Well, the 2012 Tropical season of the Eastern Pacific has gotten going. And it's started off with a rifle salute. They've already had their first tropical system of the season, and an invest is threatening to form the second.
Hurristat has OK'd me to start this thread, and I invite him to make any changes he feels necessary to it. This thread is for discussing any tropical activity throughout the globe. Pacific season starts May 15th and runs until November 30th. Atlantic season starts June 1st and also runs until November 30. Only the areas administered by the USA have definite bounds, but in the Western Pacific, it tends to run from early May to mid-December, in the southern hemisphere it ranges from late november to early may, and in the northern indian, activity is most common in may, june, october and november.
The Atlantic season appears as though it's going to be about average/slightly above average, with predictions ranging from 11-14 named storms, 5-7 hurricanes, and 2-3 major hurricanes.
Tropical Storm Alberto, May 19 - May 22
Tropical Storm Beryl, May 26 - May 30
Tropical Storm Aletta, May 14 - May 19
Hurricane Bud, May 21 - May 26
Hurricane Carlotta, Currently active
Tropical Depression 1-W, February 17 - February 21
Typhoon Pakhar, March 24 - April 2
Typhoon Sanvu, May 21 - May 28
Typhoon Mawar, May 31 -
Cyclone Benilde, December 28 2011 - January 5 2012
Tropical Storm Chanda, January 8 - January 11
Subtropical Depression Dando, January 11 - January 16
Cyclone Ethel, January 18 - January 23
Cyclone Funso, January 19 - January 28
Cyclone Giovanna, February 9 - February 21
Tropical Storm Hilwa, February 14 - February 22
Tropical Storm Irina, February 26 - March 10
Tropical Storm 12-S, February 29 - March 3
Cyclone Koji-Joni, March 8 - March 12
The Australian region is confusing because they have several local centers that name storms, so I'll put each list separately but once the storms actually happen, I'll list them under here in the correct order.
Tropical Storm Grant, December 21 2011 - January 2 2012
Tropical Storm Heidi, January 9 - January 13
Cyclone Iggy, January 22 - February 3
Tropical Storm Jasmine, February 1 - February 6
Tropical Storm Hilwa, February 5 - February 14
Tropical Storm Koji-Joni, March 6 - March 8
Cyclone Lua, March 10 - March 18
Tropical Depression 19-S, May 7 - May 14
Papua New Guinea
Tropical Storm Cyril, February 5 - February 8
Cyclone Jasmine, February 6 - February 19
Tropical Storm Daphne, March 31 - April 3
For those of you joining us (not that I expect many, but...), here is a brief summary of the process leading to hurricanes forming.
Generally, a hurricane begins life as a group of large moisture clouds or thunderstorms over the tropics - a "Tropical wave". As these waves evolve and move over the ocean, they will either dissipate, or begin to organize - that is, the clouds and storms merging together into one large area of bad weather formed around one area of low atmospheric pressure.
When that happens, we have a tropical depression. As the tropical depression moves around (usually) over the ocean, it will draw heat and moisture from the warm water on the surface, strengthening, and begin rotating around a central point. The stronger it grows, the more visible the central point - the eye - becomes from space ; if it grows strong enough, with clearly defined features, it may eventually become a hurricane.
If not, it will return to a tropical depression, then eventually become a remnant.
A lot of tropical storms or hurricanes stay out at sea. Others get around to hitting land ; this is called landfall.
In the Atlantic and Eastern Pacific, the United States National Huricane Center is in charge of tracking hurricanes. The US Navy assists in this. They use a variety of computer models to predict how storms may evolve.
As with any other weather forecasting system, this is a bit of a touch-and-go affair : short-term predictions (the next day or three) tend to be pretty good predictions, but longer-term predictions tend to be a little off as often as not, and perhaps more often than not.
When a tropical wave begin to show signs it may become a tropical depression, the navy will call it an INVEST. This is the first sign we usually get we may have a storm about to form.
When a tropical wave actually becomes a tropical depression, the NHC or JTWC will assign it a number - these numbers go in order. So the first tropical depression of the year would be Tropical Depression One, the second Tropical Depression two, etc. For areas outside of the Atlantic, a letter is affixed to the end. For the Eastern Pacific, "-E" is added. For the Central Pacific, "-C" is added. For the Western Pacific, "-W" is added. For the Bay of Bengal, "-B" is added. For the Arabian Sea, "-A" is added. For the Southern Indian Ocean, "-S" is added. For the Southern Pacific Ocean, "-P" is added.
