 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
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 Image: The National Hurricane Center Tropical Weather Outlook on September 7th 2018.  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. If you would like to keep updated on more tropical weather information and stories, click here. © Meteorologist Alex Maynard  While in the heart of the 2018 hurricane season, we have already seen and heard about the powerful effects that these storms possess. Incredible winds, torrential downpours and drastic flooding, hurricanes are already nothing to mess with—a single hurricane that is. What happens when two hurricanes interact with one another and possibly collide?
Sakuhei Fujiwhara, a Japanese meteorologist who made his namesake for the Fujiwhara Effect, may help us answer this question. Sakuhei studied cyclonic vortices closely and discovered that under certain circumstances and if in close proximity, two cyclones can actually orbit one another and eventually converge on the center of their rotation. Dr. Fujiwhara performed numerous experiments and observations on water vortices between 1921 and 1923 and discovered that two vortices would rotate cyclonically about an axis connecting the two vortices’ center. While in Norway studying Meteorology with his advisor, Vilhelm Bjerknes, he constructed a small pool with turbines toward the bottom to replicate the rotation of cyclones. Once turned off, the vortices would freely rotate and had the tendency to orbit about a central point between the two. The two vortices would also tend to approach one another until finally merging. Once rotation began between the two, they would rotate around one another in a counter-clockwise direction (in Northern Hemisphere). The center of rotation is not necessarily the geometric center of the two. Naturally, the stronger vortex or cyclone would have a dominant effect on the weaker one. In the context of tropical cyclones, there is a larger scale to be dealt with. Extratropical cyclones, or mid-latitude cyclones, typically engage in a Fujiwhara Effect-like interaction when they are approximately 2,000 kilometers (1,200 miles) away from each other. For tropical cyclones, or Hurricanes, usually only need about 1,400 kilometers (870 miles) to potentially have some influence on one another. In a world where weird and unpredictable weather can occur, the Fujiwhara effect is an event that is as rare as one would typically hear about it. These events do not happen every year or even every other year. The proper ingredients need to be in place in order for this event to occur and that’s why when it does occur, it is quite the sight to see. To learn more about other tropical cyclone-related stories from around the world, be sure to click here ©2018 Weather Forecaster Alec Kownacki  In tropical cyclone development, one of the main sources that aid in the strengthening process is the transfer of heat from the ocean to the atmosphere. The warm sea-surface temperatures acts as a fuel pump by providing the energy needed for further development. The warmer the sea surface temperatures are in a specific area, the higher the chances the tropical cyclone will strengthen. Now, this also means the system has to be propagating through a very conducive environment with little wind shear and no dry air for strengthening to occur. The transfer of heat is enhanced through evaporation which is the process of when a liquid undergoes a change into a vapor or a gas. The water from the sea surface is evaporated by the hurricane surface winds. The newly formed water vapor is transported into the troposphere or the layer in the atmosphere where most weather occurs. As the heat is transferred into the atmosphere, the tropical cyclone will move out, leaving behind much cooler waters. This is either done by vertical mixing or by the process known as upwelling. Upwelling is when the hurricane surface winds that are blowing cyclonically (counterclockwise) causes the currents at the sea surface to move cyclonically. After this occurs, the Coriolis Force deflects the currents to the right (in the northern hemisphere), and displaces the water outward from the storms center. This allows the cooler water from below to move towards the sea surface to fill the void. Essentially, the tropical cyclone loses its main fuel source. Upwelling typically occurs along coastlines or underneath a slow moving tropical cyclone. Currently out in the western Pacific, we have category 3 typhoon Trami. Before Trami went through a weakening phase yesterday, it was a textbook category 5 super typhoon with a mesmerizing sixty mile-wide eye. Once this powerful storm made a slight turn to the north, it started to slow down in speed immensely. The environment Trami was propagating through was very conducive for further development. However, Trami had nothing in the upper-levels of the atmosphere to steer it towards warmer waters. Due to its slow speed, it started to spin over the same area for a long period of time allowing upwelling to occur. This looks to be the main reason why Trami went through a weakening phase. When a tropical cyclone slows down and sits over the same area, the fuel source from the warm sea-surface waters starts to run out. It initiates the process of upwelling underneath the tropical cyclone which brings cooler waters to the sea surface. When you have those cooler waters underneath a tropical cyclone, it starts to decouple the core of the system. The picture at the top of the article demonstrates that the water temperatures underneath Trami had cooled by about 10 degrees Celsius yesterday as it spun over the same area. Below is a current look via the Himawari-8 satellite imager of Typhoon Trami. Trami is forecast to track towards the Northeast and bring impacts to the southern Islands of Japan. To learn more about other tropical cyclone-related stories from around the world, be sure to click here! © 2018 Meteorologist Joseph Marino  Inside Edge on the Success of the Forecast Track for Hurricane Florence (Image Credit: NWS NHC)9/17/2018 
