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Spawns of El Nino? Hurricanes Iselle and Julio Aim For Hawaii

Cyclone Center is tracking two storms as we classify this afternoon.

It has been quite a remarkable week in the eastern and central Pacific that has culminated in two hurricanes taking aim at the Hawaiian Islands today.  Hurricane Iselle has shown herself to be quite resilient as she has maintained her hurricane strength despite moving over cooler ocean waters.  Hurricane warnings are out for the big island as residents prepare for a significant event.  Meanwhile, Hurricane Julio is following close behind, continuing to intensify despite his movement over cooler waters.  The graphic below from the Central Pacific Hurricane Center shows the likelihood of significant winds over the next few days in the islands:

 

 

Probability of experiencing tropical storm force (>=34 kt) or greater winds from Iselle

Probability of experiencing tropical storm force (>=34 kt) or greater winds from Iselle

The black areas on the graph show where strong winds are certain.  The black area on the left is from Iselle, while the one to the right is from Hurricane Julio.  Unlike his big sister, Julio is not expected to track directly over the big island – but rather miss a bit to the north.

We’ve written about significant Hawaiian hurricanes before.  Most occur during El Nino years, which is a time when the ocean temperatures in the central and eastern Pacific are warmer than normal.  These warmer waters provide additional energy into the tropical cyclones, allowing them to maintain their strength for longer periods of time and to move across wider areas of the ocean.  Usually, ocean temperatures near Hawaii are near 24-25 degrees Celsius (C), which is barely warm enough to sustain a minimal tropical cyclone.  Current temperatures are between 26 and 27 degrees C, making for a much better experience for these tempests.

Head on over the Cyclone Center (cyclonecenter.org) today and join our “2005” campaign as we move towards classifying the intensity of all tropical cyclones that formed during that El Nino year.

Hurricane Iselle heads for Hawaii

Hurricane Iselle heads for Hawaii

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

Early results for Charley and Frances

What a week we had! We had envisioned many classifications, but received so many more! So far we have received more than 11,000 classifications from nearly 2000 users in June. These storms had never been analyzed on CycloneCenter and Hurricane Charley was completed on the first day! Hurricane Frances is nearly complete now. We will likely have more completely new storms this month.

Learning algorithms

There are numerous crowdsourced science projects out there and each have the same goal: To better understand an issue (hurricanes, bats, animal populations, etc.) based on input from numerous clicks and selections from citizen scientists. In addition to the Zooniverse, there are other crowdsourced projects. The concept of learning from a crowd is not new. There are many mathematical and statistical papers available that provide a means to accurately learn the best possible answer based on everyone’s input.

In our analysis, we have used an approach to estimate a probability of a selection based on the selections from individuals, given what those individuals tend to select. It is a pretty complex algorithm that took me a while to understand, so I won’t belabor the point, but provide some links to the papers below. The method described by Raykar et al. is an Expectation Maximization (E-M) algorithm.

Our initial analysis is looking at what type of storm is the cyclone based on the broad categories available: No storm, Curved band, Embedded Center, Eye, Shear or Post tropical. Later, we plan to use this information to estimate of the storm’s intensity.

Hurricane Charley

Hurricane Charley was relatively short-lived: only 6 days so only about 48 images. This means it was completed relatively quickly, contrast that with Frances which has nearly 150 images.

The following graphically denotes the basic selections for Hurricane Charley. The selections (or votes) by citizen scientists are denoted in the lower graph. Each column  is the selections for a given image of a storm. The percentages show what fraction of the citizen scientists selected for an image. The upper graph denotes the probability of the image type based on the selections and the tendencies of the citizen scientists. These are most often 100% of one type, but can sometimes be a “toss-up” (i.e., no clear winner such as the case in the first two images of Charley).

Early results - Charley

Early results of citizen scientist votes and the combined storm type aggregation from a learning algorithm for Hurricane Charley (2004).

Also, there is quite a bit of variance in the selections and no clear time period when the storm had an eye. This is partly an artifact of the satellite imagery. Each pixel is about 8km while operational data available to forecasters can be as high as 1 km for each pixel. Such resolution helps identify small eyes.

Hurricane Frances

Even while Hurricane Frances is available for classifying, the early results are very good. They show a bit more consistency in the selections. Since it isn’t done yet, there are some images with less than 10 classifications, but it looks consistent so far.

Same as above, except for Hurricane Frances (2004).

Same as above, except for Hurricane Frances (2004).

The graph shows large agreement in storm type at various stages of hurricane development. The storm rapidly developed an eye by about day 3. It maintained an eye more most of the time between day 4-9. Then the primary type became embedded center with some selections of other types (e.g., shear). By day 12, the storm had begun to dissipate and was largely being classified as post-tropical or No storm.

Summary

Most of the users this month are new so these results certainly aren’t final. The learning algorithm needs lots more samples from all the new classifiers to more accurately understands their tendencies. As time goes on and those who were active on these storms classify other storms, the E-M algorithm will refine this storm.

