 DISCUSSION: As we now approach the heart of the 2018 tropical Atlantic hurricane season, there is little to no debate across the atmospheric science community that the tropical Atlantic Ocean basin has indeed finally fired up. As a result of this recent spike in tropical development across a good portion of the tropical Atlantic, there has continued to be substantial conversation regarding how long this increased activity may persist for an how much of an influence Africa may continue to have during the course of this more active period. The reason for why Africa is being so closely watched during this active period is due to the fact that on a seasonal basis there are often dozens and dozens of tropical waves which emerge off the west coast of Africa. These tropical waves are the "seed" which helps to "plant the foundation" for further potential tropical cyclone development once these tropical waves begin to interact with the warmer waters of the tropical Atlantic Ocean.
Hence, the reason for why many meteorologists are becoming increasingly concerned about Africa and the eastern tropical Atlantic Ocean is a result of the persistent progression of convectively invigorated tropical waves which are emerging one after another at the present time. Thus, the predominant thought process had by many right now is that since the earlier onslaught of Saharan Dust has finally begun to slightly abate and the corresponding average decrease in vertical wind shear associated with the African Easterly Jet (AEJ) for the time being (i.e., a factor which has been found historically unfavorable for tropical cyclone development), there is a concern for a semi-lengthy active period for basin-wide tropical activity. Even despite the fact that sea-surface temperatures across key tropical development zones have been slightly below-normal, many areas have still continued to remain sufficiently warm to support tropical cyclone development. Thus, as shown in the graphic above (courtesy of NBC 6 Miami's Chief Meteorologist John Morales), there are a pair of waves emerging off of Africa right now with even more on the way soon. Therefore, as we continue to go through the remainder of September, and then October as well as November, be sure to stay tuned and keep the future role of Africa in mind in future website articles as well as Twitter and/or Facebook posts in the coming days and weeks ahead. To learn more about other high-impact weather events and topics occurring across Africa, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz
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 A view of Johannesburg Source : https://www.goodthingsguy.com/opinion/johannesburg-living-worlds-dangerous-city/ Over the past few decades there has been a growing interest in investigating the link between weather and various types of crimes. However, most research in this area has produced inconsistent and often paradoxical results. For instance, a few studies have found no apparent seasonal fluctuations in crime. Others have found a rise in crimes during either colder winter months or warmer summer months. However, very little is known about how the amplitude and spatial distribution of criminal activity in South Africa is affected by climatic conditions. A study was performed to determine a link between criminal activity and climate in the country's capital city known as Tshwane. The aim was to investigate whether there was any correlation between the frequency in crime rate and extreme weather conditions, using temperature and rainfall as proxy. In other words: do extremely hot days or high-rainfall days experience higher or lower rates of violent, property or sexual crime? The spatial distribution of different crime types and extreme weather event were also analyzed. Simply put, does crime occur in different places on extremely cold days than it does on really hot ones? The results suggest a strong association between temperature and criminal activity, with an increase in crime rate in step with a temperature rise. There’s a less significant association between rainfall and crime. The spatial distributions of all types of crime are found to differ significantly depending on the type of weather extreme observed. These results could help law enforcement agencies better understand how weather affects crime patterns in South Africa’s urban areas and develop and implement appropriate crime prevention measures. The notion that there’s a relationship between criminal activity and climate is nothing new. Over a century ago Belgian sociologist and scholar Adolphe Quételet observed that crimes against people reach a maximum during the warmer summer months, while crimes against property reached a peak during winter. Later, he developed the temperature-aggression theory, which provides a psychological explanation for the increase in crime during warmer months. It suggests that warmer temperatures will lead to an increase in an individual’s frustration and discomfort levels and so increase the likelihood of aggression. This could in turn result in interpersonal crimes such as assault. In the case of the Tshwane study, statistical analysis was performed to find any relationship between extreme weather conditions and crime in the nation’s capital. Climate data for the city was obtained from the South African Weather Service over a 5-year period from September 2001 to the end of August 2006. Daily average temperatures was computed before extracting the ten hottest for each year of the five years resulting in a dataset of 50 days. The process was repeated for low-temperature days, high-rainfall days, no-rainfall days and random-rainfall days. Crime data for the same period were also retrieved from the South African Police Services’ Crime and Information Analysis Centre. The data included the geographical location of each crime; the date and time of day that each crime was committed; and the specific type of crime committed. A total of 1,361,220 crimes were reported in the five-year period across 32 different categories. All crime was then categorised into either violent, sexual or property crimes before calculating a count of crime per type per day. Next, a recently developed method called the spatial point pattern test was used to determine whether the spatial distribution of crime on the three types of days (very hot, very cold and rainy) changes. That is, does the spatial patterning of crime in Tshwane change depending on certain rainfall and temperature conditions? The findings demonstrate that the amount of violent, sexual and property crime in the city of Tshwane is significantly affected by temperature and, to a lesser extent, rainfall. The magnitude of violent, sexual and property crime was higher on hot days compared to cold or random temperature days. Violent crimes increased by 50% on hot days compared to very cold days. Sexual crimes increased by 41% and property crime by 12%. Violent and sexual crimes in Tshwane also decreased on high-rainfall days. Surprisingly, property crime was found to increase slightly on heavy rainfall days, though only by 2%. Second, the spatial distribution of violent and property crime was found to differ on days by temperature and rainfall. There is a considerable change in the way that particularly violent and property crime is spatially distributed in Tshwane depending on the weather conditions. More research is needed to confirm these findings and to determine if the results can be generalised to other urban areas in South Africa. Our findings can be used to identify communities that are more prone to crime under certain meteorological conditions and allow stakeholders to target these neighbourhoods and plan interventions. It also allows stakeholders to adequately develop and implement suitable intervention practices in similar at-risk neighbourhoods. For the police and others responsible for specifically addressing long-term solutions to crime, crime pattern analysis can utilise the understanding of how weather events influence crime patterning and provide measures to take appropriate action. https://theconversation.com/when-temperatures-rise-so-do-crime-rates-evidence-from-south-africa-100850 To learn more about other climate-related stories occurring across Africa, be sure to click here! © 2018 Oceanographer Daneeja Mawren  A National weather service meteorologist in Norman, Oklahoma, tracking a super cell tornado outbreak (NOAA).
