Tag Archive | cyclone center

Do cyclones develop ‘off-season’ in the Atlantic?

NHC_building

Headquarters for the U.S. National Hurricane Center

In the Atlantic, the official dates for the hurricane season are 1 June – 30 November. This certainly doesn’t mean that cyclones only exist during this time frame, yet 97% of all cyclones that have developed have occurred during those months.  While we really won’t know exactly how many cyclones have developed out of season prior to 20th century technological advances, there is evidence of off-season storms in the Atlantic dating back to May of 1771, and more recently tropical storm Beryl in May of 2012. Most cyclones that develop out of season do not typically impact the U.S., but there have been more than handful that have, giving us pause to think what a fickle planet our Earth can be.

Data records of cyclones from the 18th, 19th, and early 20th century have to be taken with a grain of salt, as the technology advancements we enjoy now weren’t available then. However, it is interesting to note that in 1908, not one, but two cyclones developed outside of the seasonal timeline; the first occurred from March 6th-9th and impacted the Lesser Antilles with estimated winds of 100mph (161km/h); the second occurred from May 24th to May 31st with estimated winds of 75mph (121km/h), affecting the Outer Banks of North Carolina. The Outer Banks were impacted yet again in May of 1951 when Hurricane Able made landfall as a category 3 with winds of 115mph (185km/h). Hurricane Alice, a category 1 storm, became the first recorded to exist in two different calendar years, when it developed on December 30th, 1954, and dissipated on January 6th, 1955. This has occurred recently, with tropical storm Zeta developing on December 30th, 2005 and dissipating on January 7th, 2006.

Going back over the past 50 years, there have been several years that have seen more than one cyclone develop out of season; 1969 (2), 1973 (2), 2003 (3), 2005 (2), 2007 (2), and 2012 (2).

Tropical Storm Beryl (May 2012)

Tropical Storm Beryl (May 2012)

Of these years, it is interesting to note that in 2003, tropical cyclones developed both before and after the standard begin/end dates (1 June/30 November). Ana developed in April, and Odette and Peter continued the already lengthened season when they both developed in early December. Also of note is that during the 2012 season, both out of season storms occurred in May within a week of each other (Alberto and Beryl), and both did  impact the U.S. With the vast amount of satellite data stored at cyclonecenter.org, it is possible that you may classify images of Alberto and/or Beryl. The take-home from all of this is that while the majority of cyclones occur within a 5-month window, cyclones can develop any time of year, which is a good reason to stay aware of what is going on in the tropics all year long.

- Kyle Gayan is an undergraduate student in Atmospheric Sciences at the University of North Carolina at Asheville and is also a retired USAF Master Sergeant; his 20 years of service was spent exclusively in the weather career field. He recently joined the Cyclone Center team as a classifier and contributor to our social media.

Featured Storm – Super Typhoon Fengshen (2002)

Origin and Track of Typhoon Fengshen

Origin and Track of Typhoon Fengshen

Typhoon Fengshen was the strongest storm of the 2002 Pacific typhoon season. It developed on July 13 near the Marshall Islands and rapidly intensified due to its small size. Fengshen went from being a tropical depression to a cyclone in only 6 hours. By July 15, Fengshen was given typhoon status, and after initially moving to the north, it turned toward the northwest. On July 18, the typhoon reached its peak intensity of 185 km/h (115 mph), according to the Japan Meteorological Agency; the Joint Typhoon Warning Center (JTWC) estimated peak winds of 270 km/h (165 mph). Disparities like this between agencies are the driving force behind the creation/purpose of  Cyclone Center, and with your help these dissimilarities can be smoothed out. Your classifications are important to us, so we ask that you please take a moment and provide your input on Typhoon Fengshen to help us determine its peak winds.

Typhoons Fengshen (north) and Fung-Wong

Typhoons Fengshen (north) and Fung-Wong (south) undergo the Fujiwhara effect

The JTWC estimated that Fengshen was a super typhoon for five days, which broke the record for longest duration at that intensity. This record would later be tied by Typhoon Ioke in 2006. While approaching peak intensity, Typhoon Fengshen underwent the Fujiwhara effect with Typhoon Fung-wong, causing the latter storm to loop to its south. The Fujiwhara effect is when two nearby cyclonic vortices orbit each other and close the distance between the circulations of their corresponding low-pressure areas. Interaction of smaller circulations can cause the development of a larger cyclone, or cause two cyclones to merge into one.

