What is the difference between a typhoon and a hurricane? | Cornell Climate Change Contact What is the difference between a typhoon and a hurricane? Question: What is the difference between a typhoon and a hurricane? Will they be affected differently by climate change? Typhoon Haiyan (NASA photo) Jonathan Comstock, research support specialist in the Department of Horticulture, replies: ‘Typhoon’ and ‘hurricane’ are regional names for the same kind of storm. They are both special names given to tropical cyclones (large regional storm systems forming over warm tropical ocean water and rotating around a central eye) that have grown strong enough to have very damaging effects. If you were somewhere bordering the Western North Pacific Ocean, that is, in the Philippines, the coast of China or Japan, and experiencing such a tropical storm with sustained winds over 74 mph, you would be in a typhoon that has moved off the Pacific ocean and hit land. If you were having a similar experience in the Eastern North Pacific Ocean (Hawaii to the Mexican coast) or in the North Atlantic Ocean (Caribbean, Gulf of Mexico and east coast of North America), you would be in a hurricane.

A ‘Super Typhoon’ is the equivalent of a very strong category 4 or a category 5 Hurricane. Despite being the same as individual storms, there are also some important differences for the people living in these different regions. Because of the very large expanse of warm, tropical ocean in the western Pacific and other global atmospheric patterns, typhoons are more common than hurricanes. On average, there are 25 to 30 storms that rise to the status of a named typhoon every year, and only 6-10 that become named hurricanes. The likelihood of a storm gaining strength to become either kind of named storm depends in part on large-scale atmospheric patterns as well as ocean temperatures. These atmospheric patterns are so large that when conditions are good in the western North Pacific for forming typhoons, they aren’t so good in the North Atlantic for forming hurricanes, and vice versa. For this reason it is not common to hear about major storms occurring in both regions at once. Even though they don’t often happen at the exact same time, both hurricanes and typhoons are most common in the months of June through November.

Around the North Atlantic basin, this period is often referred to as ‘Hurricane season’, and it is relatively unheard of to experience a hurricane mid-winter. Only 4 winter hurricanes have been recorded since 1886. In contrast, although typhoons have the same peak season, they can occur in mid-winter as well and on average there are two winter-month typhoons every year. Is climate change making typhoons and hurricanes worse? This is an area of intensifying study by climate scientists. Because storm systems are so complex, with many interrelated factors affecting their formation and strength, climate scientists are not yet certain about the impact of climate change. Some argue that warming oceans will feed more powerful storms, but others counter that the required atmospheric conditions might be affected by climate change in a way that actually inhibits storm development. The changing balance of all these factors is not yet clear, and could even turn out to be different in different ocean basins. The most recent Intergovernmental Panel on Climate Change concluded that for Atlantic hurricanes, at least, there was a likelihood that climate change might increase the intensity of the biggest storms while the total number of storms could actually decrease.

Tropical Northwest Pacific Ocean Sets Record Historic Tropical Cyclone Drought | The Weather Channel Tropical Northwest Pacific Ocean Sets Record Historic Tropical Cyclone Drought By Jon Erdman and Jonathan Belles Jul 2 2016 11:00 PM EDT weather.com Things We Will Remember About the 2015 Hurricane Season Meteorologist Ari Sarsalari looks at the most interesting aspects of the 2015 hurricane season. 2015 Hurricane Season Storm Chaser Endures Hurricane Patricia! Interesting 2015 Hurricane Season Josh Morgerman On Hurricane Patricia A Look Inside Hurricane Patricia Powerful Hurricane Patricia Makes Landfall The dearth of named tropical cyclones in the tropical northern Pacific Ocean in 2016 has now set a pair of records immediately following one of the most hyperactive years in 2015. (MORE: Hurricane Season Outlook | Hurricane Season Q & A | Debunking Hurricane Myths ) There wasn't a single named storm of at least tropical storm intensity in the North Pacific Basin since Hurricane Pali became a January oddball just north of the equator and well southwest of Hawaii until July 2, when Tropical Storm Agatha developed in the Eastern Pacific.

Most impressive is the lack of a single tropical storm, much less a typhoon (the term for a hurricane in the western North Pacific Basin), west of the international date line since mid-December 2015, in the world's typically busiest tropical cyclone corridor. Year-to-date northwestern Pacific basin tropical cyclones of at least tropical storm strength through July 1 2015 vs. 2016. This has now set a new record for the longest stretch without at least a single tropical storm in the western North Pacific basin in 66 years of records, according to Colorado State University tropical scientist Dr. Phil Klotzbach . The record ended on July 3rd, when a tropical depression developed into Tropical Storm Nepartak, as classified by the Japan Meteorological Agency. Longest Northwest Pacific Stretches Without a Single Tropical Storm (Source: Joint Typhoon Warning Center archive) Start, End Dates Dec.

