The 2012 Tropical Cyclone Summary

 

   Today marks the end of 2012; it also marks the end of the 2012 Tropical Cyclone season. The season began with Tropical Cyclone Alenga in the South Indian Ocean on December 5, 2011 and ended with Tropical Storm Wukong on December 28, 2012. There have been a lot of notable storms this year in all basins, most notably in the Atlantic and Northwest Pacific (as usual). So, here is a summary of the most significant storms of the year, in my opinion, organized by basin. The number of storms listed for each basin is somewhat a reflection on the activity there, so the North Indian had only four storms, so it has just one entry. By contrast, the Northwest Pacific had twenty-seven storms, so it has four entries. The criteria used in making this list is primarily based on the human and economic damage due to a storm, followed by wind speed, central pressure, and storm size. Finally, any meteorologically or climatologically (i.e. records) interesting aspect is taken into consideration. In addition to these listed storms will be an “honorable mention” storm for each basin, which was in some way interesting, even though it might not have necessarily had a large impact. Due to its record breaking season, the Atlantic basin is covered last and is presented differently. Most of the images used were taken from Wikipedia, and the satellite images were originally captured by the MODIS instrument package on board the Aqua and Terra satellites.

 

SOUTH INDIAN

Alenga began the 2012 South Indian season in early December, 2011. By its unusually late end in June, the basin had witnessed 16 storms, 8 reached Tropical Cyclone strength (>64kts), and 2 reached category 3 (equivalent to a major hurricane).

Tropical Storm Irina:

29 FEB-10 MAR
MAX 60kts 
Irina’s impact came not from particularly high winds, but from its track. While fluctuating between tropical storm and tropical depression status, Irina tracked right along the coast of Madagascar from its northern most point to its southwest. It also brought heavy rains to parts of Mozambique and South Africa. It was by far the Deadliest Tropical Cyclone of the season.

 

Cyclone Funso:

19-28 JAN
MAX 120kts 
Category 4 Cyclone Funso was the second most intense storm of the South Indian season, as well as the second deadliest. Its largest impact was on Mozambique in the form of large floods after the storm stalled of its coast for over two days.

 

Cyclone Giovanna:
09-21 FEB
MAX 125kts
Giovanna was the strongest storm of the season and was highly resilient. Not only did it survive passing over Madagascar, it managed to regenerate and track around the island and nearly passed over its own track from days earlier.

 

Honorable Mention: Kuena:
06-07 JUN
MAX 50kts 
Although only a medium strength tropical storm, Kuena is notable as being one of the most out of season storms on record, having formed about two months after the season’s official end.

 

 
SOUTH PACIFIC

The 2012 South Pacific season was very quiet, with only four storms. It didn’t begin until early February, but lasted until July.

Cyclone Jasmine:
04-15 FEB
MAX 115kts 
Jasmine was a very long-lived, category four tropical cyclone that ended up affecting five different countries. Although no deaths were reported, significant damage occurred across a wide area, especially to crops.

 

Honorable Mention: Twentyone:
29-30 JUN
MAX 35kts
Tropical storm 21P was a short lived, but very late storm that formed just to the southeast of Papua New Guinea.

 

NORTHWEST PACIFIC

The Northwest Pacific was very active this year with 27 Tropical Cyclones, of which 16 reached Typhoon strength, and 5 of those reached Super Typhoon strength. These numbers are actually quite average, what made this year notable was in the details.

Super Typhoon Bopha:

25 NOV-09 DEC
MAX 140kts 
Bopha formed very close to the equator late in the season. It became a category five storm while at only 7.4 degrees north, making it the second closest storm to the equator of that strength to exist on record. Bopha also became the strongest storm to ever make landfall on the southern Philippine island of Mindanao. As of 12/31/12, it is responsible for over 1000 deaths and $900 million (2012 USD). It is now listed as the costliest Philippine typhoon.

 

Typhoon Haikui:
02-08 AUG
MAX 65kts 
While only a category 1 storm, Haikui was by far the costliest storm of the year. It was also the third tropical cyclone to impact mainland China in a week’s time. Hundreds of thousands of people evacuated and over 100 deaths were reported.