Fengshen gradually weakened while approaching Japan, and it crossed over the country’s Ōsumi Islands on July 25 as a severe tropical storm. The typhoon swept a freighter ashore, killing four of the 19 crew members aboard. In Japan, Fengshen dropped heavy rainfall that caused mudslides and left $4 million (¥475 million Japanese Yen) in crop damage. After affecting Japan, Fengshen weakened in the Yellow Sea to a tropical depression, before moving across China’s Shandong Peninsula and dissipating on July 28. The typhoon produced strong winds and heavy rain in Japan. A station in Miyazaki Prefecture reported the highest rainfall in Japan with a total of 717 mm (28.2 in). Most of the precipitation fell in a 24 hour period, and the heaviest 1 hour total was 52 mm (2.0 in) in Taira, Toyama. The remnants of Fengshen produced heavy rainfall in northeastern China. The storm affected the capital city of Beijing, becoming the first storm to produce significant impact there since Typhoon Rita in 1972.

- Kyle Gayan is an undergraduate student in Atmospheric Sciences at the University of North Carolina at Asheville and is also a retired USAF Master Sergeant; his 20 years of service was spent exclusively in the weather career field. He recently joined the Cyclone Center team as a classifier and contributor to our social media.

Featured Storm – Hurricane Rita (2005)

Hurricane Rita is now the featured storm from the 2005 record-breaking Atlantic season.  She was the third Category 5 hurricane of the season, producing an estimated $10 billion in damage across the southern United States.

Hurricane Rita at peak intensity in the Gulf of Mexico

Hurricane Rita at peak intensity in the Gulf of Mexico

Less than a month after Katrina had hit the central Gulf region, Rita was in the works.  On September 16th, 2005 a tropical wave interacted with the remains of a trough from a dissipating stationary front. This was her beginning.  The next day, near the Turks and Caicos Islands, this interaction turned into a tropical depression.

The depression started moving westward and Tropical Storm Rita was named that afternoon.  Rita began a rapid intensification phase when she moved through the Florida Straits on September 20th, with a wind speed of over 60 knots. That day she reached hurricane status and peaked at Category 2 intensity on the Saffir-Simpson scale. When Rita entered the Gulf she went from a Category 2 to Category 5 intensity in just 24 hours. This was only the third time in history that two Category 5 storms had been recorded forming in the Atlantic during the same year, and it was the first time that two hurricanes reached Category 5 intensity in the Gulf of Mexico in the same year.  Rita reached her peak intensity on September 24th when her sustained winds exceeded 155 knots.

Track of Hurricane Rita (2005)

Track of Hurricane Rita (2005)

Rita began weakening as she made landfall just east of the Texas/Louisiana border on September 24th.  She was still at tropical storm intensity when she reached northwestern Louisiana later that day,  turning northeastern and merging with a frontal system.  She produced torrential rainfall of as much as 5 to 9 inches in many areas of Louisiana, Mississippi, and eastern Texas. Storm surge flooding and wind damage were some of the major causes of the devastating damage Rita left behind, along with  an estimated 90 tornadoes across the southern US.

Rita was definitely a memorable one.  Luckily, with forecasters being on alert, they evacuated an estimated 3 million people from their homes in preparation for the storm.  Of course, with Katrina only being in the recent past, no one was prepared for the damage Rita would cause.  She was directly responsible for seven deaths, and indirectly responsible for 113.

Go to Cyclone Center today to start classifying Rita.  She was a historic, one-of-a-kind storm. To learn more about her, you can go to US National Hurricane Center tropical cyclone report for Rita.

- Kelly Dobeck is an undergraduate student in Atmospheric Sciences at the University of North Carolina at Asheville.  She recently joined the Cyclone Center team as a classifier and contributor to our social media.  