22, 1997 - July 7, 1998 198 (Note: A correction has been made to the current streak, previously reported to have started on December 15, 2015.) By the end of June 2015, there had already been nine tropical cyclones in the northwest Pacific basin, including three super typhoons of Category 5 equivalent intensity. The eastern North Pacific basin has already set a record long wait for the first tropical storm in 2016. June 21, 2009, was the previous record latest date of the eastern Pacific hurricane season's first named storm (Andres). Reliable records in the eastern Pacific basin date to 1971. Tropical Depression One-E made a failed attempt to become the first of the season in early June. On average, the basin would've seen two named storms, one of which would reach hurricane strength, by late June . Tropical Storm Agatha finally ended this Eastern Pacific record-long wait July 2, becoming the season's first tropical storm, well off the Mexican coast.

Current Satellite Image: Northeast Pacific Ocean The highest cloud tops, corresponding to the most vigorous convection, are shown in the orange and red colors. One year ago, there already had been a pair of Category 4 hurricanes – Andres and Blanca – in the eastern Pacific Basin, and a third named storm, Carlos , also became a hurricane by mid-June 2015. Recommended Articles Five Metro Areas That Have Gone the Longest Without Hurricane Conditions Five Metro Areas That Have Gone the Longest Without Hurricane ... These five metropolitan areas have gone the longest without seeing hurricane force winds. Fueled in part by a record-tying El Niño , the eastern Pacific Basin saw a record nine hurricanes reach at least Category 3 intensity in 2015, as well as the strongest tropical cyclone on record in the Western Hemisphere, Hurricane Patricia . The Central Pacific Basin (from 140 degrees west longitude until the international date line, including Hawaii) also set a record for activity in 2015, with 14 named storms and eight hurricanes, five of which reached at least Category 3 intensity.

At one time, three Category 4 hurricanes were active at once in the central and eastern Pacific basins for the first time on record. — Philip Klotzbach (@philklotzbach) June 23, 2016 How Unusual Is This 'Drought?' This is the first time in records dating to 1950 that the entire North Pacific Basin has failed to generate a single tropical storm from Jan. 15 through June 21, according to Klotzbach (Note: "Agatha" formed on June 13, 1998, putting an end to the previous record streak). (MORE: You Can Help Improve the Historical Record of Hurricanes ) Despite that, these long dry spells have happened before. "These types of tropical cyclone droughts are fairly common when moving away from strong El Niño seasons," said Klotzbach via Twitter. As shown in the previous table, Klotzbach noted the longest such droughts in the western Pacific Basin, including the current event, all immediately followed strong El Niños . "Both the El Niño and the Madden Julian Oscillation (MJO) have tended to force sinking motion over the Northwest Pacific," said Klotzbach.

The MJO is a large-scale, long-period wave of upward and downward motion that propagates around the tropical latitudes. Why has the NW Pacific been so quiet? One reason... anomalous sinking motion has dominated over past two months. pic.twitter.com/BFJSJms4cU — Philip Klotzbach (@philklotzbach) June 14, 2016 This sinking motion leads to drier, more stable air, fewer clouds, showers and anomalously high pressure at the surface over the western Pacific Ocean. All these factors work against the formation of tropical cyclones. Typical tropical cyclone activity by month in the western Pacific basin from 1959-2010. (Paul Stanko/WFO Guam via NOAA/AOML/HRD) The western Pacific Basin is typically the most active area for tropical cyclones on Earth, where named storms, even typhoons, can form any month of the year. As is the case in the eastern Pacific and Atlantic basins, western Pacific activity typically reaches a peak in August and September, so this drought won't last long.

However, with a potential developing La Niña (cooler-than-average equatorial Pacific water; opposite of El Niño) later this summer and fall, Klotzbach also pointed out tropical cyclone activity tends to be less in the Pacific during La Niña years . So perhaps the hard-hit Pacific basin may get a bit of a breather after a frenetic, record-smashing 2015 . Then again, it's important to keep in mind that it only takes one landfall to make any season "active" or "destructive." Published Aug 15 2015 06:53 AM EDT weather.com Follow @wxjerdman EDITOR'S NOTE: The tropical depressions mentioned in this forecast article were upgraded to tropical storms on Aug. 14, and this article is no longer being maintained. Please see our article on tropical cyclones Goni and Atsani for the latest information, or go to Hurricane Central . Just one week after Typhoon Soudelor raked Saipan, Taiwan, Japan's Ryukyu Islands and southeast China, the tropical western Pacific is recharging, with a pair of systems likely to become twin typhoons in the days ahead.

Even as cleanup efforts continue, Saipan is once again under a typhoon watch. The first storm to become a tropical storm would be named Goni. The second would be Atsani. Saipan/Guam Threat The most immediate concern will be with Tropical Depression 16W, the system closer to the Marianas, as it approaches the islands this weekend. The National Weather Service has issued a typhoon watch for Saipan and Tinian, meaning typhoon-force winds of 74 mph or greater are possible within 48 hours. The agency has also issued a tropical storm watch farther south for Guam and Rota. This couldn't be worse news for Saipan, still struggling to recover from Typhoon Soudelor. The Pacific News Center reported about 4,000 households in Saipan, or over 25 percent, have requested assistance from the Federal Emergency Management Agency. Power outages and a lack of running water and food have plagued the 44-square-mile island about 135 miles northeast of Guam since an intensifying Soudelor hit the island square on Aug. 2.

