Helene

Post-Event Wind and Storm Surge | Summary
Posting Date: October 2, 2024, 6:00:00 AM

The Verisk ALERT Team has completed the modeling of wind and storm surge from Hurricane Helene, and we are providing modeling resources to help you better understand the impacts from these sub-perils.  Modeling work continues on the inland flood aspect of Helene; this sub-peril is not included in today’s ALERT.

ALERT™ subscribers can now download Touchstone® and Touchstone Re™ event sets, loss-based similar stochastic events (SSEs), and hazard shapefiles of the median loss event for the wind and storm surge impacts from Hurricane Helene from the Downloads tab for this posting on the ALERT Website. Please see the commentary in the download for the loss-based similar stochastic events for guidance on how to best utilize these. The information provided herein is strictly confidential and is solely for the use of Verisk clients; disclosure to others is prohibited unless noted in your Verisk software license.

Modeling Information and Assumptions

Today’s wind and storm surge modeling resources for Helene do not include:

• Losses from precipitation-induced flooding
• Losses paid out by the National Flood Insurance Program
• Losses exacerbated by litigation, fraudulent assignment of benefits, or social inflation
• Storm surge leakage losses paid on wind only policies due to government intervention
• Losses to inland marine, ocean-going marine cargo and hull, and pleasure boats
• Losses to uninsured properties
• Losses to infrastructure
• Losses from extra-contractual obligations
• Losses from hazardous waste cleanup, vandalism, or civil commotion, whether directly or indirectly caused by the event
• Losses resulting from the compromise of existing defenses (e.g., natural and man-made levees)
• Loss adjustment expenses
• Other non-modeled losses, including those resulting from tornadoes spawned by the storm
• Losses for U.S. offshore assets and non-U.S. property

Meteorological History of Helene

On September 23rd, the National Hurricane Center (NHC) identified and designated a low-pressure system over the northwestern Caribbean as Potential Tropical Cyclone Nine. The broad area of showers and thunderstorms became more organized throughout the day, as it slowly moved north-northwest towards the Yucatan Peninsula. By evening, there was still no defined center of the system, but convective wind speeds continued to increase. Tropical Storm Warnings were issued for parts of Yucatan, Mexico and Cuba.

By late morning on September 24th, the system became a little better organized and intensified into Tropical Storm Helene as it moved through the northwestern Caribbean Sea. By late the following morning, upon entering the southeast Gulf of Mexico, Helene had quickly strengthened to a Category 1 Hurricane with maximum sustained winds of 80 mph.  Helene then became ensnared in the flow passing between a ridge over the Atlantic and a mid-level trough over the Tennessee Valley, which served to accelerate the system forward in a north-northeastern direction into the Gulf of Mexico and toward the eastern Florida Panhandle.  Owing to Helene’s large wind field, portions of south Florida began to experience tropical storm conditions on the 25^th, which spread northward overnight as the system grew larger and nearer to the coast. Starting early on the 26th, Helene began a prolonged period of rapid intensification that saw maximum sustained winds increase from 90 mph at 5am to 140 mph at 11pm, shortly before landfall.  During this time, Helene’s wind field of tropical storm-force winds grew to be 430 miles wide, a purported record for Florida, just edging out 2017’s Hurricane Irma (420 miles).

Conditions along the Florida Peninsula continued to deteriorate throughout the day. On the more exposed Gulf Coast, storm surge in Tampa Bay led to extensive flooding and several prominent road and highway closures by late afternoon of the 26th as Helene tracked through the Gulf of Mexico 100 miles offshore.  A peak gust of 82 mph and sustained wind of 53 mph was observed at Albert Whitted Airport in St. Petersburg around this time.  By nightfall, hurricane conditions had begun spreading into the northern Gulf coast of Florida as Category 4 Helene was making its final approach.

