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In the past two weeks, two major hurricanes have impacted the Baja Peninsula in Mexico. Hurricane Norbert bypassed a large portion of the west coast of the peninsula from September 5 to 7, and Hurricane Odile made landfall near Cabo San Lucas on September 14th as a Category 3 hurricane on the Saffir-Simpson Wind Scale. A third system, Hurricane Polo, formed Tuesday, September 16 and is forecasted to follow a similar track to Norbert and Odile, making it the third such tropical cyclone to develop in the region since the beginning of the month.

This serial cluster of storms has been driven primarily by steady, favorable conditions for tropical cyclone development and consistent atmospheric patterns present over the Eastern Pacific. A serial cluster is defined as a set of storms that form in the same part of a basin, and subsequently follow one another in an unbroken sequence over a relatively short period of time. To qualify as a cluster, there needs to be measurable consistency between the tracks. This is typically a result of steady, predominant atmospheric steering currents, which play a major role in influencing the speed and direction of tropical cyclones. One example of a serial cluster is the four major hurricanes (Charley, Francis, Ivan, and Jeanne) that impacted Florida during a six-week period in 2004.

During this recent two-week period, the area off the west coast of Mexico has maintained high sea-surface temperatures near 85.1 degree Fahrenheit and limited vertical wind shear, leading to an active tropical development region. A mid-level atmospheric ridge over northern Mexico has provided a consistent steering pattern towards the north-northwest, producing similar observed tracks for Norbert and Odile and forecasted track for Polo. Devastating amounts of rainfall have occurred with these storms. Hurricane Odile dropped nearly 18 inches of rain in areas around Cabo San Lucas, representing nearly 21 months-worth of typical rainfall. This cluster, while generating significant wind and flood damage along the Baja Peninsula, has also caused torrential rainfall in the southwestern U.S., including Arizona, southern Nevada, and southern California. Last week, Phoenix, AZ, one of the hardest hit areas, experienced over 3 inches of rain in a 7 hour span due to the remnants of Hurricane Norbert. This was the most rainfall to occur in a 24-hour period in the city since 1911, an estimated 1-in-200 year event by the National Oceanic and Atmospheric Administration. Significant rainfall and inland flooding is forecast to continue as the remnants of Odile and Polo move inland, which may lead to widespread flood losses and the potential for compound post-event loss amplification.

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California Wildfires: Exposure Impacted by the Thomas Fire

As the Thomas Fire continues to climb the list of the top twenty largest California wildfires for both acres burned and structures destroyed, many in the insurance industry are asking how this fire, in addition to the other burned areas across Southern California, will impact their portfolio. A critical element in understanding the industry impact, but also the significance for an individual book, is the insured value of the burned structures. The Thomas Fire, which at 60 percent containment at the time of publication is already the second largest fire in California history with a reported burn area of 272,000 acres (110,074 hectares), has affected several different communities with wide ranges of average insured value. Figure 1: Top 20 Largest California Wildfires. Source: CAL FIREWhile damage assessments are still ongoing and counts of damaged or destroyed structures are actively being reported, we can use RMS high resolution exposure data and the latest burn footprint available from Geospatial Multi-Agency Coordination (GeoMAC) to gain a perspective on the total amount and average value of exposure across different areas within the perimeter. Figure 2: Map of the Thomas Fire Perimeter. Source: GeoMAC as of 0100 UTC on December 18, 2017.As of December 18, portions of ten different ZIP codes are located within the Thomas Fire perimeter, spanning across Santa Barbara and Ventura counties. While the fire started north of Santa Paula around sunset on December 4, it has now spread approximately 50 miles (80 kilometers), primarily to the west, to the hills north of Montecito and Santa Barbara. So far, during two weeks of spread the fire has impacted the communities of Santa Paula, Ojai, Ventura, Oak View, Wheeler Springs, Carpinteria, Montecito, and several others. Each of these communities vary in average residential exposure value, making “average” estimates across the entire perimeter more difficult. Table 1 below compares the residential exposure for the high value 93108 ZIP postal code that spans the Montecito area against the exposure outside of that ZIP code. All values correspond only to exposure located within the Thomas Fire perimeter, according to the RMS high resolution exposure database. The average residential structure exposure value for 93108 is on average three and a half times higher than structures located outside of that ZIP code. Structures in 93108 accounts for only three and a half percent of the number of structures within the fire perimeter, but 12 percent of the total exposure value. Table 1: Residential Exposure Values in the Thomas Fire Perimeter.As noted in prior blogs about the Wine Country wildfires, it is important to note that only a fraction of the structures within the perimeter will be damaged or destroyed in this event. The reported numbers so far from CAL FIRE are 1,024 structures destroyed and 250 damaged. Comparing this against the total number of structures within the perimeters, the ratio is approximately 37 percent, which is far lower than the 75 to 80 percent seen in the Wine Country wildfires in October this year, but higher than the other historical Southern California events that have been analyzed (Cedar in 2003 and Witch in 2007). Figure 3: Percentage of damaged or destroyed structures within historical fire footprints.Also, a comparison of the percentage of destroyed structures versus the total number in the perimeter between the Thomas Fire (1,024 destroyed versus 1,274 total or 80 percent) and the Wine Country Tubbs Fire (6,957 destroyed versus 7,443 total or 93 percent), raises important questions for understanding the key differences between the events. This may indicate a stronger presence of fire suppression, lower impacts of embers, more distributed exposure, differences in surface fuel characteristics (e.g. chaparral versus forest) or a combination of these and other factors in the Thomas Fire. A further review of these event-specific factors, including the weather conditions, will provide more clarity around key drivers of these differences. By extracting information about the differences between these two events, RMS will continue to build insight into the development of the RMS® U.S. Wildfire HD model, part of the RMS North America Wildfire HD Models suite, due for release in 2018. RMS is still monitoring the ongoing events affecting Southern California and will continue to provide updates through RMS Owl.…

Kevin Van Leer
Kevin Van Leer
Senior Product Manager, Model Product Management

As a senior product manager in the Model Product Management group at RMS, Kevin is responsible for RMS climate-peril products for the Americas, including wildfire and custom vulnerability analytics. Kevin has been actively involved in model releases for both severe convective storm and hurricane models over the last four years at RMS. Kevin holds a master’s degree in atmospheric science from the University of Illinois at Urbana-Champaign, where he authored a thesis on tornado-genesis and severe convective storms, and a bachelor’s degree in atmospheric science from Purdue University. He also holds the Certified Catastrophe Risk Analyst (CCRA) designation from RMS. Kevin is a member of the American Meteorological Society (AMS), a mentor for the AMS Board of Private Sector Meteorologists, and a voting member of the ASCE Standards Committee on Wind Speed Estimation in Tornadoes.

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