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BMS News

May Severe Weather Update

The Onslaught of Severe Weather
Last week I posted some general ideas of what to expect over the next few months and briefly touched on U.S. severe weather. In this update I will provide a bit more detail on 2017 severe weather and what to expect over the next few months.
As mentioned in my last blog, this year is off to a record pace in terms of severe weather reports and U.S. insured loss. In fact, if you think a major severe weather event is occurring about every week so far in 2017, you’re likely correct as there have been only four severe weather free weeks so far in 2017 according to PCS wind and thunderstorm event designations.

Highlighted dates in 2017  in which PCS has a wind  thunderstorm designations

Historically, in terms of number of PCS wind thunderstorm events, the activity has been unprecedented with 19 events so far, which is 271% above the average number of events that have occurred since 2000.

Number of PCS event designations by year as of May 1

 

January – April Wind and Thunderstorm PCS losses in billions adjusted for CPI by year.

However, in terms of insured loss it is difficult to estimate how the recent PCS events might develop. Given the wide scope of impact, it would be safe to say at least another billion dollars (or two) could still be expected to develop from existing PCS designated events that have occurred at the end of April.  If this development occurs, insured loss through the end of April would be at a historically high level. However, it would be far lower than the costly severe storm year of 2011, where the loss was driven by the deadly April tornadoes in Alabama and the Joplin, Missouri tornado in May.  This highlights the remarkable luck that has occurred with tornado related insured loss over the last several years and especially this year since reports of tornadoes are running above normal for the first time since 2012.

Since the U.S. has not experienced a major marquee tornado loss this year, most of the insured loss continues to be related to hail or localized wind damage with smaller tornado losses mixed in such as the East New Orleans tornado on February 7th of this year.   Below is a break down how insured losses have compared to 2016 by state thru May 1st, keeping in mind further development of 2017 losses is expected.  As of right now Texas, which last year saw 47% of the total reported U.S. insured loss, is reporting a lower level of loss as of May 1 compared to last year at this time.

Insured PCS Loss Difference (%) from 2016

Possible Cause of Severe Weather
The main stream media continue to put focus on El Niño–Southern Oscillation (ENSO) and its possible impacts on this year’s severe weather, but severe weather cannot be tied to just one atmosphere climate forcer. As mentioned in my previous post, several bits of research have been done around this relationship of Gulf of Mexico Sea Surface Temperatures (SST) and severe weather Convective Available Potential Energy (CAPE). Currently, the SST, are at record high levels, which appears to be helping provide extra fuel for any storm system that traverses across the U.S.

 

However, another hypothesis is the relationship the Rocky Mountains and Northern Plains snowpack has on severe weather and tornado occurrence.   There is little research around this connection, but a quick crude analysis shows there is possibly a connection here suggesting in years when May snowpack is below normal in the Colorado basin U.S. tornado count in May is also below normal.  This is not the case this year with near record snow pack across the Rocky Mountain; however, the correlation between above average snowpack years and tornadoes is not as clean.  Combining this theory with warmer than normal Gulf of Mexico SSTs creating warmer, moister air and the extensive spring snowpack in the Rocky Mountains provides an interesting hypothesis that would be a great master thesis for some young inspiring meteorologist.

Forecasted Severe Weather

As shown with the severe weather losses and number of events the first few months have been active, but the first few months of the year historically make up only 19.5% of the severe weather activity on average as recorded by NOAA Local Storm Reports (Tornado, Hail, Wind). An active January thru April can quickly be superseded by a quiet May, June, & July. In attempting to understand if early activity will lead to an overall above active year, I used a trailing 17 year average to find above and below average periods. In this sample approach, over the last 17 years, 7 years were above average in the January-April period. Of the years that had an above average January – April reports of severe weather, only one year (2016) went on to have above average numbers for the remainder of the year, the remainder of those years ended quieter then normal.

In fact other researchers have done some similar studies that suggest a fast start does not necessarily mean the reminder of the season will be active.

Source: NOAA – Michael Tippett

Annual PCS January – April loss development as a percent of yearly total loss.

In terms of insured loss as of May 1, historically the U.S. insured loss is developed at 42% and we know there will be further development of 2017 losses that have occurred at the end of April. Regionally, it would appear severe weather will continue to be a common occurrence across the Southern Gulf States into the Carolinas into June. More typical periods of warmth across the Northern Plains will trigger severe weather into the summer. However, the stormy periods are not expected to last long like the current persistence pattern the south has seen so far this year.

Note on Wildfire Risk
Florida will continue to see a higher risk for wildfire, but after June the risk could shift to Western states. Despite significant rain and mountain snow across California early this year, wildfires will still pose a threat this summer. Significant precipitation has led to abundant vegetation which can serve as fuel for fires. Early in the season, heat may be inconsistent across California, but temperatures are predicted to rise in July, which will likely dry out this new vegetation and increasing the chances for fires.

BMS Seasonal Outlook April 2017

Summary:

  • An El Niño is forecasted to emerge for late this summer, but weather patterns suggest that it has already arrived.
  • Late spring-early summer warming will occur over the central and eastern U.S.; then, temperatures will trend cooler into the summer for the northern plains.
  • Heavy spring rains across the Gulf States and into the Great Plains will accompany storm systems, but nothing like past record years (like 1993).
  • Best matching analog years: 1982, 1986, 2004, 2006 and 2014

The Pattern

There has been no shortage for the insurance industry of severe weather during the first quarter of 2017. A warmer-than-normal start to the year, aided by record Gulf of Mexico sea surface temperatures, has produced a relatively active period of severe weather. Will this weather pattern continue into the next few months, or are we on the road to a quieter-than-normal weather pattern?

Severe weather reports from Jan 1 – April 20, 2017. Bar graph shows the number of reports per day so far this year.