Source : http://www.noaa.gov/explainers/improving-weather-forecasts Weather forecasting in an imperfect science. Through decades of research, meteorologists have come up with tools that allow us to fairly accurately predict weather in the short term using numerical modeling and forecast analysis. Beyond the scope of about a week however, the certainty in these forecasts drops off significantly. This is because weather is based on an infinitely complex and constantly changing system, with a little bit of chaos thrown in for fun. There are many steps involved in weather forecasting. Firstly, a global snapshot of the atmosphere is captured at a given time and mapped onto a 3-D grid of points that extend over the entire globe from the surface to the stratosphere. Using a powerful computer and a numerical model that describes the behaviour of the atmosphere incorporated with physics equations, this snapshot is therefore stepped forward in time to produce terabytes of raw forecast data. These data are then interpreted by human forecasters which turn them into a meaningful forecast broadcasted to the public. Forecasting the weather is challenging as we attempt to predict something that is inherently unpredictable. Since the atmosphere is a chaotic system, any small change at one location will cause remarkable consequences elsewhere over time, which was analogised as the so-called butterfly effect. Therefore, any error that develops in the forecast will grow rapidly causing further errors on a larger scale. As such, to obtain a perfect forecast, every single error would need to be removed. Forecasting skills have improved over time. Modern forecasts are certainly more reliable than they were before the supercomputer era. The UK’s earliest published forecasts date back to 1861, when Royal Navy officer and meteorologist Robert Fitzroy began to publish forecasts in the Times newspaper. Their methods involved drawing weather charts using observations from a few locations and making predictions based on how the weather evolved in the past when the charts were similar. However, their forecasts were often wrong, and the press were usually quick to criticise. The advent of supercomputers in the 1950s brought so much of insights to the forecasting community. This work paved the way for modern forecasting, the principles of which are still based on the same approach and the same mathematics, although models today are much more complex and predict many more variables. Nowadays, a weather forecast typically consists of multiple runs of a weather model. Operational weather centres usually run a global model with a grid spacing of around 10km, the output of which is passed to a higher-resolution model running over a local area. To reduce the errors, many weather centres also run a number of parallel forecasts, each with slight changes made to the initial snapshot. These small changes grow during the forecast and give forecasters an estimate of the probability of something happening – for example, the percentage chance of it raining. The supercomputer age has been crucial in allowing the science of weather forecasting (and indeed climate prediction) to develop. Modern supercomputers are capable of performing thousands of trillions of calculations per second and can store and process petabytes of data. This means we have the processing power to run our models at high resolutions and include multiple variables in our forecasts. It also means that we can process more input data when generating our initial “snapshot”, creating a more accurate picture of the atmosphere to start the forecast with. This progress has led to an increase in forecast skill. A neat quantification of this was presented in a Nature study from 2015 by Peter Bauer, Alan Thorpe and Gilbert Brunet, describing the advances in weather prediction as a “quiet revolution”. They show that the accuracy of a five-day forecast nowadays is comparable to that of a three-day forecast about 20 years ago, and that each decade, we gain about a day’s worth of skill. Essentially, today’s three-day forecasts are as precise as the two-day forecast of ten years ago. But is this skill increase likely to continue into the future? This partly depends on what progress we can make with supercomputer technology. Faster supercomputers mean that we can run our models at higher resolution and represent even more atmospheric processes, in theory leading to further improvement of forecast skill. According to Moore’s Law, our computing power has been doubling every two years since the 1970s. However, this has been slowing down recently, so other approaches may be needed to make future progress, such as increasing the computational efficiency of our models. So, will we ever be able to predict the weather with 100% accuracy? In short, no. There are 2×10⁴⁴ molecules in the atmosphere in random motion – trying to represent them all would be unfathomable. The chaotic nature of weather