Helene made landfall shortly before midnight on September 26th near Perry, Florida as a Category 4 hurricane with maximum sustained winds of 140 mph.  This makes Helene the strongest hurricane to make landfall in the Big Bend region in recorded history (i.e., since 1851), shattering the previous record set by the Cedar Keys Hurricane of 1896 (125 mph).  Helene’s minimum central pressure at landfall was 938 mb, which is the lowest for a landfalling hurricane in Florida since Michael in 2018 (919 mb) and the 9th lowest since 1900.  Record storm surge was observed farther north along the coast, including Cedar Key (9.3 feet) and Steinhatchee, which went offline after recording 10 feet of storm surge at 11:30pm.  Fortunately, the forecasts for up to 20 feet of storm surge failed to materialize; however, widespread coastal flooding coupled with major hurricane-force winds still resulted in catastrophic damage and near-total utility outages near the landfall point.

Helene’s massive size allowed the storm’s most powerful winds to reach well inland even before landfall.  Compounding this was Helene’s forward speed of 24 mph at landfall, which quickly moved the storm inland before significant weakening could occur.  The maximum reported wind gust was 99 mph in Perry, Florida, where Helene made landfall. 

Validation of the Verisk’s Modeling of Helene

Wind and Storm Surge Damage

Helene’s wind footprint scathed the Gulf coast of Florida and eventually made landfall along the Big Bend region in Taylor County. This region is sparsely populated with pockets of communities along the coastline that bore the brunt of the winds. Observed wind damage was limited to roof cover and wall cladding damage with occasional structural damage. Much of the damage was similar in locality and intensity to 2023 Hurricane Idalia but with a much larger storm surge impact and footprint extent.

Storm surge damage on the Florida Gulf coast was substantially more evident with towns such as Horseshoe Beach, Cedar Key, Steinhatchee and northern communities in the populous Pinellas County such as Clearwater Beach and Palm Harbor.  

As Hurricane Helene tracked north and crossed into Georgia, the wind field extended significantly east of the track impacting large swaths of central counties. Substantial tree induced damage was observed from Valdosta up to Augusta and Savannah. As a result of tree damage, water ingress and debris induced damages were observed across the eastern portion of the state. Wind damage to cladding, roof cover and attached structures was also widely observed and reported.

A wide majority of damage was related to hurricane precipitation induced flooding when it came to communities and cities in North and South Carolina. Flooding will certainly be the cause when it comes to insured and economic losses across these states. In some cases, wind induced damage observations were generally limited to tree collapses on structures, downed powerlines and cladding damage. Significant uncertainty exists when it comes to losses paid out as a consequence of flood induced tree falls and subsequent damage to roofs and envelope in structures.

Putting Damage in Perspective from the Context of Building Codes

Florida has a long history when it comes to the evolution and adoption of building codes. Right from its very first adoption of the statewide building code in 2002, it has been a pioneer nationally in wind design specifications. The Big Bend region of Florida where hurricane Helene made landfall has the lowest design winds statewide, between 120 and 130 mph. Further, areas along the coast and inland are excluded from the wind-borne debris region which means opening protection and stronger opening requirements are not required during in the buildings in this region. The same is true for southwestern parts of Georgia that experienced strong winds from hurricane Helene. Helene’s impacts in this region from a wind perspective should be similar to that from Hurricane Idalia last year. A significant portion of the building inventory along the track of hurricane Helene predate the International Codes i.e. are built prior to the year 2000.

National Flood Insurance Program

The flood insurance take-up on residential risks in Florida is variable depending on the county. Recent data from the National Flood Insurance Program (as of 8/31/2024) shows that the risk count based take-up rates of policies-in-force varies from 48-50% in Pinellas, Charlotte and Lee county to as low as 5-15% in a majority of counties along the Gulf coast including Taylor, Citrus, Dixie, Hernando, Levy, Pasco, Hillsborough counties. Within those counties, homes inside the government-designated floodplain, the area most exposed to flooding, the take-up rate tends to higher in comparison to areas outside the floodplain — many of which are still likely to have been damaged by flooding from Helene.