In reviewing the first three months of 2017, the weather patterns have been dominated by Pacific influences, with storm after storm pounding the West Coast. As these storm systems moved across the U.S. and into the central U.S., they were enhanced by tapping a large amount of warm air from the Gulf of Mexico, which also produced warmth across the eastern U.S. This weather pattern has provided plenty of opportunity for severe weather, and resulted in several significant severe weather outbreaks that impacted the insurance industry. Some of the bigger events occurred on January 2, 21-23, February 28-March 1, March 6-7, and most recently, April 2-3.

So far in April, it would appear this weather pattern has continued the pattern established in March, with a series of infrequent, but very energetic storm systems digging into the western U.S. before lifting up into the mid-west and northeastern U.S.  This has meant that much of the U.S. should continue to experience similar above-normal severe weather activity; but these storm systems should start traversing a more northern track across the northern-tier states.  This pattern indicates that June-like weather might appear in April and May.

Long-Range Forecasts

Many long-range climate forcer signals can provide seasonal forecasters clues about what weather to expect over the next few months.  The El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) are some of the most common signals.  Although ENSO seems the most popular climate forcer in recent seasonal forecasts, a few words of caution are required:  fickle spring weather is notoriously misleading and results in difficult forecasts (this phenomenon is so familiar that it has its own name, the “spring predictability barrier”).   Second, we are technically coming out of a weak La Niña (which has a traditionally predictable outcome), but the atmosphere isn’t following its typical pattern following a weak La Niña.  Instead, the weather pattern over the continental U.S. reflected more of an El Niño pattern, with widespread warmth across much of the country and above-normal precipitation across parts of the southern tier and West Coast states.

The PDO has been positive for a record 39 months (during a positive phase, the west Pacific becomes cooler and part of the eastern ocean warms), but the weather pattern over the western U.S. has been anything but reflective of a positive PDO pattern.  Usually a positive PDO will lead to warmer and drier conditions in the western U.S., but this has not been the case over the last few months.

Weekly U.S. Drought Monitor, which uses a composite index on the level of drought that is occurring

Seasonal forecasting can also help us understand current areas of drought.  Large areas of moderate-to-severe drought can create a positive feedback loop, meaning that already-dry regions are more susceptible to warm and dry weather than non-drought areas.  As illustrated by the above map, patches of drought are currently scattered throughout the country, but these scattered patches are too insignificant to raise red flags for long-term warm and dry conditions over next few months.

Research suggests that the continued warm water temperatures in the Gulf of Mexico will likely mean severe weather will continue to erupt over the southern and central U.S. into late spring.  Historically, when the Gulf of Mexico trends warmer than normal, there is more energy to fuel severe storms and tornadoes.

Convective energy is needed for storm development and correlates to storm activity.

The Verdict

Evaluating recent weather patterns and various climate forcers produces the following analog years: 1982, 1986, 2004, 2006, and 2014.  These years suggest an active storm pattern that may result in:

  • Much of the U.S. experiencing near-normal temperatures between April-August
  • The western U.S. and southeast warmer then normal
  • The northern states slightly colder than normal

Combining the analog years yields the following temperature and precipitation anomalies. Note the temperature scale is less than a 1 degree +/- long term average.

However, above-normal national temperatures now and into early summer should give way to more normal temperatures or cooling temperature patterns in the Great Plains later in the year.  Hit-or-miss precipitation across much of the country will be a by-product of severe weather and will provide rain in some areas but not others.  As a result, dry conditions in the southeast could progress into summer.  Severe weather should remain active until May, with activity waning to more normal levels as summer progresses; but overall, the insurance industry should expect to see much higher levels of insured loss than in the last few years.

 

BMS Tropical Update 4/20/2016 4 PM CDT

You might have noticed that the first named storm (Arlene) of the 2017 Atlantic Hurricane season has formed in the middle of the North Atlantic Ocean – 815 miles west of the Azores Islands.   The biggest impact from this storm will be the discussion in the meteorology community as to whether this system should even be monitored by the National Hurricane Center.  Currently Arlene is over relatively cold ocean water (66 F (19 C)) for a tropical system, and according to satellite data, it is questionable if the system has a warm core.

IR Satellite image show the system is over 19C water.

Typically a tropical cyclone is characterized by lack of warm/cold fronts attached, a “warm core” (air is warmer in center of the cyclone than elsewhere), and persistent deep convection wrapped close to the center; these attributes are commonly referred to as “tropical characteristics” of a cyclone.

It would appear that the decision to track Arlene is very subjective: there have likely been dozens of similar systems over the last 100 years (systems that develop in water warmer than 66 F and with a marginally warm core) that have gone unclassified, including systems that have impacted the U.S. (Sept 2008 SC coast, Sept 2009 NJ).

All this matters to the insurance industry because our hurricane catalogs in the catastrophe models are tuned to the historical data, and after decades there is still no objective guidance as to what type of system gets tracked by the NHC. In some cases like Sandy, questionably categorized storms can have large impacts on landfall definitions as well.

Regardless, Arlene is now in our record books as a storm in the North Atlantic, but it will not be around for long as a strong mid-latitude trough will merge with this system later this weekend and make it unrecognizable. These early-season tropical systems should be no surprise (this will be the sixth early-season storm in the past six years). In fact, history suggests that tropical/subtropical systems in April are uncommon, but not necessarily rare. There have been a few, but they are typically short-lived and innocuous.

Historical Storms that have occurred in April

I am currently tracking the various early season forecasts for the 2017 Atlantic basin season.  I should have my views formulated in a couple of weeks.  What I can tell you right now there is no correlation for April storms and the rest of the season, partly because of a small sample size.

Another New Hurricane Landfall Study

Three weeks ago, James Kossin published a major study in the scientific journal Nature: “Hurricane intensification along United States coast suppressed during active hurricane periods” (http://www.nature.com/nature/journal/v541/n7637/full/nature20783.html). This paper has gotten a bit of press in various insurer publications as over the last decade near term hurricane risk has dramatically influenced the insurance industry in hurricane-prone states. In short, Kossin’s paper provides valuable insight into rapid hurricane intensification during active and inactive periods of hurricane activity in the Atlantic basin (known as the warm and cold phase of the Atlantic Multi-Decadal Oscillation [AMO]). The findings suggest that approaching hurricanes are more likely to intensify before landfall during colder phases of the AMO and are more likely to weaken before landfall during warmer phases. Suggesting that during times when the sea surface temperatures are anomalously warm in the main development region, regions along the U.S. coast experience higher then normal vertical wind shear. Furthermore, the local sea surface temperatures are substantially cooler than the main development region which tend to inhibit intensification and form a “protective barrier” along the United States coastline during this period.