 

Super Typhoon Sanba:
10-17 SEP
MAX 150kts 
Sanba holds the title of the world’s strongest Tropical Cyclone of 2012, with maximum winds of 150kts. Luckily, only a total of 6 people killed by Sanba, but it caused over $350 million (2012 USD). It was the fourth storm of the year to hit Korea, something that has not occurred for fifty years.

 

 

Typhoon Bolaven:
20-28 AUG
MAX 125kts 
This large storm followed a somewhat similar path as Sanba but was considerably weaker. However, Bolaven is responsible for more damage with over 80 people lost and over $470 million (2012 USD) in damages. It is notable in that several times during its life multiple eyewalls could be observed from both satellite and ground radar.

 

Honorable Mention: Tembin:
19-30 AUG
MAX 115kts 
Typhoon Tembin’s track is incredibly unique. It made landfall first on Taiwan but emerged back over water to the west of the island and managed to reorganize some. It drifted to the southwest and made a counter-clockwise loop while interacting with Bolaven, who was currently developing to the east. It began to move back towards Taiwan, but by the time it made a second landfall, it was under heavy shear due to outflow from Bolaven, which was now to its north-northeast. Once past Taiwan, Tembin accelerated northward and made landfall as a tropical storm over South Korea, just a few days after Bolaven had pasted through the region.



At this time, Tembin (bottom left) and Bloaven (top) were interacting with each other and affecting each other's movement

 

NORTHEAST PACIFIC

The Northeast Pacific basin had a relatively average year that began right on time and ended a little early. In all, 17 named storms formed, 10 of these became hurricanes, and 5 of these became major hurricanes.

Hurricane Carlotta:

14-17 JUN
MAX 90kts 
This category two storm occurred in mid-June and ended up being the most destructive storm of the season, impacting much of coastal southern Mexico. One factor in how much damage it caused was that its track was nearly parallel to the coastline, bringing heavy rains to a large area. Carlotta is responsible for 7 deaths and over $107 million (2012 USD).

 

Hurricane Paul:
13-17 OCT
MAX 105kts 
Paul was a category three major hurricane that significantly impacted the Baja California Peninsula. Although it had degenerated into a remnant low by the time it got to land (but never actually made landfall), it brought heavy rains across the southern peninsula triggering minor flooding and a few landslides. No one was killed, but over $15 million (2012 USD) of damage occurred.

 

Hurricane Emilia:
07-15 JUL 
MAX 120kts 
While Emilia never made landfall or caused any damage, it was the strongest storm of the season in the NE Pacific (and the Atlantic for that matter). What is really interesting is that the remnants of the storm persisted in a very disorganized area of rotation all the way across the Pacific and eventually helped form Typhoon Damrey.

Honorable Mention: Hector:

11-17 AUG
MAX 40kts
Hector never became anything more than a weak tropical storm, but its origins are rather interesting. A day before the Tropical Depression that would become Hector formed, Hurricane Ernesto had dissipated over southern Mexico. Ernesto’s remnants moved across Central America and as it emerged over the East Pacific it began to organize. A few hours later and what had been Ernesto was now Hector.

 

NORTH INDIAN

The North Indian Ocean basin has been particularly quiet this year without a single storm strengthening past tropical storm status. In fact, the first storm didn’t even form until late October. However, as usual, even weak storms have big impacts.

Tropical Storm Nilam:

29-31 OCT
MAX 55kts 
Nilam formed in the Bay of Bengal and ended up significantly affecting southern India and Sri Lanka with widespread flooding. All told, 75 people died and over $55 million (2012 USD) in damages occurred.

 

Honorable Mention: Murjan:
24-25 OCT
MAX 35kts 
This tropical storm, which formed in the Arabian Sea, made landfall in Somalia as a weak system. In a strange reversal from what is usually associated with tropical cyclones, this storm brought beneficial rains to parts of the region.

 

NORTH ATLANTIC

There is no easy way to classify the Atlantic basin’s eventful 2012 season. Instead, I’ll post an image and the name of each storm this season in the order of their formation. For a through summary of the season and all the interesting details I suggest the Wikipedia article on the season at http://en.wikipedia.org/wiki/2012_Atlantic_hurricane_season.