(WATCH: Saipan Struggles After Soudelor ) Tropical Depression 16W is forecast to become a tropical storm and eventually a typhoon as it moves through the Marianas this weekend. Unfortunately, like Soudelor, this new system may begin to undergo a period of rapid intensification just as it crosses the northern part of that island chain, including Saipan. As a result, bands of locally heavy rain are possible Saturday through Monday in Guam and the northern Marianas. In fact, Doppler radar from Guam already indicated a shield of heavier rain pushing toward the Marianas well ahead of the disturbance. This slow-moving system may not clear the islands until Monday. The wind impacts are still quite uncertain at this time, dependent on the degree the system can intensify through Monday. (FORECAST: Guam | Saipan ) Two Threats to Asia Ahead? Once 16W departs the Marianas, or possibly even sooner, rapid intensification is possible, with the system possibly attaining super typhoon status (sustained winds at least 150 mph) about the middle of next week.

Steered by high pressure aloft just south of mainland Japan, this system may eventually pose a threat as a strong typhoon anywhere from the northern Philippines to Taiwan or Japan's Ryukyu Islands, including Okinawa, late next week. Parts of eastern China may be threatened early the next week. But that's just the first system. What about its twin to the east, Tropical Depression 17W? While it's much too far out in time to be certain, current indications suggest the eastern system, instead of following in the wake of the first system, may instead track more toward the northwest next week. This may occur thanks to a weakening upper-level high to its north, shifting instead to its east. This would be well northeast of Saipan and Guam, if it holds true. However, this second system may eventually pose a threat to mainland Japan late next weekend or early in the following week, if the jet stream doesn't curve it into the open waters of the north Pacific Ocean in time. Hurricanes, Typhoons, Cyclones: Definitions and Differences By Rachelle Oblack Updated June 25, 2016.

During hurricane season, you may hear the terms hurricane, typhoon, and cyclone used often, but what does each mean? While all three of these terms have to do with tropical cyclones , they are not the same thing. Which one you use depends on which part of the world the tropical cyclone is in. Hurricanes Mature tropical cyclones with winds of 74 mph or more that exist anywhere in the North Atlantic Ocean, Caribbean Sea, Gulf of Mexico, or in the eastern or central North Pacific Ocean east of the International Date Line are called "hurricanes." As long as a hurricane stays within any of the above-mentioned waters, even if it crosses from one basin to a neighboring basin (i.e., from the Atlantic to the Eastern Pacific ), it will still be called a hurricane. A notable example of this are Hurricane Flossie (2007). Hurricane Ioke (2006) is an example of a tropical cyclone that did change titles. It strengthened into a hurricane just south of Honolulu, Hawaii; then 6 days later crossed the International Date Line into the Western Pacific basin, becoming Typhoon Ioke.

continue reading below our video 10 Best Universities in the United States The National Hurricane Center (NHC) monitors and issues forecasts for hurricanes occurring in these regions. The NHC classifies any hurricane with wind speeds of at least 111 mph as a major hurricane. The NHC Saffir-Simpson Hurricane Scale Category Name Typhoon, Hurricane, Cyclone: What's the Difference? Typhoon, Hurricane, Cyclone: What's the Difference? View Images A girl runs for shelter in heavy rain brought by Cyclone Phailin in the southern Indian state of Andhra Pradesh on October 12, 2013. Photograph by Adnan Abidi, Reuters A massive cyclone that slammed into India's east coast on Saturday has left more than a dozen dead and forced more than a half a million people to flee homes that lie in vulnerable coastal and low-lying areas. Related Content Rare, Colorful Lightning Sprites Dance Over Hurricane "This is one of the largest evacuations undertaken in India," M. Shashidhar Reddy, vice chairman of the National Disaster Management Authority, told reporters in the capital, New Delhi.

"Our priority is to minimize loss of life." Cyclone Phailin (a Thai word for "sapphire") is officially the strongest storm to batter India since Cyclone Odisha made landfall in the same region in 1999 and killed 10,000 people. At the peak of Phailin's power, its winds reached speeds of up to 160 miles per hour (257 kilometers per hour). By Sunday, Phailin's fierce winds had diminished to 80 miles per hour (129 kilometers per hour), and the cyclone's strength continues to lessen as it moves farther inland. If you've never lived in Asia, you might be wondering what it feels like to experience a typhoon. But if you've ever survived a hurricane or cyclone, you already know the answer. That's because hurricanes, cyclones, and typhoons are all the same weather phenomenon. Scientists just call these storms different things depending on where they occur. In the Atlantic and northern Pacific, the storms are called "hurricanes," after the Caribbean god of evil, named Hurrican.