DISCUSSION: There is no debate that despite the horrific flooding, wind, and storm surge impacts which have unfolded and "revealed their ugly head" in the wake of the landfall and the subsequent gradual weakening of Hurricane Florence, there are still parts of this tropical cyclone which are going to be looked more highly upon. Once such issue happens to be the evolution of the forecast track of Hurricane Florence in the days leading up to the first and final landfall which occurred in the vicinity of Wrightsville Beach, North Carolina. It goes without saying that there were great strides made by the operational forecasters at the NWS National Hurricane Center located in Miami, Florida along with other regional National Weather Service forecast offices. However, one question which has been circulating around social media rather quickly is regarding just how good the forecast track projections for Hurricane Florence actually were when all was said and done?
Attached above is a brief video briefing which goes into greater detail regarding just how good the evolving forecast track of Hurricane Florence actually was throughout its lifetime. Note how good the future forecast track was during the latter part of the forecast track in the days leading up to landfall of Florence and what this may mean in a positive sense for atmospheric science moving forward in time! To learn more about other tropical cyclone-related stories from around the world, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz  DISCUSSION: Major Hurricane Florence is taking aim at South Carolina, North Carolina and Virginia towards the end of the week. As of 5:00 PM on 10 September 2018, Hurricane Florence is a category 4 storm with sustained winds of 140 miles per hour. South Carolina, North Carolina, Virginia and, most recently, Maryland have declared a State of Emergency in preparation of Florence. Mandatory evacuation stretches from South Carolina, through North Carolina into Virginia. Know your zone if you live in an evacuation area so when the order comes in, you are ready to evacuate. The main threats associated with Hurricane Florence are high winds, high surf, storm surge, and torrential rain. Florence is not only a coastal storm as it will impact inland areas as well. People in Southwestern Virginia are on alert as Florence has the potential to drop feet of rain which can cause not only flooding but also landslides.
Hurricane Florence is currently (as of 6:45 PM EST on 10 September 2018) located southeast of Bermuda. It is expected to head westward towards the Carolinas. Pinpointing the exact landfalling location is still difficult; however, areas along the coast will feel the impact starting Wednesday. Tropical storm force winds have the potential to extend outward to West Virginia and Kentucky. Unfortunately, current models are hinting at a slowing storm once Florence makes landfall which means the storm will sit over the Mid-Atlantic for days and dump inches, potentially feet of rain. In preparation for Hurricane Florence, you will want to heed the warnings. Ensure you are paying attention to the forecast in case it makes a drastic change. You will also want to go to the grocery store and get things that you’ll need should the power go out for a long period of time. This can include a first aid kit, canned food, water, flashlights, batteries, portable chargers, and also things for your pets and children. If you need to evacuate, make sure you take a video record of all of your belongings should you need to make an insurance claim. Stay up to date on the latest details regarding the status of Hurricane Florence at www.globalweatherclimatecenter.com/tropicalcyclones and www.twitter.com/gwccwx. ⓒ 2018 Meteorologist Brandie Cantrell  DISCUSSION: Tropical Storm Gordon made landfall near the Alabama, Mississippi state line just before midnight local time on Sept. 4th, 2018. Although Gordon is no longer classified as a tropical system, its remnants are still producing heavy rainfall and flash flooding. As Gordon slowly moved to the north, northwest into Arkansas and southern Missouri the tropical depression interacted with a stationary front, becoming a post-tropical system with frontal boundaries. As of 1800 UTC the Weather Prediction Center, or WPC, had the center of the now post-tropical system located over southern Illinois and are forecasting it to track east, northeast through the Ohio River Valley. 24 hour rainfall totals are expected to exceed two inches from central Indian to central Pennsylvania, with totals exceeding four inches over central eastern Ohio and western Pennsylvania.
