Typhoon Haiyan
 
Typhoon Haiyan formed in the eastern Pacific Ocean in 2013, and when it devistated the Philippines on November 8th, it was the strongest tropical cyclone on record at landfall. The tropical Pacific Ocean is well known as a prolific tropical cyclone producer at any time of year, but Haiyan was particularly intense. What was unusual about the storm was that it made landfall at peak intensity - most tropical cyclones have passed their maximum strength by this point. Maximum sustained winds were estimated at 195 mph (only surpassed by Hurricane Patricia in 2015), with a minimum central pressure of 895 hPa at landfall. 
 
 
 
 
Comparison of Typhoon Haiyan with Hurricane Katrina (2005). Here, the cloud top temperature, measured by an infra-red sensor on a satellite, act as a proxy for the height of the clouds (and also for the strength of the storm). The deep purples present around the centre of Haiyan illustrate how much more intense the storm was than the costliest hurricane of all time. 
Credit: UW/CIMMS.
Visible satellite image of Typhoon Haiyan at peak intensity, as it made landfall in Eastern Samar province, Philippines, on 8th November 2013. 
Credit: NOAA/ GOES. 
On November 2nd, a pre-existing area of low pressure was in place to the north east of New Guinea that would act to focus convection over the warm sea surface of the tropical Pacific Ocean. With low atmospheric wind shear, high humidity and very warm sea surface temperatures ahead of the disturbance, conditions were conducive for tropical cyclone development over the coming days. By November 5th, rapid intensification occurred as the storm passed over sea surface temperatures of 29.5 - 30.5˚C, which extended to an unusually great depth. This aided the storm intensification because strong winds inside tropical cyclones tend to mix warmer water close to the surface with cooler water beneath (as well as depleating energy from the ocean through evaporation and subsequent latent heat release), therefore decreasing the sea surface temperature and energy available to the storm. If water is warm to a great depth, then the mixing only mixes up mild water from below, therefore only slightly decreasing the SST - temperatures in the layer 100 m below the surface were found to be 3˚C above average. 

Haiyan became a very compact typhoon, with hurricane-force winds extending only 70 miles from the storm's centre. Development continued throughout November 6th and 7th, by which time a tropical upper-tropospheric trough to the northeast enhanced the upper-level outflow from the storm, helping it to strengthen further. Due to the maintainence of favourable atmospheric conditions and high sea surface temperatures right up to the Philippine coast, the storm made landfall at maximum intensity on November 8th. 

Sea surface temperatures in the tropical western Pacific, during the formation of typhoon Haiyan in November 2013. The track of the storm took it over waters that were mostly above 30˚C. 
From: http://cimss.ssec.wisc.edu/goes/blog/archives/14311
Ocean temperature anomalies at 100 m depth, with the track of Haiyan overlaid on top. Anomalously warm water at depth helped to sustain one of the strongest tropical cyclones on record. 
Credit: Japan Meteorological Agency
Upon landfall, Haiyan began weakening slowly as its low-level circulation was disrupted by the mountainous terrain of the Phillipine islands. Haiyan made landfall in the town of Guiuan, Eastern Samar province, at 2040 UTC on November 7th. During its 24 hour passage across the Philippines, it slowly weakened into a strong category 4 storm, before eventually emerging into the South China Sea late on November 8th. Many settlements close to the storm's eye suffered total devastation, the most well-known being the city of Tacloban, which was about 15 miles north of the storm centre and was hit directly by the eye wall. The scenes of devistation prompted a world-wide relief effort for the affected areas.

Some slight reintensification occurred as the storm passed over the warm waters of the South China Sea. However, atmospheric conditions soon became less favourable, with increasing wind shear and the entrainment of mid-level stable air helping to weaken the storm. Haiyan finally made landfall for a second time in northern Vietnam as a severe tropical storm, with 10-minute sustained winds of 70 mph, on November 10th. The storm weakened further over land eventually dissipating entirely by November 11th. 
Illustration of the path that Haiyan took through the Philippines. The country's capital, Manilla, was largely spared of the damage caused by the storm. 
​Credit: BBC.

The central swath of the Philippines was completely devistated by the storm. The eastern islands of Leyete and Samar were pumelled by storm surges up to 7 m high, as well as waves up to 5 m high on top of that. Along with the preceding Tropical Storm Thirty, which took a similar track to Haiyan three days before, over 500 mm of rain fell over much of Leyete, with similar amounts recorded over neighbouring islands. On top of this, Haiyan brought extreme winds of 195 mph, along with gusts up to 235 mph when it initially made landfall. These conditions resulted in over 6,300 casualties, 130,000 homes destroyed, and 544,000 people displaced: up to 90% of the city of Tacloban was destroyed by a combination of the storm surge and high winds. 
A scene of devistation left behind by typhoon Haiyan. Such scenes can only be compared to events such as the 2004 Indian Ocean earthquake and tsunami. 
From: http://www.webinforma.biz/articoli/news-dal-mondo/222-tifone-haiyan-le-15-immagini-piu-agghiaccianti
Looking to the future
The intensity of typhoon Haiyan upon landfall was unprecedented, and it certainly was a very unusual event. However, we need to be prepared for events of similar, if not greater, magnitude to occur in the future. Although it is currently difficult to pen a relationship between anthropogenic climate change and tropical cyclone intensity, most model projections predict an increase in their intensity by 2 - 11% by the end of this century. In a warming climate, the atmosphere can be expected to hold more moisture, and these same models predict a 10 - 15% increase in rainfall rates from tropical cyclones by the end of this century. So we can expect events of Haiyan's magnitude to increase as we journey through this century. Thermal expansion as the ocean warms and melting polar ice caps will also raise global sea levels. Coupled with a local increase in sea levels in the western Pacific due to a strengthening of the trade winds and piling up of water on the western shores of the Pacific basin, storm surges and coastal flooding can be expected to be much more deadly in this part of the world.