 

My very first thought as I read about this “protective barrier” was, finally, someone has scientifically proven the existence of HAARP and electromagnetic capabilities of the ionosphere that conspiracy theories suggest can also be used in weather modification and more. (i.e., a “protective barrier” created to control the weather (hurricane landfall))! (If you’re unfamiliar with the HAARP conspiracy theories that abound, then you won’t get this reference, but it’s one of the top questions meteorologists get asked, and you can learn more at http://www.nbcnews.com/science/weird-science/conspiracy-theories-abound-u-s-military-closes-haarp-n112576.)

How the Science has Changed

In all seriousness, to truly understand the impact of Kossin’s paper, it’s important to review how our understanding of active and inactive phases of the Atlantic Ocean has evolved and influenced the insurance industry. Since the 1960’s, the late Dr. Gray showed distinctly differing environmental conditions for tropical cyclone development. But not until the marked increase beginning in 1995 did insurers begin to notice what drives this activity. After the costly 2004 and 2005 hurricane seasons, a dozen and half papers highlighted a link to increased hurricane activity due to a warming world and/or the current phase of the AMO. About the same time, catastrophe modeling companies were being pressured to adjust for this increased frequency and severity that had impacted the insurance industry since 1995. Modeling companies incorporated a range of statistical analyses, and in some cases expert elicitation, to make assessment on future hurricane landfalling risk.

Mother Nature, however, does not always follow weather trends; and since 2005, the U.S. has entered what some have called a “U.S. landfall hurricane drought.” While overall named storm activity remains elevated across the Atlantic basin with some very active years since 2005 (2010, for example), many hurricanes have not made landfall as expected, which is actually influencing the long term landfall rates across the U.S. A few recent research papers suggest that scientists never settled on the exact impact the warmer phase of the AMO might have had on U.S. landfalls. Some of these papers suggest that in a warmer world, African dust and/or North Atlantic sea surface temperatures could actually encourage hurricanes to form further east or recurve before impacting North America, resulting in a lower U.S. hurricane landfall rate.

But Kossin’s paper provides new evidence that the science is not settled, and there is a lot to learn about hurricanes and the rate at which they make landfall. In general, the correlation between the number of hurricanes that develop in the Atlantic basin and number of hurricanes that make landfall is weak. This new study in Nature could explain part of this relationship as it highlights that elevated wind shear (changing wind speeds with height) and cooler sea-surface temperatures along the U.S. coast during the warm active phase of the AMO create conditions that tend to weaken hurricanes as they approach the U.S. coast. Conversely, the cool phase of the AMO makes approaching hurricanes more likely to intensify. This might conflict with ideas that some scientists suggested prior to 2004 and 2005, that the warmer phase of the AMO was correlated to more landfalls and possibly stronger landfalling storms (and fewer landfalls during the cooler phase of the AMO).

The Hurricane “Drought” can be Explained

Kossin suggests in his paper’s closing that this new research could possibly explain the recent “drought” of major hurricane landfalls. However, in late 2015 another research paper funded by Risk Prediction Initiative (“The Arbitrary Definition of the current Atlantic Major Hurricane Landfall Drought”) suggested the major hurricane drought is more a function of the definition of a major hurricane (defined as a Category 3 or higher on the Saffir-Simpson Scale) and the uncertainty in wind estimates. As an example, Ike (2008) made landfall as a high-end Category 2, but could just as easily have been classified as a low-end Category 3 at landfall. For contrast, consider a storm like Sandy (2012), which was not even classified as a hurricane at landfall, but still resulted in large wind and storm surge insurance losses.

Image created by Roger Pielke Jr. who has been keeping track of the days between major hurricane landfalls.

It’s important to remember that only 78 major hurricanes have made landfall since 1900 (117 years), which results in a particularly small sample size, and that there are likely many other factors that affect intensification before landfall. Hurricanes can experience higher levels of disruptive wind shear while turning north, which could be due to a large scale trough of low pressure or drawing in dry air from landmasses. Hurricanes can also send large waves and surge ahead of the storm causing warm water to mix with cooler water and deplete important energy from the storm as it approaches land. These vacillating factors highlight the complex interactions hurricanes may experience during a life cycle. These factors could also explain why many hurricanes have not intensified prior to U.S. landfall (with the exception of Charley [2004] and Humberto [2007]).

Future Hurricane Landfall Rate Models

As always, new research will continue to become available and catastrophe modeling companies will continue to judge how the science best fits into catastrophe models. This new research should not discredit near term view modeling work. Hindsight is 20/20, and as Hall, T.M., and K. Hereid, 2015: The frequency and duration of U.S. hurricane droughts paper suggests several observations point to the current drought being more a case of good luck than any shift in hurricane climate. Therefore this luck could have swayed higher then normal insured losses in a completely different direction over the last 10 years. These facts highlight why it is important to continuously evaluate new science. Modeling companies need to ensure they avoid knee-jerk reactions to industry demands or speculative science. Seasonal hurricane forecasts are improving, and with time, multidecadal sea surface patterns and other variables could help clarify the cause of reduced landfall rates, not just in the Atlantic basin, but in other basins near high exposure. El Niño/Southern Oscillation (“ENSO”) and other variables could also be worked into the landfall rate catalogs produced by model vendors.

As pointed out in this blog, the science might not be settled on hurricane landfall rates and what drives these rates during particular climatic conditions. Although it is short by climate standards, the U.S. landfall hurricane record is one of the best natural catastrophe databases insurers have to understand frequency and severity. There is a reason why catastrophe model companies calibrate their models to the longest period of record available.