In the northwestern Pacific, the same powerful storms are called "typhoons." In the southeastern Indian Ocean and southwestern Pacific, they are called "severe tropical cyclones." In the northern Indian Ocean, they're called "severe cyclonic storms." In the southwestern Indian Ocean, they're just "tropical cyclones." To be classified as a hurricane, typhoon, or cyclone, a storm must reach wind speeds of at least 74 miles per hour (119 kilometers per hour). If a hurricane's winds reach speeds of 111 miles per hour (179 kilometers per hour), it is upgraded to an "intense hurricane." If a typhoon hits 150 miles per hour (241 kilometers per hour)—as Usagi did—then it becomes a "supertyphoon." Different Seasons While the Atlantic hurricane season runs from June 1 through November 30, the typhoon and cyclone seasons follow slightly different patterns. In the northeastern Pacific, the official season runs from May 15 to November 30. In the northwestern Pacific, typhoons are most common from late June through December. And the northern Indian Ocean sees cyclones from April to December.

Whatever you choose call them, these monster storms are powerful natural events with the capacity to wreak some serious havoc. According to NOAA's National Hurricane Center , the average hurricane eye—the still center where pressure is lowest and air temperature is highest—stretches 30 miles (48 kilometers) across, with some growing as large as 120 miles (200 kilometers) wide. The strongest storms, equivalent to Category 5 on the Saffir-Simpson scale , have sustained winds that exceed 155 miles per hour (250 kilometers per hour). With the aid of satellites and computer models, such storms can be predicted several days in advance and are relatively easy to track. But as Hurricane Sandy showed recently, predicting the path that a hurricane or typhoon or cyclone will take after it's formed is still tricky . Effects of Global Warming? In recent years, scientists have debated whether human-caused global warming is affecting hurricanes by making them stronger or causing them to occur more frequently. (Related: " Rising Temperatures May Cause More Katrinas .") In theory, warmer atmospheric temperatures should lead to warmer sea surface temperatures, which should in turn support stronger hurricanes.

The number of Category 4 and 5 hurricanes worldwide nearly doubled from the early 1970s to the early 2000s. Moreover, both the duration of tropical cyclones and their strongest wind speeds have increased by about 50 percent over the past 50 years. But there is no scientific consensus on a link is between climate change and hurricanes. "Average tropical cyclone maximum wind speed is likely to increase, although increases may not occur in all ocean basins," according to the 2012 Intergovernmental Panel on Climate Change report. (Related: " Leaked Report Spotlights Big Climate Change Assessment. ") "It is likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged." Follow Ker Than on Twitter . Comment on This Story West Pacific Basin Typhoon & Tropical Storm Center - Hurricane 2016 - AccuWeather.com West Pacific Typhoon & Tropical Storm Center No active tropical cyclones 1/18/2017 2:00:00 AM As of Wednesday morning, EST, there are no active tropical cyclones in the Western Pacific Ocean basin, and none are expected to develop for at least the next 24 hours.

By AccuWeather Meteorologist John Schneider Basic Definitions Basic Definitions 1. What is a hurricane, typhoon, or tropical cyclone ? The terms hurricane and typhoon are regionally specific names for a strong tropical cyclone. A tropical cyclone is the generic term for a non-frontal synoptic scale low-pressure system over tropical or sub-tropical waters with organized convection (i.e. thunderstorm activity) and definite cyclonic surface wind circulation (Holland 1993). Tropical cyclones with maximum sustained surface winds of less than 34 kt (39 mph, 17 m/s) are called tropical depressions . Once the tropical cyclone reaches winds of at least 34 kt (39 mph, 17 m/s) they are typically called a tropical storm and assigned a name.

If winds reach 64 kt (74 mph,33 m/s), they are called: hurricane in the North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline, or the South Pacific Ocean east of 160E typhoon in the Northwest Pacific Ocean west of the dateline severe tropical cyclone in the Southwest Pacific Ocean west of 160E or Southeast Indian Ocean east of 90E severe cyclonic storm in the North Indian Ocean tropical cyclone in the Southwest Indian Ocean 2. What is a tropical disturbance, a tropical depression, or a tropical storm ? These are terms used to describe the progressive levels of organized disturbed weather in the tropics that are of less than hurricane status. Tropical Disturbance A discrete tropical weather system of apparently organized convection - generally 200 to 600 km (100 to 300 nmi) in diameter - originating in the tropics or subtropics, having a non-frontal migratory character, and maintaining its identity for 24 hours or more. It may or may not be associated with a detectable perturbation of the wind field.