Hurricane Katrina and the Intensifying Coastal Threat

This week Cyclone Center introduces Hurricane Katrina (2005) as one of our featured storms.  This is the 8th anniversary of Katrina’s assault on the northern Gulf of Mexico coast.  The city of New Orleans, despite a massive system of protective levees and pumps, lost over 1500 souls, almost all from drowning when water flooded about 80% of the city.  Since then,  millions of dollars have been spent on the repair and upgrade of the levee system in and around metro New Orleans.  Are they ready for the next one?

“We’ll be absolutely ready for it,” said U.S. Army Corps communications officer Wade Habshey in a recent Discovery News article. “What we have in place now can withstand a Katrina-level storm.”

New Orleans flooding caused by 60 kt. winds, 10-14 ft. storm surge.  Category-5 values: 150 kt winds, 30-35 ft. storm surge.

New Orleans flooding caused by 60 kt. winds, 10-14 ft. storm surge. Category-5 values: 140 kt winds, 25-35 ft. storm surge.

But what exactly is a “Katrina-level” storm?  Winds in downtown New Orleans rarely exceeded minimal hurricane force at the peak of the event.  Storm surge and the strongest winds from the weakening Katrina were focused well to the east in coastal Mississippi.  And yet levees failed, water flooded significant portions of the city, and over 1,500 perished.

An even bigger concern in the long-term are geological changes occurring in the area; coastal portions of Louisiana are sinking into the ocean as climate-forced sea levels continue to rise and land areas sink.  This exacerbates the threat of  hurricanes for a region that experiences one on average every couple of years.  Many climate scientists now believe that hurricanes will be stronger on average in the future as the ocean, which provides the fuel for the storms, continues to warm.

What more should be done?  Government officials exude confidence that the improvements to the levy system will hold up, but we’ve heard that story before.  Claims were made soon after Katrina that the levee system was designed to withstand a Category-3 storm , not something like “Katrina’s strength”.  We’ve already seen that Katrina wasn’t even a hurricane in New Orleans – what happens when a real Category-4 or 5 storm hits the area?  We can only hope that residents will have left, because it’s a very good bet that there will be little dry land to stand on.

- Chris Hennon is part of the Cyclone Center Science Team and Associate Professor of Atmospheric Sciences at the University of North Carolina at Asheville

New Developments on Tropical Cyclones and Climate Change

One of the goals of the Cyclone Center project is provide a more definitive answer on how tropical cyclones (TCs) have been responding to the dramatic changes that our climate is undergoing.  It is difficult for meteorologists to determine how strong tropical cyclones are getting because we rarely observe them directly, relying primarily on satellite data to give us a decent estimate of the wind speeds.  But as you can imagine, it is very hard to determine the maximum winds in a hurricane when you are in the hurricane itself, let alone flying more than 22,000 miles above it!  Our record of tropical cyclones is by no means nailed down.

http://www.epa.gov/climatechange/images/indicator_figures/sea-surface-temp-figure1-2012.gif

Ocean temperatures have been warming, which provides more energy for tropical cyclones (Image from the EPA)

So people have some differences of opinion on what has been going on in recent years.  Perhaps even more interesting is what will happen in the future.  There are theories that predict the characteristics of tropical cyclones in future years as the rate of ocean and atmospheric warming accelerate.  Most scientists believe cyclones will be more intense as global oceans warm.  There are reasonable disagreements on the number of tropical cyclones forming, since the formation of TCs are sensitive to other things like winds and moisture in the atmosphere.

In the Atlantic Ocean, which of course is of the most interest to the United States and Caribbean nations, the traditional view is that storms will be stronger but less frequent.  A recent study by Kerry Emanuel, a well-respected tropical meteorologist, suggests that we may not be so lucky.  Using the latest high-resolution computer models that simulate TC-like circulations, his results show a 40% increase globally in the strongest TCs (Category-3 or higherand an increase in numbers of TCs in several basins including the North Atlantic.  One has to always be cautious of computer model projections, and it remains to be seen if further evidence comes out to support Emanuel’s conclusions.  But we can accept without doubt that the threat of TCs will remain.

The work of citizen scientists like you on Cyclone Center is already producing results that will help rectify differences in the historical TC record.  As for the future, we’ll just have to wait a little bit on that.