There is plenty of room for debate about near term hurricane landfall rate models, the drivers of this risk, and what position an insurer should take regarding rate models. Are they a good idea or a bad idea? Should a blended approach be used? Those are interesting questions and a worthy topic, which is why I will be moderating the session, “Is Near Term vs. Long Term View of Hurricane Risk Over?” at the February RAA Cat Management Conference. We hope this subject generates lively discussion and hope to see you there!

Tis the season for severe weather across the south, but it’s been extremely quiet so far?

Tornado and hurricane drought?
It’s no surprise that the recent lack of hurricane landfalls has drawn the attention of the insurance industry. The long-standing Florida hurricane drought ended with hurricane Hermine’s landfall on September 2, and of course, Matthew threatened to end the major U.S. hurricane drought as well. However, there is another drought quietly confounding the insurance industry. After 2011 and reports of a “new normal” for severe weather, several years have now passed with lower than normal tornado activity.
So far the 2016 U.S. tornado count is among the lowest of the last 11 years. As of Nov 27, 981 tornadoes touched down in the U.S., which is 303 less than the 17-year average for that time period.

Tornado counts are below the 17-year average in eight of 10 months so far this year. Most recently, tornadoes in September and October were well below average. This is despite hurricane Hermine, which spawned eight confirmed tornadoes and hurricane Matthew which spawned two confirmed tornadoes. Hurricanes can produce a significant number of tornadoes, but neither Hermine or Matthew produced very many.

torgraph-big

U.S. Inflation Adjusted Tornado Count from 1950. It shows that this year could take the record for the lowest inflation adjusted tornado count since 1950.

This year’s unusually dry tornado spell started in June, which produced only 86, the fewest in that month since 1988. The 17-year average number of tornadoes for June is 216. February, March and August are the only months that featured above-average tornado activity this year.

Had it not been for a concentrated outbreak of 35 tornadoes in Indiana and Ohio on August 24, August would have finished below its 20-year average as well. Though the tornado pace has been slow for the year as a whole, February was an exception. With 138 confirmed tornadoes during the month, it was the second most tornadic February since 1950. Only 2008 produced more February tornadoes: 146 total tornadoes, including the record “Super Tuesday” outbreak of 84 tornadoes.

avgnovtornado

 

2016tornadoreports

2016 Tornado touch down locations and daily total count which shows the lack of tornadoes since the end of September.

Through last Monday, November 21, zero tornadoes had been reported this month, which is highly unusual. With an average November tornado tally of 58 (1991-2010), we are in near-record low territory again this month. Only four other years since the 1950’s have witnessed comparably low tornado activity in November (according to NOAA Storm Prediction Center Data): zero tornadoes in 1976, two tornadoes in 1954, and three tornadoes each in 1980 and 2009.

Severe Weather Insured Losses

As one might expect, insured losses from severe weather are often a matter of luck, and although there were some powerful tornados this year, very few impacted large populated areas. Yet despite scant tornado activity, 2016 is already the second costliest severe weather year in recent years, totaling $16.6B in insured loss. This total is far behind the $28B of insured loss experienced in 2011 as a result of several deadly and damaging tornadoes across the southeast U.S. Large insured loss losses this year were likely driven by wind and hail events. In fact, over 80% of U.S. insured loss results from hail and wind events, but luck is an ever-present factor. This year, bad luck settled over the state of Texas. Several hail storms impacted large metropolitan area such as Dallas-Fort Worth, San Antonio and El Paso, and these storms have driven the large losses experienced in the U.S this year. In fact, almost half of the total loss of $7.9B so far this year occurred in Texas.

Louisiana was also hit hard by severe weather and flooding, and that bad luck could continue today with a new severe weather threat.

This week’s severe weather threat

Tornadoes happen all year, but climatologically two seasons exhibit peak activity. Spring is prime time for tornado activity. That’s when warm Gulf of Mexico air clashes with winter’s remnant cold as dry air masses spill over the Rockies. Another peak arrives in October and November, but tends to be more erratic throughout fall. In something of a reverse of the spring air migration, jet streams again traverse and target specific parts of the country as the calendar changes from summer to winter.
It’s been over seven weeks since the U.S. has had a day with over 50 severe weather reports, and today this trend may snap due to expected severe weather across the south-central U.S. The HRRR model is forecasting the formation of prefrontal super-cells by mid-day Monday across central and northern Louisiana.

hrrr_ref_louisiana_7

Today HRRR Forecasted Radar for 2 CST over the South Central U.S.

This severe weather threat will continue to move across the southeast U.S. over the next weeks, which in some cases will be welcome given the ongoing drought conditions that triggered recent wildfires.

So although it has been quiet and the U.S is at near near-record low tornado fatalities and low tornadoes counts, we shouldn’t forget what occurred in December of 2015. That December began with a record-low of 10 tornado deaths. Then waves of tornadoes struck the South and the yearly toll jumped to 36. With a more energetic weather pattern ahead, we should stay tuned and remember that droughts won’t last forever.

Tropical Trouble In The Long Range Forecast

Tropical Storm Fiona
A few weeks ago I mentioned the approaching peak of the Atlantic hurricane season (September 10). Peak season means that tropical waves will move off the African coast, and attention will focus on the main development region of the Atlantic Ocean. Peak season also means that every tropical wave will need to be watched, and various media may highlight long-range forecasts of major hurricanes tracking toward the U.S. coastline. However, conditions off the African coast are still not ideal for development due to near-normal sea surface temperatures and an abundance of dry dusty air in the upper parts of the atmosphere (known as the Saharan Air Layer or the “SAL”).

This week the sixth named storm (Fiona) of the Atlantic hurricane season formed from a fairly strong African wave. However, as it tracks slowly west, Fiona is fighting high wind shear and the SAL, and as a result, it continues to be a weak tropical storm located about 1,295 miles west of the Cape Verde Islands. Fiona should continue to track to the northwest over the weekend and will likely stall early next week as a weak tropical depression near Bermuda – if it even makes it that far. So at this time, Fiona does not appear to threaten the insurance industry.