means that as long as we have to make assumptions about processes in the atmosphere, there is always the potential for a model to develop errors. Progress in weather modelling may improve these statistical representations and allow us to make more realistic assumptions, and faster supercomputers may allow us to to add more detail or resolution to our weather models, but, at the heart of the forecast is a model that will always require some assumptions. However, as long as there is research into improving these assumptions, the future of weather forecasting looks bright. How close we can get to the perfect forecast, however, remains to be seen. This article was originally published on The Conversation by Jon Shonk, Research scientish at the University of Reading. https://theconversation.com/why-the-weather-forecast-will-always-be-a-bit-wrong-101547 To learn more about other climate-related stories occurring across Africa, be sure to click here! © 2018 Oceanographer Daneeja Mawren  Enhanced IR image of four tropical cyclones at 1200UTC 22 Feb 2007 in the South West Indian Ocean. [Source : US Navy/NRL/ (c)EUMETSAT 2007] The Paris Agreement achieved in December 2015 established that the signatory countries should pursue to hold the increase in global average temperature to below 2 °C relative to the preindustrial period and to strive to limit the temperature increase to 1.5 °C below the preindustrial period. A recent study by Muthige et al., 2018 used the Coordinated Regional Downscaling Experiment-Africa regional climate models to downscale six global climate models of the Coupled Model Inter-comparison Project Phase 5 to high resolution. This serves towards studying changes in tropical cyclone tracks over the Southwest Indian Ocean under different extents of global warming (1.5 °C (Fig.3), 2 °C (Fig.4) and 3 °C (Fig.5) of warming with respect to preindustrial conditions). The results projected that the number of tropical cyclones making landfall over southern Africa under global warming will decrease, with 2 °C being a critical threshold, after which the rate of cyclone frequency with further temperature increases no longer has a diminishing effect. Fewer cyclones may bring benefits and reduce damage to the southern African region. Although a decrease in damages associated with flood events is desirable, general decreases in tropical cyclone and tropical lows may also be associated with decreased rainfall over the Limpopo River basin and southern, central and northern Mozambique (with negative impacts on dryland agriculture).
Journal Reference: Muthige, M.S., Malherbe, J., Englebrecht, F.A., Grab, S., Beraki, A., Maisha, T.R. and Van Der Merwe, J., 2018. Projected changes in tropical cyclones over the South West Indian Ocean under different extents of global warming. Environmental Research Letters, 13(6), p.065019. To learn more about other climate-related stories occurring across Africa, be sure to click here! © 2018 Oceanographer Daneeja Mawren  Source : https://earthobservatory.nasa.gov/images/92428/cape-townrsquos-reservoirs-rebound What a difference a few months can make. Cape Town has had to fight tooth and nail to keep itself hydrated and as NASA technology shows us, Theewaterskloof dam has come a long way in such a short space of time. The facility is the largest of its kind in the province and became the “poster child” for the Cape water crisis, as water began to drain from its reserves in 2017. Harsh, prolonged periods of drought meant that Theewaterskloof wasn’t getting replenished, which spelt disaster for the city and its residents. How Theewaterskloof dam fought back from the brink However, the rain finally revisited the Western Cape earlier in 2018. A few cold fronts and heavy rainfall helped stock the dams up with billions of litres of water. Just as important for the Mother City has been the contribution of its water-wise inhabitants. Capetonians have slashed their water consumption rates to record lows, whilst most are adhering to the 50 litres per person, per day rule. In fact, this week is the eight-consecutive period where dam levels have increased. The picture is looking a lot rosier for the region, but more hard work needs to be done to keep the momentum going. Theewaterskloof dam – drought timeline: October 2016 It’s been almost two years since the facility resembled a picture of health. From here onwards, Cape Town’s problems intensified. July 2017 Another dry and humid summer saps the water from the dams. Theewaterskloof is reduced to just 25% of its capacity by the end of the year. January 2018 Dam levels plummet to 16%, large areas of the reservoir are empty and bone dry. March 2018 A barrage of rain in February signals the briefest of relief for the dam. The reserve sees its water levels stabilise, without any great improvement. July 2018 Frequent and persistent rains falling since the middle of May onwards see Theewaterskloof dam soar to 55% of its capacity.