If the tropical depression keeps growing, it will be upgraded to a Tropical Storm, and give it a name. The name comes from a list of names. The Eastern Pacific, Atlantic, and South-western Indian Ocean have alphabetical lists that of which they start at the beginning every season. The Central Pacific, Western Pacific, North Indian, Australian Region, and the South Pacific all have set lists that they rotate through and start at wherever they left off last season
Once a tropical storm grows yet stronger, it will be upgraded to a hurricane/typhoon/cyclone. There are five categories of tropical cyclones; one is the weakest, 5 the strongest. Hurricanes of category three and above are referred to as "Major hurricanes".
After the end of the season, the world meteorological organization will meet and review the season, as well as requests from various countries to have storm names retired.
Storm names are retired when a storm was particularly lethal or damaging (although a country has to request it, and the requesting country has to have been affected by the storm). When a storm name is retired, it will never be used again, and another name will replace it the next time this year's list is used.
The eye is a small area of apparent clear weather in the middle of a hurricane's cloud system.
An invest is an area of the Atlantic where the Navy's weather forecasting services feel there is a risk of hurricane formation. It's generally the first sign we have there are serious chances of a storm forming.
Landfall refers to the EYE (or center, for those storms without eyes) of a hurricane touching ground. Thus, if it's said that a hurricane made landfall in south carolina, that means the eye of the hurricane came overland in South Carolina. Since storms and strong winds extend far from the eye, it's possible for a hurricane to cause damage and casualties without ever making landfall, if the eye remains just offshore.
Organization, with regard to tropical storm, refers to how the various smaller thunderstorms and storm clouds that form the tropical depression/storm/hurricane interact together. The more closely linked (ie, "better organized") they become, the more effective they are at transfering heat (which is what wind is), and the stronger the storm. Losing organization, for a storm, generally means becoming weaker.
A hurricane, when it moves over the ocean, causes the waters of the ocean to rise toward the eye of the hurricane. When the eye come close to the coast, especially when it makes landfall, this cause rapid and significant flooding (somewhat similar to tidal waves) of the affected region. The storm surge is one of the most damaging portion of a hurricane : hurricane Katrina of 2005 had a storm surge of up to 25 feet, which was the primary source of the damage suffered.
A tropical depression is a weather system where clouds and storms have grouped together to form one large storm area. It has yet to acquire the typical "spiral" form of hurricanes, or their eyes, and has winds 38 miles per hour or less (62 KMH). Typically, tropical depressions tend to have comma-like shapes.
A tropical storm is a tropical depression that has become better organized. It has now begun to acquire hurricane-like characteristics, such as a more spiral-like form. Tropical storms generally have winds of up to 73 MPH. (117 KMH). Once a weather system becomes a tropical storm, it gets a name. Tropical storms can be quite deadly, even if they are weaker than hurricanes ; tropical storm Allison killed about 50 and caused for several billions in damage in 2001 in Texas.
A hurricane is a tropical storm that has become further organized, and now has wind of 74 MPH or above. They are subdivided in five categories ; the last three of which are called major hurricanes. Hurricanes tend to have a well-defined spiral forms (the stronger they are, the better defined) with a clear eye in the middle.
Category 1 hurricanes have winds up to 95 MPH. Category 2 goes up to 110 MPH. For major hurricanes, category 3 goes from 111 to 130 MPH, Category 4 from 131 to 155, and anything stronger is a category 5 hurricane.
Wind Shear (sometime simply shear)
Wind shear is the difference in wind strength between different altitudes. Since hurricanes occupy a large area vertically as well as horizontally, large differences between winds five hundred meter above five kilometers above sea level and ten kilometers above can result in a tropical depression, storm or hurricane becoming disorganized (the wind break up the clouds), and therefore beginning to weaken.
A loose gathering of storm clouds around an area of low pressure in the tropical Atlantic sky. If the storm clouds begin to form together and organize, a tropical depression or worse may form.
This, effectively, is the evaporation of ocean water. Obviously, the more convection a tropical cyclone has, the stronger it is and the more likely it is to strengthen. It often arises from an unstable atmospheric environment. If an invest or a tropical depression is said to have a "burst of convection," that means that there is a large chance that it will strengthen in the near future.
The difference between tropical and subtropical storms is that subtropical storms are classified as "cold-core" storms, while tropical storms are classified as "warm-core." It sounds exactly like what it is. There is cold air at the center of the storm in a cold-core system, while a warm-core system has warm air at the center. Subtropical storms also have the majority of their thunderstorms ~100 miles from the center of circulation.