- Chris Hennon is part of the Cyclone Center Science Team and Associate Professor of Atmospheric Sciences at the University of North Carolina at Asheville

Featured Storm – Cyclone Alibera (1989)

Very Intense Cyclone Alibera

Citizen scientists working at Cyclone Center now have four storms to choose from when they sign in to classify.  Our first set of storms includes Cyclone Alibera, a long-lasting Southern Indian Ocean storm that thrashed coastal Madagascar on New Years Day 1990.

The path the Cyclone Alibera followed

The path the Cyclone Alibera followed during the first 3 weeks of its life.  The storm formed in the upper right portion of the map and moved toward the lower left.

Alibera formed in the Indian Ocean on December 14, 1989 and did not dissipate until January 7, 1990 – a whopping 25 days!  During that time, the storm traveled several thousand kilometers, which included a big loop.  Cyclones like Alibera are steered by the large-scale winds in the atmosphere.  Sometimes when these winds are weak and/or changing, storms can move in strange ways.  The first image shows the long and interesting track of Alibera.

During the second week of Alibera’s life, the atmospheric and ocean conditions became very favorable for intensification.  The storm rapidly strengthened from a subdued tropical storm into a minor or very intense tropical cyclone, depending on who you believe.

Two forecast centers tracked Alibera during this time.  The Joint Typhoon Warning Center, or JTWC, is a U.S. Navy and Air Force office in Hawaii that monitors the western Pacific and Indian Oceans.  Based on imagery like those that citizen scientists are analyzing in Cyclone Center, analysts determined that Alibera was a “Very Intense Cyclone”, with wind speeds on the threshold of Category 5 intensity in the Saffir-Simpson scale.   However, analysts at a French forecast centre on La Reunion, an island off the east coast of Madagascar, determined that Alibera was only a minimal Category 1 tropical cyclone at the same time.  The figure below shows that these differences in opinion were not limited to the time of Alibera’s strongest intensity.

Alibera best track intensities

Alibera intensities as determined by JTWC and Reunion forecast centers.

This is why Alibera is one of the first storms that we would like citizen scientists to analyze.  We want to know what YOU think Alibera’s intensity was – we will use this information to reconcile these big differences.

Alibera eventually would make landfall in coastal Madagascar on New Year’s day, killing 46 people.  Though not widely known outside of the southern Indian Ocean region, Alibera is certainly a storm worthy of our attention – and a good example of how tropical cyclone forecasters can wildly disagree on a storm’s intensity when observations are not available.

Log on to Cyclone Center today and classify Alibera.

- Chris Hennon is part of the Cyclone Center Science Team and Associate Professor of Atmospheric Sciences at the University of North Carolina at Asheville

Seasonal Tropical Cyclone Forecasts Are Coming In – But Are They Worth It?

Citizen scientists working on Cyclone Center are working with a few thousand tropical cyclones which have developed since 1978.  Beginning just a few years later, Dr. Bill Gray at Colorado State University (CSU) first began issuing forecasts for the number of tropical cyclones that will develop in the Atlantic Ocean for the upcoming Atlantic season (June 1 – November 30 each year).  Since that time, several other groups, including the U.S. National Oceanic and Atmospheric Administration (NOAA), have also developed similar techniques to predict seasonal activity.  With the official start of the Atlantic season just a couple of weeks away, this year’s predictions are in.

Hurricane Andrew

Hurricane Andrew, a devastating Category-5 storm, occurred during an extremely quiet Atlantic hurricane season.

The CSU forecast, issued in April of this year,  predicts 18 named storms (those achieving at least Tropical Storm strength), 9 hurricanes, and 4 major hurricanes (Saffir-Simpson Category 3 or higher).  This is well above the long-term average for the Atlantic.  The NOAA forecast, which relies on similar parameters to predict activity (e.g. warm ocean temperatures, El Nino phase),  puts the chances of an active season at 70%.  Groups in other parts of the world also produce seasonal forecasts for their own region.  For example, the Bureau of Meteorology in Australia issues a national as well as regional seasonal outlooks.   Recently, other groups such as the United Kingdom Met Office have begun issuing “dynamical” forecasts, which explicitly count tropical cyclone-like features in weather models rather than relating environmental conditions to past activity.