 

Tropical Storm Alberto

 

 

 Tropical Storm Beryl

 

 

Hurricane Chris

 

 

 Tropical Storm Debby

 

Hurricane Ernesto

 

 Tropical Storm Florence

 

 Hurricane Gordon

 

 Tropical Storm Helene

 

 Hurricane Isaac

 

 Tropical Storm Joyce

 

 Hurricane Kirk

 

 Hurricane Leslie

 

 Hurricane Michael

 

 Hurricane Nadine

 

 Tropical Storm Oscar

 

 Tropical Storm Patty

 

 Hurricane Rafael

 

 Hurricane Sandy

 

 Tropical Storm Tony

Cyclonic Ignition in the Southern Tropics

   Over the past few days the Southern Hemisphere has exploded with activity. At the time of this post, there are four Invest areas in the South. Three of these were identified within twenty four hours of each other. The fourth is a large region of disturbed weather that has persisted for many days, but is taking awhile to organize due to its size. Two of these areas are likely due in part to a somewhat active Madden-Julian Oscillation, or MJO. The MJO is a large scale eastward moving pulse of active weather and cloudiness that is centered on the equator and is most prevalent over the Indian Ocean and the West Pacific Ocean and recurs every thirty to sixty days on average. The details of this phenomena are a bit complicated to explain and it is currently a very active topic of research. Below are some images of the four Invest areas gathered from the NRL Monterey Marine Meteorology Division TC PAGES Page.



INVEST 94P
This is the large disturbance that has persisted for days, it currently has a high probability of becoming a Tropical Cyclone.



INVEST 95S
This disturbance, which is located between Indonesia and Australia, has developed very rapidly.



INVEST 96S
96S is not very well consolidated, but the structure that does exist is well organized.



INVEST 97S
This is the newest disturbance located in the Indian Ocean a little west of Indonesia.



Here is the map of the four Invest areas. From left to right: 96S, 97S, 95S, and 94P.



Finally, here is a image of the Indian Ocean. On the equator near the center are 96S and 97S and 95S can be seen on the far right. Notice the area of active weather and cloudiness, including 96S and 97S, near the equator, to the south and southeast of India. This zone is likely the current location of the MJO pulse.

101: Geostrophic Balance

               In the last post I mentioned the Coriolis Force and its role in adding ‘spin’ to weather. There are also several other forces that shape the weather, some more important than others. Perhaps the most important force, maybe even more important than the Coriolis, is the pressure gradient force (I’ll be calling it PGF). This force results from the differences in pressure from one place to another. It is somewhat analogous to water in hilly terrain; the tops of hills are like high pressure centers and water flows down them to the valleys and lakes below, which are like troughs and low pressure centers, respectively. Thus, air is forced toward areas of low pressure and away from high pressure. One important detail about PGF is that unlike the Coriolis Force, it can affect the speed of air, since in the absence of all other forces air would accelerate toward low pressure centers. When these two forces become balanced the air flow is said to be in Geostrophic Balance. The best way to describe what this condition means and how it comes about is with a series of diagrams.

 

               The simple hypothetical initial state is some level in the mid to upper troposphere where pressure contours run right-left (east-west) with low pressure at the top (north) and high pressure at the bottom (south). These diagrams are assumed to be in the northern hemisphere, as are all my other discussions and diagrams unless otherwise specified.

 

               Now, a small piece of air (typically called an air parcel, here represented by a black dot) is placed in this pressure field. It is being affected by the PGF (symbolized by the arrow with PGF next to it) which is exerting a force toward the low pressure in the north. Note that since the parcel has yet to begin moving, it is unaffected by the Coriolis Force.

 

               Now, the parcel has begun to accelerate thanks to the PGF and has some forward speed (symbolized by the arrow with a V next to it). Since it is now moving, the Coriolis Force (symbolized by the arrow with a C next to it) will begin deflecting it to the right (east), even though the force is minimal since the parcel has not gained much speed. It is important to note that the Coriolis Force always exerts a force 90 degrees to the right of the direction of motion.

 

               Here, as the parcel continues to pick up speed it has been deflected to the right. Note that the angle between the PGF and the direction of the parcel’s motion has increased. Therefore, the amount of the PGF that is affecting the speed of the parcel has decreased.

 

               The parcel is now highly deflected to the right due to the Coriolis Force and the amount of the PGF that influences the parcel’s speed is very small.

 

               Finally, the parcel is at a right angle to the PGF, so it no longer causes the parcel to accelerate. Now, all of the force is now being exerted to parcel’s left (north), and the Coriolis Force is exerting a force on the parcel to its right (south). At this point, the forces are in geostrophic balance. Therefore, in the absence of other forces, the parcel will continue to move to the east parallel to the pressure lines, and at a constant speed.

