If we’ve learned anything about forecasts and predictions (pick any recent event, sporting, political etc.) they give an indication of the situation, but cannot predict the absolute outcome, and surprises can most definitely happen. We are into the first weeks of the North Atlantic hurricane season, which officially runs for six months from June 1 to November 30, and a variety of forecasting groups and agencies have issued preseason forecasts. Continue reading
After a relatively quiet start, the 2016 Atlantic hurricane season grabbed the attention of the insurance industry during September and October. On October 6, all eyes fixed on Hurricane Matthew, a Category 4 storm barreling towards Florida and presenting the greatest threat to the U.S. insurance industry since Sandy in 2012. Despite Matthew’s high winds and floods, caused by both storm surge and rainfall, the storm’s offshore track certainly spared Florida and the southeast U.S. from a potential worst-case scenario.
Matthew was preceded by Hurricane Hermine, a Category 1 storm that made landfall along Florida’s Panhandle on September 2. These storms ended a nearly 11-year period where no hurricanes affected the state of Florida.
While the soft insurance market is expected to weather the effects of Hermine and Matthew, modelers at RMS are investigating whether these events provide valuable clues about future, near-term Atlantic hurricane frequency. Did either of these storms finally end the United States’ well-publicized hurricane drought?
It’s The Major Storms That Matter
The term “hurricane drought” first appeared in Geophysical Research Letters in research by Tim Hall and Kelly Hereid, and is defined as a lack of major hurricanes, ranking as Category 3 or greater on the Saffir-Simpson Hurricane Wind Scale, making landfall on the U.S.
Based on this definition, which itself ignited academic debate and drew ire from some meteorologists – the drought continues. Although a Category 4 hurricane on its approach to Florida, Matthew did not officially make landfall in the U.S. until striking South Carolina at Category 1 intensity.
Scientists agree that the Atlantic Basin entered a prolonged period of above-average hurricane frequency in 1995. To insurers, this translates into a period of increased likelihood of elevated damages and loss. As the drought stretched into record territory, scientists and insurers alike wondered whether this era had come to a close. Colorado State University’s Phil Klotzbach points out that it’s the major hurricanes, those driving the drought, that could provide us with the first clues.
An average of 2.7 major hurricanes have formed each year in the Atlantic Basin since 1950. With three major hurricanes – Gaston, Matthew, and Nicole – the 2016 season was the first since 2011 to exceed this average. But the four preceding seasons featured below-average major hurricane activity. You have to go back to the last low period of hurricane activity, around a quarter of a century ago, to see such a run of quiet years.
The Most Intriguing Statistic
This four year period is important to RMS modelers monitoring the medium-term rate (MTR), our scientific reference view of hurricane landfall frequency, looking ahead five years. It is the product of 13 individual forecast models; the contribution of each of those models is weighted according to its ability to predict the historical fluctuations in activity.
These forecast models include “shift” models that support the theory of cyclical Atlantic hurricane frequency. These shift models identify the seasons since 2011 as statistically distinct from periods observed since 1950 which are acknowledged as more active, based on the lack of recent major hurricanes.
It Ain’t Over ‘Til It’s Over
One month remains in the current season, so it is possible that more hurricanes could inform our view of the bigger picture.
The final month of the hurricane season, November has produced some notable Atlantic hurricanes, proving that the season’s latter stage requires close observation. Our attention to cyclogenesis turns primarily to the Gulf of Mexico and Caribbean, as evidenced by these past events:
- Hurricane Kate, the latest landfalling U.S. hurricane in modern history, peaked in intensity as a Category 3 storm before weakening ahead of its landfall near Mexico Beach, Florida on November 21, 1985.
- Hurricane Lenny, a Category 4 hurricane forming in 1999, is best known for its “wrong way” track that crossed the Caribbean Sea from west to east.
- Hurricane Michelle, the most intense hurricane of the 2001 season, made landfall in western Cuba as a Category 4 storm on November 4, causing over $2 billion in economic damage.
- Hurricane Paloma, following a track just to the east of Michelle, reached Category 4 strength at the height of its lifecycle, later impacting the Cayman Islands and Cuba in November 2008.
Shift models inform only one driver of activity considered by the MTR methodology. RMS plans to publish the findings of its annual medium-term rate forecast review in early 2017, after considering the most recent activity and other drivers of near-term hurricane behavior. This forecast will contribute to the updated RMS view of hurricane risk, forthcoming in spring 2017 as part of the version 17 software release.
Sports fans around the world have witnessed impressive winning streaks throughout history. After capturing two consecutive UEFA European Championships (2008, 2012) and a World Cup championship (2010), the Spanish National Football Team entered the 2014 World Cup in Brazil as the top-ranked squad in international competition. The dominant Spaniards were among the international sportsbooks’ favorites to bring home the trophy once again.
Instead, surprising defeats at the hands of the Netherlands and Chile eliminated Spain at the group stage. Spain’s streak of dominance came to a sudden end, marking the earliest World Cup exit for a defending champion since 1950.