Invest 99L
Unlike Fiona, Invest 99L may be the bigger threat to the insurance industry. Invest 99L is an area of disturbed weather currently labeled by the National Hurricane Center (NHC), and to understand Invest 99L, a football analogy may help. Fiona functions as a lead blocker. She sealed off the SAL, allowing Invest 99L to go wide left into more fertile territory later this weekend: as described in my earlier posts, as tropical systems move closer to the U.S., they are likely to develop and strengthen. Likewise, Invest 99L may intensify as it tracks westward to this more fertile territory.

8192016DryAirSAL
Invest 99 is worth mentioning because the NHC currently indicated a 50% chance that it will develop into named storm Gaston. They project this system will track into the Leeward Islands over the next five days, and as this storm tracks west, it will encounter increasingly warm sea surface temperatures.

 

Invest99L8192016
Invest 99L is currently favored by models to develop and strengthen in the coming days. However, as stated, this is also the season when the media tend to highlight a single model run as a doom-and-gloom scenario.

Often this far in advance, these forecasts don’t verify, and all forecast scenarios need to be considered at this time. There are a multitude of scenarios still in the playbook for Invest 99L after all it’s not even a named storm yet.
Below is a look at the U.S. Global Forecast Model (GFS) ensemble model output. In total, this is a model run with 21 different forecasts to create an ensemble. The current forecast run demonstrates the uncertainty in the forecast in terms of track.

99L8192016_GFSEns

Below is a summary of various forecast model intensity guidance as Invest 99L tracks westward over the next five days.

99L_intensity_latest

In summary, Invest 99L has a high chance of developing into tropical storm Gaston over the weekend. There is some uncertainty in its long-range forecast track, but we know with high confidence that the system is expected to track toward the western Caribbean where the water is warm enough to support healthy hurricane development. If atmospheric conditions are ideal next week, a potential hurricane could approach insurable risk in the Caribbean and U.S. If these conditions late next week are not ideal, the current tropical wave could be just that – a tropical wave.

Peak of 2016 Atlantic Hurricane Season Is Approaching

It’s hard to believe, but the Atlantic hurricane season began 189 days ago when Hurricane Alex formed on January 13 and went on to become the strongest hurricane ever to form in the month of January in Atlantic Basin. The early season continued with three landfalling named storms that formed this June, making it easy to assume that an early season means an active season. But an early start to the season does not necessarily mean that the heart of the hurricane season will be active. A current lull in the basin since June 21 and long-range forecasts suggest there is limited opportunity for development for the reminder of July. However, climatology suggests we are not out of the woods yet. Instead, we are only just approaching September 10: the peak of the season when storm formation becomes much more frequent.

This is the time of year when eyes are trained on the massive cloud clusters that move off the West African coastline. These clusters have been limited so far this season. The only movement off this region is massive plumes of Saharan dust.

splitEW

Current CIMSS Tropical Cyclone Team imagery that is useful for monitoring the position and movement of dry air masses such as the Saharan Air Layer (SAL) and mid-latitude dry air intrusions. Animations of the imagery are useful for tracking these features and can also help identify the source of the dry and/or dusty air that is indicated in the imagery.

In some cases, these dust plumes have traveled all the way to the Texas Gulf Coast. Known as the Saharan Air Layer (SAL), this dry, dusty air has about half the moisture of the typical tropical atmosphere and can discourage the clouds and tropical convection needed for named storm development. Although we still lack a full understanding of how the SAL affects tropical systems, there are likely several reasons why it limits cloud and tropical convection development, and thereby limits the likelihood of named storm development.

  • Dry air can enhance downdrafts (sinking air), suppressing convection around the system.
    As tropical waves move off Africa, any resulting convection quickly reaches the bottom of the SAL (typically at altitudes between 5,000 and 15,000 feet); then entrains dry air which limits further convection.
850mbPlotTempAnoms

Here is the current 850 mb temperature normalized anomalies which shows that areas of heavy dust have warmed the atmosphere at this level 3 – 5 degrees Fahrenheit.

  • Typically atmosphere cools with height, but the SAL absorbs sunlight, which retains warmth and creates an inversion for thousands of miles across the Atlantic basin. This essentially caps the development of the showers and thunderstorms that are needed in tropical cyclone development.
  • Dusty conditions can be enhanced by stronger easterly winds that increase wind shear and tilt or outright displace the convection aloft from low-level circulation, thus limiting convection and tropical cyclone development.
  • The SAL shields sea surfaces from the sun and can keep the sea surface temperatures cooler than normal across the main development region.

Data suggests decadal variability in the SALs that may impact tropical activity (unfortunately, since the insurance industry doesn’t need another multi-year decadal pattern that could influence tropical cyclone development). Records going back to the 1960s and 1970s that were collected by satellites and island stations (using dust as a tracer) show that SAL activity have ebbed and flowed over the years. In the 1980s, some studies point to quiet periods that coincided with a stretch of increased dust outbreaks. In the 1990’s, dust activity decreased and tropical cyclone activity began ramping up.
At this time it is difficult to say if the dry, dusty air will continue into the heart of the Atlantic Hurricane season which effectively peaks around September 10th. We are only one-third of our way through hurricane season, and June and July are not usually good indicators of what is to come: on average, those months account for only 4% of Atlantic major hurricane activity.

CnxstHyUMAARuX9

— Philip Klotzbach (@philklotzbach) July 20, 2016

And just as a reminder, the 2004 named storm season didn’t have its first named storm form until August 1, but 2004 ultimately became one of the most active seasons on record for U.S. Florida landfalls.