NASA time-lapse for Theewaterskloof dam is available : https://earthobservatory.nasa.gov/images/92428/cape-townrsquos-reservoirs-rebound
To learn more about other high-impact weather and weather-related stories occurring across Africa, be sure to click here! © 2018 Meteorologist Daneeja Mawren
DISCUSSION: According to weather experts, April-May rainfall over South Africa are determining months as these months tend to be used as a gauge for the rest of the year. The rain maps above indicate that yellow areas are places that received little to no rain. The 2018 map already shows a healthier shade of green in the Western Cape, indicating that more regions received between 25 mm – 50 mm of rain in one week, compared to 0 - 10 mm for year 2017 for the same area. The rains are good news for the Western Cape‚ but strict water restrictions are still enforced. According to the Western Cape government, the average level for dams across the province on Monday was 19 %, an improvement on the 16.6 % at this time last week. The forecasting system indicates above-normal rainfall during early winter, according to the South African Weather Service. The Cape Town weather has been the best performer in the battle to beat day zero over the last few weeks, as multiple cold fronts hit the city with an abundance of rain. Forecaster Cobus Olivier said in an e-mailed statement that a number of rainfall days were expected to be higher than normal for the winter rainfall areas. Some places in the region have already exceeded the average monthly rainfall targets for the month of May. Over the last few days, the downpours have even been kind enough to pay the ailing dams a visit. "It should be noted, however, that there is not sufficient confidence in the forecasting system for these forecasts, thus there is very high uncertainty in the rainfall intensity for the winter rainfall areas," Olivier noted.  Source : http://www.weathersa.co.za/observations/ @ReenvalSA The above figure shows a cold front which is expected to make landfall in the evening (Tuesday 30th May 2018) going into the night associated with Gale force winds, heavy rainfall up to 50 mm in high lying areas, 20-30 mm over the Cape Metropole, localised flooding as well as high seas into tomorrow in the Western Cape. It is worth nothing that the average May rainfall for Cape Town is 70 mm.
Local Government, Environmental Affairs and Development Planning MEC Anton Bredell says it is heartening to see dam levels increasing but has cautioned that the drought is still far from over. “We have always warned that we need an above-average rainfall season and it needs to rain in the catchment areas for our dams to recover adequately,” says Bredell. Also, models show that an El Nino weather pattern seems to be developing during the region’s winter and spring, but it was too early to forecast if it would last into the summer growing season. The last El Nino was linked to a severe drought that hit crop production and economic growth across southern Africa, and the region is still emerging from its effects two years later. To learn more about other high-impact weather and weather-related stories occurring across Africa, be sure to click here! © 2018 Meteorologist Daneeja Mawren 
DISCUSSION: Through the course of a given year, there are often periods of time during which many parts of northern Africa as well as parts of the Middle East feel the effects of dust storms. During the final approach and ultimate impacts from prolific dust plume intrusions, often times, there are pronounced impacts inflicted on both life and property. During the heart of dust plume events, winds often rapidly increase and visibility is quickly reduced down to dangerous thresholds. In the particular situation, captured in the live footage from part of the Sudan, visibility with this particular dust plume was reduced to as little as 10 meters in some places for a brief period of time. Thus, it just goes to show that something as simple as a dust plume has the potential to induce severe problems with respect to both travel and/or communication.
In addition, aside from potential impacts from dust plumes across parts of the Middle East, dust plumes can also impact other weather phenomena around the world on different scales. For example, dust plumes originating from the central and western Saharan Desert can often encounter developing tropical storms across the Tropical Atlantic Ocean basin and inhibit their development due to stronger dry air intrusions. In addition, dust plumes (even in a more weakened state) can reach mainland areas across North and/or South America can create hazy conditions as well as invigorate respiratory issues with people dealing with asthmatic or other related conditions due to higher dust concentrations in given regions. The second image from the top illustrates the classic structure and approximate scaling of such dust plumes which emerge off of western Africa (courtesy of the UW-CIMSS research group). In addition, you will notice how there also tends to be mid-latitude dry air intrusions nearby as well which can sometimes be confused with dust plumes from a satellite-based perspective and are important to differentiate. Lastly, you can see how such dust plumes which emerge off of western Africa are often the size of entire regions of the United States which speaks to the massive amounts of coverage have the ability to achieve during their existence. To learn more about other high-impact weather stories/topics occurring across Africa, click on the following link: https://www.globalweatherclimatecenter.com/africa. © 2018 Meteorologist Jordan Rabinowitz 
DISCUSSION: During the course of a given calendar year, there are substantial differences which occur with respect to the transition of primary vegetation cover across parts of northern and central Africa. This is primarily a result of the progression of atmospheric features such as the Hadley Cell and Walker Circulation which act to modulate the general magnitude and location of both rising and sinking motion around the world at any given point in time. Thus, at different times of the year, there is a variable amount of rising and sinking motion present over various parts of the Sahel (i.e., the more tropical and equator-oriented regions of central and northern Africa).