From a meteorological perspective, the United States is currently riding its own streak: ten Atlantic hurricane seasons without a major hurricane (category 3 or above) making landfall, the longest such stretch in recorded history. With another hurricane season upon us, many will be keeping a keen eye on the Atlantic this summer to see if this impressive streak will continue.
Global forecasting groups, such as Colorado State University and Tropical Storm Risk, have issued their tropical storm and hurricane activity forecasts for the 2016 Atlantic hurricane season. Christopher Allen of the RMS Event Response team has authored an excellent summary of their forecasts in the RMS 2016 North Atlantic Hurricane Season Outlook published this week on RMS.com.
You can also listen to my summary of the season’s forecasts during my talk to AM Best TV’s John Weber. In summary, most forecasts are predicting anywhere between near-average to above-average activity in the Atlantic basin, reflecting conflicting signals in the key indicators that influence hurricane formation.
Will we have increased hurricane activity?
One factor that may support increased hurricane activity this season is the anticipated state of the El Niño-Southern Oscillation, or ENSO. As reported on this blog several months ago, many ENSO forecasts project a transition out of last year’s historic El Niño phase into a La Niña phase, which is historically more favorable for hurricane development. Wind shear, detrimental to tropical cyclone formation, typically is reduced in the Atlantic basin during La Niña phases of ENSO.
Mid-May 2016 observations and model forecasts of ENSO, based on the NINO3.4 index, through March 2017. Positive values correspond with El Niño, while negative values correspond with La Niña. Source: International Research Institute for Climate and Society
Conversely, some forecasts predict a cooling of Atlantic sea surface temperatures (SSTs), which would oppose any support provided by a forecasted La Niña and reduce the potential for an active hurricane season. This cooling has been driven by a lengthened positive phase of the North Atlantic Oscillation (NAO), which causes stronger than normal trade winds in the tropical North Atlantic and upwelling of deeper cold ocean water near the surface.
February-April 2016 sea level pressure anomalies in the North Atlantic Ocean (hPa, anomalies with respect to 1981-2010 climatology). Anomalously high pressure evident in the Azores and the mid-latitude North Atlantic signals a positive phase of the NAO. Source: National Centers for Environmental Prediction Monthly Reanalysis (Kalnay, E. and Coauthors, 1996: The NCEP/NCAR Reanalysis 40-year Project. Bull. Amer. Meteor. Soc., 77, 437-471).
The Atlantic Multidecadal Oscillation may also be transitioning into a prolonged phase detrimental to tropical cyclone development, a theory often mentioned on this blog, although one that is still debated in the scientific community.
If considered in isolation, La Niña conditions and cooling Atlantic SSTs exert conflicting influences on Atlantic tropical cyclone development. However, forecasts contain key caveats that will ultimately determine this season’s activity:
- Although a transition into a La Niña phase is widely anticipated, a late arrival would limit its ability to support development in the basin.
- Further, forecasts of Atlantic sea surface temperature during August and September, the peak of hurricane season, remain conflicted.
Does the season’s early storm activity signify more activity?
Forecasts predicting above-average basin activity are understandable, given the early activity observed prior to the season’s official start. Tropical Storms Bonnie and Colin both formed before the second week in June, bringing heavy rainfall to South Carolina and the Gulf coast of Florida, respectively. Bonnie and Colin followed Hurricane Alex, the first January hurricane since 1938.
Bonnie’s formation marked the first time since 2012 that two named storms developed before June 1, the official start of hurricane season. The 2012 season ended with 19 total named storms, the third-most on record, including Superstorm Sandy, which caused more than $18 billion in insured losses.
Would the industry be prepared for the next major hurricane landfall? According to Fitch, the answer is yes: insurers and reinsurers in 18 coastal U.S. states would be equipped to handle one major event this season, although this resiliency has not been recently tested. More worrying, though, are the prospects of a large tail event or even multiple landfalling events, which may be supported by the right combination of oceanic and atmospheric influences.
With the hurricane season now officially underway, we will watch, wait and see how the season’s activity unfolds over the next few months. What is certain, though, is that streaks are made to be broken. It’s just a matter of when.
RMS recently released its 2015 North Atlantic Hurricane Season Outlook. So, what can we expect from this season, which is now underway?
2015 season could be the 10th consecutive year without a major landfalling hurricane over the United States.
The 2014 season marked the ninth consecutive year that no major hurricane (Category 3 or higher) made landfall over the United States. Although two named storms have already formed in the basin so far this year, Tropical Storm Ana and Tropical Storm Bill, 2015 looks to be no different. Forecast groups are predicting a below-average probability of a major hurricane making landfall over the U.S. and the Caribbean in the 2015 season.
The RMS 2015 North Atlantic Hurricane Season Outlook highlights 2015 seasonal forecasts and summarizes key meteorological drivers in the Atlantic Basin.
Forecasts for a below-average season can be attributed to a number of interlinked atmospheric and oceanic conditions, including El Niño and cooler sea surface temperatures.