               This balance explains why air travels clockwise around a high and counter-clockwise around a low, since those are really like the diagrams above, just curled up. Geostrophic balance is a great way to estimate roughly the direction of wind based solely on pressure. Of course, I use to term ‘roughly’ since there are many other forces on air flow, especially near the ground where one must consider the effects of terrain and friction with the ground. Regardless, the concept of Geostrophic Balance is a great rule of thumb when reading weather maps, whether at the surface or upper levels, just check out the image below. This IR satellite image has height contours and wind barbs from 500mb, the flow up there was clearly close to being geostrophically balanced.

 

 

Bopha and Coriolis

   After weeks of next to no activity in the Northwest Pacific basin, there is finally some sign of life. Earlier today TD 26W became TS Bopha. It might not seem like much now, but this storm is actually very rare. What makes it special is the fact that officially became a tropical cyclone (TD 26W) while at a latitude of just 3.6 degrees north. Generally, storms form much further away from the equator due to its lack of a crucial force called the Coriolis Force.
   Technically, the Coriolis Force is not a real force, it is an apparent force resulting from the rotation of the Earth. If one were to observe the Earth from a fixed point in space, they would not be aware this kind of force. The result of the Coriolis Force is that objects in motion are deflected, to the right in the northern hemisphere and to the left in the southern hemisphere, from traveling in a straight path. This force is very important because it is the primary source of rotation in both the atmosphere and the ocean. However, at small scales it is insignificant as other forces become much more dominant. Therefore, something like a single storm cloud is going to be relatively unaffected by this force. It goes with out saying that this force will not cause you to mess up your ball game and it is not the reason for the direction your toilet flushes.
   The magnitude of the Coriolis Force is proportional to the sine of latitude [sin(lat)], so it is at its maximum at the poles (90 degrees) and zero on the equator (0 degrees). This is why tropical cyclones typically form some distance from the equator: to get some 'spin' from the Coriolis Force. Generally, I think of about eight degrees to be the closest a storm will likely get to the equator. This is why Bopha is so incredible, in the entire history of tracked storms (back to the 1840s) only a handful of storms have come so close to the equator. The map below shows the tracks of all Indian and Pacific storms ever recorded, the segments in yellow show where a tropical cyclone has tracked closer than 3.6 degrees from the equator (there were no cases in the other basins). As far as I can tell, first prize goes to Typhoon Anges (then a TD) in 1984, it was first recorded when at just 0.1 degrees north! If the Coriolis Force is so small, how did Bopha do it? The best I can figure is that it caught a bit of spin from a frontal zone in the South Pacific that included the invest area 97P.

 

 

UPDATE: 

This interesting statistic was posted on the blog of Japan's Digital Typhoon site:

"...since 1951 there are only 13 typhoons born to the south of 5 degree north. The most recent one is Typhoon 200206 [Chataan] ,so this typhoon [Bopha] is the first in these 10 years. It is known that areas around the equator is where the typhoon is formed infrequently due to weak force (Coriolis force) for spiral motion."

 

Note that this site refers to both typhoons and tropical storms as 'typhoons'.

 



So Quiet

   For the first time in months there is not a single named tropical cyclone anywhere in the world. Sure, there have been some invest areas and one unimpressive tropical storm, but other than that, there has been nothing out there since the end of October. This is kind of strange, since the southern hemisphere basins should be more active about now, and although it is in the northern hemisphere, the northwest pacific is typically still quite active this time of year. I have some ideas why the tropics are so quiet, but each basin's reason seems to be entirely different from the others.
   In the north Atlantic, activity does begin to slow down this time of year. Right now, the specific reason is likely the fronts associated with several strong extratropical cyclones that have been moving through the northern part of the basin the past few days. Fronts are not a tropical cyclone's friend; the temperature gradients and wind shear associated with them will tear even a powerful tropical cyclone apart. The result is something like dough being fed through an extruder.
   The northeast Pacific's problem also seems to related to some rather far south mid-latitude systems. To compound the problem is the very narrow band of sea surface temperatures warm enough to fuel a tropical cyclone. This basin has a tendency for this problem since there is a very cold ocean current that runs down the pacific coast all the way from the Gulf of Alaska.
   Normally the northwest pacific should still be active right now. However, it seems like persistent heavy wind shear has suppressed development for a number of days. The sources of this shear include a very powerful sub-tropical jet that ran nearly west to east north of the Philippines and over Taiwan. Generally, I don't expect so see such strong upper-level winds so far south.
   In the Indian ocean, it is not surprising that the north Indian has seen little activity, they rarely do. As for the south Indian; many invest areas have occurred near the equator, but all seem to either lose their convection or get sheared apart altogether.
   Finally, the south pacific tends to be slow to get going, so inactivity there is the least surprising. That basin seems highly sensitive to the El Nino cycle, with some years be quiet and others being exceptionally explosive.
   Right now, the best chance for a tropical cyclone to develop is from invest 96W in the South China Sea, rather near the equator.