The system has also prompted the WPC to issue numerous Mesoscale Precipitation Discussions, or MPD, with one currently focused over the Ohio River Valley, see above image. Within this region expect embedded regions of extreme rainfall, with rainfall rates possibly exceeding three inches per hour. Rainfall rates close to this have already been recorded in Mount Vernon, IL, where 2.41 inches of rainfall was measured in one hour. In addition to the embedded regions of extreme rainfall, prolonged rainfall is also a concern. The continuous rainfall could lead to three to four inches of rainfall occurring over the next six hours across the region. Such rainfall rates and totals could lead to localized flash flooding and rivers and streams overflowing their banks. Remember to be alert and if you see flooded road ways turn around and find an alternate route. Although the immediate impact from the system is heavy rainfall and flooding near its center and to its east, another threat is the development of showers and thunderstorms along its cold front, across the Lower and Mid-Mississippi Valley. These storms are not likely to be severe, though there is a slight chance of localized strong winds. The largest threat will be flash flooding due in part to the already saturated conditions from the first round of rain from Gordon. Another factor is the effects the daytime heating will have in combination with the tropical moisture being supplied by the post-tropical system. Such a combination could lead to hourly rainfall rates exceeding two inches and has resulted in an additional MPD being issued for eastern Arkansas. Aside from the flash flood threat, the rain from the remnants of Gordon has been and will continue to impact American Football games. Currently, none of the college games have been postponed due to the rain, though the wet conditions have resulted in dropped balls and missed kicks. The larger impact on the sport will likely be tomorrow, Sunday Sept. 9, when the Cleveland Browns play the Pittsburgh Steelers. Heavy rainfall is excepted across the Cleveland region, with winds gusting to 40 mph. These conditions could result in the postponement of the game, though currently the game is expected to start as scheduled. To stay update with the rainfall associated with the remnants of Gordon go to https://www.wpc.ncep.noaa.gov To learn more about other high-impact tropical cyclone stories from around the world, be sure to click here! © 2018 Meteorologist Sarah Trojniak  DISCUSSION: On Saturday, September 1, Tropical Storm Florence was officially declared a tropical storm just west of the Cape Verde Islands in the Atlantic Ocean. The storm started as a tropical wave over Senegal in Western Africa which was first detected on August 28 as an area of low pressure. Florence then became Tropical Depression Six as it crossed over warm water and gained momentum over the Cape Verde Islands on Friday, August 30. Florence is the sixth named storm in a hurricane season which has had a large amount of Saharan dust which has led to an increased persistence and depth in the level of dry air in the atmosphere for much of the summer. This layer of dry air inhibits the formation of hurricanes over much of the Tropical Atlantic Basin in most circumstances.