The insurance industry shouldn’t let its guard down. If the dust persists and Cape Verde storms are hampered by the SAL, storms may instead develop in the western Atlantic which provides a higher likelihood of making U.S. landfall. And given the Western Caribbean and Gulf of Mexico is experiencing record warm surface temperatures and heat content, there is plenty of energy for these storms to become powerful hurricanes should they track over such warm waters.

tchp-2005-2016

Total oceanic heat content (called the Tropical Cyclone Heat Potential, or TCHP) in kilojoules per square centimeter (kJ/cm^2), for July 15 for the years 2005 – 2016. TCHP was at near-record or record values over much of the Caribbean, Gulf of Mexico, and waters surrounding the Bahamas in July 2016. TCHP in excess of 90 kJ/cm^2 (orange colors) is commonly associated with rapid intensification of hurricanes. Image credit: NOAA/AOML.

In summary, El Niño is gone and La Niña conditions are slowly building in the Central Pacific, and the SAL is currently hampering development in the main development region of the Atlantic. Long range forecast models remain quiet with little development chances. However, the warm ocean heat content and sea surface temperatures near the U.S. coastline would provide plenty of fuel for a strong hurricane if one were to track over these waters.

Already off to a head start – Hurricane season officially begins June 1

After two years of below normal named storm activity in the Atlantic basin most prognostication suggests that the 2016 Atlantic hurricane season will be above average. Many of these forecasts are citing a weakening El Niño and warmer than average seas surface temperatures over much of the Atlantic basin as a reason to expect conditions would slightly favor more named storm activity.

So far the prediction of an active season seems to be holding, with named storm Alex forming in January and most recently tropical storm Bonnie making landfall in South Carolina this past Memorial Day weekend. In fact, 2016 now joins the year 2012 as the only years, since reliable satellite coverage began; to have two named storms form prior to June 1.

Season

Univ. of Miami – Calendar of activity during the Atlantic Hurricane Season

Historically, the average number of named storms to develop in a season is 12, with six reaching hurricane status and three becoming major hurricanes. This year the overall number of named storms will likely be higher due to the lack of El Niño that tends to dampen hurricane formation in the Atlantic by increasing wind shear. In an environment with high wind shear, weak tropical disturbances have a more difficult time reaching into the atmosphere and forming into named storms. A La Niña looks to be rapidly developing and historically this climate forcer has lead to an above normal Atlantic hurricane season, which increase the chances of U.S. landfall named storm activity.

Wildcards

Like most hurricane seasons there are a few wild cards that could factor into more or less storm activity on top of general El Niño/ La Niña influences. One of these factors would be the Atlantic Multidecadal Oscillation (AMO) which has two phases: —a high hurricane activity phase and a low hurricane activity phase. Given the decrease of hurricane activity over the past few years, forecasters are uncertain as to whether the high-activity phase, which began in 1995, has ended. If it has, we could continue to see fewer hurricanes despite the otherwise favorable conditions of La Niña and warm ocean water.

Atlantic mutidecadal oscillation from 1950 to 2015

Atlantic mutidecadal oscillation from 1950 to 2015

Another wildcard could be the Saharan Air Layer (SAL) which is a mass of very dry, dusty air which forms over the Sahara Desert during the late spring, summer, and early fall and usually moves out over the tropical North Atlantic Ocean every 3-5 days. The SAL can have a significant negative impact on tropical cyclone intensity and formation. Its dry air can act to weaken a tropical cyclone by promoting downdrafts around the storm, while its associated strong winds can substantially increase the vertical wind shear in and around the storm environment also making it difficult for storm formation. The SAL can cover an area the size of the continental U.S. and has been tracked as far west as the Caribbean Sea, Central America, and the Gulf of Mexico.

Current position and movement of dry air masses (SAL) (Orange / Red mean dry air)

Lack of Named storm Landfall forecasts

Many of the seasonal outlooks don’t predict how many storms could make landfall, but there has been a dearth of major hurricane landfalls over nearly the past decade, and even more so the lack of any hurricane landfall of any intensity in Florida since Wilma in 2005. In that time, more than 2.5 million people have moved to Florida who might have no experience preparing for or responding to a landfalling hurricane.

To get an idea of possible landfall areas for this up-coming Atlantic hurricane season some seasonal forecasts use current atmospheric and global sea surface temperature patterns to put together analogs years of past storm tracks. These analog years (1988, 1995, 1998, 2007, 2010, 2012) provide ideas of where storms have tracked when past condition were similar to this years conditions. This year it would appear there will be more named storm activity forming closer the U.S. coastline vs storms forming in the middle of the Atlantic Ocean in the main development region. This would yield a higher chance of named storm / hurricane landfall. The analog years point toward more storm activity in the Western Caribbean Sea which could increase the chances of a storm tracking into the Gulf of Mexico as well.

All

Storm track maps of the current analog years

 

In summary NOAA’s outlook is in line with those from other organizations, both academic and private. Last month, Colorado State University research scientist Phil Klotzblach issued an outlook for a nearly-average season. Britain’s Met Office predicts a slightly above average season, as does private weather companies like WeatherBELL Analytics and WSI. The London-based weather consortium Tropical Storm Risk is forecasting a season 40 percent more active than the past 10 years, with 17 named storms, nine hurricanes and four major hurricanes. On the lower side would be the algorithm derived by University of Colorado Boulder which suggests only 6-12 named storms this season.

Fading El Niño – What’s Next For Insurance Industry?

A Q1 and El Niño wrap up

With winter and Q1, 2016, behind us, the insurance industry can review the active weather pattern and resulting insured losses. As mentioned in my blog post last fall, Florida experienced lots of weather activity, which is typical during strong El Niño winters such as this past one.  However, overall insured losses, while not historic, haven’t been benign either: Q1 losses ran about 31% above the 10-year average insured loss according to my estimates with Texas and the Southern Gulf states taking the brunt of the insured losses.  Although the remarkable blizzard (January 22–24) resulted in limited insured impacts based on the Property Claim Services (PCS) initial estimate, winter storms increased losses in the West.  In fact, the PCS issued four separate bulletins for the state of California more than any other year during the last 10 winter seasons.  Examples like this highlight the relatively predictable impacts of an El Niño winter.