Nonetheless, the results are very encouraging. In fact, we’ve made more than 180 of these plots for all storms that are complete (or nearly complete). The next step will be to further analyze the results and see how best to estimate storm intensity from these classifications.

Bibliography

The following papers were crucial in our initial analysis of the CycloneCenter data.

Learning from crowds 2010: VC Raykar, S Yu, LH Zhao, GH Valadez, C Florin, L Bogoni, L Moy, The Journal of Machine Learning Research 11, 1297-1322

This article is the basis for our current algorithm.  At first I used the binary approach to determine which images had eyes. Then I applied the multi-class approach (section 3) for all storm types.

Supervised learning from multiple experts: whom to trust when everyone lies a bit, 2009:VC Raykar, S Yu, LH Zhao, A Jerebko, C Florin, GH Valadez, L Bogoni, L Moy, Proceedings of the 26th Annual international conference on machine learning
This is basically the same method but with a bit more explanation for some aspects of the algorithm. Also, it has a great title.

Trouble in Paradise: Hawaii and Tropical Cyclones

Hawaii – a tropical paradise, full of sun, fun, palm trees, beauty, mountains, volcanoes and more.  But wait…have you ever thought about Hawaii and tropical cyclones?  Although not frequent, tropical cyclones have battered the Hawaiian Islands several times in recent memory.

The 1950’s were a very active period for Hawaiian tropical cyclones.  Hurricane Nina (1957) passed 100 miles west of Kauai, producing winds of 71 knots (kt) on the island of Honolulu. Nina brought heavy rain and wind to the islands, causing over $100,000 in damage.  Two years later, Hurricane Dot (1959) impacted the islands of Hawaii.  Days before landfall, Dot threatened the Hawaiian Islands with maximum sustained winds of 130 kt. However, she made landfall as a Category 1 storm, with gusts up to 87 kt. This weakening in strength lessened the extent of damages, although it left its mark in the form of 6 million dollars in damage.

Iniki passing over the island of Kauai.  Image courtesy of NOAA.

Iniki passing over the island of Kauai.  Image courtesy of NOAA.

Next on the list of memorable cyclones is Hurricane Iwa of 1982. Like Dot, Iwa was also a Category 1 hurricane. The island of Kauai felt the force of Iwa on November 3, 1982. Iwa brought winds of 96 kt., gusts over 104 kt., 30 foot waves, and storm surge.

Following this event, Hawaii was left with 234 million dollars in damages.

10 years later, in 1992, Hurricane Iniki released its wrath on Hawaii. In the Hawaiian language, Iniki means “strong and piercing wind’; this storm truly lived up to its meaning. Its eye passed over and slammed Kauai as a powerful Category 4 hurricane with winds up to 126 kt. Iniki claimed 6 lives and left the citizens of Hawaii to recover from 1.8 billion dollars in damages. Iniki destroyed over 1,000 homes and severely damaged more than 4,000.

To this day, Iniki may still carry a ring that brings back memories of devastation to the citizens of Hawaii.

Structural Damage caused by Iniki's fierce winds

Structural Damage caused by Iniki’s fierce wind.  Photo credit: Nick Galante (Honolulu Magazine)

It remains the strongest storm to date to hit Hawaii. Due to its devastation, the name ‘Iniki’ was retired in 1993.  When the name of a hurricane has been retired, it cannot be used to name other storms for at least 10 years.

Hurricane Flossie (2013) was the most recent cyclone to affect Hawaii. It caused minor damage to the islands.

Visit Cyclone Center today, while there you may get the chance to classify images of Hurricanes Iwa and Iniki.

Davanna G. Saunders 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.

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.

Where did the tropical cyclones go this season?

In short – the western Pacific.

The Atlantic Basin was predicted by many to have an active season. But the season ended November 30th, and it was a very quiet one. There were 13 named storms in the Atlantic, of which two developed into hurricanes.  The Accumulated Cyclone Energy (ACE) Index is used by the National Oceanic and Atmospheric Administration (NOAA) to measure the severity of hurricane seasons.  It considers the intensity and the lifespan of storms.  The 2013 Atlantic season was well below normal; the ACE index came in at 33, about 31% of the 1981-2010 average of 104.

Super Typhoon Dale-one of our featured cyclones this year.

Super Typhoon Dale (1996) was one of our featured storms on Cyclone Center this year.

On the other side of the planet, in comparison to the Atlantic Basin, the western Pacific appears to be the ‘hot spot’ this season for strong tropical cyclones. The western Pacific has seen 31 storms, 13 being typhoons (in this region, hurricanes are called typhoons). This makes the western Pacific season slightly above the 1981-2010 average of 26 named storms. The ACE index for the Western Pacific, however,  stands at 268.3 – about 88% of the 1981-2010 average of 302.

Typhoons such as Lekima, Usagi, Fransico and of course Super Typhoon Haiyan(Yolanda) will be recorded in the 2013 history book.  A super typhoon is a typhoon whose winds exceed 150 mph, equivalent to a Category 4 or 5 hurricane on the Saffir-Simpson scale.