Disturbances associated with perturbations in the wind field and progressing through the tropics from east to west are also known as easterly waves . Tropical Depression A tropical cyclone in which the maximum sustained wind speed (using the U.S. 1 minute average standard) is 33 kt (38 mph, 17 m/s). Depressions have a closed circulation. Tropical Storm A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1 minute average standard) ranges from 34 kt (39 mph,17.5 m/s) to 63 kt (73 mph, 32.5 m/s). The convection in tropical storms is usually more concentrated near the center with outer rainfall organizing into distinct bands. Hurricane When winds in a tropical cyclone equal or exceed 64 kt (74 mph, 33 m/s) it is called a hurricane (in the Atlantic and eastern and central Pacific Oceans). Hurricanes are further designated by categories on the Saffir-Simpson scale . Hurricanes in categories 3, 4, 5 are known as Major or Intense Hurricanes.

The wind speed mentioned here are for those measured or estimated as the top speed sustained for one minute at 10 meters above the surface. Peak gusts would be on the order of 10-25% higher. 3. What is a super-typhoon ? What is a major hurricane ? What is an intense hurricane ? Major hurricane is a term utilized by the National Hurricane Center and Central Pacific Hurricane Center for hurricanes that reach maximum sustained 1-minute surface winds of at least 96 kt, (50 m/s, 111 mph). This is the equivalent of category 3, 4 and 5 on the Saffir-Simpson scale . Intense hurricane is an unofficial term, but is often used in the scientific literature. It is the same as major hurricane. 4. What is an easterly wave ? It has been recognized since at least the 1930s (Dunn 1940) that lower tropospheric (from the ocean surface to about 5 km (3 miles) with a maximum at 3 km (2 miles)) westward traveling disturbances often serve as the "seedling" circulations for a large proportion of tropical cyclones over the North Atlantic Ocean.

Riehl (1945) helped to substantiate that these disturbances, now known as African easterly waves, had their origins over North Africa. While a variety of mechanisms for the origins of these waves were proposed in the next few decades, it was Burpee (1972) who documented that the waves were being generated by an instability of the African easterly jet. (This instability - known as baroclinic-barotropic instability - is the are where the value of the potential vorticity begins to decrease toward the north.) The jet arises as a result of the reversed lower-tropospheric temperature gradient over western and central North Africa due to extremely warm temperatures over the Saharan Desert in contrast with substantially cooler temperatures along the Gulf of Guinea coast. The waves move generally toward the west in the lower tropospheric tradewind flow across the Atlantic Ocean. They are first seen usually in April or May and continue until October or November. The waves have a period of about 3 or 4 days and a wavelength of 2000 to 2500 km (1200 to 1500 miles) typically (Burpee 1974).

One should keep in mind that the waves can be more correctly thought of as the convectively active troughs along an extended wave train. On average, about 60 waves are generated over North Africa each year, but it appears that the number that is formed has no relationship to how much tropical cyclone activity there is over the Atlantic each year. While only about 60% of the Atlantic tropical storms and minor hurricanes ( Saffir-Simpson Scale categories 1 and 2 ) originate from easterly waves, nearly 85% of the intense (or major) hurricanes have their origins as easterly waves (Landsea 1993). It has been suggested that nearly all of the tropical cyclones that occur in the Eastern Pacific Ocean can also be traced back to Africa (Avila and Pasch 1995). It is currently completely unknown how easterly waves change from year to year in both intensity and location and how these might relate to the activity in the Atlantic and East Pacific. 5. What is a Cape Verde hurricane ?

Cape Verde-type hurricanes are those Atlantic basin tropical cyclones that develop into tropical storms fairly close (<1000 km or 600 miles or so) to the Cape Verde Islands and then become hurricanes before reaching the Caribbean. Typically these occur in August and September, but in rare years (like 1995) there may be some in late July and/or early October. The numbers range from none up to around five per year - with an average of around 2. 6. What is a sub-tropical cyclone ? A sub-tropical cyclone is a low-pressure system existing in the tropical or subtropical latitudes (anywhere from the equator to about 50°N) that has characteristics of both tropical cyclones and mid-latitude (or extratropical) cyclones. Many of these cyclones exist in a weak to moderate horizontal temperature gradient region (like mid-latitude cyclones), but also receive much of their energy from convective clouds (like tropical cyclones).

Often these storms have a radius of maximum winds which is farther out (on the order of 100-200 km [60-125 miles] from the center) than what is observed for purely tropical systems. Additionally, the maximum sustained winds for sub-tropical cyclones have not been observed to be stronger than about (64 kt (74 mph, 33 m/s). Many times these subtropical storms transform into true tropical cyclones. A recent example is the Atlantic basin's Hurricane Florence in November 1994 which began as a subtropical cyclone before becoming fully tropical. Note there has been at least one occurrence of tropical cyclones transforming into a subtropical storm (e.g. Atlantic basin storm 8 in 1973).

Subtropical cyclones in the Atlantic basin are classified by the maximum sustained surface winds : less than 18 m/s (34 kts, 39 mph) - subtropical depression greater than or equal to 18 m/s (34 kts, 39 mph) - subtropical storm Prior to 2002 subtropical storms were not given names, but the National Hurricane Center in Miami issued forecasts and warnings similar to those for tropical cyclones. Now they are given names from the tropical cyclone list. For more information see Penn State University's article on the Subtropical Cyclones . Forecasts are not issued for subtropical cyclones in the Pacific basin. 7. What is an extra-tropical cyclone ? The top schematics show horzontal maps of the surface temperature and wind fields associated with a tropical cyclone (left) and an extratropical cyclone (right). Colors indicate temperature (blue 15C=59F, blue green 20C=68F, green 25C=77F).