In looking at the animated graphic which displays a typical year may look like from space in terms of the vegetative cover across northern and central Africa, it is critical to understand how this graphic is created by way of the Normalized Difference Vegetation Index (NDVI). Attached below are some exact excerpts from the NASA Earth Observatory article which explains the process by which this graphic is generated. "To determine the density of green on a patch of land, researchers must observe the distinct colors (wavelengths) of visible and near-infrared sunlight reflected by the plants. As can be seen through a prism, many different wavelengths make up the spectrum of sunlight. When sunlight strikes objects, certain wavelengths of this spectrum are absorbed and other wavelengths are reflected. The pigment in plant leaves, chlorophyll, strongly absorbs visible light (from 0.4 to 0.7 µm) for use in photosynthesis. The cell structure of the leaves, on the other hand, strongly reflects near-infrared light (from 0.7 to 1.1 µm). The more leaves a plant has, the more these wavelengths of light are affected, respectively. NDVI is calculated from the visible and near-infrared light reflected by vegetation. Healthy vegetation (left) absorbs most of the visible light that hits it, and reflects a large portion of the near-infrared light. Unhealthy or sparse vegetation (right) reflects more visible light and less near-infrared light. Nearly all satellite Vegetation Indices employ this difference formula to quantify the density of plant growth on the Earth — near-infrared radiation minus visible radiation divided by near-infrared radiation plus visible radiation." To learn more about the inside scoop on the process by which such information is collected, click on the following link. To learn more about other interesting weather and weather-related stories from across Africa, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz  DISCUSSION: When people think of tropical cyclones, most would quickly think of open ocean genesis situations and favorable environmental conditions which would keep an organized low-pressure system intact. After all, any tropical low is essentially a self-sustaining heat engine that transports heat from the tropics and poleward towards the mid-latitudes (i.e., regions located between 10 and 30 degrees North and between 10 and 30 degrees South respectively). Many people generally tend to think that once a tropical cyclone impacts land, weakening of the core circulation tends to happen rather quickly. That greater rate of weakening is presumed to be due to greater friction with terrain that effectively disrupts the center of circulation and negatively affects both spiral rain-bands and core convection alike. But a generous void exists in the meteorological literature about tropical lows that form over land (i.e., those which form primarily over central and southern Africa).
Most commonly found during the heavier precipitation months (i.e., between December through March), these tropical low-pressure systems form over land as a consequence of moisture that is displaced from the intertropical convergence zone (ITCZ). More specifically, the ITCZ is an area of persistent deep thunderstorm activity that oscillates between the Northern and Southern Hemispheres depending on the time of year. Around this time of the year, high moisture content and instability generated by the release of latent heat in the mid-troposphere (i.e., between roughly 2 and 5 kilometers up) combine with a favorable wind shear profile to generate a cyclonic structure similar to what is observed across tropical ocean basins. Although peak surface winds are not as strong as those found in association with tropical storms over open waters (e.g., the strong core wind speeds which were observed with both Hurricane Irma and Hurricane Maria), some of these land-based cyclones can still have high winds that can inflict substantial wind damage. However, these systems are mostly known for their potentially copious amounts of precipitation and thus are considered high-impact events as flooding is the principal threat in this otherwise semi-arid region of Africa. Fortunately, the development of such a tropical low-pressure system would likely weaken the grip of excessive heat impacting southwestern South Africa at a given point in time. In recent days, there have been confirmed observations for maximum temperatures over inland areas in excess of 38°C (100°F) and these same areas have been hit excessively hard by a long-lasting drought. This low-pressure system is expected to develop over Angola and slowly travel southward through Botswana and Zambia. Heavy (and very much needed) rainfall (i.e., on the order of 6 inches (or 0.16 meters) or more) is expected to fall over southwestern South Africa over the next 7 days. This heavy rainfall may also help to provide relief from the lengthy period of drought previously noted above. The photo attached above can be found at the following web address: https://www.eumetsat.int/website/home/Images /ImageLibrary /DAT_IL_10_01_24_A.html. To learn more about other high-impact weather events occurring across Africa, be sure to click here! © 2018 Meteorologist Brian Matilla and Meteorologist Jordan Rabinowitz  The dried up Theewaterskloof dam in Viliersdorp, South Africa. The single biggest dam supplying water to the metropole of Cape Town. [Source : Jon Kerrin]
Cape Town's drought and associated water restriction has officially gone up to the level of a disaster. The news of the drought crisis has spread across the globe, and the world is now paying attention to know the fate of the city. This drought has been caused by three years of very low rainfall, associated with increasing consumption by a growing population. “Day Zero”, currently forecast for April 16, is the day when the taps will run dry in Cape Town. According to the latest data, dam levels for Cape Town are 26.3% as at January 29, 2018. The day has been approaching faster– brought forward by the city's excessive consumption despite proactive measures like the implementation of water restrictions. The four million inhabitants will be forced to collect a daily water ration of only 25 litres from 200 water collection points – barely enough for a two-minute shower. How did this happen? It has been a slow-motion crisis, triggered by three factors:
Some studies suggest that the possibility of extreme drought is increasing in the western part of South Africa. Future climate projections show a possible shift towards a drier, more drought-prone climate. This means that it is possible that man-made influenced climate change has contributed to the severity of the current drought, and even though it is an extremely rare event, similar droughts may not be rare in the future. On a positive note, there will still be wet years, but likely not as many. What solutions are being implemented?