So what factors are driving these predictions? A strong El Niño phase of the El Niño Southern Oscillation (ENSO) is a large factor, as Jeff Waters discussed previously.
Another key factor in the lower forecast numbers is that sea surface temperatures (SSTs) in the tropical Atlantic are quite a bit cooler than previous years. SSTs higher than 80°F (26.5°C) are required for hurricane development and for sustained hurricane activity, according to NOAA Hurricane Research Division.
Colorado State University (CSU)’s June 1st forecast is calling for 8 named storms, 3 hurricanes, and 1 major hurricane this season, with an Accumulated Cyclone Energy (ACE) index—used to express activity and destructive potential of the season—of 40. This is well below the 65- and 20-year averages, both over 100.
However, all it takes is one significant event to cause significant loss.
Landfalls are difficult to predict more than a few weeks in advance, as complex factors control the development and steering of storms. Despite the below-average number of storms expected in the 2015 season, it only takes one landfalling event to cause significant loss. Even if the activity and destructive energy of the entire season is lower than previous years, factors such as location and storm surge can increase losses.
For example, Hurricane Andrew made landfall as a Category 5 storm over Florida in 1992, a strong El Niño year. Steering currents and lower-than-expected wind shear directed Andrew towards the coastline of Florida, making it the fourth most intense landfalling U.S. hurricane recorded. Hurricane Andrew also holds the record for the fourth costliest U.S. Atlantic hurricane, with an economic loss of $27 billion USD (1992).
Sometimes, a storm doesn’t even need to be classified as a hurricane at landfall to cause damage and loss. Though Superstorm Sandy had Category 1 hurricane force winds when it made landfall in the U.S., it was no longer officially a hurricane, having transitioned to an extratropical storm. However, the strong offshore hurricane force winds from Sandy generated a large storm surge, which accounted for 65 percent of the $20 billion insured losses.
While seasonal forecasts estimate activity in the Atlantic Basin and help us understand the potential conditions that drive tropical cyclone activity, a degree of uncertainty still surrounds the exact number and paths of storms that will form throughout the season. For this reason, RMS recommends treating seasonal hurricane activity forecasts with a level of caution and to always be prepared for a hurricane to occur.
The 2014 Atlantic Hurricane Season officially kicked off this week (June 1), running through November 30. Coming off a hurricane season with the lowest number of hurricanes in the Atlantic Basin since 1983, will 2014 follow suit as a less active season? If so, is the Atlantic Basin officially signaling a shift out of an active phase of hurricane activity? Or will we revert back to the above-average hurricane numbers and intensities we’ve grown accustomed to over most of the last 20 years? And regardless of the season’s severity, what should be done to prepare?
Forecasting the 2014 Hurricane Season
Most forecasts to date, including those of Colorado State University and the National Oceanic and Atmospheric Administration (NOAA), are calling for an average to below-average season in terms of the number of named storms (8–13), hurricanes (3–6), and major hurricanes (0–3). The same holds true for the overall intensity forecasts, where projected seasonal values of Accumulated Cyclone Energy (ACE) range from just 55 to 84, compared to the average overall seasonal ACE of 101.8.
So what’s driving this outlook? Most forecasting organizations are attributing it to two major atmospheric drivers that have been known to suppress hurricane activity: the strong likelihood of an El Niño event developing this summer into the peak part of the season from July through October, and below-average sea surface temperatures in the Atlantic Basin’s Main Development Region (MDR).
El Niño conditions create stronger-than-normal upper-level winds, which inhibit storms from forming and maintaining a favorable structure for intensification. Similarly, below-average ocean temperatures in the MDR essentially reduce the energy available to fuel storms, making it difficult for them to develop and intensify.
However, low activity does not always translate into a decrease in landfalling hurricanes. Also, all it takes is one landfalling event to cause catastrophic losses. For example, 1992 was a strong El Niño year, yet Hurricane Andrew made landfall in Florida as a Category 5 storm, eventually becoming the fourth most intense U.S. landfalling hurricane recorded, and the fourth costliest U.S. Atlantic hurricane. Of course, while a landfalling storm like Andrew may have occurred during the last significant El Niño year, there’s no guarantee it will happen this season. The U.S. has not experienced a major landfalling hurricane since Hurricane Wilma in August of 2005. This eight-year drought is the longest in recorded U.S. history.
Preparing for Hurricane Season
Whether or not the 2014 Atlantic hurricane season is active, it is imperative to monitor and prepare for impending storms effectively to help reduce the effects of a hurricane disaster.
The NOAA National Hurricane Center provides several tips and educational guides for improving hurricane awareness, including forecasting tools that assess the potential impacts of landfalling hurricanes. This year, NOAA also offers an experimental mapping tool, as well as other new tools, to help communities understand their potential storm surge flood threat.
The RMS Event Response team provides real-time updates for all Atlantic hurricanes, among other global hazards, 24 hours a day, seven days a week. Similarly, when it comes to preparation, along with the essentials, such as bottled water, canned foods, and battery-powered flashlights, consider purchasing these ten items.
Are you ready for the 2014 Atlantic Hurricane season?