Homeowners who choose to purchase flood insurance most commonly do so through the National Flood Insurance Program (NFIP), and Florida has the highest proportion of NFIP policies of any state – about 35%, according to Fitch Ratings. These policies typically cover up to $250,000 in damages and do not include additional living expense coverage, suggesting that even for some homeowners with flood insurance, there may be a gap between coverage and rebuilding costs. 

Other Verisk Resources for Hurricane Helene

Verisk Respond Hurricane Data

Verisk’s Respond Hurricane solution uses a multi-input model to provide a comprehensive and accurate view of tropical cyclone winds. The solution couples a five-day forecast of wind with a post-event view to provide a full wind field understanding of the impacts that have already occurred alongside the potential impacts that have yet to occur from a tropical system. The Respond Hurricane solution updates every six hours for any named storm in the Atlantic Ocean basin. Wind information is expressed both in terms of one-minute sustained wind speeds as well as three-second wind gusts. In addition, wind speed durations of 39 mph or greater (tropical storm force), 50 mph or greater, and 74 mph or greater (hurricane force) are also conveyed to provide a more comprehensive understanding of the wind threat.

In the event of a landfalling U.S. hurricane, within 24 hours of downgrade of the system to a tropical depression or post-tropical system, the Verisk Respond Hurricane maximum wind gust data are corrected by assimilating actual wind observations from multiple sources into the wind field to bias and error correct the modeled estimate. Special consideration is taken in this process to ensure the wind observations being incorporated accurately reflect the conditions at the location at a 10-meter height. This final maximum wind gust field will not only more closely match the assimilated observations, but final wind field values will be more accurate in general across the entire wind field, although typical differences between the modeled estimates and the observation-corrected post-storm are 10% or less.

Please contact your Verisk representative for more information on Verisk Respond.

Additional ALERT Plans for Helene

The Verisk Flood team is underway in modeling the inland flood impacts from Helene.  We will provide updated event sets, similar stochastic events, a flood extent shapefile, and an insured industry loss estimate covering wind, storm surge, and inland flood from Helene next week.  We will provide additional guidance on specific timing for release as we near completion of our remodeling exercise.  Please contact your Verisk representative with additional questions about this Hurricane Helene.

Post-Event Wind and Storm Surge | Downloads
Posting Date: October 2, 2024, 6:00:00 AM

The information provided herein is strictly confidential and is solely for the use of Verisk clients; disclosure to others is prohibited.

Simulated Event Sets

These event sets contain five custom modeled scenarios for Hurricane Helene's wind and storm surge, allowing for uncertainty in key model parameters such as radius of maximum winds and central pressure.  All scenarios follow the official NHC track.

Product	Description	Download
Touchstone Re	Selected set of simulated scenarios
Touchstone	Selected set of simulated scenarios

Loss Based Similar Stochastic Event IDs

These stochastic events were selected as best matches to the insured industry loss footprints generated by the custom modeled scenarios in the Simulated Event Set

Product	File Type	Description	Download
Touchstone / Re	Excel (xls)	Selected set of stochastic events, with Readme in Excel format
Touchstone / Re	CSV (csv)	Selected set of stochastic events, formatted for import into Touchstone/Re

Additional Downloads

Note: Additional downloads related to the posting are listed below. Please use the appropriate application to view these files.

Title	File Type	Description	Download
Hurricane Helene Modeled Wind Shapefile	.zip	A shapefile for the median loss scenario wind footprint from the Simulated Event Set
Hurricane Helene Modeled Storm Surge Shapefile	.zip	A shapefile for the median loss scenario storm surge inundation footprint from the Simulated Event Set
Hurricane Helene Custom Modeled Scenarios Information	.xlsx	Event parameters and modeled insured industry loss estimates for the five custom scenarios for Hurricane Helene found in the Simulated Event Sets.