After virtually tying the record for the strongest El Niño (as defined by a three-month running mean sea-surface temperature anomaly in the so-called Niño 3.4 region of the central and eastern equatorial Pacific Ocean), sea-surface temperatures (SST) are steadily cooling. NOAA’s March El Niño outlook suggests this El Niño may be all but gone by late spring or early summer.  In fact, some climate models and a recent government outlook suggest a shift to its opposite, La Niña by this fall.  As a result, the insurance industry needs to consider the potential for higher losses which are often associated with the La Niña phenomenon.

March_ENSO_Anomaly_SubSurface

Looking below the surface in the ocean waters in the Central Pacific, you can also see a trend of colder-than-average water working its way eastward across the International Date Line, eating away at the warmer-than-average equatorial Pacific water from below – another sign of a weakening El Niño.  Source: CPC

The unpredictable El Niño-La Niña relationship

Scatterplot showing the relationship in El Niño / La Niña states from one year to the next, for every year since 1950 in which an El Niño occurred. Each dot represents a pair of “year 1 vs. year 2” El Niño / La Niña states. In general, the stronger the El Niño (higher values on the x-axis), the stronger the subsequent La Niña (lower values on the y-axis). For more details and a larger version of the graphic, see the associated ENSO Blog post

Scatterplot showing the relationship in El Niño / La Niña states from one year to the next, for every year since 1950 in which an El Niño occurred. Each dot represents a pair of “year 1 vs. year 2” El Niño / La Niña states. In general, the stronger the El Niño (higher values on the x-axis), the stronger the subsequent La Niña (lower values on the y-axis). For more details and a larger version of the graphic, see the associated ENSO Blog post

El Niño and La Niña events each typically last for only 9-12 months, and they typically recur every 2-7 years, according to Columbia University’s International Research Institute for Climate and Society.  Flip-flops from a strong El Niño to La Niña are not unusual. For example, the record-setting El Niño of 1997-98 was almost immediately followed by La Niña the following summer, reaching moderate-to-strong intensity before finally ending in Spring, 2001. A similar pattern followed the strong El Niño of 1972-73.  However, neutral conditions followed three other strong El Niño’s that occurred in 1982-83, 1965-66 and 1957-58.

What Does It All Mean for the Insurance Industry?

Expect higher losses! If La Niña develops, historical insurance industry losses suggest worldwide impacts, but likely these impacts won’t be fully felt until 2017 when the La Niña is fully developed.  However, there are some broad trends that have shown up in past weakening El Niño events that could give a hint on what to expect in 2016.

Severe Weather Season

Various climate forcers such as North American snowpack, Pacific Decadal Oscillation and Gulf of Mexico SST can influence North American severe weather, muddling the impacts that El Niño or La Niña might have. Disregarding these factors and only looking at past weakening El Niño events that transitioned to La Niña, the data suggests weather will vary based on location. A moderate-to-strong La Niña tends to promote severe weather across the Southeast (conversely, El Niño promotes severe weather in Florida, the high plains of Texas, and up through Colorado to Minnesota).

Although insurance loss data suggest on average a La Niña year sees about double the insured loss that might occur during El Niño years, the reason for increased losses may have more to do with the location of the losses than the severity of the storms. La Niña years seem to favor stronger storms over the Southeast (Dixi Alley). This area is densely populated, which may lead to more claims of severe weather.  But like with any weather peril, even a quiet year can have an EF-5 roll into a city and cause devastation.  In the end, insured losses are largely based on good luck or bad luck.  Example: if the Joplin tornado of 2011 had shifted a few miles south during that La Niña year, no one would talk about it today.

This severe weather season the key could be the summer heat expected in the central Plains and Great Lakes could mix with the wet spring expected in Texas and Louisiana and increase instability leading to storms in the Northern Plains and Ohio River Valley.

Atlantic Hurricane Season 2016

Much hype accompanied last hurricane season due to El Niño’s tendency to produce stronger wind shear, which tends to tear apart developing or mature tropical cyclones and result in less tropical development. Sure enough, June through October, 2015, Caribbean wind shear was the highest on record since 1979, according to Dr. Phil Klotzbach, tropical scientist at Colorado State University (CSU). The team at CSU has also in the past pointed out that the timing makes a big difference:  If a transition to La Niña happens late in the year, it’s less likely to influence the Atlantic hurricane season.  The forecast team at CSU will issue their first outlook for the 2016 Atlantic season on April 14.

However, the CSU team and other leading researches have pointed out that U.S. hurricane impact rises dramatically in a La Niña or neutral season compared to an El Niño season. On an annualized basis since 1950, major hurricane landfall rates during La Niña years are 20% higher than neutral conditions and almost 280% higher than El Niño rates.

Hist_ENSO_Impacts

General stats of past La Niña and El Niño Atlantic hurricane seasons and the number of landfalls with adjusted historical total insured losses when accounting for all hurricane and tropical storm impacts for those years.

With El Niño potentially vanishing by the start of the 2016 hurricane season, the chance increases for tropical cyclones surviving to make U.S. landfall. If El Niño was the only factor, that is. I expect the team at CSU to discuss El Niño / La Niña, but also discuss the possible switch to a cool mode of the Atlantic Multidecadal Oscillation (AMO), which might suggest less storm activity in the next decade. This is because the far North Atlantic has been quite cold for about three years, and the SST pattern continues to cool (evolving as it did in the early 1960’s [the last time the AMO switched from a warm phase to cool phase with SST cooling in the North Atlantic and a slow progression of colder anomalies propagating into the tropical Atlantic and with warmer anomalies hanging on closer to the U.S. coastline).

The odds may shift a bit toward a more active Atlantic hurricane season in 2016, but El Niño’s absence doesn’t guarantee that outcome. Since the 2006 season, there have been some very active seasons with very few landfalling hurricanes, and the insurance industry still awaits that major hurricane landfall.