To learn more about other interesting weather events occurring across Africa, be sure to click here ! ©2018 Oceanographer Daneeja Mawren Insights into Von Kármán vortex streets offshore from Western Africa (credit: NOAA Satellites)1/23/2018 
DISCUSSION: With the advent of advanced satellite imagery platforms such as the MODIS-TERRA, MODIS-AQUA satellite class or the GOES-R (and upcoming GOES-S) next-generation satellite imagers, both atmospheric and surface-based observations have taken a major leap forward. This major lead forward is due to the fact that modern satellite imaging technology capabilities now give atmospheric researchers the consistent ability to study far smaller atmospheric phenomena in far greater detail than ever before in the course of human history. Satellite imagers including (but certainly not limited to) those noted above are allowing atmospheric scientists to view and understand finite details associated with extra-tropical low-pressure systems, tropical cyclones, Spring-time convective storms of varying types, and even trajectories of air pollution tied to anthropogenic activities or natural events such as volcanic eruptions.
Modernized satellite technology is quickly re-defining the manner in which man-kind will be able to understand the global atmosphere and various ongoing scientific problems tied to both studying and forecasting evolving trends thereof. Captured in the brief animated satellite imagery above is a recent occurrence of an interesting atmospheric phenomena referred to as Von Kármán vortex streets. Von Kármán vortex streets are essentially manifestations of disrupted low-level atmospheric flow around physical obstacles present over relatively open oceanic basins (e.g., the far eastern Atlantic Ocean in this particular case). Von Kármán vortex streets form as relatively uni-directional flow is disturbed by a physical feature (e.g., the presence of the Cape Verde Islands just offshore from the west coast of Africa). By looking closely in the brief satellite imagery loop attached above, you can denote a subtle swirling of the clouds and dust (i.e., mineral dust associated with a larger Saharan Dust plume) ejecting off of western Africa) to the west and southwest of the Cape Verde Islands. This swirling occurring within the dust plume in the vicinity of the Cape Verde Islands is the visual confirmation of the reality that the Cape Verde Islands were inducing the generation of Von Kármán vortex streets. This is just one of many other recent examples in which higher-resolution satellite imagers have drastically changed the way in which atmospheric research is more exciting than ever before. To learn more about other interesting weather events occurring across Africa, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz Upper ocean freshening and intensification of Tropical Cyclone Bansi in the South West Indian Ocean10/12/2017  In the South Indian Ocean, most cyclones originate just south of the Inter Tropical Convergence Zone (ITCZ) and move westward until they approach Madagascar before recurving east and back into the open South Indian Ocean. However, severe Tropical Cyclone Bansi formed near northern Madagascar, intensified and moved toward the east-southeast during 11–18 January 2015. Several weeks of very heavy rainfall occurred over Malawi and Mozambique, associated with the passage of TC Bansi and tropical storm Chedza, caused widespread flooding, which displaced more than 100,000 people and led to several deaths and considerable damage (http://www.bbc.com/news/magazine-30980324, http://edition.cnn.com/2015/01/17/africa/malawi-flooding/). The 850 hPa Geopotential height anomaly prior to Bansi, showed that strong anticyclonic conditions were present to the west-northwest of the formation region of Bansi, thus making propagation toward Madagascar unlikely. The movement of Bansi may be explained by the strengthening of the monsoonal north westerlies toward northern Madagascar, steering the storm toward the southeast. On the 13 January 2015, Bansi intensified to a Category 5 cyclone with maximum sustained wind speed of 220 km/h and minimum pressure of 923 hPa as monitored by Meteo France. Under WMO agreements, Meteo France through the RMSC at La Reunion, is responsible for forecasting TCs in the South West Indian Ocean. On 14 January 2015, the eye of Bansi was about twice as large as the size of Mauritius due to eyewall replacement (Moderate Resolution Imaging Spectroradiometer aboard NASA’s Aqua satellite) and decreased its intensity to Category 2 before strengthening back to Category 4 within 24 h. On the 15 January, the maximum sustained winds reached 185 km/h, with a minimum pressure of 940 hPa (http://www.meteofrance.re/cyclone/saisons-passees/2014-2015/dirre/BANSI). The rapid intensification of TC Bansi might be due to what scientists describe as the ‘barrier layer’, a layer created by fresh water from rains or rivers lying on top of the saline sea surface. Karthik Balaguru, Ocean Scientist at the Department of Energy's Pacific Northwest National Laboratory say that during such cyclones, fresh water from rains or river discharges falls on oceanic saltwater creating a barrier layer from the cold water below. This intermediate layer prevents mixing of waters, and thus reduces cooling. The heat keeps pumping fuel into the cyclone and hence they become very severe. Mawren and Reason [2017] presented a case study of TC Bansi with the objective of investigating how changes in the barrier layer may have influenced its evolution. In the Southwest Indian Ocean, the Barrier layer is sensitive to freshwater inputs by both precipitation and the advection of low-salinity waters by the South Equatorial Current. 