While extratropical storms are NOT named, hurricanes that survive to reach latitudes of 40 degrees or more often transition to extratropical storms. What this is is merely a cold-core system with a front attached to it. Nor'easters that strike New England in the winter are examples of extratropical systems.
Saharan Air Layer (SAL)
I know you look at this and think, whaaa? What does the Sahara have to do with anything? Well, the Saharan Air Layer is well, a layer of air, but it is also extremely dry. It protrudes into the eastern Atlantic. It carries a lot of dust within it. Hurricanes need a relatively wet environment to form/survive, and the SAL can interfere with that process. Dust also reflects a lot of the sun's rays, dropping sea surface temperatures by as much as 1 degree Celsius. This causes obvious problems for hurricanes. The SAL disrupts hurricanes.
Cape Verde Season
The Cape Verde Season is named after the Cape Verde Islands off the coast of Africa. Lasting typically from August through early October, this is the time of year thunderstorm clusters that come off Africa form tropical systems. These are casually called Cape Verde storms.
Cape Verde Storm
Tropical Systems that start off as thunderstorm clusters that come off the African Coast. Many of the strongest storms in the Atlantic Basin were Cape Verde storms. They spend a long time over the warm waters of the Tropical Atlantic before reaching the Americas giving them plenty of time to gain strength.
The region immediately surrounding the eye. This is where the hurricane's strongest winds are found.
Central Dense Overcast
The core of the storm which is solid clouds.
"Arms" of a tropical system. These bands of clouds and rain wrap around the system. It's common for supercells to form within these bands and thus are where most of the tornadoes a landfalling system generates are located.
The exhaust system of the hurricane if you will. Hurricanes draw tremendous amounts of air upwards and it needs to go somewhere. Strong, long-lived hurricanes have outflow where the air escapes horizontally away from the storm. This is usually seen as fibrous cirrus clouds rotating clockwise around the storm. Without outflow, the only place the air can go is down, which can choke off the storm's updrafts. Wind sheer can cut off outflow, which is another reason is weakens tropical systems.
Eye Wall Replacement
A process within very strong hurricanes in which the eye disappears and then reappears. This is usually accompanies with temporary weakening and then restrengthening of the hurricane.
As the term suggests, it's the system strengthening a lot over a short period of time. This process has gained more attention in recent years.
Inter(T)ropical Convergence Zone (ITCZ)
The Intertropical Convergence Zone is where the two most equatorial Hadley Cells meet. What does this mean? A lot of warm air is being pushed down into a small area of air. This destabilizes the atmosphere and helps to create thunderstorms. Do you see satellite pictures where there are thunderstorms over the tropics in a big long line? This is the ITCZ. The ITCZ is below the region of development for hurricanes. So how do they affect hurricane seasons? A low pressure system can spin up out of the ITCZ and become a tropical cyclone.
http://www.nrlmry.navy.mil/tc_pages/tc_home.html - the Navy's hurricane page. This is where invests are announced.
http://www.nhc.noaa.gov/ - the National Hurricane Center
http://www.wunderground.com/blog/JeffMasters/show.html - Jeff Master's tropical weather observations blog at Weather Underground
http://en.wikipedia.org/wiki/Hurricane - The Wikipedia page about hurricanes. Generally more detailed than my summary above.
http://www.prh.noaa.gov/hnl/cphc/ - The Central Pacific Hurricane Center
http://www.usno.navy.mil/JTWC/ - The Joint Typhoon Warning Center
http://www.bom.gov.au/weather/ - The Bureau of Meteorology in Australia, responsible for naming storms within the Australian region.
http://www.jma.go.jp/en/typh/ - The Japan Meteorological Agency, in charge of naming storms in the Western Pacific.
http://www.met.gov.fj/ - Fiji Meteorological Service, in charge of naming storms in the Southern Pacific
http://www.meteo.fr/temps/domtom/La_Reunion/ -- Reunion, in charge of naming storms in the Southwestern Indian Ocean (also, in French, which shouldn't be a problem for Evil Figment, but...)
http://www.tropicwx.com/ -- Satellite imaging for Eastern Pacific and Atlantic, courtesy of Rayne ^^
Latest Satellite Imagery
Tropical Cyclone Climatology
Some of this is adapted from posts by Evil Figment, Big Al, hurristat, and Eredar Warlock.