101: Extratropical Cyclones

   Most people in the world will never experience a tropical cyclone. This is because the majority of the population lives in the mid-latitudes, which is typically considered to be between 30 and 60 degrees latitude. If this is the case, what are those giant weather making spirals that regularly roll through? Well, those are Extratropical Cyclones, also called Mid-Latitude Cyclones (or MLC, which is what I will typically refer to them as). These storms play a significant role in world weather, especially during the winter. Although they appear somewhat like their tropical counter parts, they are vastly different. For this post I’m going to start off with just a comparison between the two types of cyclones, the specific features of MLCs are each interesting on their own, so I’ll reserve detailed descriptions of them for later posts.

 

-Size: 
Perhaps the most apparent difference between tropical cyclones and MLCs is their size. While tropical cyclones certainly look impressive, the main cluster of clouds near the center is only on the order of 100 km or so. In atmospheric science terminology this size is labeled meso-scale (as in middle), alongside other weather phenomena such as squall lines. MLCs, on the other hand, are on the order of 1000 km or more, a size that belongs in the category of synoptic-scale. It should be noted that while tropical cyclones are considered meso-scale, they are very near the upper boundary of that category. Furthermore, some individual tropical cyclones do grow significantly larger, such as Hurricane Sandy, and might be considered synoptic-scale storms in some respects.

 

-Energy Source:
While not as apparent as some other factors, the source of the storm’s energy is a fundamentally defining characteristic. Tropical cyclones derive their energy from heat released by warm moist air as the water vapor inside it condenses. This causes the core to become very warm, which causes a drop in pressure. This in turn enhances the flow of the warm air into the system, thus acting as a positive feedback loop as long as the storm remains over warm water. The power behind MLCs is entirely different, although it is also organized about a low pressure center. The fuel for MLCs is the temperature gradient between the cold air descending from the polar regions and the warm air rising from the tropics. When a weak low pressure center forms, it twists the gradient cyclonically (counter-clockwise in the northern hemisphere). This allows the dense cold air to slip southward and around the low, while the warm air is allowed to proceed northward.

 

-Fronts:
Fronts are a feature exclusive to MLCs. In a basic sense, fronts are where the two air masses (warm and cold) meet and form a steep gradient of temperature. The cold front is often more dominant that the others. Due to its density, it plows straight into warm air, which is forced to rise sharply up the frontal boundary. The warm front is much more passive, it is caused by warm air gently sliding up the retreating cold air mass. Besides warm and cold fronts, there are also occluded fronts and stationary fronts. Occluded fronts form when a MLCs cold front ‘catches’ up to the warm front in a manner reminiscent of a zipper. At this point, warm air at the surface is no longer connected to the low’s center. Finally, a stationary front is similar to a cold front in structure, but the cold air mass isn’t really advancing into the warm air.

 

-Weaknesses: 
Perhaps the most dramatic display of the two cyclones’ differences are the mechanisms that weaken them. For starters, if a tropical cyclone encounters a high shear environment it will be torn apart, unlike a MLC thrives on shear, in fact they would die without it. Furthermore, while a tropical cyclone must remain over warm water, MLCs can exist over cold water, or land for that matter. Lastly, due to the heated center, tropical cyclones are referred to as warm core lows, which is just the opposite as most MLCs, which are appropriately referred to as cold core lows.

Below are a several images of MLCs of all shapes and sizes. Notice that often, the clouds associated with these systems are not arranged in anything that resembles a spiral.