On Wednesday, September 5, Florence gained strength from a Category 1 hurricane to a major Category 4 hurricane with windspeeds of 130 mph. By the rapid intensification, Florence officially becomes the first hurricane of the season to be at Category 3 or higher. Florence increased in intensity due to warmer sea-surface temperatures as well as encountering low vertical wind shear. Sea-surface temperatures are one of the key components as warmer sea-surface temperatures lead to higher amounts of evaporation which then leads to condensation and the release of heat which leads to even more water being evaporated. A low shear environment is the other key fundamental ingredient for hurricanes as a high amount of vertical wind shear would often have the effect of disrupting and tearing apart convection within the core of a hurricane due to the change in both wind speed and wind direction. However, Florence encountered strong directional shear on Thursday, September 6, as an area of high pressure to the north weakened and moved away which in turn also decreased the wind speed. The shear and decrease in wind speed led to Florence being downgraded from a Category 4 hurricane to a Tropical Storm on September 6. The latest forecast track from the National Hurricane Center (NHC) has Florence traveling west-northwest re-gaining strength. The newest track has Florence going towards the eastern coast of the United States with much of the southeast from Florida to Virginia within the cone of uncertainty. The cone of uncertainty is the cone which shows the area where the different models forecast the area where the tropical cyclone will travel with the edges being the most extreme models. The regain in strength is due to a decreasing shear and a climb in sea-surface temperatures in its west-northwesterly course. The tracks for much of the past few days had Bermuda possibly being hit before Florence hit the large area of shear on September 6. As of right now, there are no warnings as Florence is not expected to come close to land until at least Wednesday, September 12. To learn more about other high-impact tropical cyclone stories from around the world, be sure to click here! © 2018 Meteorologist JP Kalb 
DISCUSSION: Over the past couple of days, there has been an increasing amount of attention paid to the development and intensification of Hurricane Florence which remains at major hurricane status as of earlier on Wednesday night (09/05/2018). Having said that, there is a lot of reason to be as well as to not be overly concerned at this point with regard to the future track of Hurricane Florence. First off, let's establish the reasons for why someone living in Bermuda and/or somewhere along the East Coast of the United States will definitely want to continue paying attention to the future intensity and track of this hurricane which is currently spinning over the open waters of the eastern Tropical Atlantic Ocean basin.
For starters, the fact is that this is indeed a major hurricane as of tonight and therefore represents a certainly dangerous natural hazard to anyone in its path as long as it maintains a similar intensity moving forward. In addition, even if it continues to weaken a bit more, this would still be a relatively larger tropical cyclone with plenty of rainfall and more than likely a decent storm surge tied to it as well. Therefore, as with any tropical cyclone, Hurricane Florence should continue to be taken seriously even despite some apparent weakening and structural breakdown being observed with it tonight in the wake of increasing southwesterly vertical wind shear. It is worth noting that the environment both right along and around Hurricane Florence will likely improve a bit within the next 24 to 36 hours as well, so the storm may still have an opportunity to re-gain some of the "steam" it lost during the evening of 09/05/2018. Now, on the flip-side, here are some reasons for why anyone potentially in the future path of Hurricane Florence should not be worrying too much just yet. As reflected in the content of the spectacular tweet which has been attached above (courtesy of Meteorologist Stu Ostro from The Weather Channel), there are a number of other atmospheric components which may very well end up changing the future track and speed of Hurricane Florence as it continues on its current northwest track. For example, the larger trough which is currently positioned over north-central Canada could quite possibly help to nudge Hurricane Florence further offshore if it ends up reaching the Eastern United States well prior to the closest future approach of Florence to the East Coast of the United States. In addition, the couple of other smaller systems which are identified on this same graphic and noted accordingly, could potentially help to break down the ridge of high pressure which is currently in place over southeast Canada. If that were to happen, then this would make the trough that much more influential in being able to nudge any reasonably close approach of Hurricane Florence much further offshore. However, at this point in the forecast process, all of these factors are simply VERY far out in the future as of the present time. Therefore, it would simply be foolish and premature to read into any of these possibilities this far out from any possible impacts which would still be at least 7 to 10 days away from now. To conclude in short, as always at the Global Weather and Climate Center, we will continue to keep you updated as this situation evolves so stay tuned for further updates on the future of Hurricane Florence as the storm's future evolves. To learn more about other high-impact tropical cyclone stories from around the world, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz |
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