Solid lines indicate surface windspeeds - 34 kt=39 mph=63 kph and 64 kt=74 mph=117 kph . The bottom schematics show vertical maps of the pressure surfaces and circulation at the surface and tropopause. An extra-tropical cyclone is a storm system that primarily gets its energy from the horizontal temperature contrasts that exist in the atmosphere. Extra-tropical cyclones (also known as mid-latitude or baroclinic storms) are low pressure systems with associated cold fronts, warm fronts, and occluded fronts. Tropical cyclones, in contrast, typically have little to no temperature differences across the storm at the surface and their winds are derived from the release of energy due to cloud/rain formation from the warm moist air of the tropics (Holland 1993, Merrill 1993). Structurally, tropical cyclones have their strongest winds near the earth's surface , while extra-tropical cyclones have their strongest winds near the tropopause - about 8 miles (12 km) up.

These differences are due to the tropical cyclone being warm-core in the troposphere (below the tropopause) and the extra-tropical cyclone being warm-core in the stratosphere (above the tropopause) and cold-core in the troposphere. Warm-core refers to being relatively warmer than the environment at the same pressure surface (pressure surfaces are another way to represent height or altitude). Often, a tropical cyclone will transform into an extra-tropical cyclone as it recurves poleward and to the east. Occassionally, an extra-tropical cyclone will lose its frontal features, develop convection near the center of the storm and transform into a full-fledged tropical cyclone. Such a process is most common in the North Atlantic and Northwest Pacific basins. The transformation of tropical cyclone into an extra-tropical cyclone (and vice versa) is currently one of the most challenging forecast problems (i.e., Jones et al. 2003).

References: Jones, S.C., Harr, P.A., Abraham, J., Bosart, L.F., Bowyer, P.J., Evans, J.L., Hanley, D.E., Hanstrum, B.N., Hart, R.E., Lalaurette, F., Sinclair, M.R., Smith, R.K., Thorncroft, C. 2003: The Extratropical Transition of Tropical Cyclones: Forecast Challenges, Current Understanding, and Future Directions. Weather and Forecasting, 18, 1052-1092. Merrill, R. T., (1993): "Tropical Cyclone Structure" - Chapter 2, Global Guide to Tropical Cyclone Forecasting, WMO/TC-No. 560, Report No. TCP-31, World Meteorological Organization; Geneva, Switzerland. Web version of Guide 8. What is storm surge and how is it different from tidal surge ? Storm surge is the onshore rush of sea or lake water caused by the high winds associated with a landfalling cyclone and secondarily by the low pressure of the storm.

Tidal surge is often misused to describe storm surge, but storm surge is independent of the usual tidal ebb and flow. In some inlets, such as the Bay of Fundy, rapid changes in sea level due to the tides will cause a tidal bore or surge to move in to or out of the inlet. This surge occurs independently of the present weather. 9. What is a CDO ? CDO is an acronym that stands for central dense overcast. This is the cirrus cloud shield that results from the thunderstorms in the eyewall of a tropical cyclone and its rain bands. Before the tropical cyclone reaches hurricane strength (33 m/s, 64 kts, 74mph), typically the CDO is uniformly showing the cold cloud tops of the cirrus with no eye apparent. Once the storm reaches the hurricane strength threshold, usually an eye can be seen in either the infrared or visible channels of the satellites. Tropical cyclones that have nearly circular CDO's are indicative of favorable, low vertical shear environments. 10. What is a TUTT ? A TUTT is a Tropical Upper Tropospheric Trough.

A TUTT low is a TUTT that has completely cut-off. TUTT lows are more commonly known in the Western Hemisphere as an upper cold low. TUTTs are different than mid-latitude troughs in that they are maintained by subsidence warming near the tropopause which balances radiational cooling. TUTTs are important for tropical cyclone forecasting as they can force large amounts of vertical wind shear over tropical disturbances and tropical cyclones which may inhibit their strengthening. There are also suggestions that TUTTs can assist tropical cyclone genesis and intensification by providing additional forced ascent near the storm center and/or by allowing for an efficient outflow channel in the upper troposphere. For a more detailed discussion on TUTTs see the article by Fitzpatrick et al. (1995). 11. What is the Saharan Air Layer (SAL) ? How does it affect tropical cyclones ? The Saharan Air Layer (SAL) is a mass of very dry, dusty air which forms over the Sahara Desert during the late spring, summer, and early fall and usually moves out over the tropical Atlantic Ocean.

