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Wet East Coast Increases Loss Concern this Hurricane Season

As we approach the peak of the 2013 Atlantic hurricane season (which peaks around September 10), the forecasts (for an active season) made back in April have partially panned out – if you consider the total number of named storms. Looking at the last 50 years (1976-2012), the average formation dates of the fourth named storm and first hurricane are August 19 and August 3. So in terms named tropical storms, the season is ahead of par with climatology, but slipping behind on the occurrence of the first hurricane for 2013. In terms of Accumulated Cyclone Energy (ACE), 2013 is essentially average for this date. We’re at 6.6 compared to the 1981-2010 average of 9 for this date.

With August being the month where typically the number of tropical systems ramps up and Colorado State University’s August forecast calling for an active landfalling season, the likelihood of the season’s wet soil conditions leading to increased losses from a landfalling named storm must be considered.

The Ohio Valley and East Coast were much wetter than average. June precipitation totals for 18 states – from Georgia to Maine – ranked among their 10 wettest in the historical record. The fact that this weather continued into July undoubtedly creates concern over a named stormed impacting these rain-soaked areas.

 

 

NOAA Advanced Hydrologic Prediction Service view of the past 60-day Percent of Normal Precipitation. Over the past 60 days, much of the East Coast has seen 150% – 350% of normal precipitation.

Research shows that past hurricanes have demonstrated the combined effects of subsequent excessive rainfall and a named-storm wind speed that can have a major impact on insured losses. These losses might not otherwise be represented if the subsequent seasonal rainfall was normal or below normal. This loss increase is primarily associated with increased basement leakage and tree fall. (When soil is saturated, the connection between the root plate of a tree and the soil is lessened, which can increase tree fall.) Research also shows that the average wind speed expected to snap a hard- or softwood tree trunk is a 90 mph gust. Therefore, while more intense winds wouldn’t necessarily increase the loss, lower wind speeds might – given the weakened condition of saturated soil.

Recent examples of events that might have seen increased losses due to higher soil moisture are hurricane Isabel 2003 and Irene 2011. With New Jersey and Delaware having had their wettest June on record and 18 other eastern states having had Junes ranking in their top 10 wettest, this August has seen some of the highest soil moisture levels ever recorded. And this could increase the risk of river and basement flooding as well as tree fall if a named storm were to impact the area.

 

Severe Weather in a Warming World

Andy Siffert, BMS’ resident Meteorologist, discusses Severe Weather in a Warming World

As we have all seen in the media it would appear that on May 15 Mother Nature has turned on the severe convective storm season, which to date had been historically quiet in terms of insurance losses and severe convective storm reports.

Since May 15 the preliminary tornado count stands at 305 tornadoes, but considering the nation is currently at the climatological peak of the severe convective storm season and the tornadoes are occurring precisely where historically they should occur, the impacts of the severe weather should be expected and can be easily explained by understanding the current weather pattern.

The reason we have seen the recent uptick in severe weather activity to more normal levels is the spring of 2013 has been climatologically cooler than normal over the eastern two-thirds of the country, which has kept instability levels low. This is most likely due to a weather pattern associated with the a negative phase of the Arctic Oscillation (AO), which has kept a low amplitude jet stream pattern in place over the eastern portion of the U.S., allowing cool air from Canada to spill southwards into the U.S. blocking warm moist air northward progression from the Gulf of Mexico.

Starting in mid May a shift in the jet stream winds resulted in a weather pattern that allowed for frequent weather systems to draw upon the warm moist air from the Gulf of Mexico to clash with the cooler, drier air moving east off the Rocky Mountains. This different weather pattern has provided the main ingredients necessary to produce what have been widespread multi-day severe weather events.

Understanding weather patterns can fluctuate explains the last three years of tornado activity, which have experienced both a record minimum and record maximum tornado count. These two extremes of recent tornado surplus (2011) and the current tornado drought are rare and considering they are back to back it makes the occurrence even more unusual. However, these patterns have resulted in several contradictory views on the impact a warming world might have on severe convective storms in the U.S. In a warming world should we experience more seasons like 2011 or fewer tornadoes like 2012? Are extreme tornadoes like Moore, OK, a result of this warming world?

In the latest BMS Introspect – Severe Weather in a Warming World and Its Impact to the Insurance Industry we attempt to answer these questions.

Predictions for the 2013 Atlantic hurricane season

Andy Siffert, BMS’ resident Meteorologist, discusses the 2013 Atlantic hurricane season:


Forecast groups predict a very active 2013 Atlantic hurricane season.

The start of the hurricane season is three weeks away and eight independent forecast outlets unanimously agree it will be a busy Atlantic hurricane season with a few calling for a higher probability of a landfalling hurricane along the coastal USA.

It is reasonable to wonder whether these early hurricane forecasts are accurate. Last year, forecasters in April called for an average to quieter than normal season, and it turned out to be a busy year with 19 named storms, tied for the third most on record. Seasonal forecasters emphasize the difficulties in predicting hurricane activity in April and, in fact, it is most likely impossible, given current methods and technology, to precisely predict the named storm activity level in April. However, many forecasting groups say they have made progress in developing these predictions and there is improvement based on using climatology alone. We do know that skill does climb slowly as the hurricane season approaches, with moderate to good skill levels being achieved in early August.

Hurricane season begins June 1 and ends November 30 and in the linked, BMS Introspect – Atlantic Hurricane Outlook – April, we highlight the skill needed for an April hurricane forecast and what these forecasts are saying for the 2013 Atlantic hurricane season.