One of the best ways to manage the uncertainties associated with ENSO related events is to hold someone responsible for the consequences for those events. For example, the Peruvian government has issued an El Nino warning for April 2014 (see Reply #380), as the serious consequences of an El Nino to their economy forces them to use robust decision making, RDM, to take precautionary measures. Another example (that is the focus of this post) is the insurance industry, who will bear significant economic losses from a severe El Nino unless their forecasts adequately justify either higher premiums and/or cancellation of high-risk policies; as illustrated by the following linked article (from March 3 2014) about a statistical based model to better assess the risks for tropical cyclones (typhoons) in the Western North Pacific (WNP) linked to variations of storm tracks associated with ENSO fluctuations. While, the whole article is educational, I post the abstract and a key extract from the article below (together with few of my comments on the interpretation of these finding as related to our current situation):
http://insurancenewsnet.com/oarticle/2014/03/04/enso-effect-on-east-asian-tropical-cyclone-landfall-via-changes-in-tracks-and-ge-a-468934.html#.UzQZFaPn_IUAbstract: "Improvements on a statistical tropical cyclone (TC) track model in the western North Pacific Ocean are described. The goal of the model is to study the effect of El Niño-Southern Oscillation (ENSO) on East Asian TC landfall. The model is based on the International Best-Track Archive for Climate Stewardship (IBTrACS) database of TC observations for 1945-2007 and employs local regression of TC formation rates and track increments on the Niño-3.4 index and seasonally varying climate parameters. The main improvements are the inclusion of ENSO dependence in the track propagation and accounting for seasonality in both genesis and tracks. A comparison of simulations of the 1945-2007 period with observations concludes that the model updates improve the skill of this model in simulating TCs. Changes in TC genesis and tracks are analyzed separately and cumulatively in simulations of stationary extreme ENSO states. ENSO effects on regional (100-km scale) landfall are attributed to changes in genesis and tracks. The effect of ENSO on genesis is predominantly a shift in genesis location from the southeast in El Niño years to the northwest in La Niña years, resulting in higher landfall rates for the East Asian coast during La Niña. The effect of ENSO on track propagation varies seasonally and spatially. In the peak activity season (July-October), there are significant changes in mean tracks with ENSO. Landfall-rate changes from genesis- and track-ENSO effects in the Philippines cancel out, while coastal segments of Vietnam, China, the Korean Peninsula, and Japan show enhanced La Niña-year increases."
Selected Extract: "The most important change of WNP TCs with ENSO appears to be the shift in genesis location to the southeast during strong El Nino events and to the northwest during strong La Nina events (Chan 1985, 2000; Dong 1988; Lander 1994; Saunders et al. 2000; Wang and Chan 2002; Chia and Ropelewski 2002; Camargo et al. 2007a). The shift is explained by the location of the monsoon trough in the WNP shifting eastward during El Nino events (Lander 1994) along with a reduction in vertical wind shear (Clark and Chu 2002), which both dictate favorable conditions for genesis. This shift results in changes in the tracks of the subsequent TCs: those that form in the southeast have longer lifetimes and tend to recurve northward as compared with those that form in the northwest that move straight westward onto land (Wang and Chan 2002). Elsner and Liu (2003) further studied the ENSO effect on tracks and implications for landfall, finding that strong El Nino years correspond with northward recurving TC tracks, which are likely to make landfall on Japan, the Korean Peninsula, and northern China. During La Nina years, TC tracks move in a straighter westward path, putting the Philippines, southern China, and Vietnam at higher risk. The TC-track cluster analysis performed by Camargo et al. (2007c) for the WNP demonstrates that the different genesis regions associated with El Nino (La Nina) years are also associated with longer (shorter) tracks. One important implication is that El Nino-year TC tracks in the WNP have more of an opportunity to reach higher intensities as they travel over the warm tropical ocean given a genesis location closer to the equator and farther eastward. El Nino-year TCs may also reach higher latitudes when they curve northward, before making landfall (Camargo and Sobel 2005; Chan and Liu 2004; Camargo et al. 2007c). The last two effects are important when making a landfall risk assessment in terms of landfall intensity and landfall location."
Key considerations relating these findings to our current situation include:
- Super Typhoon Haiyan, which occurred in ENSO neutral conditions in November 2013, fed rapidly on the very warm deep waters piled-up in the Western Pacific by the historically strong trades winds for the several years preceding that event, and then moved nearly due west to hit the Philippines as the strongest storm in history.
- Super Typhoons are more likely to occur (resulting in more numerous events) during a strong El Nino event because in El Nino years the storm tracks occur closer to the equator and farther eastward (than during neutral or La Nina conditions), and thus the storms have more opportunity to reach higher intensities as they travel longer distances over the warm tropical ocean, while curving northward towards high targets with high economic value in Japan, Korea and Northern China.
- Due to the more southeasterly locations for the locations of genesis of typhoons during strong El Nino conditions; the westerly wind bursts, WWBs, associated with these geneses provide a strong positive feedback to strength the El Nino event.
- The closer that we get to the peak typhoon (tropical cyclone/storm) activity season (July-October), the more likely we are to get positive WWB feedback from tropical storms for strengthening the current fledgling El Nino; which is one of the reasons (together with the projected coming of the MJO in the Pacific) that I am concerned about a major typhoon occurring in April (similar to Super Typhoon Isa) that could kick our current El Nino into the Super category.