
Tropical storm conditions are expected over portions of the central and northern Baja California peninsula on Monday, possibly spreading to the northern Gulf of California Monday night. Interests in those locations should monitor the progress of Rosa.
The forecast discussion from the National Hurricane Center is as follows:
This initial motion estimate is 005/10 kt. Rosa is forecast to continue moving northward around the western edge of a deep-layer ridge for the next 24 h or so, followed by a turn toward the north-northeast on Tuesday as a mid-/upper-level trough approaches from the west. As the low- and upper-level circulations continue to decouple, Rosa should essentially maintain its current forward speed until landfall occurs in 36-48 hours due to the cyclone not being influenced by the faster deep-layer steering flow. The new NHC track forecast is a little slower than the previous advisory track, and closely follows the consensus models HCCA and IVCN. A 72-hour forecast position continues to be provided for continuity purposes, but Rosa's surface circulation is likely to dissipate before that time over northwestern Mexico or southern Arizona, with the mid-level remnants continuing northward across the Desert Southwest and Intermountain West.
Rosa is now moving over waters colder than 25ºC, with colder water near 22ºC ahead of the cyclone just prior to landfall. The combination of increasing wind shear, cooler waters and drier and more stable air being entrained from the west should result in steady or even rapid weakening of the cyclone until landfall occurs. The official forecast follows the sharp weakening trend indicated in the previous advisory, which is supported by the latest intensity guidance. Rosa is expected to devolve into an exposed low-level center with the associated deep convection being sheared off to its north and northeast by the time it is nearing the Baja California coast on Monday. However, it will take some time for the circulation to spin down, and Rosa is still expected to bring tropical-storm-force winds to portions of Baja California in 36-48 hours.
Stay updated on tropical weather at www.globalweatherclimatecenter.com/tropicalcyclones
ⓒ 2018 Meteorologist Brandie Cantrell
As we are in the heart of Hurricane Season, it is important to understand the logistics of hurricane strength and what typically falls within the guidelines for determining the category. Originally developed by wind engineers Herb Saffir and Bob Simpson, the Saffir-Simpson wind scale is a categorization on a scale of one to five that bases hurricane intensity on maximum sustained surface wind speed. Maximum sustained surface wind is recorded when the highest wind speed at 10 meters above the surface holds for more than one minute. The Saffir-Simpson Hurricane Scale continues to be a useful tool when alerting the public on hurricane impact strength.
Wind speed plays a huge role in the strength of a hurricane for many reasons. Wind speeds within a hurricane can enhance the storms ability to destroy buildings, down trees, cause power outages, and increase the likelihood of death and injury caused by flying or falling debris. It is important to recognize that the Saffir-Simpson scale does not include other potential hurricane impacts such as storm surge, rainfall induced flooding, and tornadoes. These factors are all independent of the scale and can cause added damage and injury adjacent to impacts caused by the wind. This is why it is important to not underrate the impacts of a hurricane based solely off its category.
The scale not only gives a range of high wind speeds but also includes the potential damage and impacts on the United States infrastructure upon landfall. Each category of the Saffir-Simpson scale is characterized by a range of wind and its potential impacts to an area upon landfall. Although, the Saffir-Simpson scale is independent of certain factors such as storm surge, flooding, and tornadoes, it is dependent upon building structure, duration, and direction of strong wind when regarding possible damages. The following table below is a short summary of each category and its characteristics regarding possible damage outcome. This table as well as more information on the Saffir-Simpson wind scale can be easily searched on the National Hurricane Center website.
Regardless of the category, a hurricane can be a strong and powerful force of nature. It is important to know that the Saffir- Simpson scale is a wind-based scale focused solely on sustained surface wind strength and damage. It does not include damages that can occur from storm surge, tornadoes or rain-induced flooding. Continuing forward in this hurricane season, stay informed, keep updated on latest hurricane news and updates, and never underestimate a hurricanes true potential. Keep informed by your local news channel, weather app, and/or website. If one is expected to come your way, it is crucial to heed the warnings and evacuate when told to by your local officials.
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© Meteorologist Alex Maynard