Tag Archives: Models

Lessons Learned from Winter Windstorm Season in Europe

The 2013–2014 winter windstorm season in Europe will be remembered for being particularly active, bringing persistent unsettled weather to the region, and with it some exceptional meteorological features. The insurance industry will have much to learn from this winter.

Past extreme windstorms, such as Daria, Herta, Vivian, and Wiebke in 1990, each caused significant losses in Europe. In contrast, the individual storms of 2013–2014 caused relatively low levels of loss. While not extreme on a single-event basis, the accumulated activity and loss across the season was notable, primarily due to the specific characteristics of the jet stream.

A stronger-than-usual jet stream off the U.S. Eastern Seaboard was caused by very cold polar air over Canada and warmer-than-normal sea-surface temperatures in the sub-tropical West Atlantic and Caribbean Sea. Subsequently, this jet stream significantly weakened over the East Atlantic.

Therefore, the majority of systems were mature and wet when they reached Europe. These storms, while associated with steep pressure gradients, brought only moderate peak gust wind speeds onshore, mainly to the U.K. and Ireland. In contrast, the storms that hit Europe in 1990 were mostly still in their development phase under a strong jet stream as they passed over the continent.

The 2013––2014 storms were also very wet, and many parts of the U.K. experienced record-breaking rainfall resulting in significant inland flooding. Again, individual storms were not uniquely severe, but the impact was cumulative, especially as the soil progressively saturated.

Not all events this winter season weakened before impact. Windstorms Christian and Xaver were exceptions, only becoming mature storms after crossing the British Isles into the North Sea and were more damaging.

Christian impacted Germany, Denmark, and Sweden with strong winds. RMS engineers visited the region and observed that the majority of building damage was dominated by the usual tile uplift along the edges of the buildings. Fallen trees were observed, but in most cases, there was sufficient clearance to prevent them from causing building damage.

Xaver brought a significant storm surge to northern Europe, although coastal defenses mostly withstood the storm. Xaver, as well as some of this year’s other events, demonstrated the importance of understanding tides when assessing surge hazard as many events coincided with some of the highest tides of the year. The size of a storm-induced surge is much smaller than the local tidal range; consequently, if these events had occurred a few days earlier or later, the astronomical tide would have been reduced, significantly reducing the high water level.

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Wind, flood, and coastal surge are three components of this variable peril that can make the difference between unsettled and extreme weather. This highlights the importance of modeling the complete life cycle of windstorms, the background climate, and antecedent conditions to fully understand the potential hazard.

This season has also raised questions about the variability of windstorm activity in Europe, how much we understand this variability, and what we can do to better understand it in the future. While this winter season was active, we have been in a lull of storm activity for about 20 years.

Given the uncertainty that surrounds our ability to predict the future of this damaging peril, perhaps for now we are best positioned to learn lessons from the past. This past winter provided a unique opportunity, compared to the more extreme events that have dominated the recent historical record.

RMS has prepared a detailed report on the 2013–2014 Europe windstorm season, which analyzes the events that occurred and their insurance and modeling considerations. To access the full report, visit RMS publications.

120 Years Since the 1893 NY Hurricane & the Disappearance of Hog Island

As the industry and modeling organizations continue to learn from the impacts of Hurricane Sandy in 2012, it’s important to know that this event, although historical and record breaking on many counts, was not unprecedented.

The historical record shows that there have been dozens of other tropical cyclones to impact the Northeast U.S., some of which were more intense than Hurricane Sandy from both a wind and surge perspective.

Noteworthy examples include the 1938 New England Hurricane, 1954 Hurricane Carol, and the 1893 New York Hurricane, which will be marking its 120th anniversary on August 24. This storm is notable for being one of only two hurricanes to make a direct landfall in New York City, the other being the 1821 Long Island Hurricane.

First identified as a tropical storm on August 15, 1893 in the central Atlantic Ocean, the storm gradually intensified over the next seven days as it tracked northwestward toward the U.S. By August 22, it had reached its peak intensity of 115 mph (185 km/h), categorizing it as major hurricane status (Category 3). At this point, it began to recurve to the north, bringing it in-line with coastal New Jersey and New York. Two days later, after land interaction with parts of New Jersey resulted in some weakening, the storm made landfall on western Long Island with peak winds around 85 mph (140 km/h).

The hurricane impacted much of the coastal and interior portions of the Northeast with tropical-storm force winds, and much of the New York City with hurricane-force winds. From a surge perspective, the storm brought a 30-foot (9.1 m) storm surge that completely flooded southern Brooklyn and Queens, NY, along with many other low-lying regions.

Here is an extract from the New York Times on August 25, 1893.

Given the severity of this storm’s surge component, it is well known for destroying the majority of Hog Island, a 1 mile (1.6 km) long island that existed south of the modern-day Long Island coast.

According to version 13.0 of the RMS U.S. Hurricane Model, if the 1893 New York Hurricane were to occur today, the modeled insured losses from a wind-only perspective would be $6.4 billion, and $6.9 billion from a wind and surge perspective. Although not as damaging as Hurricane Sandy, this storm would be a top-10 historical event in the Mid-Atlantic and Northeast regions.

Compared to Hurricane Sandy, the 1893 New York Hurricane was estimated to have been smaller in overall size and intensity at landfall, but significantly larger in terms of surge height and extent. Model-generated hazard and damage footprints for the 1893 New York Hurricane are narrower in width and comparable in terms of peak wind gust.

Further, the impacted areas are confined to coastal New England regions due to the traditional clockwise recurving nature of the storm. On the contrary, Hurricane Sandy took a counterclockwise turn toward the coast just before landfall and prior to recurving toward the north and east, which resulted in a hazard footprint that included many Mid-Atlantic states.

Nevertheless, an event such as the 1893 New York Hurricane demonstrates that from a hazard perspective, Hurricane Sandy was not an once-in-a-lifetime type of storm.

Similar events have and will continue to occur in the future, especially given the period of heightened hurricane activity in the Atlantic, and high surge risk in the Northeast U.S. During this time, it is imperative that the industry increases awareness of these risks and monitors them accordingly.