2015-2016 was a very strong positive El Nino year and the westward advection of low salinity water during this period might have given rise to a thicker barrier layer, thus contributing to the strengthening of TC Bansi. References : [1] Mawren, D., and C. J. C. Reason (2017), Variability of upper-ocean characteristics and tropical cyclones in the South West Indian Ocean, J. Geophys. Res. Oceans, 122,doi:10.1002/2016JC012028. [2] Balaguru, K., P. Change, R. Saravanan, L. R. Leung, Z. Xu, M. Li, and J.-S. Hsieh (2012), Ocean barrier layer's effect on tropical cyclone intensification, Proc. Natl.Acad. Sci. U. S. A., 109(36), 14,343-14,347 To learn more about other high-impact weather events occurring across Africa, be sure to click here! ©2017 Oceanographer Daneeja Mawren  DISCUSSION: As we get deeper into the Summer-time season across a good portion of the Northern Hemisphere, many tropical research scientists and global forecasters are continuing to have increasing concerns for more activity in the tropics. The leading reason for this particularly heightened level of concern stems from the fact that during this part of the tropical Atlantic hurricane season, there is often the greatest frequency with which African easterly waves eject off of western Africa. Depending upon the exact sea-surface temperatures and larger-scale (i.e., basin-wide) vertical wind shear in place as these African easterly waves move off of western Africa, some of these waves can develop into what we identify as tropical cyclones.
Having said that, at the present time (as shown in the recent infrared satellite image attached above courtesy of The Weather Channel), there are several smaller waves getting ready to eject off of western Africa right now. As a result, there is a very real concern for the possibility of upcoming tropical development across various parts of the Tropical Atlantic basin as a result of this increasing African easterly wave activity which is currently gearing up across western and central portions of Africa. Therefore, in the coming days and weeks, the Global Weather and Climate Center will help to keep you updated on developing tropical situations as time moves forward. To learn more about other high-impact weather events occurring across Africa, be sure to click here! ©2017 Meteorologist Jordan Rabinowitz 
DISCUSSION: As of earlier today, Tropical Cyclone Enawo continued to intensity offshore from the eastern coast of Madagascar. As it currently stands, Enawo is maintaining the equivalent intensity of a Category 4 hurricane across the central-to-eastern Pacific Ocean as well as across the Tropical Atlantic basin. As can be clearly seen in the recent animated infrared satellite imagery (courtesy of the Cooperative Institute of Meteorological Satellite Studies or CIMSS), this current tropical cyclone (as rare as it is to occur at this higher intensity offshore from eastern Africa and/or Madagascar) even has a clear and symmetric eye and eye-wall associated with the center of the circulation. Moreover, you can also see the brighter colored cloud tops which indicates the presence of the deeper thunderstorms wrapped tightly around the center of the circulation of Tropical Cyclone Enawo. Thus, Tropical Cyclone Enawo is a very powerful, symmetric, and well-organized cyclone with a plethora of energy is associated with it. Therefore, all those in the path of this incoming tropical cyclone should give it due respect and avoid remaining in the path of this powerful tropical cyclone if at all possible.
To learn more about high-impact weather events occurring across Africa, be sure to click here! ©2017 Meteorologist Jordan Rabinowitz  NASA WorldView Image of Tropical Cyclone Dineo (credit: NASA) DISCUSSION: Tropical Cyclone Dineo is a Tropical Storm strength system with sustained winds of 40kts (46mph) and wind gusts of 50kts (57mph). Due to favorable atmospheric conditions and warm sea surface temperatures Dineo is expected to continue to strengthen over the next 24 to 48 hours across the Mozambique Channel. The tropical system is expected to reach peak strength by February 15 with sustained winds as high as 65kts (75mph). Dineo is forecasted to track towards the southwest and make landfall near Massinga, Mozambique - just north of Inhambane by February 16, 00Z (2am Mozambique local time). This system is expected to dump seven to ten inches of rain across the coastal regions and as far inland as Mapai, Mozambique. This amount of precipitation could cause flooding and landslide concerns for the affected locations. Areas from Massinga south to Maputo are forecasted to experience tropical storm force winds for 6 to 12 hours following landfall. The tropical system is expected to dissipate over land by February 17, 12Z. To learn more about other high-impact weather events from across Africa, be sure to click here! ©2017 Meteorologist Ashley Athey  Tropical Cyclone Forecast Track (credit: Joint Typhoon Warning Center) Impressive February Saharan Dust Plume Emerges Off Africa! (credit: UW-CIMSS via Anthony Sagliani)2/6/2017 
DISCUSSION: Although we normally are not captivated by Saharan Dust plumes during the winter months due to other large-scale weather events taking center-stage during the Winter-time months. Having said that, this is still quite an impressive event from a purely atmospheric standpoint due to the fact that this particular dust plume is so large in terms of its overall spatial extent. Often times, Saharan Dust plumes which travel through what is most commonly referred to as the Saharan Air Layer (or SAL) across the atmospheric science community are most important (in terms of their net impacts) during the Summer and Fall months. The reason for this is due to the fact that Saharan Dust plumes often will interact will developing or even mature tropical cyclones both throughout the Tropical Atlantic basin and tropical oceanic basins around the world.