What has contributed to the strong activity seen in the western Pacific this season? A combination of the right ingredients is the answer. A tropical cyclone needs favorable conditions, such as moisture, warm sea surface temperatures, and lack of wind shear in the upper atmosphere in order to aid development. Based on the activity in the western Pacific, it is likely that those conditions were present much of the season.

The 2013 tropical cyclone season was bittersweet for many; those in the Atlantic were glad for a quiet season while many in the western Pacific were forced to make preparations all season. Our prayers are with those affected by these forces of nature.

Visit Cyclone Center to classify many storms including those past storms that formed in the western Pacific, such as: Supertyphoon Dale (1996), Super Typhoon Herb (1996), Typhoon Faxai (2001), Super Typhoon Mike(1990) and more.

- Davanna G. Saunders 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.

Super Typhoon Haiyan Threatens Philippines

Today we urge our Cyclone Center users to pause and send positive thoughts to our friends in the Philippines.

Evacuations are underway as Super Typhoon Haiyan (known as Yolanda in the Philippines) makes its way directly towards the country. Intensifying without restraint since Sunday, Haiyan is now a Super typhoon, which is equivalent to a Category 5 hurricane on the Saffir-Simpson Scale.  Haiyan currently has winds near 170 kt (195 mph).

Super Typhoon Haiyan approaches the Philippines Friday morning with Category-5 winds

Super Typhoon Haiyan approaches the Philippines Friday morning with Category-5 winds

Moving west northwestward, Haiyan is expected to make landfall in the Philippines early Friday morning.  Because of the very warm water temperatures along her path, Haiyan is expected to maintain her status as a super typhoon through landfall.

With this super typhoon comes potentially severe damage.  Haiyan is likely to bring heavy rainfall, severe flooding, damaging strong winds, and mudslides into very heavily populated areas of the Philippines.  The forecasters at the Joint Typhoon Warning Center are encouraging evacuations across the country, especially in the central Philippines, in preparation for the biggest storm of the 2013 season thus far.  She is the fifth super typhoon to form this year in the western Pacific.

- 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

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

A tale of two storms

The mystical nature of tropical cyclones is that they even form at all. They begin as convective cells (what could be called large thunderstorms).  What appears to be a disorganized grouping of storm cells, can organize, begin spinning and in no time, appear to be a fully organized system. Of course there are very technical descriptions as to how this occurs, but from satellite imagery, it can be amazing to watch. While some of the larger convective (colder) cells can appear to be a separate system, they often are actually part of the original circulation. Here are a couple examples recently brought up on the talk forum at talk.cyclonecenter.org, both of which had two significant landfalls.

1989 Typhoon Gay

Time series of the winds associated with Typhoon Gay

Time series of the winds associated with Typhoon Gay

This system was interesting in that it is a system that began in the Gulf of Thailand – considered the Pacific Ocean – then moved west into the Indian Ocean, eventually making landfall in India as – potentially – a very strong cyclone. Of course I must qualify that statement because of the differences in the best track data. The graph at right shows the best estimates of the storm’s intensity, in maximum sustained wind speed. The system gained strength near day 2, then crossed into the Bay of Bengal and regained strength. At landfall in India, it was likely between 70 and 150 knots, kind of a large range. Some of these differences in intensity are due to the data available to each agency. Another could be in the interpretati0n of the imagery.

Typhoon Gay during development

Typhoon Gay during development

A recent talk post from ibclc2 noted the features in Typhoon Gay during its development in the Gulf of Thailand. The organization of the system is beginning to take shape. The convective cell  near B is close to a banding feature (if you were doing a detailed classification). But it is not, since the region between it and the central part of the system is not warm enough (it needs to be red or warmer, see the field guide for more information). The portion near A appears to be an embedded center. But upon further review, there appears a warm spot just north of the darkest blue colors. It could be the beginnings of an eye, but only time will tell … and it does. In the next few images, that small warm spot becomes an eye just prior to making landfall on the Kra Isthmus. So how would you classify it?  Well it’s likely best left as an embedded center with no banding. While there is the hint of an eye, the primary characteristics of an eye (cold cloud surrounding a warm center in a circular fashion) aren’t complete yet.

2005 Hurricane Dennis

Hurricane Dennis in the Caribbean

Hurricane Dennis in the Caribbean

An image of Dennis recently noted by bretarn showed a large system. Similar to Gay above, the satellite image showed a cold center (A) with a large cold band to the east. The convection near A is showing some circulation, so the center is somewhere below that cold cloud cover. So it is an embedded center. Like the Typhoon above, this is an image just prior to an eye emerging. The next question is what to do with B. It is definitely associated with the system, because it appears to be wrapping around the circulation center near A. The region between A and B is warm, with the warmest color being red. So for a detailed classification, this might be considered a banding feature.

In its own right, Dennis was a very severe system, making landfall in Cuba and in the Gulf on the Florida panhandle. However, its fast movement lessened the impact. It is also less memorable because its Gulf landfall was eclipsed by Hurricane Katrina later in the season. Nonetheless, the name was retired from the North Atlantic hurricane names after the season.

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