The SAL usually extends between 5,000-20,000 ft (1500-6000 m) in the atmosphere and is associated with large amounts of mineral dust, dry air (~50% less moisture than a typical tropical sounding), and strong winds (~25-55 mph or ~10-25 m/s). The SAL has been shown to have significant negative impact on tropical cyclone intensity. Its dry air can act to weaken a tropical cyclone by inhibiting updrafts in the storm, while its strong winds can substantially increase the vertical wind shear in and around the storm environment. It is not yet clear what effect the SAL's dust has on tropical cyclone intensity, though some studies have suggested that it too may have a negative impact on intensification. The SAL can cover an area the size of the continental U.S. and has been tracked as far west as the Caribbean Sea, Central America, and the Gulf of Mexico. Real-time satellite imagery for tracking the SAL can be found here . References: Dunion, J.P., and C.S. Velden, 2004: The impact of the Saharan Air Layer on Atlantic tropical cyclone activity. Bull.

Amer. Meteor. Soc., vol. 85 no. 3, 353-365. 12. What is the eye ? How is it formed and maintained ? What is the eyewall ? What are spiral bands ? The eye is a roughly circular area of comparatively light winds and fair weather found at the center of a severe tropical cyclone. Although the winds are calm at the axis of rotation, strong winds may extend well into the eye. There is little or no precipitation and sometimes blue sky or stars can be seen. The eye is the region of lowest surface pressure and warmest temperatures aloft - the eye temperature may be 10°C [18°F] warmer or more at an altitude of 12 km [8 mi] than the surrounding environment, but only 0-2°C [0-3°F] warmer at the surface (Hawkins and Rubsam 1968) in the tropical cyclone.

Eyes range in size from 8 km [5 mi] to over 200 km [120 mi] across, but most are approximately 30-60 km [20-40 mi] in diameter (Weatherford and Gray 1988). The eye is surrounded by the eyewall, the roughly circular ring of deep convection which is the area of highest surface winds in the tropical cyclone. The eye is composed of air that is slowly sinking and the eyewall has a net upward flow as a result of many moderate and occasionally strong updrafts and downdrafts. The eye's warm temperatures are due to compressional warming of the subsiding air. Most soundings taken within the eye show a low-level layer which is relatively moist, with an inversion above suggesting that the sinking in the eye typically does not reach the ocean surface, but instead only gets to around 1-3 km [ 1-2 mi] of the surface. The exact mechanism by which the eye forms remains somewhat controversial.

One idea suggests that the eye forms as a result of the downward directed pressure gradient associated with the weakening and radial spreading of the tangential wind field with height (Smith, 1980). Another hypothesis suggests that the eye is formed when latent heat release in the eyewall occurs, forcing subsidence in the storm's center (Shapiro and Willoughby, 1982). It is possible that these hypotheses are not inconsistent with one another. In either case, as the air subsides, it is compressed and warms relative to air at the same level outside the eye and thereby becomes locally buoyant. This upward buoyancy approximately balances the downward directed pressure gradient so that the actual subsidence is produced by a small residual force. Another feature of tropical cyclones that probably plays a role in forming and maintaining the eye is the eyewall convection. Convection in tropical cyclones is organized into long, narrow rainbands which are oriented in the same direction as the horizontal wind. Because these bands seem to spiral into the center of a tropical cyclone, they are sometimes called spiral bands. Along these bands, low-level convergence is a maximum, and therefore, upper-level divergence is most pronounced above.

A direct circulation develops in which warm, moist air converges at the surface, ascends through these bands, diverges aloft, and descends on both sides of the bands. Subsidence is distributed over a wide area on the outside of the rainband but is concentrated in the small inside area. As the air subsides, adiabatic warming takes place, and the air dries. Because subsidence is concentrated on the inside of the band, the adiabatic warming is stronger inward from the band causing a sharp contrast in pressure falls across the band since warm air is lighter than cold air. Because of the pressure falls on the inside, the tangential winds around the tropical cyclone increase due to increased pressure gradient. Eventually, the band moves toward the center and encircles it and the eye and eyewall form (Willoughby 1979, 1990a, 1995). Thus the cloud-free eye may be due to a combination of dynamically forced centrifuging of mass out of the eye into the eyewall and to a forced descent caused by the moist convection of the eyewall. This topic is certainly one that can use more research to ascertain which mechanism is primary.

Some of the most intense tropical cyclones exhibit concentric eyewalls, two or more eyewall structures centered at the circulation center of the storm (Willoughby et al. 1982,Willoughby 1990a). Just as the inner eyewall forms, convection surrounding the eyewall can become organized into distinct rings. Eventually, the inner eye begins to feel the effects of the subsidence resulting from the outer eyewall, and the inner eyewall weakens, to be replaced by the outer eyewall. The pressure rises due to the destruction of the inner eyewall are usually more rapid than the pressure falls due to the intensification of the outer eyewall, and the cyclone itself weakens for a short period of time. 13. What is a moat in a hurricane ? NOAA/HRD The term moat usually refers to the region between the eyewall and an outer rainband, such as a secondary eyewall rainband (see the image above). The moat is the relatively light rain region between the rainband and the eyewall. 14. How do tropical cyclones form ?