Summary:

El Niño, La Niña, or the lack of either (known as the neutral phase), is only one large-scale forcing on the atmosphere. Its presence or absence does not definitely determine severe weather or hurricane.  Climate models indicate a La Niña will follow the recent powerful El Niño, and we can look at past weather patterns to speculate future impact on particular insurance portfolios.  Right now the best analog years would be 1988, 1995, 1998, 2007, and 2010 during those years PCS losses averaged 10.6B, but what is more important is using those years to understand where the severe weather and hurricanes occurred to get an ideas of what might occur this year.  For example: U.S. landfalling hurricanes were limited, but in almost all those year the western Caribbean and Gulf of Mexico experienced some named storm activity.

2016_AnalogYears_v2

Historical hurricane tracks of the 1988, 1995, 1998, 2007, and 2010 hurricane seasons  Source: NOAA Historical Hurricane Tracks

Climate forcers like El Niño and La Niña can help predict the frequency of overall extreme weather activity, but truthfully, long-term predictions about the number of named storms, location of landfall or the power of other severe weather is impossible. The best way for the insurance industry to prepare is to carefully consider the risks and their potential impact. BMS’ weather risk management module in iVision can help carriers better understand their risk and manage portfolio accumulation in areas prone to hurricanes and severe weather. iVision also has tools to track forecasted hurricanes, including detailed hurricane wind fields. It has several severe variables around severe weather which can be combined with hurricane layers to provide a holistic view of an event and help carriers understand the range of potential loss outcomes from extreme weather events.  Learn more about the Hurricane Risk Management Module and Severe Storm Risk Management Module.

First East Coast winter storm of the season

If you have been living under a rock the last few days, you might not know that the first big nor’easter of the 2015/2016 winter season is expected to hit the East Coast of the U.S. this weekend. This storm summary will focus on the insured impacts of and provide a historical context for this intensely forecasted event. However, it should be noted that much uncertainty accompanies the forecasts, so predicted impacts could change as the storm develops over the next two days.

The media hyp-o-meter around this storm is at an all-time high due to the fact that there is good agreement among all the various models we use that a big nor’easter is going to happen, and some of its impacts will be major or even record breaking.

 

Collapse from weight of snow
The biggest question that everyone wants answered is how much snow is going to fall. No one can accurately answer that question today, unfortunately. What we do know is that a number of factors will contribute to a high-moisture storm. In other words, there will be a lot of snow. It’s just not possible at this point to say where the most of the snow will fall – but plenty of forecasters are trying! I highly suggest following the local National Weather Services office for the most accurate snowfall forecasts.

NWS human-made snowfall grids look great ... continuous like a global model. Totals thru Sat 7 PM

NWS human-made snowfall grids look great … continuous like a global forecast model.  Totals thru Sat 7 PM. Source WeatherBell Ryan Maue

So far, the storm has slowly trended south on the weather models. Additionally, it has a very sharp temperature moisture gradient on the north side. Due to the uncertainties on the northern fringe of this storm, there’s going to be a razor thin margin between major snow and conversational snow. However, due to the lack of existing snow pack, collapse due to weight of snow at this point in the season is unlikely to cause insured losses to buildings with standard structural integrity.
Of course the first significant snowfall of the year also means drivers must adapt to slippery conditions which will result in accidents and higher auto related losses. Finally, the snow, ice and wind from this storm could also cause prolonged power outage which could results in insured losses.

 

Wind and flood risks
Despite the fact that most of the media coverage is focused on snowfall, potentially destructive wind and coastal flooding often go unreported. This storm is big and slow, and due to the tight pressure gradient, as the storm strengthens off the east coast, it will allow for a strong on-shore flow, which could cause damaging wind gusts and storm surge along the coast. Winds and flooding could cause serious issues for the insurance industry. Depending on its ultimate track, this storm has the potential to become one of the top 5-10 coastal flooding events for folks from the Jersey Shore into Virginia.

blizzard_storm_surge.png.CROP.promo-xlarge2

A National Weather Service storm surge model forecasts water levels more than 5 feet above normal in parts of New Jersey and New York, rivaling some of the biggest coastal floods in history.

To illustrate the threat posed by this storm, consider that an 8.5 foot tide level would rank in the top 8 tide levels of all time at Cape May, New Jersey. As illustrated by the chart below, the Extratropical water Level Guidance from the National Weather Service, highlights the wind/flood risk associated with storm surge guidance for various cities along the coast. For Cape May, NJ, you’ll see the highest tide cycle for this storm ends up at a water level of about 8.5-8.7 feet.

CapeMayNJSurge

For historical comparison in the same location, consider that Sandy produced a tide level of 8.9 feet, an October, 2011, storm produced a tide level of 8.7 feet, and a December, 1992, storm produced a tide level of 8.6 feet.

NE_StormSurgeChart

Forecast as of 01/21/2016 9:20: EST (units in feet MLLW)

Insured property along the coast or back bays of New Jersey, Delmarva, and Virginia, are likely to be the most impacted as the storm has the possibility of lasting 2-3 high tide cycles. If the storm track shifts a bit or the intensity changes, we could see these values change. It’s a fluid but serious forecast for the insurance industry: the coast is where the highest winds will hit, and those winds may gust as high as those of a tropical storm. Speaking of winds, expect severe storms to produce wind damage and possibly an isolated tornado across the state of Florida.

 

Insured Loss Analogs
Historically, the East Coast is no stranger to large nor’easters. In fact, last year’s large snow event and winter time insured losses should be fresh in the insurance industry’s mind given the record breaking snowfall over New England and one of the costliest winters ever for the industry.
On average over a 56-year period, 1.3 nor’easter occur every year, and 2.3 large snow storm events occur as defined by the Northeast Snowfall Impact Scale (NESIS). In the last ten years, these non-inflation adjusted event level losses have averaged out to cost just over $300M per event.
The table below provides a few analog storms that resemble the forecast guidance for the current storm. Right now, the model guidance does not suggest a repeat of the first Superstorm / “Storm of the Century” (March 12 – 15th of 1993) which still stands as the costliest nor’easter to impact the insurance industry.
NE_SnowStormEventLossChart

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Source: http://www.eas.slu.edu/CIPS/ANALOG/analog.php