Seasonal forecasts receive quite a bit of publicity, despite questions about their skill and usefulness.    Statistical schemes such as the CSU forecast, rely on past connections between environmental factors and TC activity.  They fail especially in predicting extreme seasons, such as the 1995 or 2005 Atlantic seasons, because the models just don’t know about hyperactive years like that.   Dynamical predictions, which theoretically can predict record breaking years since they do not rely on past seasons, have been shown to have better predictive skill than statistical techniques for seasonal TC prediction.

But even if a model were 100% accurate, would it really make a difference?  The majority of systems that do develop into tropical cyclones do not affect land.  Predictions of landfall are made by several groups but have not shown any skill so far.  For any given location of coastline, the chances of a TC impact in any given year are very small.  So if a homeowner hears that the upcoming season will be active, should any action be taken?  Does it really matter if we’re going to get 12 storms this year or 11?  Remember that some of the most devastating hurricane events in U.S. history, such as Andrew in 1992,, occurred during inactive seasons.  In the end, how do seasonal forecasts help society?

One could argue that any publicity that gets people to assess their readiness is good – but I think that most will not do anything.   Perhaps more effort should be invested in determining how the nature of tropical cyclones will change in our warming world.  Cyclone Center is going to provide researchers with new data that will help determine if and by how much the nature of global tropical cyclone activity has been recently changing.  With stronger tropical cyclones predicted in the Atlantic and other parts of the world – along with rising sea levels – time and energy is better spent developing plans for mitigation for the big ones rather than issuing forecasts with little or no value for coastal residents.

- Chris Hennon is part of the Cyclone Center Science Team and Associate Professor of Atmospheric Sciences at the University of North Carolina at Asheville

How do I classify this? False eyes

One of the challenging aspects of determining the storm type in Cyclone Center is the inability to view a storm snapshot in context.  While classifying a set of images, you do not know which storm you are viewing and how that storm had been evolving before those times shown to you.  This can lead to images that can be misleading to classify – one such image is the “false eye” storm.

A false eye is a circular feature of warm cloud that at first glance appears to be a genuine tropical cyclone eye (the center of a powerful tropical cyclone).  Since we cannot look at other times during the process to see if the feature persists,  we must look for other clues to determine if the feature really is an eye or not.  The primary thing to look for is the storm structure outside of the suspicious eye.  Does the storm look well organized?  Are there distinct and tightly wound spiral bands?  Are cloud tops very cold or not so much?  Consider the following examples, all examined and discussed in the Cyclone Center Talk feature.

Odette (1985)

Odette (1985) The black circle indicates where an eye could possibly be analyzed.  But look at the cloud patterns outside of the “eye” for confirmation.  Here we see no organized spirals and no circular eyewall (the cold ring the typically surrounds the eye).  The clouds are certainly very cold, which is sometimes an indication of strength; but the overall lack of organization leads me to conclude that the “eye” feature is actually just a gap in the cold clouds and not really an eye at all.  I would probably classify this as a weak spiral band type pattern, but nothing more.

Ami (2003)

The second example is from a very complicated cloud pattern, typically seen in what meteorologists call the “monsoon trough” region.  This is an area where the ocean waters are very warm and atmospheric winds tend to come together in the lower atmosphere, creating a situation that is quite favorable for thunderstorms and sometimes tropical cyclones.

Ami_2003_falseeye

The black circle again indicates a circular area of warm clouds that may be mistaken for an eye.  What I immediately notice is that there are two distinct areas of thunderstorms, labeled “1″ and “2″.  Area 1 is showing some signs of organization, shown by the black lines, which indicate a turning or spiraling of the clouds.  Little organization is seen in area 2, which is essentially a large blob of thunderstorms at this point.  The eye in the middle is actually just a gap in between the 2 systems – there is no organization in clouds around this area.

I classified area 1 as a spiral band pattern.  The center of area 1 is probably very close to the circled area (follow the black lines in).  Since we are only classifying one system at a time in Cyclone Center, I ignored area 2.