To undergo tropical cyclogenesis, there are several favorable precursor environmental conditions that must be in place (Gray 1968,1979) : Warm ocean waters (of at least 26.5%deg;C [80°F]) throughout a sufficient depth (unknown how deep, but at least on the order of 50 m [150 ft]). Warm waters are necessary to fuel the heat engine of the tropical cyclone. An atmosphere which cools fast enough with height such that it is potentially unstable to moist convection. It is the thunderstorm activity which allows the heat stored in the ocean waters to be liberated for the tropical cyclone development. Relatively moist layers near the mid-troposphere (5 km [3 mi]). Dry mid levels are not conducive for allowing the continuing development of widespread thunderstorm activity. A minimum distance of at least 500 km [300 mi] from the equator. For tropical cyclogenesis to occur, there is a requirement for non-negligible amounts of the Coriolis force to provide for near gradient wind balance to occur. Without the Coriolis force, the low pressure of the disturbance cannot be maintained.

A pre-existing near-surface disturbance with sufficient vorticity and convergence. Tropical cyclones cannot be generated spontaneously. To develop, they require a weakly organized system with sizable spin and low level inflow. Low values (less than about 10 m/s [20 kts 23 mph]) of vertical wind shear between the surface and the upper troposphere. Vertical wind shear is the magnitude of wind change with height. Large values of vertical wind shear disrupt the incipient tropical cyclone and can prevent genesis, or, if a tropical cyclone has already formed, large vertical shear can weaken or destroy the tropical cyclone by interfering with the organization of deep convection around the cyclone center. Having these conditions met is necessary, but not sufficient as many disturbances that appear to have favorable conditions do not develop. Recent work (Velasco and Fritsch 1987, Chen and Frank 1993, Emanuel 1993) has identified that large thunderstorm systems (called mesoscale convective complexes [MCC]) often produce an inertially stable, warm core vortex in the trailing altostratus decks of the MCC.

These mesovortices have a horizontal scale of approximately 100 to 200 km [75 to 150 mi], are strongest in the mid-troposphere (5 km [3 mi]) and have no appreciable signature at the surface. Zehr (1992) hypothesizes that genesis of the tropical cyclones occurs in two stages: stage 1 occurs when the MCC produces a mesoscale vortex stage 2 occurs when a second blow up of convection at the mesoscale vortex initiates the intensification process of lowering central pressure and increasing swirling winds 15. Why do tropical cyclones require 80°F (26.5°C) ocean temperatures to form ? Tropical cyclones can be thought of as engines that require warm, moist air as fuel (Emanuel 1987). This warm, moist air cools as it rises in convective clouds (thunderstorms) in the rainbands and eyewall of the hurricane The water vapor in the cloud condenses into water droplets releasing the latent heat which originally evaporated the water.

This latent heat provides the energy to drive the tropical cyclone circulation, though actually very little of the heat released is utilized by the storm to lower its surface pressure and increase the wind speeds. In 1948 Erik Palmen observed that tropical cyclones required ocean temperatures of at least 80°F (26.5°C) for their formation and growth. Later work (e.g., Gray 1979) also pointed out the need for this warm water to be present through a relatively deep layer (~150 ft, 50 m) of the ocean. This 80°F value is tied to the instability of the atmosphere in the tropical and subtropical latitutes. Above this temperature deep convection can occur, but below this value the atmosphere is too stable and little to no thunderstorm activity can be found (Graham and Barnett 1987). References: Graham, N. E., and T. P. Barnett, 1987: Sea surface temperature, surface wind divergence, and convection over tropical oceans. Science, No.238, pp. 657-659. Gray, W.M.

1979 : "Hurricanes: Their formation, structure and likely role in the tropical circulation" Meteorology Over Tropical Oceans. D. B. Shaw (Ed.), Roy. Meteor. Soc., James Glaisher House, Grenville Place, Bracknell, Berkshire, RG12 1BX, pp.155-218. Palmen, E. H., 1948: On the formation and structure of tropical cyclones. Geophysica , Univ. of Helsinki, Vol. 3, 1948, pp. 26-38. 16. What is UTC ? UTC stands for Universal Time Coordinated, what used to be called Greenwich Mean Time (GMT) and Zulu Time (Z). This is the time at the Prime Meridian (0° Longitude) given in hours and minutes on a 24 hour clock. For example, 1350 UTC is 13 hours and 50 minutes after midnight or 1:50 PM at the Prime Meridian. The Greenwich Royal Observatory at Greenwich, England (at 0° Longitude) was where naval chronometers (clocks) were set, a critical instrument for calculating longitude.

This is why GMT became the standard for world time. Meteorologists have used UTC or GMT times for over a century to ensure that observations taken around the globe are taken simultaneously. Local Time Zone

Question: What is the north Pacific equivalent of a hurricane?
Answer: Typhoon