Thus, these dust plumes which emerge off of western Africa will often have what has most often been observed as a "weakening or limiting" effect on the intensity of tropical cyclones. In light of the fact that it is now the heart of Winter across the Northern Hemisphere, there is much less influence in that regard from such a massive Saharan Dust plume such as this one. Nonetheless, several million tons of Saharan dust still is deposited on an annual basis across much of the Amazon River basin and other nearby regions as well. Thus, even if this Saharan Dust plume is not having a truly profound impact on larger-scale atmospheric dynamics and/or atmospheric thermodynamics, there are still other impacts which result from the presence and longer-term evolution of these Saharan Dust plumes. To learn more about other high-impact weather and weather-related events occurring across Africa, be sure to click here! ©2017 Meteorologist Jordan Rabinowitz  DISCUSSION: Though this is not typically a common point of discussion across much of the African continent, a fairly interesting event occurred earlier today. This phenomena which caught the attention of the world news was the confirmed occurrence and touchdown of a sizeable tornado which impacted a relatively small area within South Africa. That being said, despite the historically low frequency in which tornadoes occur anywhere across the entire continent of Africa, there were certainly favorable conditions in place (i.e., in terms of the larger-scale atmospheric flow regime in place within the lower-to-middle parts of the atmosphere.
In looking at the series of three successive images included in the slideshow attached above, you can clearly see the southerly "dip" which is visible in 850 mb geopotential height contours (i.e., the lines which represent the large-scale orientation of atmospheric height values approximately 1 mile above the surface of the Earth). This "dip" in the 850 mb height contours indicated the presence of an enhanced temperature gradient in the lower portions of the atmosphere. This enhanced temperature gradient was facilitated by the particularly persistent southerly transport of warmer air which emanated from the Sahara Desert and collided with cooler air which emanated from areas to the north of northern Antarctica. Thus, the collision of hot/dry, warm/moist, and cool/dry air created a favorable "battlezone" atmosphere which was conducive for the generation of strong to severe thunderstorms. As proven by the image attached above the slideshow, the official confirmation of a tornado occurring quickly went from probable to definite earlier today as a consequence of these combined factors converging. To learn more about other high-impact weather events from across Africa, be sure to click here! ~Meteorologist Jordan Rabinowitz
DISCUSSION: In light of the recent passing of tropical cyclone Fantala, there has been a lot of initial work done with respect to studying the evolution and behavior of this intense tropical cyclone which rapidly strengthened off the coast of Madagascar (relatively close to the Eastern Africa). Here is a fascinating view of this historic tropical cyclone by way of a satellite-derived 72-hour precipitation accumulation graphic! Note the incredibly intense rainfall associated with this particular tropical cyclone! Fortunately, it's land-based impacts were fairly minimal overall. For more neat weather content from across Africa, be sure to click here!
DISCUSSION: Over the past few days, a weak tropical low-pressure moving in a southwesterly direction across the Western Indian Ocean has rapidly strengthened into the most powerful tropical cyclone on-record across the Indian Ocean basin. At its peak intensity, Tropical Cyclone Fantala had maximum sustained winds of 173 MPH with higher gusts! Note the eyewall replacement cycles which occurred during the course of Fantala's period of maximum intensity. This is relatively common with tropical cyclones near the time of maximum intensity as various ambient atmospheric parameters induce slight fluctuations in storm intensity and satellite imagery appearance due to the expansion or contraction of the central dense overcast (the cirrus cloud shield which results from intense thunderstorms which wrap around the center of the tropical cyclone) as well as the aforementioned eyewall replacement cycles which often take place near the time of maximum intensity. Click here for more high-impact weather content across Africa!
 DISCUSSION: Here is a great image from the NASA SNPP/VIIRS satellite depicting a dust storm across the Sahara Desert earlier this week. You can clearly see the large area over which the dust plume covers (i.e., on the order of hundreds or sometimes even thousands of miles). It is also important to note that Saharan Dust has impacts over both North and South America in many different respects!
To learn more about other high-impact weather or weather-related events from across Africa, be sure to click here! ~Meteorologist Jordan Rabinowitz |
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