Keith (1997)

To contrast the two examples above, lets look at a real eye.  Keith was a very strong tropical cyclone that exhibited a well pronounced eye feature.

Keith (1997)

At first glance we immediately notice the features of an eye pattern storm: distinct spiral band features, high degree of symmetry, and cold/circular clouds completely surrounding the eye.  Although there are even better examples of eye storms, I would classify this image as a mid-level eye pattern.  The storm intensity is probably in the Category 2 to Category 3 range on the Saffir-Simpson scale.

I hoped that this helps you to become a better Cyclone Center classifier.  Look for more help articles like this on a more regular basis throughout the next few months.

- Chris Hennon is part of the Cyclone Center Science Team and Associate Professor of Atmospheric Sciences at the University of North Carolina at Asheville

Hurricane Sandy and Climate Change – Checkmate?

During election season I will occasionally tune in to a few of the news networks to get my 10 minute dose of partisan noise.  As Hurricane Sandy churned in the Atlantic and aimed herself at the New Jersey coast, I happened to come across a show that featured an economist and a political analyst discussing the nuances of tropical cyclones and climate change.  I don’t recall exactly what was said, but it went something like this:

Economist: Sandy is huge!  Why isn’t anyone talking about climate change?

Analyst [very eager to break in to the conversation]: “Yes!  Look at Sandy – an ‘S’ storm!  When was the last time we’ve had an ‘S’ storm in the Atlantic?  Usually we only make it to the H’s, or I’s, or K’s.  Look at 1992 – the ‘A’ storm that year didn’t form until mid-August!”

Now I’m sure both of these gentlemen are very bright people and I have a lot of respect for the analyst (when he talks about politics), but having them discuss hurricanes and climate is like me commentating on a grandmaster chess match – I know how the pieces move but that’s only 10% of the battle.

There was nothing particularly unusual about Sandy in the beginning – we have seen plenty of hurricanes form in the deep tropics in October, and she moved and behaved in a pretty typical fashion.  Nor has there been anything outright weird about the 2012 hurricane season in the Atlantic Ocean.   Before the season, every documented seasonal forecast of the number of named storms was above the long-term average, and the season has played out accordingly (even exceeding expectations in many cases).

But a season is usually remembered by one or two storms, and Sandy has made 2012 quite historic.  Weather forecast models accurately predicted days in advance that Sandy would have a major impact on the northeast United States.  And judging by the images and stories coming out of New Jersey, New York, and surrounding states, Sandy lived up to expectations.

As with any major storm or weather event, the inevitable question is asked: “Did climate change cause/enhance this?”  Although a definitive answer is elusive (we don’t have a big enough laboratory to create a “warming free” experiment), we can make a reasonable assessment about some of the factors that probably played a role.

Individual storms such as Sandy respond to the instantaneous ocean and atmosphere environment they find themselves in – or in a way, weather.  Climate is the palette, not the paint; it sets the scene for the actors to do their part.  So what was Sandy’s “scene”?

We know that the world’s oceans are warming – warm water means more energy is available for the hurricane.  We know that sea levels are rising, leading to larger hurricane storm surges.  And we know that coastal development continues to expose millions of people to storms like Sandy.

Most climate scientists believe that we are in for stronger hurricanes in a warmer world and that we are already seeing a move toward this new era.  But our data are just not good enough to know for sure if tropical cyclones have already been becoming stronger.  Almost all tropical cyclones, even in recent years, are not measured directly; and even when they are, we can only measure small samples of these vast storms at any one time.  This is a big reason why there are conflicting accounts on recent tropical cyclone trends.

Cyclone Center was created to help resolve these questions.  By having the public analyze 30+ years of tropical cyclone images, we will provide meteorologists with new data that can be used to reconcile differences in individual storms, as well as long-term trends.

And by the way, the last year with an ‘S’ storm in the Atlantic was 2011.  And that ‘A’ storm in August of 1992, one of only six named storms that year?  Hurricane Andrew, a category-5 storm that devastated South Florida.  To those residents affected by Andrew and Sandy, climate change is a secondary concern.

- Chris Hennon is part of the Cyclone Center Science Team and Associate Professor of Atmospheric Sciences at the University of North Carolina at Asheville

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